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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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Effects of continental boundary layer evolution convection  turbulence and entrainment on... Effects of continental boundary layer evolution convection turbulence and entrainment on...

Date added: 08/06/2001
Date modified: 07/01/2009
Filesize: 740.44 kB

Nilsson, E.D., U. Rannik, G. Buzorius, C.D. O'Dowd, Effects of continental boundary layer evolution, convection, turbulence and entrainment on aerosol formation, Tellus B, 53, 441-461,, 2001.


Abstract


Aerosol nucleation events occurring in the continental boundary layer over the boreal forest region in Finland, during the BIOFOR experiment, have been examined to elucidate the rôle of micrometeorology in promoting such events. Invariably, during the spring campaign of 1999. nucleation events occurred in Arctic and polar air masses during cold air outbreaks. Under clear-sky conditions, typical of these synoptic meteorological patterns, the boundary layer evolution was characterized by the rapid growth of a mixed layer, convection and strong entrainment, first from the residual later and later from the free troposphere. It was found that the freshly nucleated particles were detected within two hours from the onset of strong turbulent kinetic energy, independent of how fast the boundary layer evolved. When considering the growth time from cluster size of ≃ 1 nm to detectable sizes of 3 nm. the nucleation and onset of strong turbulence coincided almost exactly. The most likely site for nucleation to take place was the mixed layer or the entrainment zone, while the forest canopy and the free troposphere could be excluded as the nucleation region. There are several possible explanations for the correlation between the onset of turbulence and nucleation: (1) new aerosols or clusters may have been entrained from the residual layer into the mixed layer where they then (in the case of clusters) underwent growth to detectable sizes: (2) two or more precursor gases may have been mixed with each other over the entrainment zone; (3) the adiabatic cooling in the rising convective plumes and the turbulent fluctuation in temperature and vapors by the entrainment flux may have enhanced aerosol formation; (4) a sudden decrease in preexisting aerosol due to dilution of the mixed layer aerosol by entrained air may have reduced the vapor sink enough to initiate nucleation. However, the lack of vertical profile measurements of nucleation mode aerosols, precursor vapors and turbulent fluctuations throughout and above the mixed-layer results in it remaining an open question as to which one of these processes dominates.

 

Gas-Aerosol Relationships of OH, H2SO4, and MSA Observations in the Coastal Marine Boundary Layer at Mace Head Gas-Aerosol Relationships of OH, H2SO4, and MSA Observations in the Coastal Marine Boundary Layer at Mace Head

Date added: 07/31/2002
Date modified: 07/27/2009
Filesize: 542.87 kB
H. Berresheim, T. Elste, H.G. Tremmel, C O'Dowd, A.Allen, H.C. Hansson, K Rosman, M. dal Maso, J. Makela, and Markku Kulmala. Gas-Aerosol Relationships of OH, H2SO4, and MSA: Observations in the Coastal Marine Boundary Layer at Mace Head, Ireland. J. Geophys. Res., 107, 10.1029/2000JD000229, 2002.

Abstract

 

Atmospheric concentrations of gaseous sulfuric acid (H2SO4), methane sulfonic acid (MSA), and hydroxyl radicals (OH) were measured by chemical ionization mass spectrometry (CIMS) during the second New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign in June 1999 at Mace Head, Ireland. Overall median concentrations in marine background air were 1.5, 1.2, and 0.12 × 106 cm−3, respectively. H2SO4 was also present at night indicating significant contributions from nonphotochemical sources. A strong correlation was found between daytime OH and H2SO4 levels in clean marine air suggesting a fast local production of H2SO4 from sulfur precursor gases. Steady state balance calculations of ambient H2SO4 levels agreed with measured concentrations if either very low H2SO4 sticking coefficients (0.02–0.03) or sources in addition to the SO2 + OH reaction were assumed. Overall, variations in ambient H2SO4 levels showed no correlation with either the tidal cycle or ultrafine particle (UFP) concentrations. However, on particular days an anticorrelation between H2SO4 and UFP levels was occasionally observed providing evidence for the contribution of H2SO4 to new particle formation and/or particle growth. Gaseous MSA concentrations were inversely correlated with dew point temperature reflecting a highly sensitive gas-particle partitioning equilibrium of this compound. The present observations seriously question the general use of MSA as a conservative tracer to infer the relative production yield of H2SO4 from dimethylsulfide (DMS) oxidation. MSA/H2SO4 concentration ratios typically ranged between 0.06 and 1.0 in marine air at ground level. Measured diel OH profiles showed a significant deviation from concurrent variations of the ozone photolysis frequency. They also showed up to 1 order of magnitude lower values compared to OH concentrations calculated with a simple photochemical box model. These differences were most pronounced during particle nucleation events occurring on sunny days around noon and at low tide. The present results suggest that both the oxidation capacity and the particle formation potential in the coastal boundary layer were significantly affected by reactions of unknown compounds prevailing in this type of environment.

The Impact of Ship-Produced Aerosols on the Microstructure and Albedo of Warm The Impact of Ship-Produced Aerosols on the Microstructure and Albedo of Warm

Date added: 08/06/2000
Date modified: 07/08/2009
Filesize: 176.35 kB

Durkee, P. and co authors, 2000: The impact of ship-produced aerosols on the microstructure and albedo of warm marine stratocumulus clouds: A test of MAST hypotheses 1i and 1ii. J. Atmos. Sci., 57, 2554-2569.


Abstract


Anomalously high reflectivity tracks in stratus and stratocumulus sheets associated with ships (known as ship tracks) are commonly seen in visible and near-infrared satellite imagery. Until now there have been only a limited number of in situ measurements made in ship tracks. The Monterey Area Ship Track (MAST) experiment, which was conducted off the coast of California in June 1994, provided a substantial dataset on ship emissions and their effects on boundary layer clouds. Several platforms, including the University of Washington C-131A aircraft, the Meteorological Research Flight C-130 aircraft, the National Aeronautics and Space Administration ER-2 aircraft, the Naval Research Laboratory airship, the Research Vessel Glorita, and dedicated U.S. Navy ships, participated in MAST in order to study processes governing the formation and maintenance of ship tracks. This paper tests the hypotheses that the cloud microphysical changes that produce ship tracks are due to (a) particulate emission from the ship's stack and/or (b) sea-salt particles from the ship's wake. It was found that ships powered by diesel propulsion units that emitted high concentrations of aerosols in the accumulation mode produced ship tracks. Ships that produced few particles (such as nuclear ships), or ships that produced high concentrations of particles but at sizes too small to be activated as cloud drops in typical stratocumulus (such as gas turbine and some steam-powered ships), did not produce ship tracks. Statistics and case studies, combined with model simulations, show that provided a cloud layer is susceptible to an aerosol perturbation, and the atmospheric stability enables aerosol to be mixed throughout the boundary layer, the direct emissions of cloud condensation nuclei from the stack of a diesel-powered ship is the most likely, if not the only, cause of the formation of ship tracks. There was no evidence that salt particles from ship wakes cause ship tracks.

 

Physicochemical Properties of Aerosols Over the Northeast Atlantic: Evidence for Wind-Speed-Related Physicochemical Properties of Aerosols Over the Northeast Atlantic: Evidence for Wind-Speed-Related

Date added: 08/06/1993
Date modified: 07/03/2009
Filesize: 1.04 MB

O'Dowd, C. D., and M. H. Smith (1993), Physicochemical Properties of Aerosols Over the Northeast Atlantic: Evidence for Wind-Speed-Related Submicron Sea-Salt Aerosol Production, J. Geophys. Res., 98(D1), 1137–1149.


Abstract


Physicochemical characteristics of submicron aerosol particles over the Northeast Atlantic (63°N, 8°W) during October/November 1989 have been examined using a thermal analytical technique and are classified according to air mass origin. Aerosol associated with anthropogenically influenced air masses contained typically 80% sulphate particles by number, the remainder being soot carbon and sea salt. For Arctic air masses the contribution of sulphate to the total aerosol was reduced to around 65%, due to low concentrations relative to sea salt which is dependent on wind speed. In situations with clean maritime air and high wind speeds, sulphate aerosol accounted for less than 25% of the total accumulation mode particles, the remainder consisting predominantly of sea salt. Arctic air masses and clean maritime air during periods of high winds were consistently acidic with inferred molar ratios of NH4 +/SO4 = near 0.2. The continental and modified maritime aerosol encountered was found to have molar ratios of about 0.8. Soot carbon was present in all air masses to a similar degree (5–13%). In clean air masses, submicron sea salt aerosol concentrations showed a strong exponential increase with wind speed (correlation coefficients cc ≥ 0.8), down to a dry particle radius of 0.05 μm. Under these “clean air” conditions and high winds the sea salt aerosol dominated all particle sizes for r > 0.05 μm and accounted for approximately 75% of the total concentration, suggesting that under these conditions, sea salt aerosol would comprise the primary source of cloud condensation nuclei (CCN) in stratiform clouds.

