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Journal Publications

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

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Documents

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Biogenically-driven organic contribution to marine aerosol Biogenically-driven organic contribution to marine aerosol

Date added: 08/01/2004
Date modified: 07/27/2009
Filesize: 296.9 kB

O'Dowd, C.D., M.C. Facchini, F. Cavalli, D. Ceburnis, M. Mircea, S. Decesari, S. Fuzzi, Y.J. Yoon, and J.P. Putaud, Biogenically-driven organic contribution to marine aerosol, Nature, doi:10.1038/nature02959,. 2004.


Abstract


Marine aerosol contributes significantly to the global aerosol load and consequently has an important impact on both the Earth's albedo and climate. So far, much of the focus on marine aerosol has centred on the production of aerosol from sea-salt1 and non-sea-salt sulphates2, 3. Recent field experiments, however, have shown that known aerosol production processes for inorganic species cannot account for the entire aerosol mass that occurs in submicrometre sizes4, 5, 6. Several experimental studies have pointed to the presence of significant concentrations of organic matter in marine aerosol7, 8, 9, 10, 11. There is some information available about the composition of organic matter12, 13, 14, but the contribution of organic matter to marine aerosol, as a function of aerosol size, as well as its characterization as hydrophilic or hydrophobic, has been lacking. Here we measure the physical and chemical characteristics of submicrometre marine aerosol over the North Atlantic Ocean during plankton blooms progressing from spring through to autumn. We find that during bloom periods, the organic fraction dominates and contributes 63% to the submicrometre aerosol mass (about 45% is water-insoluble and about 18% water-soluble). In winter, when biological activity is at its lowest, the organic fraction decreases to 15%. Our model simulations indicate that organic matter can enhance the cloud droplet concentration by 15% to more than 100% and is therefore an important component of the aerosol–cloud–climate feedback system involving marine biota.

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.

Black carbon measurements at Mace Head, 1989–1996 Black carbon measurements at Mace Head, 1989–1996

Date added: 07/31/1997
Date modified: 07/27/2009
Filesize: 625.86 kB

W.F. Cooke., Jennings, S.G., and Spain, T.G. (1997) Black-carbon measurements at Mace Head, 1989-1996, J. Geophys. Res.,102, 25, 339-25, 346.


Abstract


Black carbon mass concentrations have been measured using an aethalometer at Mace Head on the west coast of Ireland on an almost continuous basis from February 1989 to June 1996. The purpose of this paper is to report on the monthly averaged black carbon concentration at this site over the 7 year period and to examine the influence of air mass on the black carbon mass concentration. The seasonal variation of black carbon mass concentration for clean marine and continental air masses is also investigated.

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.

Boundary layer concentrations and landscape scale emissions of volatile organic compounds in early s Boundary layer concentrations and landscape scale emissions of volatile organic compounds in early s

Date added: 08/01/2007
Date modified: 07/10/2009
Filesize: 579.61 kB

Happanala, S., J. Rinne, H. Hakola, L. Laakso, H. Lihavainen, R. Janson, C O’Dowd and M Kulmala. Boundary layer concentrations and landscape scale emissions of volatile organic compounds in early spring. Atmos. Chem.. Phys., Atmos. Chem. Phys., 7, 1869–1878, 2007.


Abstract


Boundary layer concentrations of several volatile organic compounds (VOC) were measured during two campaigns
in springs of 2003 and 2006. The measurements were conducted over boreal landscapes near SMEAR II measurement
station in Hyyti¨al¨a, Southern Finland. In 2003 the measuremens were performed using a light aircraft and in
2006 using a hot air balloon. Isoprene concentrations were low, usually below detection limit. This can be explained
by low biogenic production due to cold weather, phenological stage of the isoprene emitting plants, and snow cover.
Monoterpenes were observed frequently. The average total monoterpene concentration in the boundary layer was
33 pptv. Many anthropogenic compounds such as benzene, xylene and toluene, were observed in high amounts. Ecosystem scale surface emissions were estimated using a simple mixed box budget methodology. Total monoterpene emissions varied up to 80μgm−2 h−1, -pinene contributing typically more than two thirds of that. These emissions were somewhat higher that those calculated using emission algorithm. The highest emissions of anthropogenic compounds were those of p/m xylene.

