Payday loans
Home Publications Journal Publications

Journal Publications

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

Click on the "Search Document" icon above to find a publication based on the search criteria you create.

 


Documents

Order by : Name | Date | Hits [ Ascendant ]

Electrical charging of water drops in polarizing electric fields. Electrical charging of water drops in polarizing electric fields.

Date added: 08/01/1975
Date modified: 07/01/2009
Filesize: 2.02 MB

Jennings, S.G.  (1974)- Electrical charging of water drops in polarizing electric fields.  J. Electrostatics, 1,  15-25.


Abstract


Measurements were made of the electric charge acquired by drops of mean radius of about 750 μm as they fell through a cloud of water droplets of mean radius 16 μm, in the presence of a vertical electric field E, the value of which could be varied from 4.5 to 27 kV m−1. It was found that the proportion of interactions which resulted in separation (and, therefore, in electric charge transfer, as a consequence of the inductive process of electrification) decreased from about 1% in the weaker fields to about 0.2% in the strongest ones.

This work suggests that the collisions between polarised raindrops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30 kV m−1 but that significantly larger fields could not be produced since all collisions in higher fields would result in permanent coalescence.

Effects of source temporal resolution on transport simulations of boreal fire emissions Effects of source temporal resolution on transport simulations of boreal fire emissions

Date added: 08/06/2006
Date modified: 07/27/2009
Filesize: 427.81 kB

Hyer, E. J., E. S. Kasischke, and D. J. Allen (2007), Effects of source temporal resolution on transport simulations of boreal fire emissions, J. Geophys. Res., 112, D01302, doi:10.1029/2006JD007234.


Abstract


The quality of temporal information from daily burned area inputs was evaluated using a transport and chemistry experiment. Carbon monoxide emissions from boreal forest fires were estimated using burned area inputs with daily resolution. Averaging of emissions data to create 30-day aggregate data reduced the variance by 80%, indicating a substantial loss of information. Data from Russia, Canada, and Alaska were tested for periodicity to uncover systematic gaps in daily data. Some evidence of periodicity was found in data from Alaska, where temporal information came from fire mapping by the Alaskan Fire Service. Autocorrelation decayed rapidly and nearly monotonically for Canada and Russia, where temporal information came from Advanced Very High Resolution Radiometer (AVHRR) satellite observations. Daily data as well as 7-day and 30-day aggregates were used as input to the University of Maryland Atmospheric Chemistry and Transport Model, and output was compared with CO observations from the Cooperative Air Sampling Network (CASN); continuous measurements from Mace Head, Ireland; and total column CO retrievals from the Measurement of Pollution in the Troposphere (MOPITT) instrument. CASN flask measurements showed no sensitivity to high-frequency variability in the source, indicating the effectiveness of the filtering protocol at ensuring only well-mixed air masses are sampled in this data set. Differences between daily and 7-day simulations were too small for quantitative comparison in any of the data. For cases where the differences were substantial, simulations using daily and 7-day average sources agreed better with observations than 30-day average sources.

 

Effects of particulate complex refractive index and particle size distribution variations on atmospheric extinction Effects of particulate complex refractive index and particle size distribution variations on atmospheric extinction

Date added: 08/01/1978
Date modified: 07/01/2009
Filesize: 851.05 kB
Jennings, S.G., and Pinnick, R.G.  (1978)- Effects of particulate refractive index and particle size distribution variations on atmospheric extinction and absorption for visible to middle-IR wavelengths. American Meteorological Society Third Conference on Atmospheric Radiation, Davis, California, 6-9.

Abstract


A comprehensive sensitivity study has been made, using Mie theory, to determine the effect of realistic variations in values of real and imaginary parts of the complex index of refraction on volume extinction and absorption coefficients for a wide range of lognormal particle size distributions (defined by geometric mean radius r sub g and geometric standard deviation sigma sub g). Wavelengths lambda from visible (0.55 micrometers) through middle-infrared (10.6 micrometers) were considered. Extinction is independent of complex index to within 20 percent for the majority of realistic particle size distributions, providing lambda < or = 2 micrometers. However, changes in extinction by up to an order of magnitude are caused by realistic variations in refractive indexes for 2 < or = lambda < or = 10.6 micrometers, with real index being more important in affecting extinction than imaginary index.

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.

 

Effect of instrumental particle sizing resolution on the modelling of aerosol radiative parameters Effect of instrumental particle sizing resolution on the modelling of aerosol radiative parameters

Date added: 03/04/2010
Date modified: 03/04/2010
Filesize: 886.14 kB

Chamaillard, K., S. G.  Jennings, D. Ceburnis, Y.J. Yoon and C. O’Dowd.  Effect of instrumental particle sizing resolution on the modelling of aerosol radiative parameters. doi:10.1016/j.jqsrt.2009.11.005, Journal of Quantitative Spectroscopy and Radiative Transfer Volume 111, Issue 5, 2010, Pages 753-771


 

 Abstract.

 

A more realistic estimation of the scattering and hemispheric backscattering coefficients, ssp and sbsp, and their respective optical cross section, Csca and Cbk, of aerosol particles is presented on the basis of the exact resolution of the width of the size bins of the particle counter instruments when size distribution measurements are used, and, with the exact optical detector instruments ability. The scattering and hemispheric back scattering cross sections, Csca and Cbk, of the particles are averaged over the full size bins of the particle counter instrument, while the sequantities are usually estimated only on the value of the mean geometric diameter of each size bin. Six instruments, the APS, ASASP-X, DMPS,FSSP-100, ELPI, and SMPS frequently used in particle size distribution measurements are reviewed, for spherical sea-salt particles at a wavelength l=0.55 mm. The comparison using the conventional geometric mean diameter versus the use of the full size bin leads to large amount of errors for the optical cross section with non-negligible effects on their respective optical coefficients.The maximal accuracy expected for these optical quantities depend on the particle diameter as well as on the channel width of the instruments, and are also function of the angular detector probe used to measure them..

 


Effect of Horizontal Resolution on Meteorology and Air-Quality Prediction with a Regional Scale Mode Effect of Horizontal Resolution on Meteorology and Air-Quality Prediction with a Regional Scale Mode

Date added: 05/12/2011
Date modified: 05/12/2011
Filesize: 4.49 MB

Varghese, S., B. Langmann and C. D. O’Dowd, Effect of Horizontal Resolution on Meteorology and Air-Quality Prediction with a Regional Scale Model, Atmos. Res., doi:10.1016/j.atmosres.2011.02.007, 2011

 


 

Horizontal resolution sensitivity can significantly contribute to the uncertainty in predictions of meteorology and air-quality from a regional climate model. In the study presented here, astate-of-the-art regional scale atmospheric climate-chemistry-aerosol model REMOTE is used to understand the influence of spatial model resolutions of 1.0°, 0.5° and 0.25° on predicted meteorological and aerosol parameters for June 2003 for the European domain comprising North-east Atlantic and Western Europe. Model precipitation appears to improve with resolution while wind speed has shown best results for 0.25° resolution for most of the stations compared with ECAD data. Low root mean square error and spatial bias for surface pressure, precipitation and surface temperature show that the model is very reliable. Spatial and temporal variation in black carbon, primary organic carbon, sea-salt and sulphate concentrations and their burden are presented. In most cases, chemical species concentrations at the surface show no particular trend or improvement with increase in resolution. There has been a pronounced influence of horizontal resolution on the vertical distribution pattern of some aerosol species. Some of these effects are due to the improvement in topographical details, flow characteristics and associated vertical and horizontal dynamic processes. The different sink processes have contributed very differently to the various aerosol pecies in terms of deposition (wet and dry) and sedimentation which are strongly linked to the meteorological processes. Overall, considering the formance of meteorological parameters and chemical  pecies concentrations, a horizontal model resolution of 0.5° is suggested to achieve easonable results within the limitations of this model.

Eddy correlation measurements of ozone fluxes over coastal waters west if Ireland Eddy correlation measurements of ozone fluxes over coastal waters west if Ireland

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 980.87 kB

McVeigh, P., C. O’Dowd, and H. Berresheim, Eddy correlation measurements of ozone fluxes over coastal waters west if Ireland,  Adv. in Meteorol., Volume 2010, Article ID 754941, doi:10.1155/2010/754941, 2010.