 

Investigating organic aerosol loading in the remote marine environment Investigating organic aerosol loading in the remote marine environment

Date added: 09/01/2011
Date modified: 11/17/2011
Filesize: 2.42 MB

Lapina, K., C.L. Heald, D.V. Spracklen, S.R. Arnold, J.D. Allan, H Coe, G. McFiggans, S.R. Zorn, F. Drewnick, T.S. Bates, L.N. Hawkins, L.M. Russell, A. Smirnov, C. O'Dowd and A.J. Hind. Investigating organic aerosol loading in the remote marine environment, Atmos. Chem. Phys., 11, 8847–8860, 2011, doi:10.5194/acp-11-8847-2011.

 

  

Abstract: Aerosol loading in the marine environment is investigated using aerosol composition

measurements from several research ship campaigns (ICEALOT, MAP, RHaMBLe, VOCALS

and OOMPH), observations of total AOD column from satellite (MODIS) and ship-based instruments (Maritime Aerosol Network, MAN), and a global chemical transport model (GEOS-Chem). This work represents the most comprehensive evaluation of oceanic OM emission inventories to date, by employing aerosol composition measurements obtained from campaigns with wide spatial and temporal coverage. The model

underestimates AOD over the remote oceans on average by 0.02 (21 %), compared to satellite observations, but provides an unbiased simulation of ground-based Maritime Aerosol Network (MAN) observations. Comparison with cruise data demonstrates that the GEOS-Chem simulation of marine sulfate, with the mean observed values ranging between 0.22 μgm−3 and 1.34 μgm−3, is generally unbiased, however surface organic matter (OM) concentrations, with the mean observed concentrations between 0.07 μgm−3 and 0.77 μgm−3, are underestimated by a factor of 2-5 for the standard model run. Addition of a a sub-micron marine OM source of approximately 9 TgCyr−1 brings the model into agreement with the ship-based measurements, however this additional OM source does not explain the model underestimate of marine AOD. The model underestimate of marine AOD is therefore likely the result of a combination of satellite retrieval bias and a missing marine aerosol source (which exhibits a different spatial pattern than existing aerosol in the model).

  


In situ chloroform measurements at Advanced Global Atmospheric Gases Experiment atmospheric research stations from 1994 to 1998 In situ chloroform measurements at Advanced Global Atmospheric Gases Experiment atmospheric research stations from 1994 to 1998

Date added: 08/01/2001
Date modified: 07/24/2009
Filesize: 1.54 MB
O'Doherty, S., et al. (2001), In situ chloroform measurements at Advanced Global Atmospheric Gases Experiment atmospheric research stations from 1994 to 1998, J. Geophys. Res., 106(D17), 20,429–20,444.

Abstract


Measurements of atmospheric chloroform (CHCl3) by in situ gas chromatography using electron capture detection are reported from the Advanced Global Atmospheric Gases Experiment (AGAGE) network of atmospheric research stations. They are some of the most comprehensive in situ, high-frequency measurements to be reported for CHCl3 and provide valuable information not only on clean “baseline” mixing ratios but also on local and regional sources. Emissions from these sources cause substantial periodic increases in CHCl3 concentrations above their baseline levels, which can be used to identify source strengths. This is particularly the case for measurements made at Mace Head, Ireland. Furthermore, these local sources of CHCl3 emissions are significant in relation to current estimates of global emissions and illustrate that the understanding of competing sources and sinks of CHCl3 is still fragmentary. These observations also show that CHCl3 has a very pronounced seasonal cycle with a summer minimum and winter maximum presumably resulting from enhanced destruction by OH in the summer. The amplitude of the cycle is dependent on sampling location. Over the 57 months of in situ measurements a global average baseline concentration of 8.9±0.1 ppt was determined with no appreciable trend in the baseline detected.

Biogenic sulphur emissions and inferred non-sea-salt-sulphate CCN around Antarctica Biogenic sulphur emissions and inferred non-sea-salt-sulphate CCN around Antarctica

Date added: 08/06/1997
Date modified: 07/01/2009
Filesize: 1.53 MB

O'Dowd, C. D., J. A. Lowe, M. H. Smith, B. Davison, C. N. Hewitt, and R. M. Harrison (1997), Biogenic sulphur emissions and inferred non-sea-salt-sulphate cloud condensation nuclei in and around Antarctica, J. Geophys. Res., 102(D11), 12,839–12,854.


Abstract


Accumulation mode aerosol properties and biogenic sulphur emissions over the South Atlantic and Antarctic Oceans are examined. Two contrasting air masses, polar and maritime, each possessing distinct aerosol properties, were encountered during the summer months. By examining aerosol volatile properties, polar air masses arriving from the Antarctic continent were shown to consist primarily Of H2SO4 in the accumulation mode size range, with inferred NH+ 4 to SO= 4 molar ratios close to zero. By comparison, air masses of temperate maritime origin were significantly neutralized with molar ratios of ≈1. These results suggest a deficit of ammonia in polar air masses compared with that in maritime air masses. Dimethyl sulphide (DMS) exhibited no correlation with its putative aerosol oxidation products, although spatial coherence in atmospheric concentrations of DMS, methane sulphonic acid (MSA), and non-sea-salt (nss)-sulphate mass was observed. Volatility analysis, used to infer nss-sulphate cloud condensation nuclei (nss-sCCN) active at a supersaturation of ≈0.2%, indicates that nss-sCCN mass and number concentration were best correlated with MSA mass (r≈0.63). Aerosol volatility identified the presence of MSA in submicron non-sea-salt aerosol; however, its contribution to the aerosol mass was small relative to the contribution of sulphuric acid and ammonium bisulphate/sulphate aerosol. The marine sulphur cycle appears strongly coupled to the sea-salt cycle with, typically, 80–90% of nss-sulphate thought to be internally mixed with sea-salt aerosol. During the austral Summer of 1992/1993, a period of strong biological productivity in the Weddell Sea and sub-Antarctic Ocean, particularly during ice-melt, the cruise-average DMS flux of 61 μg m−2 d−1 corresponded to a very modest average nss-sCCN concentration of 21 cm−3. Observed peak values of DMS flux and inferred nss-CCN concentrations during the cruise were 477 μg m−2 d−1 and 64 cm−3, respectively. Events of new particle formation were identified in the Weddell Sea and occurred under conditions of high DMS flux and low aerosol surface area.

 

On the spatial extent and evolution of coastal aerosol plumes On the spatial extent and evolution of coastal aerosol plumes

Date added: 07/31/2002
Date modified: 07/23/2009
Filesize: 757.91 kB

Colin O'Dowd.On the spatial extent and evolution of coastal aerosol plumes, J. Geophys. Res, 107, 10.1029/2001JD000422, 2002.


Abstract


Airborne mapping and pseudo-Lagrangian experiments were conducted in coastal and tidal-induced nucleation plumes along the west coast of Ireland in June 1999. The mapping flights confirmed that the source of the previously reported coastal nucleation events is indeed the tidal zone around the coastline. Additionally, the mapping flights also confirmed that coastal nucleation is typically ubiquitous along the coastline, at least on the Irish coast. Along with the large horizontal extent of coastal nucleation events, these new particles were observed to be mixed up to >1000 m in the vertical despite slightly stable meteorological conditions. On the clean air mapping flight the background particle concentration (r > 1.5 nm) was observed to increase from <1000 cm−3 to >100,000 cm−3, while accumulation mode (r > 50 nm) particle concentration remained constant at approximately 50 cm−3. During a semipolluted mapping flight, concentrations increased from 3000 to >100,000 cm−3 in places. The enhancement in particle concentration was confirmed to be in the size range 1.5–5 nm radius at the start of the nucleation event, while growth into larger sizes was observed later. During this semipolluted event, owing to favorable wind conditions, it was possible to perform a pseudo-Lagrangian experiment in a coastal plume advecting out over the northeast Atlantic. This plume was observed to be >60 km in width and >1000 m in the vertical and was encountered for >250 km off the coast. During this plume evolution the growth of the new particle mode at sizes <5 nm up to sizes >40 nm was observed. After the plume had evolved for 3 hours, increases in scattering coefficients were observed along with significant increases in cloud condensation nuclei concentrations. These results confirm that the spatial extent of tidal-related particle production is regionally significant, and after a few hours, the growth of these recently formed coastal aerosols significantly increase the concentration of radiatively active aerosol particles.

Attenuated total reflectance measurements of the complex refractive index of kaolinite powder at CO2 laser wavelengths Attenuated total reflectance measurements of the complex refractive index of kaolinite powder at CO2 laser wavelengths

Date added: 07/31/1985
Date modified: 06/30/2009
Filesize: 1.63 MB

Pinnick, R.G., Jennings, S.G., Boice, D.C., and Cruncleton, J.P. (1985). - Attenuated total reflectance measurement of the complex refractive index of kaolinite powder at CO2 laser wavelengths. Appl. Opt., 24, 3274 - 3285.