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Bromine oxide in the mid-latitude marine boundary layer Bromine oxide in the mid-latitude marine boundary layer

Date added: 08/07/2004
Date modified: 07/27/2009
Filesize: 153.87 kB

Saiz-Lopez, A., J. M. C. Plane, and J. A. Shillito (2004), Bromine oxide in the mid-latitude marine boundary layer, Geophys. Res. Lett., 31, L03111, doi:10.1029/2003GL018956.


Abstract


We report direct observations of bromine oxide (BrO) in the mid-latitude marine boundary layer (MBL), using long-path Differential Optical Absorption Spectroscopy (DOAS). The measurements were made at the Mace Head observatory on the west coast of Ireland. Over six days of observations, the BrO concentration varied from below the detection limit (≈0.8 parts per trillion (ppt)) at night, to a maximum daytime concentration of 6.5 ppt. At the average daytime concentration of 2.3 ppt, BrO causes significant O3 depletion in the MBL through catalytic cycles involving the iodine oxide and hydroperoxy radicals, and also oxidises dimethyl sulfide much more rapidly than the hydroxyl radical. A post-sunrise pulse of BrO was observed, consistent with the build up of photolabile precursors produced by heterogeneous reactions on sea-salt aerosol during the previous night. This indicates that significant bromine activation occurs over the open ocean.

 

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.

 

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.

 

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.

 

Carbon Mass Concentration Measurements at Mace head, On the West Coast Of Ireland Carbon Mass Concentration Measurements at Mace head, On the West Coast Of Ireland

Date added: 08/01/1993
Date modified: 07/27/2009
Filesize: 3.5 MB
Jennings, S.G., McGovern, F.M. and Cooke, W.F., 1993. Carbon mass concentration measurements at Mace Head, on the west coast of Ireland. Atmospheric Environment 27A, pp. 1229–1239

Abstract


Measurements of the mass concentration of particulate carbon aerosol at Mace Head atmospheric research station on the west coast of Ireland are reported. The measurements were made using an aethalometer manufactured by Magee Scientific, which operates by measuring the light transmission through a quartz fibre filter, whilst air is drawn through the filter. Mass concentration measurements taken between February 1990 and April 1991 are presented and interpreted in terms of air mass and meteorological parameters. Average carbon mass concentration levels of 38±11 ng m−3 were found during periods when the clean sector sampled air masses had traversed over the North Atlantic for several days

CCN Determination Comparing Counters with single drop counting and photometric detector at Macehead CCN Determination Comparing Counters with single drop counting and photometric detector at Macehead

Date added: 08/01/1996
Date modified: 07/27/2009
Filesize: 5 MB

Gras, J.L., Jennings, S.G., and Geever, M., (1996). CCN determination comparing counters with single drop counting and photometric detectors at Mace Head, Ireland. Idojaras, 100, 171-182.


Abstract


Two static thermal-gradient cloud condensation nucleus (CCN) counters utilising different detection methods were operated over a three week period during May 1994, at Mace Head on the west coast of Ireland. One was a DH Associates model (MI), the other was custom built at the CSIRO Division of Atmospheric Research. Concentrations of CCN at a supersaturation of 0.5% were determined during this period for artificial NaCI aerosol particles and for ambient particles in clean maritime westerly, and continental easterly conditions. No significant differences were found between the relative performance of the counters with artificial NaCI particles and ambient particles, and no statistically significant differences in response were observed between maritime and continental conditions. Overall agreement between the two counters, for concentrations less than 1000 cm-3 was better than 15%.

CCN measurements at Mace Head, on the West Coast of Ireland CCN measurements at Mace Head, on the West Coast of Ireland

Date added: 08/07/1998
Date modified: 07/27/2009
Filesize: 60.19 kB

G. Mc Sweeney, S.G. Jennings, M. Geever, CCN measurements at Mace Head, on the West Coast of Ireland, Journal of Aerosol Science, Volume 29, Supplement 1, Proceedings of the 1998 International Aerosol Conference Part 1, September 1998, Page S199, ISSN 0021-8502, DOI: 10.1016/S0021-8502(98)00297-3.


Abstract

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.