 


 Measurements of ozone fluxes using the eddy-correlation (EC) technique were carried out for the first time at the Mace Head atmospheric research station, on the west coast of Ireland between August-October 2009. Vertical exchange of ozone was measured from a tower platform at 22m above mean sea level to study fluxes over coastal waters excluding the tidal region. The results were averaged over 30 min and exhibited predominantly downward but also upward transport of ozone in the boundary layer. Data quality was found to be high based on inspection of cospectra and micrometeorological measurements. During the study period, a major physical influence on O3 fluxes was found to be wind speed. Measured fluxes were of the same magnitude as reported in previous open ocean studies ranging from approximately +0.2 to 0.5 μg m2 s1 (0.017 μg m2 s1 on average, corresponding to a deposition velocity of 0.25mm s1 or a surface resistance of 4.13 s mm1). These results are considered to represent ozone fluxes over shallow coastal waters west of Ireland for conditions during summer and fall not affected by phytoplankton blooms.

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

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

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


Abstract


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

 

Eastern Atlantic Spring Experiment 1997 (EASE97) 2 Comparisions of model concentrations of OH... Eastern Atlantic Spring Experiment 1997 (EASE97) 2 Comparisions of model concentrations of OH...

Date added: 08/06/2002
Date modified: 07/27/2009
Filesize: 640.01 kB

Carslaw,m N.; Creasey, D.J.; Heard, D.E.; Jacobs, P.; Lee, J.D.L.; Lewis, A.C.; McQuaid, J.B.; Pilling, M.J.; Bauguitte, S.; Penkett, S.A.; Monks, P.S.; Salisbury, G. (2002) Eastern Atlantic Spring Experiment 1997 (EASE97) - 2. Comparisons of model concentrations of OH, HO2, and RO2 with measurements, Journal of Geophysical Research, 107, pp.4190/ ACH5


Abstract


An observationally constrained box model has been used to investigate the chemistry of the marine boundary layer at the Mace Head Atmospheric Research Station, a remote site on the west coast of Ireland. The model aims to simulate concentrations of the hydroxyl (OH) and hydroperoxy (HO2) radicals measured by an in situ fluorescence assay by gas expansion instrument, and the sum of peroxy radicals ([HO2] + Σ[RO2]) as determined by a peroxy radical chemical amplification instrument. The model has been constructed based on observed concentrations of nonmethane hydrocarbons, measured in situ during the campaign by gas chromatography. The chemical mechanism for the model is a subset of a comprehensive master chemical mechanism. This paper details comparisons of the concentrations of modeled and measured radical species from a field campaign held at Mace Head during spring 1997. The air masses arriving at the site have been split into three categories depending on their origin and chemical characteristics and model-measurement comparisons carried out for each air mass. The average model-measurement ratios are 2.4 for [OH], 3.6 for [HO2], and 0.9 for ([HO2] + Σ[RO2]), respectively, between 1100 and 1500 hours: the level of agreement is better for all three sets of radicals in the cleanest air mass. Possible reasons for the observed discrepancies are discussed. In addition, a rate of production analysis is used to identify key OH and HO2 reactions in the three air masses. The rate of OH production from HO2 with NO exceeds that from ozone photolysis by factors of 2–6 in the polluted air masses studied. In cleaner air from the northern polar region, primary production from ozone photolysis exceeds that from HO2 + NO by a factor of 2.5. HO2 and CH3O2 dominate the peroxy radical composition in all air masses, but peroxy radicals derived from the oxidation of nonmethane hydrocarbons are more important in polluted air masses.

 

Dual pathways for atmospheric sulfuric acid-water nucleation mechanisms Dual pathways for atmospheric sulfuric acid-water nucleation mechanisms

Date added: 04/08/2009
Date modified: 11/01/2009
Filesize: 988.72 kB
Laaksonen, A.,  M. Kulmala, T. Berndt, F. Stratmann, S. Mikkonen, A. Ruuskanen, K.E.J. Lehtinen, M. Dal Maso, P. Aalto, T. Petäjä, I. Riipinen, R. Janson, F. Arnold, M. Hanke, J.Ücker, B. Umann, K. Sellegri,  C.D. O’Dowd, Y. Viisanen, Dual pathways for atmospheric sulfuric acid-water nucleation mechanisms,, Atmos. Chem. Phys.,  8, 7255–7264, 2008.

Abstract


Atmospheric new particle formation is generally thought to occur due to homogeneous or ion-induced nucleation of sulphuric acid. We compare ambient nucleation rates with laboratory data from nucleation experiments involving either sulphuric acid or oxidized SO2. Atmospheric nucleation occurs at H2SO4 concentrations 2–4 orders of magnitude lower than binary or ternary nucleation rates of H2SO4 produced from a liquid reservoir, and atmospheric H2SO4 concentrations are very well replicated in the SO2 oxidation experiments. We hypothesize these features to be due to the formation of free HSO5 radicals in pace with H2SO4 during the SO2 oxidation. We suggest that at temperatures above 250K these radicals produce nuclei of new aerosols much more efficiently than H2SO4. These nuclei are activated to further growth by H2SO4 and possibly other trace species. However, at lower temperatures the atmospheric relative acidity is high enough for the H2SO4–H2O nucleation to dominate.

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.

Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site

Date added: 08/07/1999
Date modified: 07/27/2009
Filesize: 210.82 kB

A.C. Lewis J.B. McQuaid, N. Carslaw, M.J. Pilling.,; Short Communication Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site,. Atmospheric Environment 33 (1999) 2417Ð2422 2419


Abstract


Observation of diurnal cycles in atmospheric concentrations of reactive alkenes are reported from measurements performed at a North Atlantic coastal site (Mace Head, Eire 53°19'34N; 9°54'14W). Species seen to exhibit distinct cycles included isoprene, ethene, propene, 1-butene, iso-butene and a substituted C6 alkene. Five hundred and thirty air mass classified measurements were performed over a 4 week period at approximately hourly frequency and demonstrate that during periods when air flow resulted from unpolluted oceanic regions a clear daily cycle in concentrations existed, peaking at around solar noon for all species. These observations support the proposed mechanism of production via photochemical degradation of organic carbon in sea water. The observed concentrations showed strong correlation (propene R2 > 0.75) with solar flux, with little relationship to other meteorological or chemical parameters. The species' short atmospheric lifetimes indicate that the source of emission was from local coastal waters within close proximity of the sampling site. At solar noon concentrations of reactive alkenes from oceanic sources were responsible for up to 88% of non-methane hydrocarbon reaction with the hydroxyl radical at this coastal marine site.

 

Distribution and Sea-Air Fluxes of Biogenic Trace Gases in the Eastern Atlantic Ocean Distribution and Sea-Air Fluxes of Biogenic Trace Gases in the Eastern Atlantic Ocean

Date added: 08/06/2000
Date modified: 07/27/2009
Filesize: 1.44 MB

Baker, A. R., S. M. Turner, W. J. Broadgate, A. Thompson, G. B. McFiggans, O. Vesperini, P. D. Nightingale, P. S. Liss, and T. D. Jickells (2000), Distribution and Sea-Air Fluxes of Biogenic Trace Gases in the Eastern Atlantic Ocean, Global Biogeochem. Cycles, 14(3), 871–886.


Abstract


A number of atmospherically important trace gases (dimethyl sulphide (DMS), methyl iodide (CH3I), and nonmethane hydrocarbons (NMHCs)) were measured simultaneously in the eastern Atlantic Ocean during May 1997. This investigation was part of the U.K. Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) Community Research Program and covered a 200 by 200 nautical mile (1 nautical mile is 1.852 km) area to the west of the Mace Head Atmospheric Research Station on the coast of Ireland. Different spatial and temporal patterns were observed for each of the gases, showing that distinct sources dominate their production in this region: specific species of phytoplankton (DMS), macroalgae (CH3I), total phytoplankton biomass (isoprene), and photochemistry (ethene). Sea-to-air fluxes of the gases are calculated for near and offshore domains, and their temporal variations are discussed. A simple photochemical box model has been used to assess the contributions of the gas fluxes to the levels of the gases observed at Mace Head. Results show that the area studied may constitute a substantial source of DMS, a weak source of CH3I, a small source of ethene at night, and an insignificant source of isoprene to atmospheric levels of these gases measured at Mace Head in western Ireland.

