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Journal Publications

This section contains all refereed journal publications that have some connection either with the Mace Head Research Station or with members, both present and past, of the Atmospheric Physics Research Cluster at NUI, Galway.

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Documents

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Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber

Date added: 08/01/2005
Date modified: 07/03/2009
Filesize: 520.58 kB

Pirjola, L., C. O’Dowd, Y. J. Yoon, K. Sellegri, Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber. Environ. Chem. 2, 271. doi:10.1071/EN05075, 2005.


Abstract


A sectional atmospheric chemistry and aerosol dynamics box model (AEROFOR) was further developed and used to simulate ultra-fine particle formation and growth from seaweed in a chamber flushed with particle-free atmospheric air. In the model, thermodynamically stable clusters were formed by dimer nucleation of OIO vapour, whose precursor was assumed to be molecular I2 emitted by seaweed. Fractal geometry of particles was taken into account. For the I2 fluxes of (0.5–1.5) × 109 cm-3 s-1 the model predicted strong particle bursts, the steady state concentrations of I2 vapour and particles larger than 3 nm were as high as 4 × 109–1.2 × 1010 cm-3 and 5.0 × 106–9.2 × 106 cm-3 respectively. The steady state was reached in less than 150 s and the predicted growth rates of 3–6 nm particles varied in the range of 1.2–3.6 nm min-1. Sensitivity of the size distribution against I2O3 cluster formation, an extra condensable vapour, the photolysis rate of the OIO vapour as well as against the density of (OIO)n-clusters was discussed. The modelled results were in good agreement with the chamber measurements performed during the BIOFLUX campaign in September, 2003, in Mace Head, Ireland, confirming that I2 emissions and nucleation of iodine oxides can largely explain the coastal nucleation phenomenon.

Regional model simulation of North Atlantic cyclones Present climate and idealized response to incre Regional model simulation of North Atlantic cyclones Present climate and idealized response to incre

Date added: 08/01/2008
Date modified: 07/23/2009
Filesize: 2.79 MB
Semmler, T., S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, and C. O'Dowd, Regional model simulation of North Atlantic cyclones: Present climate and idealized response to increased sea surface temperature, J. Geophys. Res., 113, D02107, doi:10.1029/2006JD008213, 2008.

Abstract

 

The influence of an increased sea surface temperature (SST) on the frequency and intensity of cyclones over the North Atlantic is investigated using two data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by reanalysis data for May to December 1985–2000 at the lateral and lower boundaries, using SST and lateral boundary temperatures. A realistic interannual variation in tropical storm and hurricane counts is simulated. In an idealized sensitivity experiment, SSTs and boundary condition temperatures at all levels are increased by 1 K to ensure that we can distinguish the SST from other factors influencing the development of cyclones. An increase in the count of strong hurricanes is simulated. There is not much change in the location of hurricanes. Generally weaker changes are seen in the extratropical region
and for the less extreme events. Increases of 9% in the count of extratropical cyclones and 39% in the count of tropical cyclones with wind speeds of at least 18 m/s are found.

Application of a compact all solid-state laser system to the in situ detection of atmospheric OH, HO Application of a compact all solid-state laser system to the in situ detection of atmospheric OH, HO

Date added: 08/06/2003
Date modified: 06/30/2009
Filesize: 184.19 kB
W. J. Bloss, T. J. Gravestock, D. E. Heard, T. Ingham,G. P. Johnson and J. D. Lee, "Application of a compact all solid-state laser system to the in situ detection of atmospheric OH, HO2, NO and IO by laser-induced fluorescence", Journal of Environmental Monitoring., 5, 21-28 (2003).

Abstract


A tuneable, high pulse-repetition-frequency, solid state Nd:YAG pumped titanium sapphire laser capable of generating radiation for the detection of OH, HO2, NO and IO radicals in the atmosphere by laser induced fluorescence (LIF) has been developed. The integration of the laser system operating at 308 nm into a field measurement apparatus for the simultaneous detection of hydroxyl and hydroperoxy radicals is described, with detection limits of 3.1 6 105 molecule cm23 (0.012 pptv in the boundary layer) and 2.6 6 106 molecule cm23 (0.09 pptv) achieved for OH and HO2 respectively (30 s signal integration, 30 s background integration, signalto- noise ratio ~ 1). The system has been field tested and offers several advantages over copper vapour laser pumped dye laser systems for the detection of atmospheric OH and HO2 radicals by LIF, with benefits of greater tuning range and ease of use coupled with reduced power consumption, instrument footprint and warm-up time. NO has been detected in the atmosphere at y 1 ppbv by single photon LIF using the A 2S1 B X 2P1/2 (0,0) transition at 226 nm, with absolute concentrations in good agreement with simultaneous measurements made using a chemiluminescence analyser. With some improvements in performance, particularly with regard to laser power, the theoretical detection limit for NO is projected to be y 2 6 106 molecule cm23 (0.08 pptv). Whilst operating at 445 nm, the laser system has been used to readily detect the IO radical in the laboratory, and although it is difficult to project the sensitivity in the field, an estimate of the detection limit is v 1 6 105 molecule cm23 (v 0.004 pptv), well below previously measured atmospheric concentrations of IO.

Elemental and organic carbon in PM10 a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP Elemental and organic carbon in PM10 a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP

Date added: 08/01/2007
Date modified: 07/27/2009
Filesize: 2.18 MB

Yttri, K.E., W. Aas, A. Bjerke, J.N. Cape, F. Cavalli, D. Ceburnis, C. Dye, L. Emblico, M.C. Facchini, C. Forster, J.E. Hanssen, S.G. Jennings, W. Maenhaut, J.P. Putaud, and K. Torseth, Elemental and organic carbon in PM10: a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP, Atmos. Chem. Phys., 7, 5711-5725, 2007.


Abstract


In the present study, ambient aerosol (PM10) concentrations of elemental carbon (EC), organic carbon (OC), and total carbon (TC) are reported for 12 European rural background sites and two urban background sites following a one-year (1 July 2002–1 July 2003) sampling campaign within the European Monitoring and Evaluation Programme, EMEP http://www.emep.int/). The purpose of the campaign was to assess the feasibility of performing EC and OC monitoring on a regular basis and to obtain an overview of the spatial and seasonal variability on a regional scale in Europe.

Analyses were performed using the thermal-optical transmission (TOT) instrument from Sunset Lab Inc., operating according to a NIOSH derived temperature program. The annual mean mass concentration of EC ranged from 0.17±0.19 μg m−3 (mean ± SD) at Birkenes (Norway) to 1.83±1.32 μg m−3 at Ispra (Italy). The corresponding range for OC was 1.20±1.29 μg m−3 at Mace Head (Ireland) to 7.79±6.80 μg m−3 at Ispra. On average, annual concentrations of EC, OC, and TC were three times higher for rural background sites in Central, Eastern and Southern Europe compared to those situated in the Northern and Western parts of Europe. Wintertime concentrations of EC and OC were higher than those recorded during summer for the majority of the sites. Moderate to high Pearson correlation coefficients (rp) (0.50–0.94) were observed for EC versus OC for the sites investigated. The lowest correlation coefficients were noted for the three Scandinavian sites: Aspvreten (SE), Birkenes (NO), and Virolahti (FI), and the Slovakian site Stara Lesna, and are suggested to reflect biogenic sources, wild and prescribed fires. This suggestion is supported by the fact that higher concentrations of OC are observed for summer compared to winter for these sites. For the rural background sites, total carbonaceous material accounted for 30±9% of PM10, of which 27±9% could be attributed to organic matter (OM) and 3.4±1.0% to elemental matter (EM). OM was found to be more abundant than SO42- for sites reporting both parameters.

An overview of the Lagrangian experiments undertaken during the NA regional ACE An overview of the Lagrangian experiments undertaken during the NA regional ACE

Date added: 08/06/2000
Date modified: 06/30/2009
Filesize: 1.51 MB

Johnson, D. W., S. R. Osborne, R. Wood, K. Suhre, M. O. Andrae, R. Johnson, S. Businger, P. K. Quinn, T. Bates, P. Durkee, H. Johnson, L. M. Russell, K. Noone, P. Glantz, B. Bandy, C. O'Dowd, S. Rapsomanikis and J. Rudolph. An overview of the Lagrangian experiments undertaken during the North Atlantic Regional Aerosol Characterisation Experiment (ACE - 2). Tellus, 52B, 290-320. 2000.


Abstract

 

One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic.

 

 Nanoparticles in boreal forest and coastal environment: a comparison of observations and implicatio Nanoparticles in boreal forest and coastal environment: a comparison of observations and implicatio

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 1.15 MB

Lehtipalo, K., Kulmala, M., Sipilä, M., Petäjä, T., Vana, M., Ceburnis, D., Dupuy, R., and O'Dowd, C


Abstract.

 1

 

The detailed mechanism of secondary new particle formation in the atmosphere is still under debate. It is proposed that particle formation happens v a activation of 1–2 nm atmospheric neutral molecular clusters and/or large molecules. Since traditional instrumentation does not reach these sizes, the hypothesis has not yet been verified. By directly measuring particle size distributions down to mobility  diameters of about 1.3 nm with a pulse-height CPC, we  provide evidence of the nucleation mechanism in a coastal environment (Mace Head, Ireland) and in a boreal forest  (Hyyti¨al¨a, Finland). In both places neutral sub-3 nm condensation nuclei (nano-CN) were continuously present, even  when no new particle formation was detected. In Mace Head,  however, the concentration of the nano-CN was far too low to account for the particle formation rates during particle bursts. Thus the results imply that at coastal sites new particle formation initiates, as previously proposed, via homogenous nucleation  from biogenic iodine vapors. In contrast, activation  of pre-existing nano-CN remains a possible explanation in the boreal forest, but the observed concentrations are not the limiting factor for the particle formation events.

 

 

Global trends, seasonal cycles, and European emissions of dichloromethane, trichloroethene, and tetrachloroethene..... Global trends, seasonal cycles, and European emissions of dichloromethane, trichloroethene, and tetrachloroethene.....

Date added: 08/05/2006
Date modified: 07/02/2009
Filesize: 1.92 MB
Simmonds, P. G., et al. (2006), Global trends, seasonal cycles, and European emissions of dichloromethane, trichloroethene, and tetrachloroethene from the AGAGE observations at Mace Head, Ireland, and Cape Grim, Tasmania, J. Geophys. Res., 111, D18304, doi:10.1029/2006JD007082.

Abstract


In situ observations (every 4 hours) of dichloromethane (CH2Cl2) from April 1995 to December 2004 and trichloroethene (C2HCl3) and tetrachloroethene (C2Cl4) from September 2000 to December 2004 are reported for the Advanced Global Atmospheric Gases Experiment (AGAGE) station at Mace Head, Ireland. At a second AGAGE station at Cape Grim, Tasmania, CH2Cl2 and C2Cl4 data collection commenced in 1998 and 2000, respectively. C2HCl3 is below the limit of detection at Cape Grim except during pollution episodes. At Mace Head CH2Cl2 shows a downward trend from 1995 to 2004 of 0.7 ± 0.2 ppt yr−1 (ppt: expressed as dry mole fractions in 1012), although from 1998 to 2004 the decrease has been only 0.3 ± 0.1ppt yr−1. Conversely, there has been a small but significant growth of 0.05 ± 0.01 ppt yr−1 in CH2Cl2 at Cape Grim. The time series for C2HCl3 and C2Cl4 are relatively short for accurate trend analyses; however, we observe a small but significant decline in C2Cl4 (0.18 ± 0.05 ppt yr−1) at Mace Head. European emissions inferred from AGAGE measurements are compared to recent estimates from industry data and show general agreement for C2HCl3. Emissions estimated from observations are lower than industry emission estimates for C2Cl4 and much lower in the case of CH2Cl2. A study of wildfires in Tasmania, uncontaminated by urban emissions, suggests that the biomass burning source of CH2Cl2 may have been previously overestimated. All three solvents have distinct annual cycles, with the phases and amplitudes reflecting their different chemical reactivity with OH as the primary sink.