Characteristic features of air ions at Mace Head on the west coast of Ireland Characteristic features of air ions at Mace Head on the west coast of Ireland

Date added: 08/07/2008
Date modified: 07/27/2009
Filesize: 917.86 kB

Marko Vana, Mikael Ehn, Tuukka Petaja, Henri Vuollekoski, Pasi Aalto, Gerrit de Leeuw, Darius Ceburnis, Colin D. O'Dowd, Markku Kulmala, Characteristic features of air ions at Mace Head on the west coast of Ireland, Atmospheric Research


Abstract


Coastal nucleation events and behavior of cluster ions were characterized through the measurements of air ion mobility distributions at the Mace Head research station on the west coast of Ireland in 2006. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.34–40 nm. These measurements allow us to characterize freshly nucleated charged particles with diameters smaller than 3 nm. The analysis shows that bursts of intermediate ions (1.6–7 nm) are a frequent phenomenon in the marine coastal environment. Intermediate ion concentrations were generally close to zero, but during some nucleation episodes the concentrations increased to several hundreds per cm3. Nucleation events occurred during most of the measurement days. We classified all days into one of seven classes according to the occurrence and type of new particle formation. Nucleation events were observed during 207 days in 2006, most prominently in the spring and summer months. Rain-induced events, in turn, were observed during 132 days. Particle formation and growth events mostly coincided with the presence of low tide. Also small cluster ions (0.34–1.6 nm) were characterized. Average concentrations of small ions were 440 cm− 3 for the negative ions and 423 cm− 3 for the positive ions. Average mean mobilities of small ions were 1.86 cm2V− 1s− 1 and 1.49 cm2V− 1s− 1 for the negative and positive polarities, respectively. Concentrations of small ions were observed to be strongly dependent on the variations of meteorological parameters including wind speed and direction.

 

Characterization and intercomparison of aerosol absorption photometers: result of two intercompariso Characterization and intercomparison of aerosol absorption photometers: result of two intercompariso

Date added: 02/16/2011
Date modified: 02/16/2011
Filesize: 3.86 MB

Müller, T., Henzing, J. S., de Leeuw, G., Wiedensohler, A., Alastuey, A., Angelov, H., Bizjak, M., Collaud Coen, M., Engström, J. E., Gruening, C., Hillamo, R., Hoffer, A., Imre, K., Ivanow, P., Jennings, G., Sun, J. Y., Kalivitis, N., Karlsson, H., Komppula, M., Laj, P., Li, S.-M., Lunder, C., Marinoni, A., Martins dos Santos, S., Moerman, M., Nowak, A., Ogren, J. A., Petzold, A., Pichon, J. M., Rodriquez, S., Sharma, S., Sheridan, P. J., Teinilä, K., Tuch, T., Viana, M., Virkkula, A., Weingartner, E., Wilhelm, R., and Wang, Y. Q.: Characterization and intercomparison of aerosol absorption photometers: result of two intercomparison workshops, Atmos. Meas. Tech., 4, 245-268, doi:10.5194/amt-4-245-2011, 2011.


Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.


Characterization of individual airborne particles by using aerosol time-of-flight mass spectrom Characterization of individual airborne particles by using aerosol time-of-flight mass spectrom

Date added: 08/06/2004
Date modified: 07/27/2009
Filesize: 425.52 kB

Dall'Osto, M., D. C. S. Beddows, R. P. Kinnersley, R. M. Harrison, R. J. Donovan, and M. R. Heal (2004), Characterization of individual airborne particles by using aerosol time-of-flight mass spectrometry at Mace Head, Ireland, J. Geophys. Res., 109, D21302, doi:10.1029/2004JD004747.


Abstract


An aerosol time-of-flight mass spectrometer was deployed at Mace Head (Ireland) during August 2002. The measurements provide qualitative chemical composition and size distribution (0.3–3 μm) information for single particles. Three broad categories of particles: sea salt, dust, and carbon-containing particles were identified and apportioned, and their temporal evolution (1 hour resolution) is described. Aerosol sources were correlated with meteorological factors and with air mass trajectories, demonstrating long-range transport of different continental air masses from Europe, Africa, and America. The major class of particles was derived from sea salt and was subdivided into pure, mixed, and aged sea salt according to the extent of displacement of chloride by nitrate. Two types of dust particles were found mainly in the coarse mode (>1 μm); the former, thought to originate from the Sahara, presented an aluminium/silicon signature, while the latter, of more local origin, had a calcium-rich composition. Carbon-containing particles were mainly distributed in the fine mode (<1 μm) and associated with different chemical species in different size modes, suggesting different mechanisms of formation.

 

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.

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.

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.

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
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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.

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
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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.

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
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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 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
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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 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
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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 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
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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.

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
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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.

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
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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.

 

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
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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 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
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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.

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
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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.

 

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
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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 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
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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.

 

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.

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.

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
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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 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
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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.

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
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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.

 

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 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.

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.



 

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.

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 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.

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.

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.

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.

 

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.

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.

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.

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.

 

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