 

Direct Measurements of New-Particle Fluxes in the Coastal Environment Direct Measurements of New-Particle Fluxes in the Coastal Environment

Date added: 08/06/2005
Date modified: 07/27/2009
Filesize: 228.88 kB

Flanagan, Robert J., Michael Geever, and Colin D. O'Dowd (2005), Direct Measurements of New-Particle Fluxes in the Coastal Environment, Enviro Chem, 2(4), 256, doi:10.1071/EN05069.


Abstract


Measurements of the flux of new secondary aerosol particles during nucleation events in the coastal environment using an eddy-correlation technique are reported for the first time. Events are divided into two types based on the prevailing wind direction. During tidal-related nucleation events, new-particle upward fluxes are typically of the order of 109–1010 particles m-2 s-1. A close correlation (r2 = 0.86) was found between total particle concentration and total (positive) flux when air masses were not affected by multiple sources. This would suggest that continuous measurements of particle number concentration at Mace Head can be translated into a flux using the resulting parameterization. It is expected that parameterizations obtained from similar data and analysis would be equally feasible at other coastal locations.

Dimethyl sulfide, methane sulfonic acid and physicochemical aerosol properties in Atlantic air Dimethyl sulfide, methane sulfonic acid and physicochemical aerosol properties in Atlantic air

Date added: 08/06/1996
Date modified: 07/01/2009
Filesize: 1.18 MB

Davison, B.M., C.N. Hewitt, R.M. Harrison, M. Schwikowski, U. Baltensperger, C. O'Dowd and M.H. Smith. Dimethyl sulfide, methane sulfonic acid and physico-chemical aerosol properties in Atlantic air from the United Kingdom to Halley Bay. J. Geophys. Res., 101, 22855-22874, 1996.


Abstract


The concentrations of dimethyl sulfide in air were obtained during a cruise between the United Kingdom and the Antarctic in the period October 1992 to January 1993 using a method of sampling and analysis optimized to avoid interferences from oxidants. In equatorial regions (30°N to 30°S) the atmospheric DMS concentration ranged from 3 to 46 ng (S) m-3, with an average of 18 ng (S) m-3, In the polar waters and regions south of the Falkland Islands, concentrations from 3 to 714 ng (S) m-3 were observed, with a mean concentration of 73 ng (S) m-3. The concentrations of a range of DMS oxidation products were also obtained. No clear relationships between reactant and product concentrations were seen. Information on particle number concentration, Fuchs surface area and the thermal volatility characteristics of the ambient aerosol was obtained, but again no clear relationships with sulfur concentrations were observed. Accumulation mode particle concentrations averaged 25 cm-3 in the clean marine and polar air masses south of 58°S while background condensation nuclei (CN) concentrations were of the order of 400-600 cm-3. Simplistic calculations suggest that a particle source strength of about 20-60 particles cm-3 d-1 is required to sustain this background CN concentration. It is not clear whether boundary layer nucleation of new CN or entrainment from the free troposphere provided the source of CN. Periods of elevated CN concentrations (>4000 cm-3) were regularly observed in the boundary layer over the Weddell Sea and were attributed to bursts of new particle formation. However, shortly after these nucleation events the CN concentration rapidly decayed to the background level through coagulation losses, suggesting little impact on the background CN or cloud condensation nuclei (CCN) concentration.

 

Dimethyl sulfide and its oxidation products in the atmosphere of the Atlantic and Southern Ocea Dimethyl sulfide and its oxidation products in the atmosphere of the Atlantic and Southern Ocea

Date added: 08/06/1996
Date modified: 07/23/2009
Filesize: 823.17 kB

Davison, B., C.D. O'Dowd, C.N. Hewitt, M.H. Smith, R.M. Harrison, D.A. Peel, E. Wolf, R. Mulvaney, M. Schwikowski and U. Baltensperger, Dimethyl Sulfide and its Oxidation Products in the Atmosphere of the Atlantic and Southern Oceans, Atmos. Environ., 30, 1895-1906, 1996


Abstract


Dimethyl sulfide, methane sulfonate, non-sea-salt sulfate and sulfur dioxide concentrations in air were obtained during a cruise between the U.K. and the Antarctic during the period October 1992-January 1993. In equatorial regions (30°N to 30°S) the atmospheric DMS concentration ranged from 3 to 46 ng (S)m-3 with an average of 18 ng(S)m-3. In the polar waters and regions south of the Falkland Islands concentrations from 3 to 714 ng(S)m-3 were observed with a mean concentration of 73 ng(S)m-3. Methane sulfonate concentrations were also enhanced in the vicinity of the Antarctic Peninsula and in the Weddell Sea. A simple model of DMS oxidation was used to estimate the ocean to atmosphere flux rate, and this was found to be within the range of previous estimates, with a mean value of 1011 ng (S) m-2 h-1.

 

Determination of biogenic volatile organic compounds (C8–C16) in the coastal atmosphere at Mace Determination of biogenic volatile organic compounds (C8–C16) in the coastal atmosphere at Mace

Date added: 08/07/2001
Date modified: 07/27/2009
Filesize: 357.39 kB

Determination of biogenic volatile organic compounds (C8 - C16) in the coastal atmosphere at Mace Head, Ireland (2001) J. Sartin, C.J. Halsall, B. Davison, S. Owen and C.N. Hewitt, Analytica Chimica Acta, 428, 61-72


Abstract


A methodology describing the sampling and analysis of biogenic volatile organic compounds (VOCs) in ambient coastal air is presented. Air samples were collected during a field campaign (September 1998) at Mace Head on the west coast of Ireland. In addition, air samples from seaweed enclosures were taken to assess the VOC source potential of macro-algae at low tide. VOC identification was confirmed using GC-MS and an n-alkane retention index, with quantification carried out using GC-FID. A suite of compounds (C8-C16) were routinely quantified; these included a series of n-alkanes (C11-C16) and oxygenated hydrocarbons (C8-C14). Their mixing ratios in coastal air ranged from <10-400 parts per trillion (pptv). The most abundant oxygenates included 2-ethyl-1-hexanol (mean = 175 pptv) and two ubiquitous ketones (geranyl acetone and 6-methyl-5-hepten-2-one) with average mixing ratios of 123 and 28 pptv, respectively. Air mass back trajectories indicated higher levels of the oxygenates when air flow was off the land (easterly continental) rather than from the ocean, although the opposite was observed for the n-alkanes. Mixing ratios of the n-alkanes (>C12) were significantly higher in the seaweed enclosure air than in ambient air, suggesting seaweed to be a source of long chain n-alkanes. Oxygenates, however, did not show a significant difference between enclosure and ambient air. Unlike studies carried out in the vicinity of woodlands, no monoterpenes or sesquiterpenes were detected in this study.

 

Description of a biofluorescence optical particle counter Description of a biofluorescence optical particle counter

Date added: 05/09/2009
Date modified: 07/23/2009
Filesize: 371.82 kB
Ryan, O., R. Greaney, S.G. Jennings and C.D. O’Dowd, Description of a biofluorescence optical particle counter J.Q.S.R.T., DOI: 10.1016/j.jqsrt.2009.01.033, 2009

Abstract

 

A bioaerosol fluorescence detection system is being constructed using an ellipsoid reflector-based optical particle counter. The flux measuring device is to size submicron marine spray aerosol particles smaller than 100nm in diameter. It will simultaneously non-destructively excite and detect fluorescence from organic matter contained in the aerosol. Chlorophyll-a is the primary fluorophor target, used as a marker for detecting phytoplankton (or derivatives thereof) in the particles. Particles have been sized to 500nm in diameter and fluorescence detection testing is underway. The device will aid the quantification and identification of this organic material contained in marine spray aerosols, providing improved inputs into climate models and air quality assessments.

Deposition in ionic Diffussion Deposition in ionic Diffussion

Date added: 08/07/1968
Date modified: 07/27/2009
Filesize: 1.69 MB

TC OConnor, F Anderson, PJ Nolan, Electrostatic Deposition in ionic Diffussion ,Proceeding of the Royal Irish Academy 1968, Volume 66 Section A No. 5


Abstract

 

Errors in the determination of ionic diffusion coefficients caused by the neglect of electrostatic deposition are examined. Correction formulae applicable to low ionic concentrations are derived for cylindrical channels. These are similiar to the Fuchs formulae for rectangular channels. Formulae applicable in the case of high ionic concentration are also derived.