Ozone and peroxy radical budgets in the marine boundary layer Modeling the effect of NOx Ozone and peroxy radical budgets in the marine boundary layer Modeling the effect of NOx

Date added: 08/06/1999
Date modified: 07/23/2009
Filesize: 971.22 kB

Cox, R. A. (1999), Ozone and peroxy radical budgets in the marine boundary layer: Modeling the effect of NOx, J. Geophys. Res., 104(D7), 8047–8056.


Abstract


A one-dimensional box model has been formulated to describe the ozone budget and HOx photochemistry in the marine boundary layer. The model includes a simple description of vertical exchange with the free troposphere and the ocean surface, and a photochemical scheme including oxidation of CO and CO4. Model calculations are compared with data collected during the summer season at two midlatitude coastal sites in the northern and southern hemispheres (Mace Head, Ireland, and Cape Grim, Tasmania). Results using small, prescribed NOx concentrations gave compensation points, where ozone loss by photolysis and physical removal is balanced by its production via NOx chemistry, of ∼30 ppt and ∼15 ppt at the two sites, respectively, in line with conclusions from the observational data. Changes in the dependence of peroxy radical concentrations on solar intensity were also in line with observations. The simple model involving CO and CH4 chemistry should be adequate for defining oxidizing capacity in the unpolluted marine boundary layer.

 

Observations of the evolution of the aerosol cloud and boundary layer ACE2 LE Observations of the evolution of the aerosol cloud and boundary layer ACE2 LE

Date added: 08/06/2000
Date modified: 07/03/2009
Filesize: 1.95 MB

Osborne, S. R., D. W. Johnson, R. Wood, B. J. Bandy, M. O. Andrae, C. D. O'Dowd, P. Glantz and K. Noone (1999). Observations of the evolution of the aerosol, cloud and boundary layer dynamic and thermodynamic characteristics during the second Lagrangian experiment of ACE-2. Tellus. 52B, 375-400, 2000


Abstract


During the 1st Lagrangian experiment of the North Atlantic Regional Aerosol Characterisation Experiment (ACE-2), a parcel of air was tagged by releasing a smart, constant level balloon into it from the Research Vessel Vodyanitskiy. The Meteorological Research Flight's C-130 aircraft then followed this parcel over a period of 30 h characterising the marine boundary layer (MBL), the cloud and the physical and chemical aerosol evolution. The air mass had originated over the northern North Atlantic and thus was clean and had low aerosol concentrations. At the beginning of the experiment the MBL was over 1500 m deep and made up of a surface mixed layer (SML) underlying a layer containing cloud beneath a subsidence inversion. Subsidence in the free troposphere caused the depth of the MBL to almost halve during the experiment and, after 26 h, the MBL became well mixed throughout its whole depth. Salt particle mass in the MBL increased as the surface wind speed increased from 8 m s-1 to 16 m s-1 and the accumulation mode (0.1mum to 3.0 mum) aerosol concentrations quadrupled from 50 cm-3 to 200 cm-3. However, at the same time the total condensation nuclei (>3 nm) decreased from over 1000 cm-3 to 750 cm-3. The changes in the accumulation mode aerosol concentrations had a significant effect on the observed cloud microphysics. Observational evidence suggests that the important processes in controlling the Aitken mode concentration which, dominated the total CN concentration, included, scavenging of interstitial aerosol by cloud droplets, enhanced coagulation of Aitken mode aerosol and accumulation mode aerosol due to the increased sea salt aerosol surface area, and dilution of the MBL by free tropospheric air.

 

Global Average Concentration and Trend for Hydroxyl Radicals Deduced From ALE GAGE Trichloroeth Global Average Concentration and Trend for Hydroxyl Radicals Deduced From ALE GAGE Trichloroeth

Date added: 08/07/1992
Date modified: 07/24/2009
Filesize: 1.53 MB

Prinn, R., et al. (1992), Global Average Concentration and Trend for Hydroxyl Radicals Deduced From ALE/GAGE Trichloroethane (Methyl Chloroform) Data for 1978–1990, J. Geophys. Res., 97(D2), 2445–2461.


Abstract

Atmospheric measurements at several surface stations made between 1978 and 1990 of the anthropogenic chemical compound 1,1,1-trichloroethane (methyl chloroform, CH3CCl3) show it increasing at a global average rate of 4.4 ± 0.2% per year (1σ) over this time period. The measured trends combined with industrial emission estimates are used in an optimal estimation inversion scheme to deduce a globally averaged CH3CCl3 tropospheric (and total atmospheric) lifetime of 5.7 (+0.7, −0.6) years (1σ) and a weighted global average tropospheric hydroxyl radical (OH) concentration of (8.7 ± 1.0) × 105 radical cm−3 (1σ). Inclusion of a small loss rate to the ocean for CH3CCl3 of 1/85 year−1 does not affect the stated lifetime but lowers the stated OH concentration to (8.1 ± 0.9) × 105 radical cm−3 (1σ). The rate of change of the weighted global average OH concentration over this time period is determined to be 1.0 ± 0.8% per year (1σ) which has major implications for the oxidation capacity of the atmosphere and more specifically for methane (CH4), which like CH3CCl3 is destroyed primarily by OH radicals. Because the weighting strongly favors the tropical lower troposphere, this deduced positive OH trend is qualitatively consistent with hypothesized changes in tropical tropospheric OH and ozone concentrations driven by tropical urbanization, biomass burning, land use changes, and long-term warming. We caution, however, that our deduced rate of change in OH assumes that current industry estimates of anthropogenic emissions and our absolute calibration of CH3CCl3 are accurate. The CH3CCl3 measurements at our tropical South Pacific station (Samoa) show remarkable sensitivity to the E1 Nino-Southern Oscillation (ENSO), which we attribute to modulation of cross-equatorial transport during the northern hemisphere winter by the interannually varying upper tropospheric zonal winds in the equatorial Pacific. Thus measurements of this chemical compound have led to the discovery of a previously unappreciated aspect of tropical atmospheric tracer transport.

On the Photochemical production of new particles in the coastal boundary layer On the Photochemical production of new particles in the coastal boundary layer

Date added: 09/11/1999
Date modified: 07/13/2009
Filesize: 420.57 kB

O’Dowd, C., et al. (1999), On the Photochemical Production of New Particles in the Coastal Boundary Layer, Geophys. Res. Lett., 26(12), 1707–1710.


Abstract


Concurrent measurements of ultra-fine (r<5 nm) particle (UFP) formation, OH and SO2 concentrations in the coastal environment are examined to further elucidate the processes leading to tidal-related homogeneous heteromolecular nucleation. During almost daily nucleation events, UFP concentration approached ≈300,000 cm−3 under conditions of solar radiation and low tide. Simultaneous measurements of OH illustrate that, as well as occurring during low tide, these events occur during conditions of peak OH concentration, suggesting that at least one of the nucleating species is photochemically produced. Derived H2SO4 production also exhibited remarkable coherence, although phase-lagged, with UFP formation, thus suggesting its involvement, although binary nucleation of H2SO4 and H2O can be ruled out as a plausible mechanism. Ternary nucleation involving NH3 seems most likely as a trigger mechanism, however, at least a fourth condensable species, X, is required for growth to detectable sizes. Since UFP are only observed during low tide events, it is thought that species X, or it’s parent, is emitted from the shore biota - without which, no nucleation is detected. Species X remains to be identified. Model simulations indicate that, in order to reproduce the observations, a nucleation rate of 107 cm−3 s−1, and a condensable vapour concentration of 5 × 107 cm−3, are required.

Eastern Atlantic Spring Experiment 1997 (EASE97)1. Measurements of OH and HO2 concentrations at Eastern Atlantic Spring Experiment 1997 (EASE97)1. Measurements of OH and HO2 concentrations at

Date added: 08/06/2002
Date modified: 07/01/2009
Filesize: 285.24 kB

Creasey, D. J., D. E. Heard, and J. D. Lee (2002), Eastern Atlantic Spring Experiment 1997 (EASE97) 1. Measurements of OH and HO2 concentrations at Mace Head, Ireland, J. Geophys. Res., 107(D10), 4091, doi:10.1029/2001JD000892.


Abstract


We report measurements of the hydroxyl (OH) and hydroperoxy (HO2) radicals, taken over 20 days, in the remote marine boundary layer at Mace Head, Ireland, during April and May 1997. OH was monitored directly by laser-induced fluorescence (LIF) spectroscopy at 308 nm, and HO2 was measured by chemical conversion to OH upon the addition of NO, with subsequent detection by LIF. The detection limit of the instrument at midday for OH was 6.0 × 105 molecule cm−3 (0.0024 parts per trillion by volume (pptv)) and for HO2 was 3.0 × 106 molecule cm−3 (0.12 pptv), as defined for a signal integration period of 2.5 min and a signal-to-noise ratio of 1. Midday OH and HO2 concentrations were between 2.0–6.0 × 106 molecule cm−3 (0.08–0.24 pptv) and 0.5–3.5 × 108 molecule cm−3 (2.5–14 pptv), respectively. OH concentrations correlated well with the rate of OH production from ozone photolysis for clean air from the Arctic containing low concentrations of both NOx and nonmethane hydrocarbons. A lower correlation was observed in more polluted air that originated from the United Kingdom and continental Europe. Measurements of OH and HO2 were made throughout two nights, and although no evidence was seen for OH above the detection limit, up to 2 pptv of HO2 was observed. The measured HO2/OH ratio was in good agreement with the predictions of a steady state expression for NO in the range 75–400 pptv.

 

MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN

Date added: 08/06/2004
Date modified: 07/23/2009
Filesize: 33.16 kB

R. Sommariva, W.J. Bloss , L.J. Carpenter, N. Carslaw, A.-L. Haggerstone, D.E. Heard, A.C. Lewis, G. McFiggans, M.J. Pilling, J.M.C. Plane,MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN, Geophysical Research Abstracts, Vol. 6, 00232, 2004


Abstract

 

The North Atlantic Marine Boundary Layer Experiment (NAMBLEX) campaign took place at the Mace Head Atmospheric Research Station, Ireland, in July-September 2002. An extensive set of measurements was taken during the campaign including NMHCs, NOx, HCHO, peroxides, photolysis rates, aerosols and radical species (OH, HO2, HO2+RO2, NO3, IO and BrO). Several different zero-dimensional box models based on the Master Chemical Mechanism (MCMv3.1) with different levels of chemical complexity have been used to study the HOx radicals chemistry under comparatively unpolluted conditions. The comparison between the model results and the measurements, based on the FAGE (Fluorescence Assay by Gas Expansion) measurements is satisfactory for OH, but HO2 is overestimated by almost a factor of two.
The effect of constraining the models to the measured oxygenates (methanol, acetaldehyde and acetone) and the effect of IO and BrO on HOx chemistry have been investigated. Aerosol uptake treatment for the relevant species has been  improved with respect to previous analyses by using a transition regime expression, which resulted in better agreement between modelled and measured HOx. A detailed study of the radical chemistry on selected days using a rate of production/ destruction analysis, shows the importance of previously unmeasured oxygenated compounds and of halogen chemistry on the HOx budget in the Marine Boundary Layer.