Abstract

 

Attenuated total reflectance measurements of the complex refractive index of kaolinite powder-air mixtures are made for nine CO2 laser wavelengths. The Maxwell-Garnett effective medium theory and generalizations of it that account for either the shape distribution of kaolinite grains in the medium (in which the grains are approximated by a shape distribution of small arbitrarily oriented ellipsoids) or the size distribution of grains (in which finite grain sizes are accounted for by considering, in addition to the electric dipole interaction, magnetic dipole and electric quadrupole interactions) are used to deduce from these measurements the complex refractive index of kaolinite. Most success is achieved with a generalization which assumes a shape distribution of small ellipsoidal grains but which neglects all but electric dipole interactions. In spectral regions where kaolinite displays very strong absorption (in the 9.6-10-,um spectral region) all effective medium theory solutions for kaolinite refractive index either are plagued with ill-conditioning or are nonphysical. It appears that the attenuated total reflectance method, at least as we have applied it here to loosely packed powders comprised of nonspherical grains, is not suitable for measurement of powders in spectral regions of strong absorption.

Hygroscopic properties of nucleation mode and Aitken mode particles during nucleation bursts an Hygroscopic properties of nucleation mode and Aitken mode particles during nucleation bursts an

Date added: 08/06/2002
Date modified: 07/24/2009
Filesize: 925.58 kB

Väkevä, M., K. Hämeri, and P. P. Aalto (2002), Hygroscopic properties of nucleation mode and Aitken mode particles during nucleation bursts and in background air on the west coast of Ireland, J. Geophys. Res., 107(D19), 8104, doi:10.1029/2000JD000176.


Abstract


The hygroscopic and cloud condensation nuclei (CCN) properties of submicrometer atmospheric aerosol particles were investigated using an Ultrafine Tandem Differential Mobility Analyzer (UF-TDMA) and a CCN counter at the Mace Head Monitoring Station on the west coast of Ireland during the New Particle Formation and Fate in the Coastal Environment (PARFORCE) field campaign in September 1998 and June 1999. These measurements give indirect in situ information on the composition and state of mixing of the aerosol particles. The UF-TDMA was used for monitoring of hygroscopic diameter growth factors of aerosol particles with dry mobility diameters 8–20 nm when taken from dry state to a controlled humid environment (RH 90%). The CCN counter was used to study the activation of aerosol particles when exposed to supersaturated conditions (dry diameters of 15–150 nm). It was seen that in clean marine air masses during the observed particle formation events, the newly formed nucleation mode particles (8 and 10 nm) most often had low growth factors (between 1.0 and 1.1) resulting from low solubility. This indicates that the nucleation mode particles consist of nonsoluble or weakly soluble species, possible accompanied by a small soluble part; however, when nucleation mode particles were observed outside the event periods, the growth factors were higher (about 1.3–1.4). In contrast, the 20 nm particles usually clearly belonged to the Aitken mode (based on number size distribution measurements) and had hygroscopic properties similar to some common salts (growth factors 1.4–1.5).

 

Physicochemical properties of atmospheric aerosol at South UIST Physicochemical properties of atmospheric aerosol at South UIST

Date added: 08/06/1996
Date modified: 07/03/2009
Filesize: 906.46 kB

J. A. Lowe, M. H. Smith, B. M. Davison, S. E. Benson, M. K. Hill, C. D. O'Dowd, R. M. Harrison, C. N. Hewitt, Physicochemical properties of atmospheric aerosol at South UIST, Atmospheric EnvironmentVolume 30, Issue 22, , November 1996, Pages 3765-3776.


Abstract


Four field campaigns over the period November 1993 to August 1994 were undertaken on the island of South Uist, off the northwest coast of Scotland as part of the BMCAPE project. Measurements were made of the concentration and chemical composition of aerosol particles, utilising a variety of instruments. Sulphur and nitrogen gas species were also measured throughout these campaigns, together with appropriate meteorological parameters. A variety of air mass types were encountered during the campaigns and the relationship between the physical and chemical aerosol properties are discussed in terms of air mass histories and season factors.

Comparisons of box model calculations and measurements of formaldehyde from the 1997 North Atlantic Comparisons of box model calculations and measurements of formaldehyde from the 1997 North Atlantic

Date added: 08/31/2002
Date modified: 07/01/2009
Filesize: 953.85 kB
Frost, G. J., et al. (2002), Comparisons of box model calculations and measurements of formaldehyde from the 1997 North Atlantic Regional Experiment, J. Geophys. Res., 107(D8), 4060, doi:10.1029/2001JD000896.

Abstract


Formaldehyde (CH2O) measurements from two independent instruments are compared with photochemical box model calculations. The measurements were made on the National Oceanic and Atmospheric Administration P-3 aircraft as part of the 1997 North Atlantic Regional Experiment (NARE 97). The data set considered here consists of air masses sampled between 0 and 8 km over the North Atlantic Ocean which do not show recent influence from emissions or transport. These air masses therefore should be in photochemical steady state with respect to CH2O when constrained by the other P-3 measurements, and methane oxidation was expected to be the predominant source of CH2O in these air masses. For this data set both instruments measured identical CH2O concentrations to within 40 parts per trillion by volume (pptv) on average over the 0–800 pptv range, although differences larger than the combined 2σ total uncertainty estimates were observed between the two instruments in 11% of the data. Both instruments produced higher CH2O concentrations than the model in more than 90% of this data set, with a median measured-modeled [CH2O] difference of 0.13 or 0.18 ppbv (depending on the instrument), or about a factor of 2. Such large differences cannot be accounted for by varying model input parameters within their respective uncertainty ranges. After examining the possible reasons for the model-measurement discrepancy, we conclude that there are probably one or more additional unknown sources of CH2O in the North Atlantic troposphere.

Continuous high-frequency observations of hydrogen at the Mace Head baseline atmospheric monitoring station over the 1994–1998 period Continuous high-frequency observations of hydrogen at the Mace Head baseline atmospheric monitoring station over the 1994–1998 period

Date added: 08/01/2000
Date modified: 07/09/2009
Filesize: 1.57 MB
Simmonds, P. G., R. G. Derwent, S. O'Doherty, D. B. Ryall, L. P. Steele, R. L. Langenfelds, P. Salameh, H. J. Wang, C. H. Dimmer, and L. E. Hudson (2000), Continuous high-frequency observations of hydrogen at the Mace Head baseline atmospheric monitoring station over the 1994–1998 period, J. Geophys. Res., 105(D10), 12,105–12,121

Abstract


Continuous high-frequency (every 40-min) automatic measurements of hydrogen have been made at the Mace Head atmospheric research station on the Atlantic Ocean coast of Ireland throughout 1994–1998. These observations represent one the most comprehensive in situ records of a trace gas that has received comparatively little attention. Individual measurements have been sorted by four independent methods to separate clean, maritime air masses from regionally polluted European air masses. Hydrogen concentrations in midlatitude Northern Hemisphere baseline air show a distinct seasonal cycle with highest concentrations during spring and lowest concentrations during late autumn, with a peak-to-trough amplitude of 38 ± 6 ppb, averaged over the observed seasonal cycles from 1994 to 1998. The mean hydrogen concentration in midlatitude Northern Hemisphere baseline air on January 1, 1995, was estimated as 496.5 ppb with an upward trend of 1.2 ± 0.8 ppb yr−1. Evidence has also been obtained for European pollution sources with source strength of about 0.8 Tg yr−1 and for deposition of hydrogen to soils. The observation of slightly elevated hydrogen concentrations relative to baseline levels in tropical maritime air masses points to a latitudinal gradient in hydrogen with higher concentrations in lower latitudes of the Northern Hemisphere and in the Southern Hemisphere. This is confirmed by comparable hydrogen observations at Cape Grim, Tasmania, which are consistently higher than measurements recorded at Mace Head. Mean hemispheric concentrations of 504 and 520 ppb have been estimated for the Northern and Southern Hemispheres, respectively, for January 1, 1996, corresponding to a total atmospheric hydrogen burden of 182 Tg.

Concurrent Measurements of Black Carbon aerosol and Carbon Monoxide at Mace Head Concurrent Measurements of Black Carbon aerosol and Carbon Monoxide at Mace Head

Date added: 07/31/1996
Date modified: 07/27/2009
Filesize: 3.16 MB

Jennings, S.G., Spain, T.G., Doddridge, B.G., Maring, H., Kelly, B.P., and Hansen, A.D.A. (1996) - Concurrent measurements of black carbon aerosol and carbon monoxide at Mace Head. J.Geophys. Res., 101, 19,447 - 19,454.