For singly charged particles the correction tot the diffusion coefficient under the usual experimental conditions is about two or three per cent. The error becomes large when the number electronic charges per ion aproaches 100. Previous Dublin experiments with multiply charged nuclei are examined in this connection and corrections applied. The Corrections do not invalidate the main conclusion of these experiments that the Einstein equation B=D/KT does not apply in the absence of charge equilibrium.

Decreasing trends in total gaseous mercury observations in baseline air at Mace Head, Ireland from 1 Decreasing trends in total gaseous mercury observations in baseline air at Mace Head, Ireland from 1

Date added: 05/25/2011
Date modified: 05/25/2011
Filesize: 649.24 kB

R. Ebinghaus, S.G. Jennings, H.H. Kock , R.G. Derwent , A.J. Manning , and T.G. Spain,  Decreasing trends in total gaseous mercury observations in baseline air at Mace

Head, Ireland from 1996 to 2009, Atmos. Environ., doi:10.1016/j.atmosenv.2011.01.033


In this study, the concentrations of total gaseous mercury in baseline air masses arriving at Mace Head, Ireland after having traversed the thousands of kilometres uninterrupted fetch of the North Atlantic Ocean, have been used for the assessment of possible trends in the atmospheric mercury background concentration over a 14-year period (i.e., 1996 -2009), a statistically significant negative (downwards) trend of -0.028 ±0.01 ng m-3 yr-1, representing a trend of 1.6 - 2.0% per year, has been detected in the total gaseous mercury levels in these baseline air masses. These findings are set in the context of the available literature studies of atmospheric Hg trends.

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.

 

Contributions of Primary Organic Matter to Marine Aerosol Contributions of Primary Organic Matter to Marine Aerosol

Date added: 01/31/2011
Date modified: 01/31/2011
Filesize: 583.72 kB

Ovadnevaite, J., M. Dall'Osto, D. Ceburnis, C. Monahan, D. Worsnop, C. O’Dowd and H. Berresheim Detecting Very High Contributions of Primary Organic Matter to Marine Aerosol, Geophys. Res. Letts., doi:10.1029/2010GL046083 , 2011.


Using on‐line High‐Resolution Aerosol Mass Spectrometry, we report submicron organic marine aerosol plume concentrations peaking at 3.8 mg m−3. These concentrations are far greater than previously determinedby off‐line techniques and can exceed typica terrestrial concentrations of organic aerosol. The organic mass comprised 77% of the total submicron non‐refractory mass and such plumes were associated with regions of high biological activity and moderately‐high wind speeds over the N.E. Atlantic. High‐resolution mass spectra analysis revealed a unique marine organic aerosol fingerprint, when compared to anthropogenic organic aerosol, and in particular, anthropogenic hydrocarbons. 37% hydrocarbon and 63% oxygenated hydrocarbon speciation was observed for the organic mass, indicating that at least 37% of the organic mass is produced via primary sea‐spray. The hydrocarbon and oxygenated hydrocarbon species were highly correlated (r > 0.99) suggesting a significant, if not dominant, fraction of the oxygenated component is also likely to be sea‐spray in origin.

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

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

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


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

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

Continuous observations of carbon dioxide at Mace Head, Ireland from 1995 to 1999 and its net European ecosystem exchange Continuous observations of carbon dioxide at Mace Head, Ireland from 1995 to 1999 and its net European ecosystem exchange

Date added: 07/31/2002
Date modified: 07/27/2009
Filesize: 376.57 kB
Derwent, R.G., Ryall, D.B., Manning, A.J., Simmonds, P.G., O’Doherty, S., Biraud, s., Ciais, P., Ramonet, M., and Jennings, S.G., 2002. Continuous observations of carbon dioxide at Mace Head, Ireland from 1995 to 1999 and its net European ecosystem exchange, Atmos. Environ., 36, pp. 2799 – 2807.

Abstract


A 5-yr record of continuous high-frequency carbon dioxide CO2 observations over the 1995-1999 period for the Mace Head Atmospheric Research Station has been examined to reveal a complex interplay between local- and regional-scale sources and sinks. During the winter months, an additional CO2 source, over and above fossil fuel combustion, is required to support the observed concentrations of CO2 in European regionally polluted air masses. During the summer months, an additional CO2 sink is required. Over the entire study period, the additional net European ecosystem exchange source-sink required is -0.36+/-0.4Gtonne Cyr-1.

Continuous Measurements of the natural aerosol size distribution at rural mountain and maritime sites Continuous Measurements of the natural aerosol size distribution at rural mountain and maritime sites

Date added: 08/01/1976
Date modified: 07/01/2009
Filesize: 937.82 kB

Jennings, S.G.  (1976)- Continuous measurements of the natural aerosol size distribution at rural, mountain and maritime sites. Conference on the Atmospheric Aerosols: Their Optical Properties and Effects. NASA Conference Publication CP-2004, MB 4-1  to  4-4.


Abstract


 


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.

Connecting marine productivity to sea-spray via nanoscale biological processes: Phytoplankton Dance or Death Disco? Connecting marine productivity to sea-spray via nanoscale biological processes: Phytoplankton Dance or Death Disco?

Date added: 02/02/2016
Date modified: 02/03/2016
Filesize: 1.03 MB

Connecting marine productivity to sea-spray via nanoscale biological processes: Phytoplankton Dance or Death Disco? O'Dowd, C,Ceburnis, D,Ovadnevaite, J,Bialek, J,Stengel, DB,Zacharias, M,Nitschke, U,Connan, S,Rinaldi, M,Fuzzi, S,Decesari, S,Facchini, MC,Marullo, S,Santoleri, R,Dell'Anno, A,Corinaldesi, C,Tangherlini, M,Danovaro, R., Scientific Reports 5, Article number: 14883, doi:10.1038/srep14883 (2015)


Bursting bubbles at the ocean-surface produce airborne salt-water spray-droplets, in turn, forming climate-cooling marine haze and cloud layers. The reflectance and ultimate cooling effect of these layers is determined by the spray’s water-uptake properties that are modified through entrainment of ocean-surface organic matter (OM) into the airborne droplets. We present new results illustrating a clear dependence of OM mass-fraction enrichment in sea spray (OMss) on both phytoplankton-biomass, determined from Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP). The correlation coefficient for OMss as a function of Chl-a increased form 0.67 on a daily timescale to 0.85 on a monthly timescale. An even stronger correlation was found as a function of NPP, increasing to 0.93 on a monthly timescale. We suggest the observed dependence is through the demise of the bloom, driven by nanoscale biological processes (such as viral infections), releasing large quantities of transferable OM comprising cell debris, exudates and other colloidal materials. This OM, through aggregation processes, leads to enrichment in sea-spray, thus demonstrating an important coupling between biologically-driven plankton bloom termination, marine productivity and sea-spray modification with potentially significant climate impacts.



 

Condensation Nuclei In maritime Air Condensation Nuclei In maritime Air

Date added: 08/07/1966
Date modified: 07/27/2009
Filesize: 858.97 kB
O'Connor, Condensation Nuclei in Maritime Air, Journal de Recherches Atmospheriques, Vol II, 2 annee (1966), no 2-3, pp 181-184
Abstract

 

Data is reported on the concentration of condensation nuclei, their size and the fraction uncharged, in maritime air at a station on the west coast of Ireland well away from sources of man-made pollution. These are correlated with some meteorological paratmeters and the state of the ocean. These observations were made mainly with on-shore winds and they supplement those of O'Connor, Sharkey and Flanagan, in Q.J..R.M.S., 87,1961,pp. 105-8.

The concentration of nuclei per cm3 varied from about 100 to 12,500 but was usually less than 1,000. The size of the nuclei decreased with increasing concentration with an average value of about 3.5 X 10^-6 cm for their radii. It did not depend markedly on the relative humidity.

Condensation Nuclei as indicators of air pollution Condensation Nuclei as indicators of air pollution

Date added: 07/31/1984
Date modified: 07/27/2009
Filesize: 2.52 MB

O'Connor, T.C. & O'Dea, J.J.(RTC Sligo) (1984)- Indicators of Air Pollution, Irish Journal of Environmental Science, III, pp. 32-39


Abstract


Condensation Nuclei (CN) are Submicron sized particles found in the atmosphere at concentrations of 10^2 to 10^6 particles per cm^3. They arise from a variety of sources but are mainly produced by combustion processes. Sensitive and reliable CN counters have been developed in Ireland to determine their concentration and size. Results from a variety of locations are presented to illustratetheir use as a general indicator of air pollution levels. The Use of CN measurement as a tool for air quality management is discussed.