 

Extinction and Liquid Water Content Measurements at CO2 Laser wavelengths Extinction and Liquid Water Content Measurements at CO2 Laser wavelengths

Date added: 07/31/1987
Date modified: 07/01/2009
Filesize: 601.9 kB

Nolan, P.F., and Jennings, S.G. (1987). - Extinction and liquid water content measurements at CO2 laser wavelengths. J. Atmos. and Oceanic Technol., 4, 391 - 400.


Abstract

 

Measurements have been made of both extinction coefficients in an evaporating laboratory cloud at wavelength λ = 10.591 μm using a CO2 laser, and of liquid water content (LWC) at the center of the cloud using a continuous filtration LWC device. Cloud uniformity has been promoted and monitored within the laboratory chamber. The measurements give an overall linear relation between extinction and liquid water content independent of droplet-size distribution in reasonably good agreement with the Chýlek prediction. The measurements show significantly better agreement with the Chýlek prediction for the narrower cloud drop-size distributions. The broader size distribution data show an underestimate in extinction compared to the Chýlek prediction, providing the first experimental evidence for the large radius limit (radius 12 μm) in use of the Chýlek relation.

Physical characterization of aerosol particles during nucleation events Physical characterization of aerosol particles during nucleation events

Date added: 07/31/2001
Date modified: 07/03/2009
Filesize: 435.73 kB

Aalto, P.P., K. Hämeri, E. Becker, R. Weber, J. Salm, J.M. Mäkelä, C. Hoell, C.D. O'Dowd, H. Karlsson, H-C. Hansson, M. Väkevä, I. Koponen, G. Buzorius, and M. Kulmala, Physical characteristics of aerosol particles during nucleation events. in press Tellus B, 53, 344-345,, 2001.


Abstract


Particle concentrations and size distributions have been measured from different heights inside and above a boreal forest during three BIOFOR campaigns (14 April–22 May 1998, 27 July– 21 August 1998 and 20 March–24 April 1999) in Hyytia¨la¨, Finland. Typically, the shape of the background distribution inside the forest exhibited 2 dominant modes: a fine or Aitken mode with a geometric number mean diameter of 44 nm and a mean concentration of 1160 cm−3 and an accumulation mode with mean diameter of 154 nm and a mean concentration of 830 cm−3. A coarse mode was also present, extending up to sizes of 20 mm having a number concentration of 1.2 cm−3, volume mean diameter of 2.0 mm and a geometric standard deviation of 1.9. Aerosol humidity was lower than 50% during the measurements. Particle production was observed on many days, typically occurring in the late morning. Under these periods of new particle production, a nucleation mode was observed to form at diameter of the order of 3 nm and, on most occasions, this mode was observed to grow into Aitken mode sizes over the course of a day. Total concentrations ranged from 410–45 000 cm−3, the highest concentrations occurring on particle production days. A clear gradient was observed between particle concentrations encountered below the forest canopy and those above, with significantly lower concentrations occurring within the canopy. Above the canopy, a slight gradient was observed between 18 m and 67 m, with at maximum 5% higher concentration observed at 67 m during the strongest concentration increases.

Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber

Date added: 08/01/2005
Date modified: 07/13/2009
Filesize: 520.58 kB

Pirjola, L., C. O’Dowd, Y. J. Yoon, K. Sellegri, Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber. Environ. Chem. 2, 271. doi:10.1071/EN05075, 2005.


Abstract

 

A sectional atmospheric chemistry and aerosol dynamics box model (AEROFOR) was further developed and used to simulate ultra-fine particle formation and growth from seaweed in a chamber flushed with particle-free atmospheric air. In the model, thermodynamically stable clusters were formed by dimer nucleation of OIO vapour, whose precursor was assumed to be molecular I2 emitted by seaweed. Fractal geometry of particles was taken into account. For the I2 fluxes of (0.5–1.5) × 109 cm-3 s-1 the model predicted strong particle bursts, the steady state concentrations of I2 vapour and particles larger than 3 nm were as high as 4 × 109–1.2 × 1010 cm-3 and 5.0 × 106–9.2 × 106 cm-3 respectively. The steady state was reached in less than 150 s and the predicted growth rates of 3–6 nm particles varied in the range of 1.2–3.6 nm min-1. Sensitivity of the size distribution against I2O3 cluster formation, an extra condensable vapour, the photolysis rate of the OIO vapour as well as against the density of (OIO)n-clusters was discussed. The modelled results were in good agreement with the chamber measurements performed during the BIOFLUX campaign in September, 2003, in Mace Head, Ireland, confirming that I2 emissions and nucleation of iodine oxides can largely explain the coastal nucleation phenomenon.

MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN

Date added: 08/06/2004
Date modified: 07/23/2009
Filesize: 33.16 kB

R. Sommariva, W.J. Bloss , L.J. Carpenter, N. Carslaw, A.-L. Haggerstone, D.E. Heard, A.C. Lewis, G. McFiggans, M.J. Pilling, J.M.C. Plane,MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN, Geophysical Research Abstracts, Vol. 6, 00232, 2004


Abstract

 

The North Atlantic Marine Boundary Layer Experiment (NAMBLEX) campaign took place at the Mace Head Atmospheric Research Station, Ireland, in July-September 2002. An extensive set of measurements was taken during the campaign including NMHCs, NOx, HCHO, peroxides, photolysis rates, aerosols and radical species (OH, HO2, HO2+RO2, NO3, IO and BrO). Several different zero-dimensional box models based on the Master Chemical Mechanism (MCMv3.1) with different levels of chemical complexity have been used to study the HOx radicals chemistry under comparatively unpolluted conditions. The comparison between the model results and the measurements, based on the FAGE (Fluorescence Assay by Gas Expansion) measurements is satisfactory for OH, but HO2 is overestimated by almost a factor of two.
The effect of constraining the models to the measured oxygenates (methanol, acetaldehyde and acetone) and the effect of IO and BrO on HOx chemistry have been investigated. Aerosol uptake treatment for the relevant species has been  improved with respect to previous analyses by using a transition regime expression, which resulted in better agreement between modelled and measured HOx. A detailed study of the radical chemistry on selected days using a rate of production/ destruction analysis, shows the importance of previously unmeasured oxygenated compounds and of halogen chemistry on the HOx budget in the Marine Boundary Layer.

 

Impact of volcanic ash plume aerosol on cloud microphysics Impact of volcanic ash plume aerosol on cloud microphysics

Date added: 03/19/2013
Date modified: 03/19/2013
Filesize: 3.41 MB

Martucci, M., J. Ovadnevaite, D. Ceburnis, H. Berresheim, S .Varghese, D. Martin, R. Flanagan, C. D. O'Dowd, Impact of volcanic ash plume aerosol on cloud microphysics., Atmos Environ, doi:10.1016/j.atmosenv.2011.12.033 , 2011


Abstract. This study focuses on the dispersion of the Eyjafjallajökull volcanic ash plume over the west of Ireland, at the Mace Head Supersite, and its influence on cloud formation and microphysics during one significant event spanning May 16th and May 17th, 2010. Ground-based remote sensing of cloud microphysics was performed using a Ka-band Doppler cloud RADAR, a LIDAR-ceilometer and a multi-channel microwave radiometer combined with the synergistic analysis scheme SYRSOC (Synergistic Remote Sensing Of Cloud). For this case study of volcanic aerosol interaction with clouds, cloud droplet number concentration (CDNC), liquid water content (LWC), and droplet effective radius (reff) and the relative dispersion were retrieved. A unique cloud type formed over Mace Head characterized by layer-averaged maximum, mean and standard deviation values of the CDNC, reff and LWC: Nmax = 948 cm-3, N = 297 cm-3, σN = 250 cm-3, reff max = 35.5 μm, reff = 4:8 μm, σreff = 4:4 μm, LWCmax =0:23 g m-3, LWC = 0:055 g m-3, σLWC =0:054 g m-3, respectively. The high CDNC, for marine clean air, were associated with large accumulation mode diameter (395 nm) and a hygroscopic growth factor consistent with sulphuric acid aerosol, despite being almost exclusively internally mixed in submicron sizes. Additionally, the Condensation Nuclei (CN, d > 10 nm) to Cloud Condensation Nuclei (CCN) ratio, CCN:CN ~1 at the moderately low supersaturation of 0.25%. This case study illustrates the influence of volcanic aerosols on cloud formation and microphysics and shows that volcanic aerosol can be an efficient CCN.

 

Lidar observations of atmospheric boundary layer structure....Ireland (PARFORCE experiment) Lidar observations of atmospheric boundary layer structure....Ireland (PARFORCE experiment)

Date added: 08/06/2002
Date modified: 07/02/2009
Filesize: 798.06 kB
Kunz, G. J., G. de Leeuw, E. Becker, and C. D. O'Dowd (2002), Lidar observations of atmospheric boundary layer structure and sea spray aerosol plumes generation and transport at Mace Head, Ireland (PARFORCE experiment), J. Geophys. Res., 107(D19), 8106, doi:10.1029/2001JD001240.

Abstract


A scanning backscatter lidar was used to measure the depth and structure of the coastal atmospheric boundary layer and the evolution of primary aerosol (sea spray) plumes produced by breaking waves during the New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign at the Mace Head Atmospheric Research Station (Ireland) in September 1998 and in June 1999. The PBL structure was observed to vary from a single-layer well-mixed structure to multilayered structures. Comparison with in situ aircraft measurements of temperature and humidity exhibited good agreement. Using the lidar in the scanning mode allowed two-dimensional profiling over a spatial scale of 10 km, revealing significant primary aerosol plumes produced by breaking waves, particularly in the surf zone and at high wind speeds on the open sea. The initial plume heights were some tens of meters and evolved to hundreds of meters while transported over only a few kilometers from the source. The plumes were traceable to distances of more than 10 km down wind from the source.

Potential for photochemical ozone formation in the troposphere over the North Atlantic as deriv Potential for photochemical ozone formation in the troposphere over the North Atlantic as deriv

Date added: 08/06/2002
Date modified: 09/11/2009
Filesize: 1.34 MB

Reeves, C. E., et al. (2002), Potential for photochemical ozone formation in the troposphere over the North Atlantic as derived from aircraft observations during ACSOE, J. Geophys. Res., 107(D23), 4707, doi:10.1029/2002JD002415.


Abstract


In this paper, ozone (O3), water vapor (H2O), carbon monoxide (CO), and peroxide concentrations and photolysis rates measured in the troposphere over the North Atlantic during two Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) aircraft field campaigns are used to calculate the concentration of nitric oxide (NO) required for net photochemical O3 production (nPO3) to be positive (NOcomp). NOcomp tended to show a decrease with altitude, although it was sometimes found to be low in the marine boundary layer (MBL) where H2O concentrations were high and O3 concentrations were low. nPO3 was calculated for the spring when NO data were available and was found to be mostly negative and generally increased from about −0.5 to −0.2 ppbv hr−1 in the MBL to +0.04 ppbv hr−1 at about 7–8 km altitude. The results suggest that much of the lower and middle troposphere over the eastern North Atlantic during spring is in a state of slow net photochemical O3 destruction. However, in the upper troposphere, the system changes to one of net photochemical production, which results from the drier environment and higher NO concentrations. Furthermore, examples of net O3 production were also observed in the lower and middle troposphere associated with either in situ sources of NO or long-range transport of pollution. The paper also illustrates the sensitivity of this O3 production/loss state to H2O and NO concentrations, photolysis rates, and temperatures.