Abstract

 

Continuous measurements of white light attenuation (ATN) through a quartz fiber filter (related to aerosol black carbon content) and of carbon monoxide (CO) carried out over the period December 1991 through July 1992 at the Mace Head atmospheric field research station (53°19'N, 9°54'W) near Carna, County Galway on the west coast of Ireland are presented. Isentropic air flow back trajectories, condensation nuclei concentration data, and meteorological data were generated as part of the Atmosphere/Ocean Chemistry Experiment. Use is made of this supporting data together with synoptic weather charts in the analysis of the measurements. Measurements of ATN and CO are reported for unmodified marine air from the North Atlantic which yield ATN and ATN/CO values in the range 1-4 × 10-3 m-3 and 1-4 × 10-5 m-3 ppbv-1. Increasing values of ATN and ATN/CO are obtained for polluted transatlantic air, modified marine air, and polluted air from the UK and/or Europe. The covariance of ATN and CO obtained for these air masses suggests a common source. Transport of air from west of the African Saharan region to Mace Head is accompanied by a rise in optical attenuation purported to be due to absorbing desert dust aerosol without a concurrent rise in CO.

Can the study of nitrogen isotopic composition in size-segregated aerosol nitrate and ammonium Can the study of nitrogen isotopic composition in size-segregated aerosol nitrate and ammonium

Date added: 08/07/2001
Date modified: 07/27/2009
Filesize: 186.81 kB

S.G. Yeatman, L.J. Spokes, P.F. Dennis, T.D. Jickells, Can the study of nitrogen isotopic composition in size-segregated aerosol nitrate and ammonium be used to investigate atmospheric processing mechanisms?, Atmospheric Environment 35 (2001) 1337}1345


Abstract


Atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters. Stable nitrogen isotope data can provide important information regarding the sources and processing of atmospheric fixed-nitrogen species and is thus important in controlling eutrophication. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland and also aboard the RRS Challenger in the Eastern Atlantic Ocean. Aerosol concentrations of ammonium and nitrate were determined prior to δ15N isotopic analysis. The isotopic enrichment factor, ε, was calculated for both the species by subtracting the respective δ15N values of the coarse-mode fraction (>1 μm diameter) from those of the fine-mode fraction (<1 μm diameter). Variations in this parameter were observed as weak functions of the percentage of each species in the coarse mode and of meteorological condition. As a result, the presence of two different size-shift processes (dissociation/gas scavenging and dissolution/coagulation) is proposed, consistent with similar arguments based upon major-ion data obtained from the same suite of samples. Dissolution/coagulation processes appear to exhibit negative isotopic enrichment factors whereas dissociation/gas scavenging processes appear to exhibit positive enrichment factors, suggesting that they may be reversible and thermodynamically driven. In offshore-flowing air masses just entering the marine environment, transferral of nitrate to the coarse mode by initial dissociation of NH4NO3 followed by scavenging of the HNO3 produced appears to be significantly more important than in samples of onshore, marine dominated air. In contrast, ammonium appears to be transferred to the coarse mode during offshore flow largely via the dissolution and coagulation of aerosol ammonium, nitrate and sulphate-containing species. During onshore flow, the uptake of gaseous NH3, arising from the continued dissociation of NH4NO3, seems to become increasingly important.

 

Measurements of Atmospheric Mercury Concentrations in Northwestern and Central Europe --- Comparison Measurements of Atmospheric Mercury Concentrations in Northwestern and Central Europe --- Comparison

Date added: 08/26/1995
Date modified: 07/10/2009
Filesize: 1.12 MB

R. Ebinghaus, H.H. Kock, S.G. Jennings, P. McCartin and M.J. Orren (1995): Measurements of Atmospheric Mercury Concentrations in Northwestern and Central Europe --- Comparison of Experimental Data and Model Results, Atmospheric Environment, Vol. 29, No. 22, pp. 3333 - 3344


Abstract


Field experiments were carried out at various sites in Europe to compare ambient air and precipitation concentrations of atmospheric mercury with model data. In addition, ozone and aerosol black carbon concentrations in air were measured simultaneously as input data for validation of the EMEP-based European long-range transport model. Data sets for mercury in air and precipitation, ozone and aerosol black carbon show that the selected sites range from background conditions for Northwestern Europe to regionally influenced air masses from heavily industrialized Central Europe. Measured 12 h averaged mercury concentrations in air range from 2.1 ng m-3 for Mace Head, Ireland to 8.2 ng m-3 for the Halle/Leipzig/Bitterfeld area in former German Democratic Republic. Precipitation concentrations of total mercury from 17 to 460 ng k-1 were measured from 1991 to 1993 for the same sites. Experimental data and model results for total gaseous mercury and mercury in precipitation are in good agreement.

Modelling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and compa Modelling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and compa

Date added: 08/06/1999
Date modified: 07/27/2009
Filesize: 1.29 MB

Carslaw, N., D. J. Creasey, D. E. Heard, A. C. Lewis, J. B. McQuaid, M. J. Pilling, P. S. Monks, B. J. Bandy, and S. A. Penkett (1999), Modeling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and comparison with field measurements, J. Geophys. Res., 104(D23), 30,241–30,255.


Abstract


An observationally constrained box model has been constructed to investigate radical chemistry at the Mace Head Atmospheric Observatory, a remote marine location on the west coast of Ireland. The primary aim of the model has been to model concentrations of the hydroxyl (OH), hydroperoxy (HO2), and the sum of peroxy Σ([HO2]+[RO2]) radicals measured by in situ instruments at this location. The model used in these studies consists of about 1670 reactions and 500 species, and model predictions of radical concentrations have been evaluated against field data. In order to further understand the chemistry, the model has been reduced using sensitivity analysis on both a clean and a semipolluted day. For reduced mechanisms that predict the concentrations of OH and HO2 to within 5% of the full mechanism, the semipolluted day can be represented using 279 species and 986 reactions, and the clean day using 249 species and 894 reactions. A further reduction has been applied whereby the reduced mechanisms predict concentrations of OH and HO2 to within 20% of the full mechanism for the daytime hours. In this way, the OH and HO2 concentrations on the semipolluted day can be represented by 42 species and 64 reactions, and the clean day by 17 species and 25 reactions. We show that these reduced mechanisms are generally applicable for this location under broadly similar conditions. Simple steady state expressions have also been derived to represent the chemistry at this location, allowing the concentrations of OH and HO2 to be deduced analytically. The expressions are based on the reduced mechanisms and on a further analysis of the reaction rates. Finally, an uncertainty analysis has been carried out to quantify the effects of propagation of uncertainties in the rate parameters and constrained concentrations through to the calculated radical concentrations in the model. For model concentrations of OH, HO2, and Σ([HO2]+[RO2]) radicals, the 2σ uncertainties are 31, 21, and 25%, respectively for clean air, and 42, 25, and 27% for semipolluted air.

Global modelling of the oceanic source of organic aerosols, Global modelling of the oceanic source of organic aerosols,

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 6.71 MB

Myriokefalitakis, S.,  E. Vignati, K. Tsigaridis, C. Papadimas, J. Sciare, N. Mihalopoulos, M. C. Facchini, M. Rinaldi, F. J. Dentener, D. Ceburnis, N. Hatzianastassiou, C.D. O'Dowd, M. van Weele and M. Kanakidou, Global modelling of the oceanic source of organic aerosols, Adv. in Meteorol., Volume 2010, Article ID 939171, doi:10.1155/2010/939171, 2010.

 


 

The global marine organic aerosol budget is investigated by a 3-dimensional chemistry-transport model considering recently proposed parameterisations of the primary marine organic aerosol (POA) and secondary organic aerosol (SOA) formation from the oxidation of marine volatile organic compounds. MODIS and SeaWiFS satellite data of Chlorophyll-a and ECMWF solar incoming radiation, wind speed, and temperature are driving the oceanic emissions in the model. Based on the adopted parameterisations, the SOA and the submicron POA marine sources are evaluated at about 5 Tg yr

 

1 (1.5 Tg C yr1) and 7 to 8 Tg yr1 (4 Tg C yr1), respectively. The computed marine SOA originates from the dimethylsulfide oxidation (78%), the potentially formed dialkyl amine salts (21%), and marine hydrocarbon oxidation (0.1%). Comparison of calculations with observations indicates an additional marine source of soluble organic carbon that could be partially encountered by marine POA chemical ageing.