Condensation and coagulation sinks and formation of NMP in coastal and boreal forest BL Condensation and coagulation sinks and formation of NMP in coastal and boreal forest BL

Date added: 08/06/2002
Date modified: 07/21/2009
Filesize: 360.63 kB

Dal Maso, M., M. Kulmala, K. E. J. Lehtinen, J. M. Mäkelä, P. Aalto, and C. D. O'Dowd (2002), Condensation and coagulation sinks and formation of nucleation mode particles in coastal and boreal forest boundary layers, J. Geophys. Res., 107(D19), 8097, doi:10.1029/2001JD001053.


Abstract


The formation and growth of new particles has been evaluated using a revised version of a simple, but novel, theoretical tool. The concentration of condensable vapors and their source rates has been estimated using the aerosol condensation sink together with the measured particle growth rate. Also, by adding the coagulation sink and the measured formation rate of 3 nm particles, the formation rate of 1 nm particles and their concentration can be estimated. Condensation and coagulation sinks can be obtained from ambient aerosol size distribution data. The method has been applied to analyze the particle formation and growth rates observed during coastal and boreal forest nucleation events. The condensation sinks are typically 4-7 x 10-3 s-1 in the forest and 2 x 10-3 s-1 under coastal conditions, while the coagulation sinks for 1, 2, and 3 nm particles are typically smaller by factors 1.5-2, 5-7, and 11-15, respectively. The measured growth rates are 2-10 nm/h for the boreal forest and range from 15 to 180 nm/h at the coast, corresponding to a vapor concentration of 2-13 x 10 cm-3 and 108 cm-3 to 109 cm-3, respectively. The vapor source rate was 1-2 x 105 cm-3 s-1 in the boreal forest and 2-5 x 106 cm-3s-1 in the coastal environment. The estimated formation rate of 1 nm particles in the forest environment was 8-20 cm-3s-1 and 300-10,000 cm-3 s-1 at the coast. The concentration of 1 nm particles was estimated to be 2000-5000 and 4 × 104-7 × 106 particles cm-3 in forest and at coast, respectively.

 

Concurrent observations of alkyl halides and dimethyl sulphide in marine air Implications for s Concurrent observations of alkyl halides and dimethyl sulphide in marine air Implications for s

Date added: 08/05/1999
Date modified: 07/27/2009
Filesize: 560.08 kB

Bassford, M.R., G. Nickless, P. Simmonds, A.C. Lewis, M.J. Pilling, M.J. Evans and J.A. Pyle, Concurrent observations of alkyl halides and dimethyl sulphide in marine air: Implications for sources of atmospheric methyl iodide, Atmos Environ, 33, 2373-2383, 1999, (Ser. No. ACP106).


Abstract


Continuous atmospheric measurements of methyl iodide and dimethyl sulphide were carried out at Mace Head, western Ireland, over a 4-week period in July 1996. The concurrent observations of methyl iodide and dimethyl sulphide reported here display a clear association, indeed statistical analysis indicated a very signiÞcant degree of covariance. A simple yet informative use of modelled 5-day back trajectories was employed in tandem with examination of local meteorology to illuminate the geographical source regions of methyl iodide and dimethyl sulphide. The  interpretation of the atmospheric observations in terms of air-mass ßow has elucidated part of the global methyl iodide cycle and provides evidence for two distinct source regions of methyl iodide:
1. Under certain synoptic meteorological conditions, long-range transport of methyl iodide and dimethyl sulphide was observed from discrete areas of the sub-tropical Atlantic Ocean located in a region between 30Ð50¡N and 20Ð50¡W.

2. Measurements taken under di¤erent conditions led us to believe that there was an additional source of methyl iodide that inßuenced the Mace Head atmosphere, most likely produced by coastal macroalgae which inhabit waters o¤ the western coast of Ireland.

Concurrent measurements of OH and ultra-fine particles in the coastal atmosphere Concurrent measurements of OH and ultra-fine particles in the coastal atmosphere

Date added: 08/05/1998
Date modified: 07/27/2009
Filesize: 144.75 kB
O'Dowd, C.D., D.J. Creasey, M. Geever, G. McFiggans, D.E. Heard, J.D. Lee, M.J. Pilling, B.J. Whitaker, M.H. Smith, and S.G. Jennings, Concurrent measurements of OH and ultra-fine particles in the coastal atmosphere, J. Aerosol Sci., 29, s611-s612, 1998, (Ser. No. ACP051).

Abstract

 

Factors controlling the nucleation of new aerosol particles in the background atmosphere not easily discernible due to the difficulties associated with measuring aerosol precursors leading to aerosol nucleation along with difficulties in determining new particle chemical composition. It is generally assumed that the primary aerosol precursors species are sulphuric acid and water, although other species such as ammonia and organics have also been implicated. Sulphuric acid is produced in the gas phase via the oxidation of SO2 by the OH radical. Further, OH is likely to also be involved in the oxidation of other precursor species leading to homogeneous heteromolecular nucleation. Simultaneous measurements of OH and ultrafine particles were measured at Mace Head during a campaign in May, 1997. The relationship between the occurrence of ultra-fine particles and the concentration of the OH radical is explored. Aerosol measurements were conducted using three condensation nucleus counters: TSI 3025 (r>1.5 nm); TSI 3022 (r>35nm) and TSI 3010 (r>5nm). Deployment of these three instruments allows determination of ultrafine aerosol concentration by examination of the

difference between the three concentrations. The particle counters were configured for 5Hz sampling in single particle mode and thus, the 3022 and 3010 are off scale at concentrations in excess of 10,000 cm-3 while the 3025 is off scale at 160,OOOcm”. It should be noted that at these concentrations, the condensation particle counters are not quantitatively accurate and can only be interpreted as qualitative. OH measurements were undertaken using the recently developed FAGE technique (Creusey et al, 1997). One typical example of coastal nucleation in anthropogenically influenced air at Mace Head is illustrated in Figure 1. Nucleation events are observed under low tide conditions during daytime. On Julian Day 144, massive concentrations of ultrafine particles are seen at midday and during low tide. Particle concentrations exceeded 150,000 cmm3 and occur shortly after the peak in OH concentration. It is interesting that there are two ultrafine particle peaks which coincide with two OH peaks suggesting that the production of new particles is related to availability of the OH radical. O’Dowd et al. (1998) have shown that nucleation occurs in clean air most days at Mace Head and that these nucleation events relate to low tide events. The measurements presented for this campaign also show that nucleation occurs most days under anthropogenically influenced conditions and that these events require low tide and solar irradiation in order to occur. Thus, it appears that under low tide conditions, there is a sufficient source of aerosol precursor material to promote nucleation. However, it is not clear why, on some days when low tide and solar irradiation occur, nucleation does not always occur. The case presented here suggests that when OH concentrations are drastically reduced, aerosol nucleation no longer proceeds suggesting that the oxidation of aerosol precursors by OH is required for nucleation in this environment.


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.

Concentrations and fluxes of aerosol particles during the LAPBIAT measurement campaign at Värriö fie Concentrations and fluxes of aerosol particles during the LAPBIAT measurement campaign at Värriö fie

Date added: 08/01/2007
Date modified: 07/10/2009
Filesize: 2.65 MB

Ruuskanen, T.M., M. Kaasik, P. P. Aalto, U. Hõrrak, M. Vana, M. Mårtensson, Y. J. Yoon, P. Keronen, D. Nilsson, C. O’Dowd, M. Noppel, T. Alliksaar, J. Ivask, M. Sofiev, M. Prank, M. Kulmala, Concentrations and fluxes of aerosols particles during the LAPBIAT measurement campaign in the Varrio field station. Atmos. Chem. And Phys., 7, 3683–3700, 2007.