 

Free-radical chemistry in the coastal marine boundary layer Measurements and modelling at Mace Free-radical chemistry in the coastal marine boundary layer Measurements and modelling at Mace

Date added: 08/06/2003
Date modified: 07/24/2009
Filesize: 21.42 kB

D. E. Heard et al. (NAMBLEX team), "Free-radical chemistry in the coastal marine boundary layer: Measurements and modelling at Mace Head, Ireland, during the NAMBLEX campaign", Geophysical Research Abstracts, European Geophysical Society, 5, 11843 (2003).


Abstract


The coastal marine boundary layer provides an ideal location to study the background chemistry of the remote troposphere, and also the effects of perturbations due to biogenic emissions from the inter-tidal zone. The North Atlantic Marine Boundary Layer EXperiment (NAMBLEX), involving ca. 50 scientists, took place at the Mace Head Atmospheric Research Station in July--September 2002. Measurements were made of a number of free-radical species, including OH, HO_2 and RO_2, together with a comprehensive suite of supporting measurements of longer-lived species and radiative parameters that define their rates of formation and destruction. This paper focuses on a comparison of the concentrations of OH and HO_2, measured using laser-induced fluorescence at low pressure, and RO_2, measured using a dual-channel peroxy radical amplifier, under predominantly clean westerly conditions ([NO] < 20 pptv), but also during polluted episodes. Full diurnal profiles were measured on a large number of days, allowing a detailed analysis of the correlations between the free-radical concentrations and the controlling variables, for example, J(O^1D), NO_x and VOCs. A zero-dimensional model, based on the Master Chemical Mechanism (v3), and constrained by measurements of CO, CH_4, H_2, O_3, H_2O, speciated non-methane hydrocarbons, oxygenated hydrocarbons, peroxides, HCHO, NO, NO-2, photolysis frequencies (determined using a scanning spectral-radiometer) and temperature, is used to calculate OH, HO_2 and RO_2. A comparison between measured and calculated levels of free-radicals is made over a range of NO levels. Agreement for OH is better than in previous campaigns at Mace Head. The destruction of OH is dominated by reaction with CO (> 50%), but reaction with the previously unmeasured oxygenated VOCs (in particular acetaldehyde) is found to be more important than reaction with CH_4 or NMHC, with significant implications for the chemistry of the marine boundary layer.

Contribution of isoprene oxidation products to marine aerosol over the North-East Atlantic Contribution of isoprene oxidation products to marine aerosol over the North-East Atlantic

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 5.12 MB

Anttila, T., Baerbel Langmann, S. Varghese, C. O’Dowd, Contribution of isoprene oxidation products to marine aerosol over the North-East Atlantic,  Adv. in Meteorol., Volume 2010, Article ID 482603,, 2010


Secondary organic aerosol (SOA) formation through isoprene oxidation was investigated with the regional-scale climate model REMOTE. The appliedmodeling scheme includes a treatment formarine primary organic aerosol emissions, aerosolmicrophysics, and SOA formation through the gas/particle partitioning of semivolatile, water-soluble oxidation products. The focus was on SOA formation taking place over the North-East Atlantic during a period of high biological activity. Isoprene SOA concentrations were up to 

5ng m3 over North Atlantic in the base case model runs, and isoprene oxidation made a negligible contribution to the marine organic aerosol (OA) mass. In particular, isoprene SOA did not account for the observed water-soluble organic carbon (WSOC) concentrations over North Atlantic. The performed model calculations, together with results from recent field measurements, imply a missing source of SOA over remote marine areas unless the isoprene oxidation products are considerably less volatile than the current knowledge indicates.

 On the effect of wind speed on submicron sea salt mass concentrations and source fluxes On the effect of wind speed on submicron sea salt mass concentrations and source fluxes

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.25 MB

Ovadnevaite, J., D. Ceburnis, M. Canagaratna, H. Berresheim, J. Bialek, G. Martucci, D. R. Worsnop, and C. O’Dowd, On the effect of wind speed on submicron sea salt mass concentrations and source fluxes, J. Geophys. Res., 117, D16201, doi:10.1029/2011JD017379, 2012.


Abstract. A High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was evaluated for its ability to quantify submicron sea salt mass concentrations. The evaluation included both laboratory and field studies. Quantification of the sea salt signal in the HR-ToF-AMS was achieved by taking the 23Na35Cl+ ion as a surrogate for sea salt and then identifying a calibration scaling factor through a comparison with mono-disperse laboratory generated sea salt aerosol. Ambient sea salt concentrations calculated using this method agreed well with those obtained by ion chromatography of filter samples, following a 1:1 regression slope and a correlation coefficient R = 0.93. A key advantage of this AMS-based method is that it allows for high time resolution measurements of sea salt (5 min) along with the speciation of other chemical compounds, including primary organics contributing to sea spray. The high-time resolution sea salt measurement capability enabled the quantification of sea salt mass in both increasing and decreasing wind speed regimes up to 26 m s-1. A mass flux source function was also derived and found to have a power law wind speed dependency with an exponent of 3.1 for increasing winds and 2.3 for decreasing winds. Comparison of the mass flux relationship in this study suggests that previous schemes based on the Monahan whitecap–wind speed approach significantly over-estimate the submicron mass flux. Both the whitecap–wind speed component and the differential whitecap–aerosol productivity component of the source flux function contribute toward the over-estimation.

 

Evaluating measurements new particle concentrations, source rates and spatial scales during .. Evaluating measurements new particle concentrations, source rates and spatial scales during ..

Date added: 07/31/2002
Date modified: 07/24/2009
Filesize: 863.78 kB

Kaarle Hameri , Colin O'Dowd, Claudia Hoell, Evaluating measurements new particle concentrations, source rates and spatial scales during coastal nucleation events using condensation particle counters. ,JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. D19, 8101, doi:10.1029/2001JD000411, 2002


Abstract


Condensation particle counters (CPCs), used to examine particle production in the coastal environment, are evaluated for their ability to differentiate ultrafine sizes between 3 and 10 nm, along with their ability to count high total particle number concentrations encountered during coastal nucleation events. Four ultrafine particles counters, with a 3 nm detection limit, were deployed in a spatial array comprising a triangular distribution with nodes approximately 100 m apart (two at 3 m height, one at 10 m). A fourth node was deployed at 20 m. The 10 m and 20 m node comprised additional CPCs with detection limits of 5 and 10 nm. Size cutoff efficiency calibrations were performed in the field, and all CPCs were found to be within the manufacturer's specifications. During the nucleation events it was found that peak particle concentrations of the order of 180,000 cm−3 were encountered, and as a result, coincidence calibrations were also performed in the laboratory. It was found that, at concentrations over 100,000 cm−3, the CPCs significantly underestimated the true concentrations by a factor of about 5–6. Total particle concentrations were also measured using a 30-times dilution system and an ultrafine CPC, along with integrated total concentration derived from the ultrafine Differential Mobility Particle Sizer (DMPS). Comparison of laboratory-derived corrections for coincidence and both the diluted CPC total concentrations and DMPS concentrations revealed very good agreement and confirmed that peak particle concentrations during coastal nucleation bursts result in new particle concentrations as high as 1.2 × 106 cm−3. The DMPS total concentration was somewhat lower than the diluted CPC concentration, suggesting that the recommended method of measuring such high concentrations is to dilute the sample significantly. The lower concentrations from the DMPS are partially due to the 10 min integration time being insufficient to resolve peaks seen by the CPC operated at 1 Hz. Taking the corrected concentrations in account, 3 nm particle source rates were calculated to be >105 cm−3 s−1. The spatial array of CPCs revealed that within the general coastal nucleation plume, there are numerous microplumes with spatial scales of the order of 10–100 m when sampling is conducted near the source region. Further from the source region these microplumes merge into the general coastal plume.

Lifetime and emission estimates of 1,1,2-trichlorotrifluorethane (CFC-113) from daily global background observations June 1982–June 1994 Lifetime and emission estimates of 1,1,2-trichlorotrifluorethane (CFC-113) from daily global background observations June 1982–June 1994

Date added: 08/01/1996
Date modified: 07/24/2009
Filesize: 1.48 MB
Fraser, P., D. Cunnold, F. Alyea, R. Weiss, R. Prinn, P. Simmonds, B. Miller, and R. Langenfelds (1996), Lifetime and emission estimates of 1,1,2-trichlorotrifluorethane (CFC-113) from daily global background observations June 1982–June 1994, J. Geophys. Res., 101(D7), 12,585–12,599.

Abstract


Observations every two hours of CCl2FCClF2 at Mace Head, Ireland (February 1987–June 1994); Cape Meares, Oregon (April 1984–June 1989); Ragged Point, Barbados (October 1985–June 1994); Cape Matatula, Samoa (October 1985–June 1989 and January 1992–June 1994); and Cape Grim, Tasmania (June 1982–June 1994) are reported. The observations from Cape Grim have been extended back to 1978 using archived air samples. The global atmospheric abundance of CCl2FCClF2 is indicated to have been growing exponentially between 1978 and 1987 with an e-folding time of approximately 7.6 years; it has been growing less rapidly since that time. On January 1, 1994, the mean inferred northern hemispheric mixing ratio in the lower troposphere was 84.4 ± 0.4 ppt and the southern hemispheric value was 80.6 ± 0.4 ppt; the global growth rate in 1991–1993 is estimated to have averaged approximately 3.1 ± 0.1 ppt/year. The differences between the northern and southern hemispheric concentrations are calculated to be consistent with the almost entirely northern hemispheric release of this gas. The annual release estimates of CCl2FCClF2 by industry, which include estimates of eastern European emissions, fairly consistently exceed those deduced from the measurements by approximately 10% from 1980 to 1993. The uncertainties in each estimate is approximately 5%. This difference suggests that up to 10% of past production might not yet have been released. The measurements indicate that atmospheric releases of CCl2FCClF2 have been decreasing rapidly since 1989 and in 1993 amounted to 78 ± 27 × 106 kg or 42 ± 15% of the 1985–1987 emissions.

Atmospheric aerosol measurements at Mace Head, Ireland Atmospheric aerosol measurements at Mace Head, Ireland

Date added: 08/07/2000
Date modified: 07/27/2009
Filesize: 247.74 kB
Jennings S.G., Atmospheric aerosol measurements at Mace Head, Ireland,Journal of Aerosol Science, Volume 31, Supplement 1, September 2000 , pp. 580-583(4)

Abstract


The atmospheric aerosol plays a fundamental role in the earth's atmosphere, involving solid particulate material. Interest in atmospheric aerosol research has increased dramatically in recent years, as evidenced by a rapidly increasing publication rate in the discipline and through an accelerating presence in both national and international conference media. In earlier decades, interest in atmospheric aerosols was mainly because of their effects on visibility. More recently the accelerated interest in aerosols is largely due to their role in climate effects and in atmospheric chemistry processes. This has also been recognised internationally through activities, such as for example the International Global Atmospheric Chemistry (IGAC) Focus on aerosols and the World Meteorological Organisation (WMO), Global Atmospheric Watch (GAW) Aerosol, (WMO, 1997).