ATMOSPHERIC MEASUREMENTS OF OH, HO2 ATMOSPHERIC MEASUREMENTS OF OH, HO2

Date added: 08/06/2003
Date modified: 07/09/2009
Filesize: 16.18 kB

Bloss, W. J.; Floquet, C.; Gravestock, T. J.; Heard, D. E.; Ingham, T.; Johnson, G. P.; Lee, J. D.,Atmospheric measurements of OH, HO2 and NO by laser-induced fluorescence spectroscopy using a compact all solid-state laser system,EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10521


Abstract


Free-radicals are key intermediates that control the budgets of many trace gases, for example ozone, greenhouse gases and harmful pollutants. Measurement of radicals and comparison with model calculations constitutes an important test of our understanding of the underlying chemistry. There is a greater need for compact and lightweight instruments for the in situ measurement of free-radical species that are suitable for deployment from a number of field-platforms. A new field instrument has been developed that incorporates an all solid-state Nd:YAG pumped titanium sapphire laser that is capable of generating radiation at high pulse-repetition-frequency for the detection of OH, HO_2, NO and IO radicals in the atmosphere by laser induced fluorescence (LIF). The system offers advantages of wide wavelength tunability, compactness, low weight, greater long-term stability (fibre-optic delivery) and short warm-up time. The instrument was successfully deployed during 2002 in the NAMBLEX field campaign at Mace Head with detection limits for OH and HO_2 (measured simultaneously with laser operation at 308 nm) of 3.1 x 10^5 molecule cm-3 (0.012 ppt) and 2.6 x 10^6 molecule cm-3 (0.09 pptv) respectively. Diurnal profiles of OH have been recorded over a period of 5 weeks. NO controls the HO_2/OH ratio and is the critical parameter in the production of tropospheric ozone, yet measurements in the boundary layer are restricted to a single indirect technique based on chemiluminescent analysers. Measurements of NO in the atmosphere have been made by LIF using the new instrument operating at 226 nm, with absolute concentrations in good agreement with simultaneous measurements made using a commercial chemiluminescent analyser. Whilst operating at 445 nm, the instrument has detected the IO radical in the laboratory, with a projected detection limit that is well below previously measured atmospheric concentrations of IO. A second instrument to be deployed on an aircraft platform is currently being developed.

Meteorological influences on coastal new particle formation Meteorological influences on coastal new particle formation

Date added: 07/31/2002
Date modified: 07/23/2009
Filesize: 1.07 MB
Gerrit de Leeuw, Gerard Kunz, Gintautas Buzorius, and Colin O'Dowd, Meteorological influences on coastal new particle formation, J. Geophys. Res. 107, 10.1029/2001JD001478, 2002.

Abstract


The meteorological situation at the midlatitude coastal station of Mace Head, Ireland, is described based on observations during the New Particle Formation and Fate in the Coastal Environment (PARFORCE) experiments in September 1998 and June 1999. Micrometeorological sensors were mounted near the shore line on a small mast with a height of 3 m and on a 22 m high tower at about 100 m away from the sea. Turbulent fields of wind speed, air temperature, and water vapor were measured. Parameters such as the friction velocity, drag coefficient, kinematic fluxes of heat and water vapor, and various variances were derived. The influence of meteorological parameters on coastal nucleation events is examined, and it is found that the occurrence of nucleation is, more or less, independent of air mass origin and is primarily driven by the occurrence of exposed shore areas during low tide and solar radiation. Micrometeorological influences were also examined in terms of promoting particle production events in this environment. A positive correlation was found between kinematic heat flux and particle production probability. In contrast, a strong negative correlation was found between production probability and both kinematic water vapor fluxes and relative humidity. These results indicate that the occurrence of new particle production events in the coastal zone are most probable during conditions when the shore area containing coastal biota has dried out and the biota are exposed directly to the solar radiation flux and increased shore, or surface, temperatures. These conditions correspond to drying and stressing of the biota, which is known to increase the emissions of biogenic vapors.

Calculated trends and the atmospheric abundance of 1,1,1,2-tetrafluoroethane, 1,1-dichloro-1-fl Calculated trends and the atmospheric abundance of 1,1,1,2-tetrafluoroethane, 1,1-dichloro-1-fl

Date added: 08/07/1998
Date modified: 07/27/2009
Filesize: 686.34 kB

Simmonds, P.G., O’Doherty, S., Huang, J., Prinn, R., Derwent, R.G., Ryall, D.B., Nickless, G., and Cunnold D., 1998: Calculated trends and the atmospheric abundance of 1,1,1,2-tetrafluoroethane, 1,1-dichloro-1-fluoroethane, and 1-chloro-1,1-difluoroethane using automated in situ gas chromatography-mass spectrometry measurements recorded at Mace Head, Ireland from October 1994 to March 1997. J. Geophysical Research, 103, 16029-16037.


Abstract


The first in-situ measurements by automated gas chromatograph-mass spectrometer are reported for 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1-dichloro-1-fluoroethane, (HCFC-141b), and 1-chloro-1,1 -difluoroethane, (HCFC-142b). These compounds are steadily replacing the chlorofluorocarbons (CFCs) as refrigerants, foam-blowing agents, and solvents. The concentrations of all three compounds are shown to be rapidly increasing in the atmosphere, with 134a increasing at a rate of 2.05 ± 0.02 ppt yr-1 over the 30 months of observations. Similarly, 141b and 142b increased at rates of 2.49 + 0.03 and 1.24 ± 0.02 ppt yr-1, respectively, over the same period. The concentrations recorded at the atmospheric research station at Mace Head, Ireland, on January 1, 1996, the midpoint of the time series, were 3.67 ppt (134a),7.38 ppt (141b), and 8.78 ppt (142b). From these observations we optimally estimate the HCFC and HFC emissions using a 12-box global model and OH concentrations derived from global 1,1,1-trichloroethane (CCl3CH3) measurements. Comparing two methods of estimating emissions with independent industry estimates shows satisfactory agreement for 134a and 141b, while for 142b, industry estimates are less than half those required to explain our observations.

 

Modelling the formation of organic particles in the atmosphere Modelling the formation of organic particles in the atmosphere

Date added: 08/01/2004
Date modified: 07/03/2009
Filesize: 1.72 MB

Anttila, T., V. -M. Kerminen, M. Kulmala, A. Laaksonen, and C. D. O'Dowd, Modelling the formation of organic particles in the atmosphere, Atmospheric Chemistry and Physics, Vol. 4, pp 1071-1083, 2004.


Abstract


Particle formation resulting from activation of inorganic stable clusters by a supersaturated organic vapour was investigated using a numerical model. The applied aerosol dynamic model included a detailed description of the activation process along with a treatment of the appropriate aerosol and gas-phase processes. The obtained results suggest that both gaseous sulphuric acid and organic vapours contribute to organic particle formation in continental background areas. The initial growth of freshly-nucleated clusters is driven mainly by condensation of gaseous sulphuric acid and by a lesser extent self-coagulation. After the clusters have reached sizes of around 2 nm in diameter, low-volatile organic vapours start to condense spontaneously into the clusters, thereby accelerating their growth to detectable sizes. A shortage of gaseous sulphuric acid or organic vapours limit, or suppress altogether, the particle formation, since freshly-nucleated clusters are rapidly coagulated away by pre-existing particles. The obtained modelling results were applied to explaining the observed seasonal cycle in the number of aerosol formation events in a continental forest site.

Ground-based and airborne observations of carbon monoxide during NASA Measurements of Air Pollu Ground-based and airborne observations of carbon monoxide during NASA Measurements of Air Pollu

Date added: 08/06/1998
Date modified: 07/24/2009
Filesize: 1.11 MB

B. G. Doddridge, R. Morales-Morales, K. P. Rhoads, J. T. Merrill, P. C. Novelli, R. R. Dickerson, V. S. Connors, and H. G. Reichle, Jr., “Ground-based and airborne observations of carbon monoxide during NASA Measurements of Air Pollution from Satellites (MAPS) missions SRL-1 and SRL-2,” J. Geophys. Res. 103, 19305–19316 (1998).


Abstract


Surface carbon monoxide (CO) data were acquired continuously at Heimaey, Iceland, (63tex2html_wrap_inline3724'N, 20tex2html_wrap_inline3718'W), Mace Head, Ireland, (53tex2html_wrap_inline3719'N, 9tex2html_wrap_inline3754'W), and Ragged Point, Barbados (13tex2html_wrap_inline3715'N, 59tex2html_wrap_inline3730'W) during April and October 1994, in support of MAPS missions SRL-1 and SRL-2, respectively, measuring middle tropospheric CO from space. Observed median CO levels from the three surface sites during these two MAPS missions approximate the monthly median for 1994, and are mostly typical of data from prior years. For two of the sites computed mission isentropic back-trajectory ensemble probability fields are compared to seasonal (March-May and September-November) probability fields for 1994 and 1986-1995. Such comparisons help gauge the representativeness of: (1) observed surface air quality at, and (2) isentropic flow to, these sites during the mission periods, in terms of intraseasonal and interannual variability. Results appear consistent with longer term flow climatological data and confirm the SRL-1 and SRL-2 mission periods are generally representative of the climatology applicable to these sites for the time of year. Lower free troposphere in situ CO data were acquired from an aircraft over the Maryland Eastern Shore on April 14 and October 3, 4 and 6. During the April flight a nearly linear gradient in CO with pressure from 1000-650 mb of 225-150 ppbv was observed. At 650 mb CO was quite steady around 150 ppbv; this value compares favorably with the MAPS CO data for the closest 5tex2html_wrap_inline37x5tex2html_wrap_inline37 grid box averaged April 13-15 of 105-120 ppbv. During SRL-2 a three flight CO average of 125 ppbv observed at  725 mb is in good agreement with the closest MAPS 5tex2html_wrap_inline37x5tex2html_wrap_inline37 grid box averaged October 3-7 of 90-105 ppbv. A layer of elevated CO at 845-740 mb, most likely the result of synoptic-scale transport, was observed during the October flights and seen to dissipate with time. The MAPS cloud filtered second-by-second CO data during concurrent Shuttle overflights show temporal structure consistent with the in situ observations, indicating the MAPS weighting function may be capable of discerning features at lower altitudes than thought previously.