Abstract

 

The LAPBIAT measurement campaign took place in the V¨arri¨o SMEAR I measurement station located in Eastern
Lapland in the spring of 2003 between 26 April and 11 May. In this paper we describe the measurement campaign,
concentrations and fluxes of aerosol particles, air ions and trace gases, paying special attention to an aerosol particle
formation event broken by a air mass change from a clean Arctic air mass with new particle formation to polluted one
approaching from industrial areas of Kola Peninsula, Russia, lacking new particle formation. Aerosol particle number
flux measurements show strong downward fluxes during that time. Concentrations of coarse aerosol particles were  high for 1–2 days before the nucleation event (i.e. 28–29 April), very low immediately before and during the observed aerosol particle formation event (30 April) and increased moderately from the moment of sudden break of the event. In general particle deposition measurements based on snow samples show the same changes. Measurements of the mobility distribution of air ions showed elevated concentrations of intermediate air ions during the particle formation event. We estimated the growth rates in the nucleation mode size range. For particles <10 nm, the growth rate increases with size on 30 April. Dispersion modelling made with model SILAM support the conclusion that the nucleation event was interrupted by an outbreak of sulphate-rich air mass in the evening of 30 April that originated from the industry at Kola Peninsula.

Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites

Date added: 08/07/2001
Date modified: 07/27/2009
Filesize: 413.74 kB

Yeatman S.G., Spokes L.J., Jickells T.D. (2001) Comparison of coarse mode aerosol nitrate and ammonium at two polluted coastal sites. Atmospheric Environment 35 1321-1335.


Abstract


Direct atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters and can be enhanced by heterogeneous reactions between gaseous atmospheric nitrogen species and aerosol sea salt, which increase deposition rates. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland. Major-ion aerosol concentrations were determined and temporal patterns were interpreted with the use of air-mass back trajectories. Low levels of terrestrially derived material were seen during periods of clean, onshore flow, with respective concentration ranges for nitrate and ammonium of 0.47-220 and below detection limit to 340 nmol/m3. Corresponding levels of marine derived material during these periods were high, with sodium concentrations ranging from 39 to 1400 nmol/m3. Highest levels of terrestrially derived material were seen during polluted, offshore flow, where the air had passed recently over strong source regions of the UK and northern Europe, with concentration ranges of nitrate and ammonium of 5.6-790 and 9.7-1000 nmol/m3, respectively. During polluted flow ∼40-60% of the nitrate was found in the coarse mode (>1 μm diameter) and under clean marine conditions almost 100% conversion was seen. In addition, the data suggests strong evidence for dissolution, coagulation processes that also shift nitrate to the coarse mode. Furthermore, such processes are thought also to give rise to the size-shifting of aerosol ammonium, since significant coarse-mode fractions of this species (∼19-45%) were seen at both sites. A comparison of the relative importance of nitrate and ammonium in the overall dry deposition of inorganic fixed-nitrogen at each site indicates that at Weybourne the mass-weighted dry deposition velocity of the latter is around double that seen at Mace Head with its resultant contribution to the overall inorganic nitrogen dry flux exceeding that of nitrate.

 

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.

Comparisons of aerosol nitrogen isotopic composition at two polluted coastal sites Comparisons of aerosol nitrogen isotopic composition at two polluted coastal sites

Date added: 08/06/2001
Date modified: 07/23/2009
Filesize: 281.41 kB

Yeatman, S.G. L.J. Spokes, P.F. Dennis and T.D. Jickells, Comparison of aerosol nitrogen isotope composition at two coastal sites, Atmos. Environ. 35, 1307-1320, 2001, (Ser. No. ACP125).


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. For both species a significant difference in mean isotopic composition was seen between samples from Weybourne (+6±6‰ for ammonium and +7±6‰ for nitrate) and Mace Head and RRS Challenger campaigns (-9±8‰ for ammonium and -1±3‰ for nitrate). At each site a strong dependence of isotopic composition on the geographical origin of the sampled air mass was also observed. For aerosol ammonium, marine and terrestrially dominated samples were found to be isotopically distinct, perhaps reflecting the presence of oceanic sources of ammonia in addition to anthropogenic or natural terrestrial sources. Further distinctions were made within terrestrially dominated samples, possibly indicative of different types of animal husbandry regimes or other forms of anthropogenic activity. For aerosol nitrate, there was found to be generally less variation between samples at each site, although at Weybourne a significant difference was observed between the mean isotopic composition of samples originating from the northern UK (+15±3‰) and that of those originating from the southern UK (+10±3‰), suggesting that aerosol δ15N data might possibly facilitate source apportionment between NOx emissions from power stations and those from vehicle exhausts. The nitrate data also appeared to show seasonality with higher concentrations and lower δ15N values seen in the summer.

 

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.

Comparison of long-term trends and seasonal variations of atmospheric mercury concentrations at Comparison of long-term trends and seasonal variations of atmospheric mercury concentrations at

Date added: 08/07/2005
Date modified: 07/27/2009
Filesize: 449.95 kB

Kock, H.H.;  Bieber, E.; Ebinghaus, R.; Spain, T.G.; Thees, B. (2005): Comparison of long-term trends and seasonal variations of atmospheric mercury concentrations at the two European coastal monitoring stations Mace Head, Ireland, and Zingst, Germany. In: Atmospheric Environment . Vol. 39 (2005) 39, 7549 - 7556


Abstract

 

Monitoring of total gaseous mercury (TGM) concentrations has been carried out at Mace Head on the west coast of Ireland and at Zingst on the southern shore-line of the Baltic Sea. We have used the continuous measurements to assess long-term trends and seasonal variations of TGM concentrations over the same time period. Between 1998 and 2004 the annually averaged TGM concentrations measured at Mace Head (1.72 ng m-3) and Zingst (1.66 ng m-3) remained fairly stable. At both stations we measured higher TGM levels during winter months and lower concentrations during summer months. We also observed an unexpected West to East gradient and found that the overall mean Mace Head TGM concentration was 0.06 ng m-3 higher than those of Zingst. For the January to June period, the Mace Head TGM values (6-year mean = 1.75 ng m-3) are significantly elevated compared to the Zingst results (6-year mean-1.64 ng m-3). Since no local anthropogenic mercury sources exist near the Mace Head station, enhanced emission from the sea appears to provide the most probable explanation for the observed differences. Multiple regression analysis with the atmospheric mercury concentrations measured at Zingst were made with selected meteorological and air quality parameters (wind component, dew point, dust and NOx concentrations). The short-term variation in the TGM concentrations at Zingst shows a strong positive correlation with weather conditions and selected air quality parameters, making TGM a usable tracer of air masses originating from different source regions.

 

Comparison of calculated and measured peroxide data collected in marine air to investigate prom Comparison of calculated and measured peroxide data collected in marine air to investigate prom

Date added: 08/06/1998
Date modified: 07/27/2009
Filesize: 1007.98 kB

Penkett, S.A., Reeves, C.E., Bandy, B.J., Kent, J.M., and Richer, H.R., Comparison of calculated and measured peroxide data collected in marine air to investigate prominent features of the annual cycle of ozone in the troposphere, J. Geophys. Res., 103 (D11): 13377-13388, 1998.


Abstract


Large amounts of data on the concentration of peroxides have been collected in vertical profiles over the North Atlantic Ocean by a Hercules aircraft. The measured peroxide concentrations have been compared with concentrations calculated by a simple algorithm derived assuming that the standing peroxide concentration is in equilibrium with its production and loss processes. In clean air where the peroxide and ozone concentrations are anticorrelated throughout the profile measured and calculated peroxide concentrations coincide, whereas in layers of polluted air within the profile, as determined from positive ozone peroxide correlations, calculated peroxide concentrations are greatly in excess of measured values. Using the degree of correlation between measured and calculated peroxide concentrations as a diagnostic, it is possible to show that many aspects of the seasonal cycle of ozone are caused by in situ tropospheric chemistry. Thus the summer minimum in the seasonal cycle of ozone, observed at clean marine ground-based sites such as Mace Head, is due to photochemical destruction, and elevated levels of ozone are associated with the transport of polluted air, on occasion over thousands of kilometers. Of particular interest if our analysis is correct, the broad maximum of ozone occurring between March and May at ground-based sites has a large contribution from ozone formed by tropospheric as well as stratospheric chemistry.

 

Combination coefficients of small positive ions with sub micrometer aerosol particles Combination coefficients of small positive ions with sub micrometer aerosol particles

Date added: 02/14/1978
Date modified: 07/01/2009
Filesize: 745.64 kB

Dixon, A.M., and Jennings, S.G. (1978).- Combination coefficients of small ions with submicrometre aerosol particles. J. Phys. D: Appl. Phys., 11, 125-136.