One of the largest uncertainties associated with climate forcing relates to the atmospheric aerosol, as noted by the Inter-Governmental Panel on Climate Change (IPCC); Houghton et al., 1995. The atmospheric aerosol shows large variability both in time and in space (Dreiling and Jaenicke, 1994) and is one of the major outstanding uncertainties in atmospheric aerosol research. Recently, there have been increasing studies of the natural aerosol since it is recognised that until natural background aerosol sources are better quantified, the influence of the more pollutant anthropogenic aerosol on climate for example, cannot be fully understood. The Mace Head Atmospheric Research Station has provided a good platform for the performance of a range of atmospheric aerosol studies some of which are summarised in the following pages.

On the spatial distribution and evolution of ultrafine aerosols in Barcelona On the spatial distribution and evolution of ultrafine aerosols in Barcelona

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.29 MB

Dall'Osto, M., X. Querol, A. Alastuey, C. O'Dowd, R. M. Harrison, J. Wenger, and F. J. Gómez-Moreno, On the spatial distribution and evolution of ultrafine aerosols in Barcelona, Atmos. Chem. Phys. 13, 741–759, 2013, doi:10.5194/acp-13-741-2013.


Abstract. Sources and evolution of ultrafine particles were investigated both horizontally and vertically in the large urban agglomerate of Barcelona, Spain. Within the SAPUSS project (Solving Aerosol Problems by Using Synergistic Strategies), a large number of instruments was deployed simultaneously at different monitoring sites (road, two urban background, regional background, urban tower 150m a.s.l., urban background tower site 80m a.s.l.) during a 4 week period in September–October 2010. Particle number concentrations (N>5nm) are highly correlated with black carbon (BC) at all sites only under strong vehicular traffic influences. By contrast, under cleaner atmospheric conditions (low condensation sink, CS) such correlation diverges towards much higher N/BC ratios at all sites, indicating additional sources of particles including secondary production of freshly nucleated particles. Size-resolved aerosol distributions (N10−500) as well as particle number concentrations (N>5 nm) allow us to identify three types of nucleation and growth events: (1) a regional type event originating in the whole study region and impacting almost simultaneously the urban city of Barcelona and the surrounding urban background area; (2) a regional type event impacting only the regional background area but not the urban agglomerate; (3) an urban type event which originates only within the city centre but whose growth continues while transported away from the city to the regional background. Furthermore, during these clean air days, higher N are found at tower level than at ground level only in the city centre whereas such a difference is not so pronounced at the remote urban background tower. In other words, this study suggests that the column of air above the city ground level possesses the optimal combination between low CS and high vapour source, hence enhancing the concentrations of freshly nucleated particles. By contrast, within stagnant polluted atmospheric conditions, higher N and BC concentrations are always measured at ground level relative to tower level at all sites. Our study suggests that the city centre of Barcelona is a source of non-volatile traffic primary particles (29–39% of N>5nm), but other sources, including secondary freshly nucleated particles contribute up to 61–71% of particle number (N>5nm) at all sites. We suggest that organic compounds evaporating from freshly emitted traffic particles are a possible candidate for new particle formation within the city and urban plume.

 

Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Adv Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Adv

Date added: 08/06/2004
Date modified: 07/23/2009
Filesize: 791.05 kB

O'Doherty, S., et al. (2004), Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Advanced Global Atmospheric Gases Experiment (AGAGE) observations at Cape Grim, Tasmania, and Mace Head, Ireland, J. Geophys. Res., 109, D06310, doi:10.1029/2003JD004277.


Abstract


An update of in situ Advanced Global Atmospheric Gases Experiment (AGAGE) hydrofluorocarbon (HFC)/hydrochlorofluorocarbon (HCFC) measurements made at Mace Head, Ireland, and Cape Grim, Tasmania, from 1998 to 2002 are reported. HCFC-142b, HCFC-141b, HCFC-22 and HFC-134a show continued rapid growth in the atmosphere at mean rates of 1.1, 1.6, 6.0, and 3.4 ppt/year, respectively. Emissions inferred from measurements are compared to recent estimates from consumption data. Minor updates to the industry estimates of emissions are reported together with a discussion of how to best determine OH concentrations from these trace gas measurements. In addition, AGAGE measurements and derived emissions are compared to those deduced from NOAA-Climate Monitoring and Diagnostics Laboratory flask measurements (which are mostly made at different locations). European emission estimates obtained from Mace Head pollution events using the Nuclear Accident Model (NAME) dispersion model and the best fit algorithm (known as simulated annealing) are presented as 3-year rolling average emissions over Europe for the period 1999–2001. Finally, the measurements of HCFC-141b, HCFC-142b, and HCFC-22 discussed in this paper have been combined with the Atmospheric Lifetime Experiment (ALE)/Global Atmospheric Gases Experiment (GAGE)/AGAGE measurements of CFC-11, CFC-12, CFC-113, CCl4, and CH3CCl3 to produce the evolution of tropospheric chlorine loading.

 

Measurements of aerosol scattering coefficient over a period of 2 years at Mace Head, Ireland Measurements of aerosol scattering coefficient over a period of 2 years at Mace Head, Ireland

Date added: 08/07/1999
Date modified: 08/07/2008
Filesize: 134.93 kB
Ch. Kleefeld, S. O'Reilly and S.G. Jennings ,MEASUREMENTS OF AEROSOL SCATTERING COEFFICIENT OVER A PERIOD OF 2 YEARS AT MACE HEAD, IRELAND,J. Aerosol Sci. Vol. 30, Suppl. 1, pp. S 157-S 158, 1999

Estimating relationships between air mass origin and chemical composition Estimating relationships between air mass origin and chemical composition

Date added: 08/06/2001
Date modified: 07/27/2009
Filesize: 1.49 MB

Methven, J., M. Evans, P. Simmonds, and G. Spain (2001), Estimating relationships between air mass origin and chemical composition, J. Geophys. Res., 106(D5), 5005–5019.


Abstract


Observations of a chemical at a point in the atmosphere typically show sudden transitions between episodes of high and low concentration. Often these are associated with a rapid change in the origin of air arriving at the site. Lagrangian chemical models riding along trajectories can reproduce such transitions, but small timing errors from trajectory phase errors dramatically reduce the correlation between modeled concentrations and observations. Here the origin averaging technique is introduced to obtain maps of average concentration as a function of air mass origin for the East Atlantic Summer Experiment 1996 (EASE96, a ground-based chemistry campaign). These maps are used to construct origin averaged time series which enable comparison between a chemistry model and observations with phase errors factored out. The amount of the observed signal explained by trajectory changes can be quantified, as can the systematic model errors as a function of air mass origin. The Cambridge Tropospheric Trajectory model of Chemistry and Transport (CiTTyCAT) can account for over 70% of the observed ozone signal variance during EASE96 when phase errors are side-stepped by origin averaging. The dramatic increase in correlation (from 23% without averaging) cannot be achieved by time averaging. The success of the model is attributed to the strong relationship between changes in ozone along trajectories and their origin and its ability to simulate those changes. The model performs less well for longer-lived chemical constituents because the initial conditions 5 days before arrival are insufficiently well known.

 

Observations and modelling of aerosol growth in marine stratocumulus - Case Study Observations and modelling of aerosol growth in marine stratocumulus - Case Study

Date added: 08/31/1999
Date modified: 07/03/2009
Filesize: 364.64 kB

O'Dowd, C.D., J.A. Lowe, and M.H. Smith, Observations and modelling of aerosol growth in marine stratocumulus - Case Study. Atmos. Environ, 33, 3053-3062, 1999.


Abstract


Airborne measurements of the growth of the marine accumulation mode after multiple cycles through stratocumulus cloud are presented. The nss-sulphate cloud residual mode was log-normal in spectral shape and it's mode radius was observed to progressively increase in size from 0.78 to 0.94 μm over 155 min of air parcel evolution through the cloudy marine boundary layer. The primary reason for this observed growth was thought to result from aqueous phase oxidation of SO2 to aerosol sulphate in activated cloud drops. An aqueous phase aerosol-cloud-chemistry model was used to simulate this case study of aerosol growth and was able to closely reproduce the observed growth. The model simulations illustrate that aqueous phase oxidation of SO2 in cloud droplets was able to provide enough additional sulphate mass to increase the size of activated aerosol. During a typical cloud cycle simulation, ≃ 4.6 nmoles kgair-1 (0.44 μg m-3) of sulphate mass was produced with ≃ 70% of sulphate production occurring in cloud droplets activated upon sea-salt nuclei and ≃ 30% occurring upon nss-sulphate nuclei, even though sea-salt nuclei contributed less than 15% to the activated droplet population. The high fraction of nss-sulphate mass internally mixed with sea-salt aerosol suggests that aqueous phase oxidation of SO2 in cloud droplets activated upon sea-salt nuclei is the dominant nss-sulphate formation mechanism and that sea-salt aerosol provides the primary chemical sink for SO2 in the cloudy marine boundary layer.

Optical properties of the atmospheric aerosol at mace head Optical properties of the atmospheric aerosol at mace head

Date added: 08/07/1999
Date modified: 07/23/2009
Filesize: 118.21 kB

O'Reilly S.; Kleefeld C.; Jennings S.G.,Optical properties of the atmospheric aerosol at mace head  ,Journal of Aerosol Science, Volume 30, Supplement 1, September 1999 , pp. 631-632(2)


Abstract

 

The atmospheric aerosol is known to cause cooling of the earth's climate through radiative forcing. This forcing is comparable but of opposite sign to the radiative forcing due to greenhouse gases [1PCC, 1995]. However, unlike greenhouse gases, the atmospheric aerosol is not uniformly distributed about the globe. It is found to vary significantly both spatially and temporally. Therefore, an analysis of global radiative forcing due to the atmospheric aerosol requires an estimation of forcing on a regional scale. Characterisation of the optical properties of the local atmospheric aerosol forms an integral part of such an estimation. The scattering coefficient, Osp, and absorption coefficient, (Yap, of the atmospheric aerosol are basic input parameters to radiative forcing models. These parameters have been measured since 1996 and 1989, respectively, at the Global Atmospheric Watch (GAW/WMO) atmospheric research station at Mace Head (53°19'N, 9°54'W), located on the west coast of Ireland. The results of measurements from 7 th January 1997 to 12 th June ! 997 are presented. The scattering measurements were conducted with a TSI Model 3563 Integrating Nephelometer, operating at three wavelengths (450nm, 550nm and 700nm). It also had the
capability of measuring aerosol hemispheric backscatter coefficient from 90 ° to 180 °. Black carbon mass concentrations were measured using a Magee Scientific Model AE9 Aethalometer. The absorption coefficient for each wavelength was obtained by dividing black carbon mass concentrations by a constant, C; C(~=450nm)=1.5, C()~=550nm)=1.9 and C(L=700nm)=2.4 [Bodhaine, 1995], in order to compare with the aerosol scattering coefficients at these wavelengths. The scattering coefficient, Osp, for ~.=550nm ranged from 7 to 280 Mm -1 with an average and standard deviation of 76 + 49 Mm "l (geometric mean of 60 + 2 Mmt). The corresponding hemispheric backscattering coefficient, Cbsp, measurements were about an order of magnitude lower than (ysp ranging from 0.9 to 35 Mm "1 (geometric mean of 7 + 2 Mm-I). This results in a hemispheric backscattered fraction, b, of 0.12 + 0.01 (geometric mean of 0.12). The AngstrOm exponent, describes the dependence of the aerosol scattering coefficient on wavelength, )~. The red-blue Angstr6m exponent (Ll=700nm, ~2=450nm) was found to range from -1.9 to 0.15 with an average of-0.66 + 0.7 (geometric mean of-0.69). The absorption coefficient, aap, for ~.=550nm ranged from 0.12 to 22 Mm "l and averaged 1.7 Mm "1 (geometric mean of 0.9 Mm'l). This results in an extinction coefficient, (yext, averaging 77.7Mm "1 (geometric mean of 53+2Mm'l). The scattering and absorption coefficients areused to calculate the single-scattering albedo, which describes the relative contributions of scattering and absorption to the total light extinction. The calculated albedo values ranged from 0.9 to 0.998 and averaged 0.97 + 0.02 (geometric mean of 0.97), indicating a highly scattering aerosol. The single scattering albedo exhibits a logarithmic correlation (R2=0.55, significant at a 99% confidence level) with black carbon concentrations. As black carbon levels increase, the albedo values can be seen to decrease  The scattering time series obtained were found to change with impact of different types of air mass (continental, marine and polar). The influence of synoptic meteorology on the scattering coefficient at Mace Head will be quantified by combining the pattern recognition capabilities of cluster analysis with air mass back-trajectory data.