 

Comparison of measured and calculated aerosol optical properties at mace head Comparison of measured and calculated aerosol optical properties at mace head

Date added: 08/07/2000
Date modified: 07/27/2009
Filesize: 126.53 kB
O'Reilly S.; Kleefeld C.; Jennings S.G.; Aalto P.; Becker E.; O'Dowd C.D., Comparison of measured and calculated aerosol optical properties at mace head, Journal of Aerosol Science, Volume 31, Supplement 1, September 2000 , pp. 274-275(2)

Abstract


There are large uncertainties associated with the estimation of the direct radiative forcing of the earth's climate by tropospheric aerosol particles (IPCC, 1996). The radiative effects of the tropospheric aerosol depend on the chemical, physical and optical properties of the aerosol. Because of their short atmospheric residence times, the distribution of tropospheric aerosols about the globe varies significantly, both spatially and temporally. Therefore, investigation of radiative forcing due to these aerosols requires analysis on a regional scale and the characterisation of the properties of the local aerosol.

Uncertainties associated with the calculation of direct radiative forcing by tropospheric aerosols can be identified and quantified using closure studies (Quinn et al., 1996). In a closure study a measured aerosol property is compared with values calculated from a model using other independently measured properties. Closure is achieved if there is agreement between the measured and calculated values within an accepted level of uncertainty. Such agreement indicates that the model may be a suitable representation of the observed system.

Can new particle formation occur in the clean marine boundary layer Can new particle formation occur in the clean marine boundary layer

Date added: 08/06/2000
Date modified: 07/27/2009
Filesize: 1.47 MB

Pirjola, L., C. D. O'Dowd, I. M. Brooks, and M. Kulmala (2000), Can new particle formation occur in the clean marine boundary layer?, J. Geophys. Res., 105(D21), 26,531–26,546.


Abstract


An analysis of new particle formation probability in the marine boundary layer (MBL) is conducted using a detailed aerosol dynamics and gas-phase chemistry model, thermodynamically correct classical binary (H2O-H2SO4) nucleation theory, and recently developed ternary (H2O-H2SO4-NH3) nucleation theory. Additionally, the effect of boundary-layer meteorology (i.e., adiabatic cooling, small scale fluctuations, and entrainment) in enhancing nucleation is also examined. The results indicate that for typical marine conditions, binary nucleation does not occur for any realistic conditions regardless of adiabatic cooling, turbulent fluctuations, or entrainment. For polar marine conditions, binary nucleation does occur due to lower temperatures, and is enhanced due to turbulent fluctuations. An increase in detectable particle sizes (N 3>3 nm), is only seen after multiple boundary layer circulations for conditions of high dimethyl sulphide (DMS) concentrations (400 ppt). Under extreme conditions of entrainment of free-troposphere layers containing very low aerosol condensation sinks and extraordinary high sulphuric acid concentrations (>108 molecules cm−3), increases in detectable particles up to 10,000 cm−3 are predicted only in polar marine air, but are viewed as unlikely to occur in reality. Comparison of model simulations with observed values of DMS and sulphuric acid in polar marine air masses suggest that binary nucleation may lead to an enhancement of ≈1000 cm−3 in N 3 particle concentration, but not to enhancements of ≈10,000 cm−3. Ternary nucleation is predicted to occur under realistic sulphuric acid (1.2 × 107 molecules cm−3) and ammonia (>5 ppt) concentrations; however, significant growth to detectable sizes (N 3) only occurs for DMS concentrations of the order of 400 ppt and very low aerosol condensation sinks, but these conditions are thought to be very infrequent in the MBL and are unlikely to make a significant contribution to the general MBL aerosol concentration. It is plausible that the background MBL aerosol concentration could be maintained by a slow, almost undetectable production rate, and not by noticeable nucleation events where large enhancements in N 3 concentrations are observed. The former requires sustained DMS concentrations of the order of 100 ppt which seems unlikely. In summary, the occurrence of new particles in the unperturbed MBL would be difficult to explain by DMS emissions alone. DMS emissions can explain the occurrence of thermodynamically stable sulphate clusters, but under most conditions, to grow these clusters to detectable sizes before they are scavenged by coagulation, an additional condensable species other than DMS-derived sulphuric acid would be required. In the event, however, of significant removal of the preexisting aerosol due to precipitation, the MBL aerosol can be replenished through growth of new particle formed through ternary nucleation under moderately high DMS concentrations.

 

Further Measurements Of Global Radiation Using Black And White Atmometers Further Measurements Of Global Radiation Using Black And White Atmometers

Date added: 08/07/1957
Date modified: 07/01/2009
Filesize: 522.76 kB
TC O Connor, Further Measurements Of Global Radiation Using Black And White Atmometers, Geofisica Pura E Apllicata- Milano Vol 38 pp 154-157 (1957)

Abstract

 

The feasibility of using the difference in the evaporation from a black and whiteatmometer for the continuous routine measurement of global radiation at a field station was examined. The atmometers were operated continously for 177 days and the results obtained were compared with measurements of the global radiation for the corresponding period as given by a Bellani pyranometer. Good agreement between the monthly totals of global radiation from both methods were obtained

Coupling Sea-Salt and Sulphate Interactions and its Impact on Cloud Droplet... Coupling Sea-Salt and Sulphate Interactions and its Impact on Cloud Droplet...

Date added: 08/06/1999
Date modified: 07/01/2009
Filesize: 489.73 kB

O’Dowd, C. D., J. A. Lowe, and M. H. Smith (1999), Coupling Sea-Salt and Sulphate Interactions and its Impact on Cloud Droplet Concentration Predictions., Geophys. Res. Lett., 26(9), 1311–1314.


Abstract


A parameterisation of internal mixing between sulphate and sea-salt aerosol is developed to determine the available externally mixed sulphate cloud condensation nuclei (CCN) population. This parameterisation is then combined with a multi-component aerosol-cloud parameterisation to predict cloud droplet concentration incorporating the physical competition between sea-salt and sulphate nuclei in the cloud nucleation processes. The results of the combined parameterisation indicate a significantly reduced role, compared to previous estimates, for sulphate in cloud droplet nucleation, and consequently, in indirect radiative forcing. However, the results also imply that cloud droplet concentration, and consequently, cloud albedo, has a greater susceptibility to change resulting from further anthropogenic SO2 emissions.

 

CFCs in Connemara Technology Ireland September 1991 CFCs in Connemara Technology Ireland September 1991

Date added: 09/28/1991
Date modified: 07/27/2009
Filesize: 1.37 MB
O'Connor, T.C. & Simmonds, P.G. (1991)- CFCs in Connemara, Technology Ireland, 23, No. 5, pp. 19-21.

Abstract

 

At an isolated research centre in Conemara, scientist are monitoring the background atmospheric levels of the CFCs and other chemicals which are destroying the ozone layer. Tom O'Connor and Peter Simmonfs write here of how the UCG centre is playing a vital role in international studies to monitor the accumulation of these gases in the global atmosphere.

Modeling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and compa Modeling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and compa

Date added: 08/06/1999
Date modified: 07/09/2009
Filesize: 1.29 MB

Carslaw, N., D. J. Creasey, D. E. Heard, A. C. Lewis, J. B. McQuaid, M. J. Pilling, P. S. Monks, B. J. Bandy, and S. A. Penkett (1999), Modeling OH, HO2, and RO2 radicals in the marine boundary layer 1. Model construction and comparison with field measurements, J. Geophys. Res., 104(D23), 30,241–30,255.