Abstract


The work was concerned with the simultaneous measurement of the combination coefficients b and eta 0, between small ions and aerosol particles, and between small ions and uncharged aerosol particle respectively, for different particle radii. The ion-ion mutual repulsion coefficient gamma had a mean experimental value of 2.39 (+or-0.14)*10-6 cm3 s-1. The decay of ions in the presence of aerosol particles in a mylar vessel was recorded and compared with a family of computed theoretical ion-aerosol decay curves to determine b. eta 0 could then be determined from concentration of uncharged nuclei present. Satisfactory agreement was found between the b eta 0 versus radius results and various theoretically computed values. Possible reasons for discrepancies between theory and experiment are indicated.

Coastal New Particle Formation: A Review of the Current State-Of-The-Art Coastal New Particle Formation: A Review of the Current State-Of-The-Art

Date added: 08/01/2005
Date modified: 07/27/2009
Filesize: 773.65 kB

O’Dowd, C. D., T. Hoffmann, Coastal New Particle Formation: A Review of the Current State-Of-The-Art. Environ. Chem. 2, 245. doi:10.1071/EN05077, 2005.


Abstract


New particle formation via secondary gas-to-particle conversion processes over the oceans is one of the main mechanisms controlling the marine aerosol number population; however, despite extensive effort over the years, this phenomenon is still not well quantified. Coastal new particle formation events are more frequent than open ocean events and consequently have been studied in greater detail. This review article summarizes the recent studies into coastal new particle formation events and summarizes the linkage of these events to iodine emissions and ultimate particle formation via iodine oxide nucleation processes. The current state of knowledge may be summarized by concluding that, in general, coastal nucleation events are driven by biogenic emissions of iodine vapours that undergo rapid chemical reactions to produce condensable iodine oxides leading to nucleation and growth of new particles. The primary source of the condensable iodine vapours is thought to be molecular iodine (I2). The role of iodine oxides in open-ocean new particle production still remains an open question and is the most pressing next step to undertake.

Coastal new particle formation Environmental conditions and aerosol physico-chemical characteristics during nucleation bursts Coastal new particle formation Environmental conditions and aerosol physico-chemical characteristics during nucleation bursts

Date added: 07/31/2002
Date modified: 07/27/2009
Filesize: 1.31 MB
Colin D. O'Dowd, Kaarle Hämeri, Jyrki Mäkelä, Minna Väkeva, Pasi Aalto, Gerrit de Leeuw, Gerard Kunz, Harald Berresheim, Hans-Christen Hansson, Edo Becker, Andrew G. Allen, Roy M. Harrion, Christoph Kleefeld, Michael Geever, S. Gerard Jennings, Harald Berresheim, and Markku Kulmala.Coastal new particle formation: Environmental conditions and aerosol physico-chemical characteristics during nucleation bursts. J. Geophys. Res. 107, 10.1029/2000JD000206, 2002.

Abstract


Nucleation mode aerosol was characterized during coastal nucleation events at Mace Head during intensive New Particle Formation and Fate in the Coastal Environment (PARFORCE) field campaigns in September 1998 and June 1999. Nucleation events were observed almost on a daily basis during the occurrence of low tide and solar irradiation. In September 1998, average nucleation mode particle concentrations were 8600 cm−3 during clean air events and 2200 cm−3 during polluted events. By comparison, during June 1999, mean nucleation mode concentrations were 27,000 cm−3 during clean events and 3350 cm−3 during polluted conditions. Peak concentrations often reached 500,000–1,000,000 cm−3 during the most intense events and the duration of the events ranged from 2 to 8 hours with a mean of 4.5 hours. Source rates for detectable particle sizes (d > 3 nm) were estimated to be between 104 and 106 cm−3 s−1 and initial growth rates of new particles were as high as 0.1–0.35 nm s−1 at the tidal source region. Recently formed 8 nm particles were subjected to hygroscopic growth and were found to have a growth factor of 1.0–1.1 for humidification at 90% relative humidity. The low growth factors implicate a condensable gas with very low solubility leading to detectable particle formation. It is not clear if this condensable gas also leads to homogeneous nucleation; however, measured sulphuric acid and ammonia concentration suggest that ternary nucleation of thermodynamically stable sulphate clusters is still likely to occur. In clear air, significant particle production (>105 cm−3) was observed with sulphuric acid gas-phase concentration as low as 2 × 106 molecules cm−3 and under polluted conditions as high as 1.2 × 108 molecules cm−3.

Coastal Iodine Emissions: Part 2. Particle Nucleation Processes Coastal Iodine Emissions: Part 2. Particle Nucleation Processes

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.57 MB

Monahan, C.; Ashu-Ayem, E. R.; Nitschke, U.; Darby, S. B.; Smith, P. D.; Stengel, D. B.; Venables, D. S.; O’Dowd, C. D. Coastal Iodine Emissions: Part 2. Particle Nucleation Processes, dx.doi.org/10.1021/es3011805 | Environ. Sci. Technol. 2012, 46, 10422−10428.


Abstract. Laboratory studies into particle formation from Laminaria digitata macroalgae were undertaken to elucidate aerosol formation for a range of I2 (0.376 ppbv) and O3 (<396 ppbv) mixing ratios and light levels (EPAR = 15, 100, and 235 μmol photons m2 s1). No clear pattern was observed for I2 or aerosol parameters as a function of light levels. Aerosol mass fluxes and particle number concentrations, were, however, correlated with I2 mixing ratios for low O3 mixing ratios of <3 ppbv (R2 = 0.7 and 0.83, respectively for low light levels, and R2 = 0.95 and 0.98, respectively for medium light levels). Additional experiments into particle production as a function of laboratory-generated I2, over a mixing ratio range of 18 ppbv, were conducted under moderate O3 mixing ratios (≈24 ppbv) where a clear, 100-fold or greater, increase in the aerosol number concentrations and mass fluxes was observed compared to the low O3 experiments. A linear relationship between particle concentration and I2 was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol concentrations typical of the coastal boundary layer suggests a I2 mixing ratio range of 693 pptv can account for the observed particle production events. Aerosol number concentration produced from I2 is more than a factor of 10 higher than that produced from CH2I2 for the same mixing ratios.

 

Coastal iodine emissions: Part 1. Release of I2 by Laminaria digitata in chamber experiments Coastal iodine emissions: Part 1. Release of I2 by Laminaria digitata in chamber experiments

Date added: 03/19/2013
Date modified: 03/19/2013
Filesize: 3.16 MB

Ashu-Ayem, E.R., U, Nitschke, C. Monahan, J. Chen, S.B. Darby, P.D. Smith, C.D. O’Dowd, D. B. Stengel, D.S. Venables. Coastal iodine emissions: Part 1. Release of I2 by Laminaria digitata in chamber experiments, dx.doi.org/10.1021/es204534v | Environ. Sci. Technol. 2012, 46, 10413−10421.


Abstract. Tidally exposed macroalgae emit large amounts of I2 and iodocarbons that produce hotspots of iodine chemistry and intense particle nucleation events in the coastal marine boundary layer. Current emission rates are poorly characterized, however, with reported emission rates varying by 3 orders of magnitude. In this study, I2 emissions from 25 Laminaria digitata samples were investigated in a simulation chamber using incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). The chamber design allowed gradual extraction of seawater to simulate tidal emersion of algae. Samples were exposed to air with or without O3 and to varying irradiances. Emission of I2 occurred in four distinct stages: (1) moderate emissions from partially submerged samples; (2) a strong release by fully emerged samples; (3) slowing or stopping of I2 release; and (4) later pulses of I2 evident in some samples. Emission rates were highly variable and ranged from 7 to 616 pmol min1 gFW1 in ozone-free air, with a median value of 55 pmol min1 gFW1 for 20 samples.

 

Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds

Date added: 07/31/1998
Date modified: 07/27/2009
Filesize: 166.47 kB

Jennings, S.G., Geever, M., and O'Connor, T.C. (1998)- Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds. Atmos. Res.,46,243-252.