 

Low European methyl chloroform emissions inferred from long-term atmospheric measurements Low European methyl chloroform emissions inferred from long-term atmospheric measurements

Date added: 08/26/2005
Date modified: 07/24/2009
Filesize: 186.75 kB

S. Reimann, A.J. Manning, P.G. Simmonds, D.M. Cunnold, R.H.J. Wang, J. Li, A. McCulloch, R.G. Prinn, J. Huang, R.F. Weiss, P.F. Fraser, S. O'Doherty, B.R. Greally, K. Stemmler, M. Hill, and D. Folini, (2005), Low European methyl chloroform emissions inferred from long-term atmospheric measurements, Nature, 433, 506-508.


Abstract


Methyl chloroform (CH3CCl3, 1,1,1,-trichloroethane) was used widely as a solvent before it was recognized to be an ozone-depleting substance and its phase-out was introduced under the Montreal Protocol'. Subsequently, its atmospheric concentration has declined steadily2-4 and recent European methyl chloroform consumption and emissions were estimated to be less than 0.1 gigagrams per year1,5. However, data from a short-term tropospheric measurement campaign (EXPORT) indicated that European methyl chloroform emissions could have been over 20 gigagrams in 2000 (ref. 6), almost doubling previously estimated global emissions1,4. Such enhanced emissions would significantly affect results from the CH3CCl3 method of deriving global abundances of hydroxyl radicals (OH) (refs 7-12) - the dominant reactive atmospheric chemical for removing trace gases related to air pollution, ozone depletion and the greenhouse effect. Here we use long-term, high-frequency data from Mace Head, Ireland and Jungfraujoch, Switzerland, to infer European methyl chloroform emissions. We find that European emission estimates declined from about 60 gigagrams per year in the mid-1990s to 0.3-1.4 and 1.9-3.4 gigagrams per year in 2000-03, based on Mace Head and Jungfraujoch data, respectively. Our European methyl chloroform emission estimates are therefore higher than calculated from consumption data1,5, but are considerably lower than those derived from the EXPORT campaign in 2000

Atmospheric particle formation events at Värriö measurement station in Finnish Lapland 1998–2002 Atmospheric particle formation events at Värriö measurement station in Finnish Lapland 1998–2002

Date added: 08/01/2004
Date modified: 06/30/2009
Filesize: 683.76 kB

Vehkamäki, H., M. Dal Maso, T. Hussein, R. Flanagan, A. Hyvärinen, J. Lauros, J. Merikanto, P. Mönkkönen, M. Pihlatie, K. Salminen, L. Sogacheva, T. Thum, T. M. Ruuskanen, P. Keronen, P. P. Aalto, P. Hari, K. E. J. Lehtinen, Ü. Rannik, and M. Kulmala. Atmospheric particle formation events at Värriö measurement station in Finnish Lapland 1998–2002. Atmospheric Chemistry and Physics, Vol 4, pp. 2015-2023, 2004.


Abstract

 

During the calendar years 1998-2002, 147 clear 8nm diameter particle formation events have been identified at the SMEAR I station in Värriö, northern Finland. The events have been classified in detail according to the particle formation rate, growth rate, event starting time, different trace gas concentrations and pre-existing particle concentrations as well as various meteorological conditions. The frequency of particle formation and growth events was highest during the spring months between March and May, suggesting that increasing biological activity might produce the precursor gases for particle formation. The apparent 8nm particle formation rates were around 0.1 /cm3s, and they were uncorrelated with growth rates that varied between 0.5 and 10nm/h. The air masses with clearly elevated sulphur dioxide concentrations (above 1.6ppb) came, as expected, from the direction of the Nikel and Monschegorsk smelters. Only 15 formation events can be explained by the pollution plume from these sources.

Evolution of the aerosol, cloud and boundary layer dynamic and ACE2 Evolution of the aerosol, cloud and boundary layer dynamic and ACE2

Date added: 08/06/2000
Date modified: 07/01/2009
Filesize: 1.38 MB

Osborne, S.M., D.W.Johnson, R. Wood, B.J. Bandy, M.O. Andreae, C.D. O'Dowd, P. Glantz, K.J. Noone, C. Gerbig, J. Rudolph, T.S. Bates, and P.K. Quinn, Evolution of the aerosol, cloud and boundary layer dynamic and thermodynamic characteristics during the second Lagrangian experiment of ACE-2, Tellus, 52B(2), 375-400, 2000, (Ser. No. ACP149).


Abstract


We present observations from the 2nd Aerosol Characterisation Experiment where over a 29-h period between 16–18 July 1997 a tagged column of air was followed by a fully instrumented aircraft. The Lagrangian framework this offered made it possible to measure the evolution of the aerosol size distribution, the cloud structure and microphysics, and the dynamic and thermodynamic structure of the marine boundary layer within a polluted airmass advecting off northwest Europe over the sub-tropical North Atlantic Ocean. The salient observations are presented and analysed. Processes responsible for the evolution are suggested, but quantification of their respective rates must be taken up by future modelling studies. Stratocumulus capped the boundary layer throughout the period that produced negligible washout of aerosol. This implies that the conversion of a continental to a maritime airmass within the cloud-capped sub-tropical marine boundary layer is not controlled by the drizzle process but by entrainment from the free troposphere. We find evidence of processing of aerosol particles by stratocumulus cloud, in particular by aqueous-phase reactions. The processing of the aerosol, realised by modification of the aerosol size distribution in the particle diameter range 0.1–0.5 mum, was complicated by rapid changes in boundary layer height and structure, and also by entrainment of both polluted and relatively clean aerosol from the free troposphere. The cloud microphysics was affected by these changes in the boundary layer aerosol through changes in the cloud condensation nuclei activation spectra. The cloud microphysics was also strongly affected by changes in the dynamics of the boundary layer which included variations (e.g., diurnal) in cloud thickness and an increase in vertical wind speed. Thermodynamic changes within the boundary layer included decoupling due to an increasing sea-surface temperature and a change in the subsidence rate in the free troposphere superimposed on diurnal decoupling. Hypotheses have been devised so that future modellers can focus their efforts to either validate or invalidate potentially important processes.

 

Model evaluation of marine primary organic aerosol emission schemes Model evaluation of marine primary organic aerosol emission schemes

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.12 MB

Gantt, B., M. S. Johnson, N. Meskhidze, J. Sciare, J. Ovadnevaite, D. Ceburnis, C. D. O’Dowd, Model evaluation of marine primary organic aerosol emission schemes, Atmos. Chem. & Phys., 12, 8553–8566, 2012

www.atmos-chem-phys.net/12/8553/2012/ doi:10.5194/acp-12-8553-2012.


Abstract. In this study, several marine primary organic aerosol (POA) emission schemes have been evaluated using the GEOS-Chem chemical transport model in order to provide guidance for their implementation in air quality and climate models. These emission schemes, based on varying dependencies of chlorophyll a concentration ([chl a]) and 10m wind speed (U10), have large differences in their magnitude, spatial distribution, and seasonality. Model comparison with weekly and monthly mean values of the organic aerosol mass concentration at two coastal sites shows that the source function exclusively related to [chl a] does a better job replicating surface observations. Sensitivity simulations in which the negative U10 and positive [chl a] dependence of the organic mass fraction of sea spray aerosol are enhanced show improved prediction of the seasonality of the marine POA concentrations. A top-down estimate of submicron marine POA emissions based on the parameterization that compares best to the observed weekly and monthly mean values of marine organic aerosol surface concentrations has a global average emission rate of 6.3 Tg yr−1. Evaluation of existing marine POA source functions against a case study during which marine POA contributed the major fraction of submicron aerosol mass shows that none of the existing parameterizations are able to reproduce the hourly-averaged observations. Our calculations suggest that in order to capture episodic events and short-term variability in submicron marine POA concentration over the ocean, new source functions need to be developed that are grounded in the physical processes unique to the organic fraction of sea spray aerosol.

 

First appearance and rapid growth of anthropogenic HFC-245fa (CHF2CH2CF3) in the atmosphere First appearance and rapid growth of anthropogenic HFC-245fa (CHF2CH2CF3) in the atmosphere

Date added: 08/05/2006
Date modified: 07/01/2009
Filesize: 398.7 kB
Vollmer, M. K., S. Reimann, D. Folini, L. W. Porter, and L. P. Steele (2006), First appearance and rapid growth of anthropogenic HFC-245fa (CHF2CH2CF3) in the atmosphere, Geophys. Res. Lett., 33, L20806, doi:10.1029/2006GL026763.

Abstract


We capture the first atmospheric appearance of HFC-245fa (CHF2CH2CF3), a new foam blowing agent. Our results from the high-altitude observatory at Jungfraujoch, Switzerland, show a rapid growth of this substance in the northern hemispheric troposphere from 0.28 ppt in July 2004 to 0.68 ppt at the end of 2005, which corresponds to an overall increase of >90% per year. By combining our observations with an atmospheric 3-box model we estimate a southern hemispheric trend for this trace gas which we compare to observations at southern hemisphere mid-latitudes. We also estimate a global HFC-245fa emissions increase from 2100–2400 tonnes in 2003 to 5100–5900 tonnes in 2005. Pollution episodes are relatively rare at Jungfraujoch compared to other hydrofluorocarbons thereby confirming the limited use of HFC-245fa in Europe. Back trajectory analysis reveals the largest potential European sources of HFC-245fa in northern Italy and northeastern Spain.

Atmospheric Sulphur Levels in Western Ireland Atmospheric Sulphur Levels in Western Ireland

Date added: 08/07/1969
Date modified: 07/27/2009
Filesize: 2.97 MB
O'Connor. TC., Atmospheric Sulphur Levels In Western Ireland, Sulphur in Agriculture, AN Foras Taluntais, Dublin, 1969

Abstract

 

Sulphur compounds can exist in the atmosphere in the solid, liquid or gaseous form, depending on their origin and subsequent history. They have deleterious effect on the health of humans, plants and animals and by their corrosive action on buildings and other materials. They have also been studied for their beneficial effects, for example, the nutrition of plants and other natural processes in soils and weathering. They can also be involved in processes of cloud formation and the geochemistry around the world. Although there have been many studies or atmospheric sulphur levels in polluted areas there is little data available on the natural background concentrations of sulphur dioxide in unpolluted areas in temperate latitudes.