Abstract


An observationally constrained box model has been constructed to investigate radical chemistry at the Mace Head Atmospheric Observatory, a remote marine location on the west coast of Ireland. The primary aim of the model has been to model concentrations of the hydroxyl (OH), hydroperoxy (HO2), and the sum of peroxy Σ([HO2]+[RO2]) radicals measured by in situ instruments at this location. The model used in these studies consists of about 1670 reactions and 500 species, and model predictions of radical concentrations have been evaluated against field data. In order to further understand the chemistry, the model has been reduced using sensitivity analysis on both a clean and a semipolluted day. For reduced mechanisms that predict the concentrations of OH and HO2 to within 5% of the full mechanism, the semipolluted day can be represented using 279 species and 986 reactions, and the clean day using 249 species and 894 reactions. A further reduction has been applied whereby the reduced mechanisms predict concentrations of OH and HO2 to within 20% of the full mechanism for the daytime hours. In this way, the OH and HO2 concentrations on the semipolluted day can be represented by 42 species and 64 reactions, and the clean day by 17 species and 25 reactions. We show that these reduced mechanisms are generally applicable for this location under broadly similar conditions. Simple steady state expressions have also been derived to represent the chemistry at this location, allowing the concentrations of OH and HO2 to be deduced analytically. The expressions are based on the reduced mechanisms and on a further analysis of the reaction rates. Finally, an uncertainty analysis has been carried out to quantify the effects of propagation of uncertainties in the rate parameters and constrained concentrations through to the calculated radical concentrations in the model. For model concentrations of OH, HO2, and Σ([HO2]+[RO2]) radicals, the 2σ uncertainties are 31, 21, and 25%, respectively for clean air, and 42, 25, and 27% for semipolluted air.

Observations of accumulation mode aerosol composition and soot carbon concentration.......volat Observations of accumulation mode aerosol composition and soot carbon concentration.......volat

Date added: 08/06/1996
Date modified: 07/03/2009
Filesize: 770.09 kB

Smith, M. H., and C. D. O'Dowd (1996), Observations of accumulation mode aerosol composition and soot carbon concentrations by means of a high-temperature volatility technique, J. Geophys. Res., 101(D14), 19,583–19,591.


Abstract


A high-temperature volatility system has been deployed for the measurement of the composition and concentration of the accumulation mode aerosol (0.05 μm < r < 1 μm) within the atmospheric boundary layer. This instrumentation comprises a volatility system based around a Particle Measuring Systems ASASP-X optical particle counter, which was operated together with an aethalometer for the direct observation of soot carbon concentrations. By cycling the heater tube through a range of temperatures from near ambient to over 1000°C, size-differentiated information upon aerosol composition may be obtained. Furthermore, by careful selection of analysis temperatures, discrimination is possible between elemental carbon and the more volatile fractions of the soot carbon aerosol. Observations made over the North Sea near the Dutch coast and in the central United Kingdom are presented for differing environmental conditions with soot carbon concentrations ranging from about 100 to over 6000 ng m-3. For polluted conditions over the North Sea the volatility technique clearly showed the dominance of soot carbon particles over other aerosol components with a narrow carbon particle distribution of mode radius around 0.06 μm accounting for about 80% of all particles with radii below 0.1 μm. Under polluted conditions, only about 25% of the total soot carbon aerosol comprised elemental carbon (with the remainder consisting of more volatile material), whereas this proportion rose to around 50% in the lower carbon loadings found in a cleaner maritime air mass. The use of soot carbon loadings as a tracer of anthropogenic aerosol inputs to oceanic regions is explored on the basis of measurements from a NE Atlantic cruise.

 

Backscatter and extinction measurements in cloud and drizzle at CO2 laser wavelengths Backscatter and extinction measurements in cloud and drizzle at CO2 laser wavelengths

Date added: 07/31/1986
Date modified: 06/30/2009
Filesize: 1.09 MB

Jennings, S.G. (1986). - Backscatter and extinction measurements in cloud and drizzle at CO2 laser wavelengths. Appl. Opt., 25, 2499 - 2505.


Abstract


The backscatter and extinction of laboratory generated cloud and drizzle sized drops have been measured at CO2 laser wavelengths (predominately at λ = 10.591 µm). Measurements of volume backscatter coefficient σb and volume extinction coefficient σe for laboratory cloud of predominantly <20-µm radius droplets are dependent on the form of the size distribution in agreement with numerical prediction. For drops of >˜20 µm at λ = 10.591 µm the relation between σe and σb has the appealingly simple size distribution independent form of σeb =8π/G,[equation] is the asymptotic value of the backscatter gain, where n and k are the real and imaginary indices of refraction. The linear relation is in good agreement with extinction and backscatter measurements made on laboratory generated drizzle sized drops (r > 20 µm). This suggests that the extinction coefficient at CO2 laser wavelengths could be inferred from lidar backscatter return signals without requiring knowledge of the size distribution for drizzle and spherical precipitation sized water drops.

Aitken Nuclei Measurements and Evidence of Gas-to-particle conversion Processes at Mace Head, Ireland.. Aitken Nuclei Measurements and Evidence of Gas-to-particle conversion Processes at Mace Head, Ireland..

Date added: 08/26/1994
Date modified: 07/23/2009
Filesize: 840.25 kB

O'Connor, T.C., McGovern, F.M., Jennings, S.G. & Philipp, C.(University of Hannover)  (1994)-
Aitken nuclei measurements and evidence of gas-to-particle conversion processes at Mace Head, Ireland. Proceedings of  EUROTRAC 94 Symposium, The Hague, SPB Academic Publishing, 1206-1209.


Black carbon aerosol and carbon monoxide in European regionally polluted air masses at Mace Head, Ireland during 1995–1998 Black carbon aerosol and carbon monoxide in European regionally polluted air masses at Mace Head, Ireland during 1995–1998

Date added: 07/31/2001
Date modified: 07/27/2009
Filesize: 364.88 kB

Derwent, R.G., Ryall, D.B., Jennings, S.G., Spain, T.G., and Simmonds, P.G. (2001). Black carbon aerosol and carbon monoxide in European regionally polluted air masses at Mace Head, Ireland during 1995-1998. Atmos. Environ., 35, 6371-6378.


Abstract


Continuous measurements of black carbon aerosol (BCA) at the Mace Head Atmospheric Research Station on the Atlantic Ocean coast of Ireland show the occurrence of dramatically elevated concentrations when regionally polluted air masses are advected to the station. These occurrences correlate well with similar elevations in carbon monoxide and a wide range of other trace gases monitored near-simultaneously with the BCA. Using daily sector allocation and a sophisticated Lagrangian dispersion model, two independent estimates of the European emission source strength of BCA that are required to explain the Mace Head observations have been made. The best estimates of the UK and European emission source strengths of BCA are 46±14 and [(482-511)±140]x103 tonnes/yr, respectively, and these estimates compare favourably with published inventories, at least to within ±25%, though they are considerably smaller than the emissions employed in some early global climate model studies.

Interannual and seasonal variability in atmospheric N 2 O Interannual and seasonal variability in atmospheric N 2 O

Date added: 08/06/2007
Date modified: 07/24/2009
Filesize: 673.42 kB

Nevison, C. D., N. M. Mahowald, R. F. Weiss, and R. G. Prinn (2007), Interannual and seasonal variability in atmospheric N2O, Global Biogeochem. Cycles, 21, GB3017, doi:10.1029/2006GB002755.


Abstract


The increase in atmospheric N2O observed over the last century reflects large-scale human perturbations to the global nitrogen cycle. High-precision measurements of atmospheric N2O over the last decade reveal subtle signals of interannual variability (IAV) superimposed upon the more prominent growth trend. Anthropogenic sources drive the underlying growth in N2O, but are probably too monotonic to explain most of the observed IAV. The causes of both seasonal and interannual variability in atmospheric N2O are explored on the basis of comparisons of a 1993–2004 atmospheric transport simulation to observations of N2O at five stations of the Advanced Global Atmospheric Gases Experiment (AGAGE). The complementary tracers chlorofluorocarbons (CFCs) 11 and 12 and SF6 also are examined. The model simulation does not include a stratospheric sink and thus isolates the effects of surface sources and tropospheric transport. Both model and observations yield correlations in seasonal and interannual variability among species, but only in a few cases are model and observed variability correlated to each other. The results suggest that tropospheric transport contributes substantially to observed variability, especially at Samoa station. However, some features of observed variability are not explained by the model simulation and appear more consistent with a stratospheric influence. At Mace Head, Ireland, N2O and CFC growth rate anomalies are weakly correlated to IAV in polar winter lower stratospheric temperature, a proxy for the strength of the mean meridional stratospheric circulation. Seasonal and interannual variability in the natural sources of N2O may also contribute to observed variability in atmospheric N2O.

 

Nanoparticle formation in marine airmasses contrasting behaviour of the open ocean and coastal Nanoparticle formation in marine airmasses contrasting behaviour of the open ocean and coastal

Date added: 08/05/1999
Date modified: 07/23/2009
Filesize: 808.31 kB

Allen, A.G., J.L. Grenfell, R.M. Harrison, J. James, and M.J. Evans, Nanoparticle formation in marine airmasses: Contrasting behaviour of the open ocean and coastal environments, Atmos. Res., 51, 1-14, 1999, (Ser. No. ACP030).