Abstract


Surface measurements of cloud condensation nuclei (CCN) number concentration (cm-3) are presented for unmodified marine air and for polluted air at Mace Head, for the years 1994 and 1995. The CCN number concentration active at 0.5% supersaturation is found to be approximately log-normal for marine and polluted air at the site. Values of geometric mean, median and arithmetic mean of CCN number concentration (cm-3) for marine air are in the range 124-135, 140-150 and 130-157 for the two years of data. Analysis of CCN number concentration for high wind speed, U, up to 20 m s-1 show enhanced CCN production for U in excess of about 10-12 m S- Approximately 7% increase in CCN per 1 m s-1increase in wind speed is found, up to 17 m s-1. A relationship of the form log10CCN = a+bU is obtained for the periods March 1994 and January, February 1995 for marine air yielding values a of 1.70; 1.90 and b of 0.035 for both periods.

Cloud condensation nuclei measurements at Mace Head, Ireland, over the period 1994-2002 Cloud condensation nuclei measurements at Mace Head, Ireland, over the period 1994-2002

Date added: 08/01/2006
Date modified: 07/27/2009
Filesize: 692.21 kB

Reade, K., S.G. Jennings, and G. McSweeney, Cloud condensation nuclei measurements at Mace Head, Ireland, over the period 1994-2002, Atmos. Res., 82, 610-621, 2006.


Abstract


Analyses of cloud condensation -nuclei (CCN) number concentrations (cm-3) measured at the Mace Head Atmospheric Research Station, near Carna, County Galway, Ireland, using a DH Associates Model M1 static thermal diffusion cloud chamber over the period from March 1994 to September 2002 are presented in this work. Air masses are defined as being 'marine' if they originate from a wind direction of 180-300° and 'continental' air masses are defined as originating from a wind direction of 45-135°. Air masses without such filtering were classified as 'undefined' air masses. Air masses were found to be dominated by marine sector air, re-affirming Mace Head as a baseline atmospheric research station. CCN levels for specific air masses at Mace Head were found to be comparable with earlier studies both at Mace Head and elsewhere. Monthly averaged clean marine (wind direction of 180-300° and black carbon absorption coefficient <1.425 Mm-1) CCN and marine CCN varied between 15-247 cm-3 and 54-670 cm-3, respectively. As expected, significant increases in number concentration were found in continentally sourced CCN over that of marine CCN and were found to follow a log-normal distribution significantly tighter than that of clean marine air masses. No significant trend was found for CCN over the 9-year period. While polluted continental air masses showed a slight increase in CCN concentrations over the winter months, most likely due to increased fuel usage and a lower mixed boundary layer, the dominance of marine sector air arriving at Mace Head, which generally consists of background CCN concentrations, reduced seasonal differences for polluted air. Marine air showed a distinct seasonal pattern, with elevated values occurring over the spring and summer seasons. This is thought to be due to enhanced biogenic aerosol production as a result of phytoplankton bloom activity in the North Atlantic.

Chemical ionization mass spectrometer for long-term measurements of atmospheric OH and H2SO4 Chemical ionization mass spectrometer for long-term measurements of atmospheric OH and H2SO4

Date added: 07/27/2000
Date modified: 07/27/2009
Filesize: 522 kB

Berresheim, H., T. Elste, C. Plass-Dulmer, F. L. Eisele and D. J. Tanner (2000). Chemical ionization mass spectrometer for long-term measurements of atmospheric OH and H2SO4. International Journal of Mass Spectrometry 202 (1-3): 91-109.

 


Abstract


An atmospheric pressure/chemical ionization mass spectrometer (AP/CIMS) has been developed for continuous long-term
measurements of atmospheric OH and H2SO4. The corresponding methods both involve chemical ionization of H2SO4 by NO3-
ions with OH being first titrated by excess SO2 to form equivalent concentrations of H2SO4 in the system. The chemical
ionization mass spectrometry (CIMS) system has been operated since April 1998 at the Meteorological Observatory
Hohenpeissenberg, a mountain research station of the German Weather Service in South Germany. A technical description of
the apparatus is presented followed by a detailed estimate of uncertainties in calibration and ambient air measurements
resulting from changes in instrumental and/or ambient parameters. Examples from both calibration runs and ambient air
measurements are shown. For the present system and operating conditions accuracy, precision, and detection limit are
estimated to be 39%, 30%, and 3 3 104 molecules cm23 for H2SO4, and 54%, 48%, and 5 3 105 molecules cm23 for OH
measurements, respectively, based on 5 min signal integration. (Int J Mass Spectrom 202 (2000) 91–109) © 2000 Elsevier
Science B.V.

Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX

Date added: 08/01/2005
Date modified: 07/01/2009
Filesize: 435.58 kB

Coe, H., J. D. Allan, R. M. Alfarra, K. N. Bower, M. J. Flynn, G. B. McFiggans, D. O. Topping, P. I. Williams, C. D. O'Dowd, M. Dall'Osto, D. C. S. Beddows and R. M. Harrison, Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 11643-11678, 2005.


Abstract


Aerosol number concentrations and size distributions from 3 nm to 20 µm diameter were measured at the Mace Head Atmospheric Research Station, Co. Galway, Ireland, a coastal site on the eastern seaboard of the north Atlantic Ocean. Both on and offline size resolved aerosol composition measurements were also made using an Aerodyne Aerosol Mass Spectrometer (AMS) and ion chromatographic analysis of daily samples collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI). Particle number concentrations, size distributions and AMS measurements were determined at 7 and 22 m above ground level to investigate local effects on the aerosol size distribution induced by the tidal zone. During periods of new particle formation ultrafine particle number concentrations are large and variable, however, outside these periods no variability in particle number was observed at any size, nor was the particle composition variable. Analysis of particle size distributions show that within each air mass observed particle number concentrations were very consistent. During anticyclonic periods and conditions of continental outflow Aitken and accumulation mode were enhanced by a factor of 5 compared to the marine sector, whilst coarse mode particles were enhanced during westerly conditions. Baseline marine conditions were rarely met at Mace Head during NAMBLEX and high wind speeds were observed for brief periods only.

Loss rates of gaseous species to aerosol surfaces were calculated for a range of uptake coefficients. Even when the accommodation coefficient is unity, lifetimes of less than 100 s were never observed and rarely were lifetimes less than 500 s. Diffusional limitation to mass transfer is important in most conditions as the coarse mode is always significant, we calculate a minimum overestimate of 50% in the loss rate if this is neglected and so it should always be considered when calculating loss rates of gaseous species to particle surfaces. HO2 and HOI have accommodation coefficients of around 0.03 and hence we calculate lifetimes due to loss to particle surfaces of 2000 s or greater. Aerosol composition measurements using the AMS show accumulation mass modes of acidified sulphate and organic material, both of which have the same shape and are centred at around 350 nm vacuum aerodynamic diameter, implying an internal mixture. The organic and sulphate are approximately equally important, though the mass ratio varies considerably between air masses. Mass spectral fingerprints of the organic fraction in polluted conditions are similar to those observed at other locations that are characterised by aged continental aerosol. Even in marine conditions a background concentration of between 0.5 and 1 µg m−3 of both organic and sulphate was observed. Key differences in the mass spectra were observed during the few clean periods but were insufficient to ascertain whether these changes reflect differences in the source fingerprint of the organic aerosol. However, in an accompanying paper (Dall'Osto et al., 2005) periods of organic dominated aerosol particles were also observed and could be separated from the aged continental aerosol. The coarse mode was composed of sea salt and showed significant displacement of chloride by nitrate and to a lesser extent sulphate in polluted conditions.

Charge separation due to water drop and cloud droplet interactions in an electric field Charge separation due to water drop and cloud droplet interactions in an electric field

Date added: 01/01/1975
Date modified: 07/01/2009
Filesize: 2.09 MB
Jennings, S.G. (1975)- Charge separation due to water drop and cloud droplet interactions in an electric field. Quart. J. Roy. Met. Soc., 101, 227-233.   
Abstract

Measurements were made of the electric charge acquired by drops of mean radius of about 750m, in the presence of a vertical electric field E, the value of which could be varied from 4·5 to 27kV/m. It was found that the average charge acquired by the water drop as a consequence of the inductive process increased from 0·1fC to about 0·25fC as the electric field strength increased from 5kV/m to about 15kV/m, but there-after decreased with increasing values of electric field.
This work suggests that the collisions between polarized rain-drops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30kV/m; but that significantly larger fields could not be produced since all collisions in the higher fields would result in permanent coalescence.
«StartPrev12345678910NextEnd»
Page 8 of 11
Copyright © 2017 Atmospheric Physics Research Cluster. All Rights Reserved.
Joomla! is Free Software released under the GNU/GPL License.
 
None