This paper is concerned with some aspects of the atmospheric portion of the natural cycle of sulphur. it describes some investigations into the concentrations of sulphur dioxide at a variety of sites. in Galway city, Sine references to recent paper on specific aspects of the sulpur cycle are also given.

Marine aerosol formation from biogenic iodine emissions Marine aerosol formation from biogenic iodine emissions

Date added: 07/31/2002
Date modified: 07/02/2009
Filesize: 373.3 kB

O'Dowd, C.D., J.L. Jimenez, R. Bahreini, R.C. Flagan, J.H. Seinfeld, K. Hämeri, L. Pirjola, M. Kulmala, S.G. Jennigns and T. Hoffmann, Marine aerosol formation from biogenic iodine emissions, Nature, 417, 632-636, 2002.


Abstract


The formation of marine aerosols and cloud condensation nuclei—from which marine clouds originate—depends ultimately on the availability of new, nanometre-scale particles in the marine boundary layer. Because marine aerosols and clouds scatter incoming radiation and contribute a cooling effect to the Earth's radiation budget1, new particle production is important in climate regulation. It has been suggested that sulphuric acid—derived from the oxidation of dimethyl sulphide—is responsible for the production of marine aerosols and cloud condensation nuclei. It was accordingly proposed that algae producing dimethyl sulphide play a role in climate regulation2, but this has been difficult to prove and, consequently, the processes controlling marine particle formation remains largely undetermined3, 4. Here, using smog chamber experiments under coastal atmospheric conditions, we demonstrate that new particles can form from condensable iodine-containing vapours, which are the photolysis products of biogenic iodocarbons emitted from marine algae. Moreover, we illustrate, using aerosol formation models, that concentrations of condensable iodine-containing vapours over the open ocean are sufficient to influence marine particle formation. We suggest therefore that marine iodocarbon emissions have a potentially significant effect on global radiative forcing.

Aerosol decadal trends – Part 1: In-situ optical measurements at GAW and IMPROVE stations Aerosol decadal trends – Part 1: In-situ optical measurements at GAW and IMPROVE stations

Date added: 03/12/2013
Date modified: 03/12/2013
Filesize: 2.64 MB

Collaud Coen, M., E. Andrews, A. Asmi, U. Baltensperger, N. Bukowiecki, D. Day, M. Fiebig, A. M. Fjaeraa, H. Flentje, A. Hyvärinen, A. Jefferson, S. G. Jennings, G. Kouvarakis, H. Lihavainen, C. Lund Myhre, W. C. Malm, N. Mihapopoulos, J. V. Molenar, C. O'Dowd, J. A. Ogren, B. A. Schichtel, P. Sheridan, A. Virkkula, E. Weingartner, R. Weller, and P. Laj,Aerosol decadal trends – Part 1: In-situ optical measurements at GAW and IMPROVE stations, Atmos. Chem. Phys., 13, 869-894, 2013, www.atmos-chem-phys.net/13/869/2013/doi:10.5194/acp-13-869-2013.


Abstract. Currently many ground-based atmospheric stations include in-situ measurements of aerosol physical and optical properties, resulting in more than 20 long-term (> 10 yr) aerosol measurement sites in the Northern Hemisphere and Antarctica. Most of these sites are located at remote locations and monitor the aerosol particle number concentration, wavelength-dependent light scattering, backscattering, and absorption coefficients. The existence of these multi-year datasets enables the analysis of long-term trends of these aerosol parameters, and of the derived light scattering Ångström exponent and backscatter fraction. Since the aerosol variables are not normally distributed, three different methods (the seasonal Mann-Kendall test associated with the Sen's slope, the generalized least squares fit associated with an autoregressive bootstrap algorithm for confidence intervals, and the least-mean square fit applied to logarithms of the data) were applied to detect the long-term trends and their magnitudes. To allow a comparison among measurement sites, trends on the most recent 10 and 15 yr periods were calculated. No significant trends were found for the three continental European sites. Statistically significant trends were found for the two European marine sites but the signs of the trends varied with aerosol property and location. Statistically significant decreasing trends for both scattering and absorption coefficients (mean slope of −2.0% yr−1) were found for most North American stations, although positive trends were found for a few desert and high-altitude sites. The difference in the timing of emission reduction policy for the Europe and US continents is a likely explanation for the decreasing trends in aerosol optical parameters found for most American sites compared to the lack of trends observed in Europe. No significant trends in scattering coefficient were found for the Arctic or Antarctic stations, whereas the Arctic station had a negative trend in absorption coefficient. The high altitude Pacific island station of Mauna Loa presents positive trends for both scattering and absorption coefficients.

 

Evidence of a natural marine source of oxalic acid and a possible link to glyoxal Evidence of a natural marine source of oxalic acid and a possible link to glyoxal

Date added: 03/14/2013
Date modified: 03/14/2013
Filesize: 410.96 kB
Rinaldi, Matteo, Stefano Decesari, Claudio Carbone, Emanuela Finessi, Sandro Fuzzi, Darius Ceburnis, Colin D. O’Dowd, Jean Sciare, John P. Burrows, Mihalis Vrekoussis, Barbara Ervens, Kostas Tsigaridis, and Maria Cristina Facchini, Evidence of a natural marine source of oxalic acid and a possible link to glyoxal, J. Geophys. Res., 116, D162,04, 12 PP., 2011, doi:10.1029/2011JD015659, 2011 __________________________________________________ Abstract. This paper presents results supporting the existence of a natural source of oxalic acid over the oceans. Oxalate was detected in “clean‐sector” marine aerosol samples at Mace Head (Ireland) (53°20’N, 9°54′W) during 2006, and at Amsterdam Island (37°48′S, 77°34′E) from 2003 to 2007, in concentrations ranging from 2.7 to 39 ng m−3 and from 0.31 to 17 ng m−3, respectively. The oxalate concentration showed a clear seasonal trend at both sites, with maxima in spring‐summer and minima in fall‐winter, being consistent with other marine biogenic aerosol components (e.g., methanesulfonic acid, non‐sea‐salt sulfate, and aliphatic amines). The observed oxalate was distributed along the whole aerosol size spectrum, with both a submicrometer and a supermicrometer mode, unlike the dominant submicrometer mode encountered in many polluted environments. Given its mass size distribution, the results suggest that over remote oceanic regions oxalate is produced through a combination of different formation processes. It is proposed that the cloud‐mediated oxidation of gaseous glyoxal, recently detected over remote oceanic regions, may be an important source of submicrometer oxalate in the marine boundary layer. Supporting this hypothesis, satellite‐retrieved glyoxal column concentrations over the two sampling sites exhibited the same seasonal concentration trend of oxalate. Furthermore, chemical box model simulations showed that the observed submicrometer oxalate concentrations were consistent with the in‐cloud oxidation of typical marine air glyoxal mixing ratios, as retrieved by satellite measurements, at both sites.

Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic

Date added: 03/12/2013
Date modified: 03/12/2013
Filesize: 677.22 kB

Aditya Vaishya, S. G. Jennings, and Colin O’Dowd. Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic, Advances in Meteorology, Volume 2011, Article ID 170490, doi:10.1155/2011/170490.


Abstract. Aerosol light scattering measurements were carried out using a TSI 3563 Nephelometer at the Mace Head Atmospheric Research Station, on the west coast of Ireland from year 2001–2010. A strong seasonal trend in the aerosol light scattering coefficient at 550nm (σscat), for clean marine air masses, is observed with a high σscat value, [average (geometric mean)] of 35.3Mm1(29.5Mm1), in January and a low σscat value of 13.7Mm1 (10.2Mm1), in July. This near threefold increase in the σscat value during the winter season is because of the large contribution of wind-speed generated sea-salt particles in the marine boundary layer. A high positive correlation coefficient of 0.82 was found between the percentage occurrence of relatively large A°ngstrom exponent (A° ) values (>1.2) and the percentage occurrence of lower σscat values (5–15Mm1) in the summer season. σscat and wind-speed have a high positive correlation coefficient of 0.88 whereas A° and wind-speed have a negative correlation coefficient of 0.89.values during the summer months indicate the dominance of sub-μm particles thus indicating the contribution of non-sea-salt sulphate and organics towards the σscat as these species show an enhanced concentration during the summer months.

 

LIDAR studies of the atmospheric boundary layer and locally generated sea spray aerosol plumes at Ma LIDAR studies of the atmospheric boundary layer and locally generated sea spray aerosol plumes at Ma

Date added: 07/31/2002
Date modified: 07/02/2009
Filesize: 798.06 kB
Gerard Kunz, Gerrit de Leeuw, Colin O'Dowd, Edo Becker.LIDAR studies of the atmospheric boundary layer and locally generated sea spray aerosol plumes at Mace Head. J. Geophys. Res., 107, 10.1029/2001JD001240, 2002.

Abstract

 

A scanning backscatter lidar was used to measure the depth and structure of the coastal atmospheric boundary layer and the evolution of primary aerosol (sea spray) plumes produced by breaking waves during the New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign at the Mace Head Atmospheric Research Station (Ireland) in September 1998 and in June 1999. The PBL structure was observed to vary from a single-layer well-mixed structure to multilayered structures. Comparison with in situ aircraft measurements of temperature and humidity exhibited good agreement. Using the lidar in the scanning mode allowed two-dimensional profiling over a spatial scale of 10 km, revealing significant primary aerosol plumes produced by breaking waves, particularly in the surf zone and at high wind speeds on the open sea. The initial plume heights were some tens of meters and evolved to hundreds of meters while transported over only a few kilometers from the source. The plumes were traceable to distances of more than 10 km down wind from the source.

Backround Bioaerosol Measurements at Mace Head Backround Bioaerosol Measurements at Mace Head

Date added: 08/26/1998
Date modified: 07/27/2009
Filesize: 113.15 kB

Kenny, C.M., and Jennings, S.G. (1998). Background bioaerosol measurements at Mace Head. J. Aerosol Sci., 29, S779-S780.