Abstract


Massive and rapid increases in nanoparticles have been observed at a remote coastal site in western Ireland. The same phenomenon was not detected aboard a ship situated approximately 160 km off-coast. On-shore nanoparticles correlated remarkably well with the march of the tide, peaking at low-water. This suggests a link between marine biogenic gas emissions (as yet unidentified) and nanoparticle formation events. This paper examines the contrasting behaviour observed at the coast and in the open ocean, with respect to nanoparticle formation.

 

 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.

 

Relative contribution of submicron and supermicron particles Relative contribution of submicron and supermicron particles

Date added: 08/01/2002
Date modified: 07/23/2009
Filesize: 399.76 kB
Christoph Kleefeld, Colin O'Dowd, Sarah O'Reilly, S. Gerard Jennings, Pasi Alto, Edo, Becker, Gerard Kunz, Gerrit de Leeuw.The Relative Contribution of sub and super micron particles to aerosol light scattering in the marine boundary layer (MBL), J. Geophys. Res., 107, 10.1029/2000JD000262, 2002.

Abstract


Measurements of the aerosol light scattering coefficient (σsp) at a wavelength of λ = 550 nm were conducted at a coastal atmospheric research station in the east Atlantic Ocean during June 1999. Size distribution measurements between diameters of 3 nm and 40 μm (at ambient humidity) were used to derive scattering coefficients from Mie theory. The calculated scattering coefficients were about a factor of 7.4 higher than the measured scattering coefficients. The discrepancy was explained by a reduced cutoff of the sampling system at particle diameters between 6 and 8 μm, dependent on wind speed. The calculated aerosol scattering was about 1 order of magnitude higher than previously reported measurements in the MBL and is attributed to supermicrometer particles at sizes d > 10 μm dominating aerosol scattering.

First experimental evidence of new particle formation from organic vapours over forests First experimental evidence of new particle formation from organic vapours over forests

Date added: 07/31/2002
Date modified: 07/01/2009
Filesize: 97.37 kB

O'Dowd, C.D. K. Hämeri, P. Aalto, and M. Kulmala, First experimental evidence of new particle formation from organic vapours over forests, Nature, 416, 497-498, 2002.


Abstract


Aerosol particles produced over forested areas may affect climate by acting as nuclei for cloud condensation, but their composition (and hence the chemical species that drive their production) remains an open question. Here we show, to our knowledge for the first time, that these newly formed particles (3–5 nm in diameter) are composed primarily of organic species, such as cis-pinonic acid and pinic acid, produced by oxidation of terpenes in organic vapours released from the canopy

DOAS measurements of I2, BrO,IO, OIO and NO3 at mace head, ireland DOAS measurements of I2, BrO,IO, OIO and NO3 at mace head, ireland

Date added: 08/06/2003
Date modified: 07/27/2009
Filesize: 33.33 kB

Saiz-Lopez, A., Shillito, J. A., Coe, H., and Plane, J. M. C.: Measurements and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude marine boundary layer, Atmos. Chem. Phys. Discuss., 5, 9731-9767, 2005.


Abstract


Time series observations of molecular iodine (I2), iodine oxides (IO, OIO), bromine oxide (BrO), and the nitrate radical (NO3) in the mid-latitude coastal marine boundary layer (MBL) are reported. Measurements were made using a new long-path DOAS instrument during a summertime campaign at Mace Head on the west coast of Ireland. I<2 was detected using the B3Π(0+u)−X1Σxg electronic transition between 535 and 575 nm. The I2 mixing ratio was found to vary from below the detection limit (~5 ppt) up to a nighttime maximum of 93 ppt. Along with I2, observations of IO, OIO and NO3 were also made during the night. Surprisingly, IO and OIO were detected at mixing ratios up to 2.5 and 10.8 ppt, respectively. A model is employed to show that the reaction between I2 and NO3 is the likely nighttime source of these radicals. The BrO mixing ratio varied from below the detection limit at night (~1 ppt) to a maximum of 6 ppt in the first hours after sunrise. A model shows that this diurnal behaviour can be explained by halogen recyling in sea-salt aerosol building up photolabile precursors of atomic Br during the preceding night. In the same campaign a zenith sky DOAS was employed to determine the column density variation of NO3 as a function of solar zenith angle (SZA) during sunrise, from which vertical profiles of NO3 through the troposphere were obtained. On several occasions a positive gradient of NO3 was observed over the first 2 km, possibly due to dimethyl sulphide (DMS) removing NO3 at the ocean surface.

 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.

 

 

How falling raindrops collide How falling raindrops collide

Date added: 08/01/1972
Date modified: 07/02/2009
Filesize: 470.45 kB

S.G Jennings, P.R. Brazier-Smith, J. Latham, ,How falling raindrops collide,Page 313, New Scientist, 10 February 1972


Abstract

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.

Boundary layer and aerosol evolution during the 3rd Lagrangian experiment of ACE-2 Boundary layer and aerosol evolution during the 3rd Lagrangian experiment of ACE-2

Date added: 08/31/2000
Date modified: 07/23/2009
Filesize: 952.82 kB

Wood, R., D. Johnson, S. Osborne, M. O. Andreae, B. Bandy, T. S. Bates, C. O'Dowd, P. Glantz, K. Noone, P. K. Quinn, J. Rudolph, and K. Suhre, Boundary layer and aerosol evolution during the 3rd Lagrangian experiment of ACE-2. Tellus, 2000. 52B: p. 401-422.


Abstract


Aircraft measurements are presented of the Lagrangian evolution of a marine boundary layer over a 30-h period during the ACE-2 field campaign. At the start of the  observational period,a 500-m deep polluted marine internal boundary layer (MIBL) was overlain by the remnants of a polluted continental boundary layer extending to around 2 km below a clean, dry free troposphere. The MIBL grew rapidly to a thickness of 900–1000 m in response to increasing sea surface temperatures. No significant aerosol spectral evolution was observed in the boundary layer. Low concentrations of SO2 were observed in the MIBL suggesting that the air mass contained relatively aged aerosol. Aerosol spectra show a broad mode with a modal diameter of around 0.1 mm. The polluted layer between the MIBL and the unpolluted free troposphere was only weakly and intermittently turbulent which prevented significant entrainment of clean air into the polluted layer from aloft. The polluted layer depth was thus controlled mainly by subsidence which as a result becomes shallower, decreasing from over 2000 m to around 1200 m during the observational period. The aerosol characteristics of the polluted layer were similar to those in the MIBL and so although the MIBL entrained considerable amounts of air from above the MIBL the aerosol characteristics underwent no significant change. This has important implications for the rate at which a polluted continental air mass is converted to a clean marine one. The dataset should prove useful in the validation of the modelling of continental pollution outbreaks.

Intercomparison Of Formaldehyde Intercomparison Of Formaldehyde

Date added: 08/31/2003
Date modified: 07/23/2009
Filesize: 36.97 kB

T.J.Still , G.Mills, S. Al-Haider, P.W Seakins, P.Quincy, N.Martin , INTERCOMPARISON OF FORMALDEHYDE

Geophysical Research Abstracts, Vol. 6, 03925, 2004, SRef-ID: 1607-7962/gra/EGU04-A-03925 ,European Geosciences Union 2004


Abstract

 

Formaldehyde is one of the most abundant gas phase carbonyl compounds present in the troposphere, which is emitted directly, and produced from photo-oxidation of biogenic and anthropogenic volatile organic compounds. The subsequent removal process of formaldehyde generates substantial amounts of HO2 radicals, which ultimately result in formation of ozone. Consequently formaldehyde has a strong influence on the global mixing ratio of ozone and HOx radicals, which govern the oxidising capacity of the troposphere. An apparatus has been developed for the direct determination of ambient, atmospheric formaldehyde using gas chromatography with an argon doped, pulsed discharge helium ionization detector. Absolute values are obtained via calibration with a permeation source. The relatively high duty cycle (˜11 hr-1) allows measurements to be taken on timescales that are short compared to the atmospheric lifetime of formaldehyde. A detection limit of 42 pptv is calculated. This instrument was deployed to the West Coast of Ireland for the North Atlantic Marine Boundary Layer Experiment (NAMBLEX). Formaldehyde was also measured using an indirect fluorometric technique, and the results of the comparison are presented. Similar diurnal profiles are observed for both methods although they have slightly different dynamic ranges, and there was a discrepancy in the absolute values. The instruments were then tested for a linear response to atmospheric formaldehyde, and for any interferences due to ozone and water, at the National Physics Laboratory. The results demonstrated that both instruments have a linear response to formaldehydeup to 8.6 ppbv. The ozone interference experiments show that each of the techniques have a response due to ozone but of different magnitudes. It has not been possible to fully characterise the water interference in the gas chromatography technique, whilst the fluormetric method was found not to have an interference from this source. Box modelling studies predict formaldehyde concentrations comparable with our measurements and indicate that decomposition of oxygenates (e.g. CH3OH, CH3CHO), contribute significantly to the observed formaldehyde  concentrations.

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.

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.

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.

 

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.

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.

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