Abstract


Primary biological aerosol particles consist of airborne viable or non-viable material which are an ubiquitous component of the atmospheric aerosol. The types of particles considered as bioaerosols cover a very large size range, smallest in size are viruses (- 0.005 pm < radius< - 0.25 pm); larger particles include bacteria (r > - 0.2 pm), algae spores and fungi (r > - 0.5 pm) and pollen grains (r > - 5 pm), (Macher, 1993). Plant debris like leaf litter, parts of insects and human and animal epithhelial cells have a supposed r > - 1 pm. Assessment of bioaerosols is generally more complicated than that of non-bioaerosols - for example bioaerosol viability may be affected by a variety of stresses (desiccation, radiation, oxygen toxicity, chemical pollutants etc.) in the environment. A background bioaerosol measurement programme is currently taking place at the Mace Head Atmospheric Field Research Station, Carna, Co. Galway. Effective biological analysis of airborne particles requires samplers operating at a high flow rate and with the capability of concentrating the air particles into a fairly small liquid volume. Use has been made of a glass Aerojet cyclone high volume sampler which has been proven to be successful for the collection of bioaerosol material. Cyclones with spray wetters have been found to be gentle with airborne microorganisms and help to maintain cell viability levels. Utilising a blue protein dye,  uantitative determination of the percentage biological and non-biological species present in the aerosol has been made. The  staining solution reacts with the carboxyl group of a protein and therefore stains the protein-containing or biological particles blue. Non-biologicals are not changed by the stain. Under the light microscope the effects of the protein dye on different particle types can be seen and biological particles can be classified by their characteristic morphology and size. Filters have been examined using a Leitz microscope (Laborlux S), equipped with a 10x ocular lens and an objective lens, Plan 40, and size distribution spectra of the bioaerosol species have been measured. The samples were evaluated into size classes (3.5 urn < diameter < 40 urn) and size distributions of the total aerosol were obtained. The percentages of biological particles in the corresponding size classes are shown in Figure 1. The highest percentage of total biological particles < 10 urn occurs during the modified marine periods 07/25/97 and 07/l l/97 which reflects the passage of the air mass over land. The marine sample 07/15/97 shows a consistently high percentage of biological particles over the larger size ranges. The two predominant peaks occuring during the marine period 07/04/97 are caused by spores. Coupling size distribution spectra with corrected fluorescence spectra of the same air sample yield quantitative effective fluorescence cross-section per unit volume of background air. Analysis of size distribution spectra of the total aerosol, will be presented for both maritime and polluted air.

Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements

Date added: 08/05/2007
Date modified: 07/23/2009
Filesize: 683.98 kB
Xiao, X., et al. (2007), Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements, J. Geophys. Res., 112, D07303, doi:10.1029/2006JD007241.

Abstract


Hydrogen (H2), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts. The magnitudes and seasonal cycles of the major (presumably microbial) soil sink of hydrogen have been estimated from high-frequency in situ AGAGE H2 observations and also from more geographically extensive but low-frequency flask measurements from CSIRO and NOAA-GMD using the Kalman filter in a two-dimensional (2-D) global transport model. Hydrogen mole fractions exhibit well-defined seasonal cycles in each hemisphere with their phase difference being only about 3 months. The global production rate of H2 is estimated to be 103 ± 10 Tg yr−1 with only a small estimated interannual variation. Soil uptake (84 ± 8 Tg yr−1) represents the major loss process for H2 and accounts for 81% of the total destruction. Strong seasonal cycles are deduced for the soil uptake of H2. The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere. Oxidation by tropospheric OH (18 ± 3 Tg yr−1) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere. The calculated global burden is 191 ± 29 Tg, indicating an overall atmospheric lifetime of 1.8 ± 0.3 years. Hydrogen in the troposphere (149 ± 23 Tg burden) has a lifetime of 1.4 ± 0.2 years.

Global trends and emission estimates of CCl4 from in situ background observations from July 1978 to June 1996 Global trends and emission estimates of CCl4 from in situ background observations from July 1978 to June 1996

Date added: 08/01/1998
Date modified: 07/24/2009
Filesize: 1.15 MB

Simmonds, P. G., D. M. Cunnold, R. F. Weiss, R. G. Prinn, P. J. Fraser, A. McCulloch, F. N. Alyea, and S. O'Doherty (1998), Global trends and emission estimates of CCl4 from in situ background observations from July 1978 to June 1996, J. Geophys. Res., 103(D13), 16,017–16,027


Abstract


Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment/Advanced Global Atmospheric Gases Experiment (ALE/GAGE/AGAGE) measurements of CCl4 at five remote surface locations from 1978 to 1996 are reported. The Scripps Institution of Oceanography (SIO) 1993 absolute calibration scale is used, reducing the concentrations by a factor of 0.77 compared to previous ALE/GAGE reports. Atmospheric concentrations of CCl4 reached a peak in 1989-1990 of 104.4 ± 3.1 parts per trillion (ppt) and have since been decreasing 0.7 ± 0.1 ppt yr-1. Assuming an atmospheric lifetime of 42 ± 12 years, the emissions averaged 94-11+22 × 106 kg from 1979 to 1988 and 49-13+26 × 106 kg from 1991 to 1995. The reduction in the emissions in 1989-1990 coincided with a substantial decrease in the global production of the chlorofluorocarbons (CFCs). The total emission of CCl4 from countries that report annual production is estimated to have declined from 11% in 1972 to 4% in 1995 of the CCl4 needed to produce the CFC amounts reported. This implies that nonreporting countries released substantial amounts of CCl4 into the atmosphere in the 1980s and that their releases have exceeded those from the reporting countries since 1991.

Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates

Date added: 08/05/2007
Date modified: 07/23/2009
Filesize: 2.28 MB
Greally, B. R., et al. (2007), Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates, J. Geophys. Res., 112, D06308, doi:10.1029/2006JD007527.

Abstract


Ground-based in situ measurements of 1,1-difluoroethane (HFC-152a, CH3CHF2) which is regulated under the Kyoto Protocol are reported under the auspices of the AGAGE (Advanced Global Atmospheric Gases Experiment) and SOGE (System of Observation of halogenated Greenhouse gases in Europe) programs. Observations of HFC-152a at five locations (four European and one Australian) over a 10 year period were recorded. The annual average growth rate of HFC-152a in the midlatitude Northern Hemisphere has risen from 0.11 ppt/yr to 0.6 ppt/yr from 1994 to 2004. The Southern Hemisphere annual average growth rate has risen from 0.09 ppt/yr to 0.4 ppt/yr from 1998 to 2004. The 2004 average mixing ratio for HFC-152a was 5.0 ppt and 1.8 ppt in the Northern and Southern hemispheres, respectively. The annual cycle observed for this species in both hemispheres is approximately consistent with measured annual cycles at the same locations in other gases which are destroyed by OH. Yearly global emissions of HFC-152a from 1994 to 2004 are derived using the global mean HFC-152a observations and a 12-box 2-D model. The global emission of HFC-152a has risen from 7 Kt/yr to 28 Kt/yr from 1995 to 2004. On the basis of observations of above-baseline elevations in the HFC-152a record and a consumption model, regional emission estimates for Europe and Australia are calculated, indicating accelerating emissions from Europe since 2000. The overall European emission in 2004 ranges from 1.5 to 4.0 Kt/year, 5–15% of global emissions for 1,1-difluoroethane, while the Australian contribution is negligible at 5–10 tonnes/year, <0.05% of global emissions.

A Statistical Analysis of North East Atlantic (submicron) Aerosol Size Distributions A Statistical Analysis of North East Atlantic (submicron) Aerosol Size Distributions

Date added: 03/19/2013
Date modified: 03/19/2013
Filesize: 516.78 kB

Dall’Osto, M., C. Monahan, R. Greaney, D.C.S. Beddows, R. M. Harrison, D. Ceburnis and C. D. O’Dowd. A Statistical Analysis of North East Atlantic (submicron) Aerosol Size Distributions., Atmos. Chem. Phys., 11, 12567–12578, 2011, doi:10.5194/acp-11-12567-2011.


Abstract. The Global Atmosphere Watch research station at Mace Head (Ireland) offers the possibility to sample some of the cleanest air masses being imported into Europe as well as some of the most polluted being exported out of Europe. We present a statistical cluster analysis of the physical characteristics of aerosol size distributions in air ranging from the cleanest to the most polluted for the year 2008. Data coverage achieved was 75% throughout the year. By applying the Hartigan-Wong k-Means method, 12 clusters were identified as systematically occurring. These 12 clusters could be further combined into 4 categories with similar characteristics, namely: coastal nucleation category (occurring 21.3% of the time), open ocean nucleation category (occurring 32.6% of the time), background clean marine category (occurring 26.1% of the time) and anthropogenic category (occurring 20% of the time) aerosol size distributions. The coastal nucleation category is characterised by a clear and dominant nucleation mode at sizes less than 10 nm while the open ocean nucleation category is characterised by a dominant Aitken mode between 15 nm and 50 nm. The background clean marine aerosol exhibited a clear bimodality in the sub-micron size distribution, with although it should be noted that either the Aitken mode or the accumulation mode may dominate the number concentration. However, peculiar background clean marine size distributions with coarser accumulation modes are also observed during winter months. By contrast, the continentally-influenced size distributions are generally more monomodal (accumulation), albeit with traces of bimodality. The open ocean category occurs more often during May, June and July, corresponding with the North East (NE) Atlantic high biological period. Combined with the relatively high percentage frequency of occurrence (32.6 %), this suggests that the marine biota is an important source of new nano aerosol particles in NE Atlantic Air.

 

On the contribution of organics to the North East Atlantic aerosol number concentration On the contribution of organics to the North East Atlantic aerosol number concentration

Date added: 03/22/2013
Date modified: 03/22/2013
Filesize: 1.01 MB

Bialek, J. M. Dall’Osto C. Monahan, D. Beddows and C. O’Dowd, On the contribution of organics to the North East Atlantic aerosol number concentration, Environ. Res. Lett. 7, 044013 (7pp) doi:10.1088/1748-9326/7/4/044013, 2012.


 

Abstract. k-means statistical-cluster analysis of submicron aerosol size distributions is combined with coincident humidity tandem differential mobility analyser data, leading to five unique aerosol categories for hygroscopic growth factors (HGFs): low sea-salt background marine, high sea-salt background marine, coastal nucleation, open ocean nucleation and anthropogenically influenced scenarios. When considering only marine conditions, and generic aerosol species associated with this environment (e.g. non-sea-salt sulfate, sea-salt, partly soluble organic matter and water insoluble organic matter), the two-year annual average contribution to aerosol number concentration from the different generic species was made up as follows: 46% (30–54%) of partially modified ammonium sulfate particles; 23% (11–40%) of partially modified sea-salt; and the remaining 31% (25–35%) contribution attributed to two distinct organic species as evidenced by different, but low, HGFs. The analysis reveals that on annual timescales, _30% of the submicron marine aerosol number concentration is sourced from predominantly organic aerosol while 60% of the anthropogenic aerosol number is predominantly organic. Coastal nucleation events show the highest contribution of the lowest HGF mode (1.19), although this contribution is more likely to be influenced by inorganic iodine oxides. While organic mass internally mixed with inorganic salts will lower the activation potential of these mixed aerosol types, thereby potentially reducing the concentration of cloud condensation nuclei (CCN), pure organic water soluble particles are still likely to be activated into cloud droplets, thereby increasing the concentration of CCN. A combination of dynamics and aerosol concentrations will determine which effect will prevail under given conditions.

 

Emissions from Ships with respect to Their Effects on Clouds Emissions from Ships with respect to Their Effects on Clouds

Date added: 08/06/2000
Date modified: 07/01/2009
Filesize: 302.93 kB

Hobbs, P.V., T.J. Garrett, and co-authors, 2000: Emissions from ships with respect to their effects on clouds, J. Atmos. Sci., 57, 2570-2590


Abstract


Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as ship tracks. Airborne measurements are used to derive emission factors of SO2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were ∼15-89 and ∼2-25 g kg-1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO2 emission factor of ∼6 g kg-1. Various types of ships, burning both MFO and navy distillate fuel, emitted from ∼4 X 1015 to 2 X 1016 total particles per kilogram of fuel burned (∼4 X 1015-1.5 X 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (∼0.03-0.05 μm) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius ∼0.02 μm). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis. The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN. The fluxes of heat and water vapor from ships are estimated to be ∼2-22 MW and ∼0.5-1.5 kg s-1, respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

 

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