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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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### Regional-scale Ozone Deposition to North-East Atlantic Waters

 Date added: 11/10/2010 Date modified: 11/10/2010 Filesize: 4.87 MB

Coleman, L., S. Varghese, O.P. Tripathi, S G. Jennings, C.D. O’Dowd, Regional-scale Ozone Deposition to North-East Atlantic Waters, Adv. in Meteorol., Volume 2010, Article ID 243701, doi:10.1155/2010/243701 2010.

A regional climate model is used to evaluate dry deposition of ozone over the North East Atlantic. Results are presented for a deposition scheme accounting for turbulent and chemical enhancement of oceanic ozone deposition and a second non-chemical, parameterised gaseous dry deposition scheme. The first deposition scheme was constrained to account for sea-surface ozone-iodide reactions and the sensitivity of modelled ozone concentrations to oceanic iodide concentration was investigated. Simulations were also performed using nominal reaction rate derived from i

n-situ ozone deposition measurements and using a preliminary representation of organic chemistry. Results show insensitivity of ambient ozone concentrations modelled by the chemicalenhanced scheme to oceanic iodide concentrations, and iodide reactions alone cannot account for observed deposition velocities. Consequently, we suggest a missing chemical sink due to reactions of ozone with organic matter at the air-sea interface. Ozone loss rates are estimated to be in the range of 0.5–6 ppb per day. A potentially significant ozone-driven flux of iodine to the atmosphere is estimated to be in the range of 2.5–500Mmolec cm2 s1, leading to amixing-layer enhancement of organo-iodine concentrations of 0.1–22.0 ppt, with an average increase in the N.E. Atlantic of around 4 ppt per day.

### Growth Rates During Coastal and Marine New Particle Formation in Western Ireland

 Date added: 11/10/2010 Date modified: 11/10/2010 Filesize: 1.75 MB

Ehn, M., H. Vuollekoski, T. Petäjä, V.-M. Kerminen, M. Vana, P. Aalto, G. de Leeuw, D. Ceburnis, R. Dupuy, C. D. O’Dowd and M. Kulmala, Growth Rates During Coastal and Marine New Particle Formation in Western Ireland, J. Geophys. Res., doi:10.1029/2010JD014292, 2010.

Growth rates of new particles during coastal and marine secondary aerosol particle

formation events were studied in western Ireland, both at the Mace Head atmospheric

research station and onboard the R/V

Production project. Strong new particle formation events are frequently detected at Mace

Head caused by the emission of precursor gases from exposed seaweed during low tide.

Although these events were usually only detected as a mode of particles at a certain size, we

were able to link the size of the mode to the growth time of these particles after the initial

formation by combining data from several events measured between January 2006 and

November 2007 with an air ion spectrometer. Typically, the early growth rates were

extremely high, reaching values of several hundred nanometers per hour during the first

seconds. The growth rates rapidly decreased and reached values below 1 nm h

1 h after nucleation. Our results were reproduced with box model calculations. All the

obtained growth rates could be explained by the model either by varying the precursor

formation time (typically a few seconds) or allowing multiple precursor vapor additions.

From the ship

ocean new particle formation detected in this region. In total, four events were detected

during this period, with three having a variable continental influence. An estimated

average growth rate in marine conditions was 3 nm h

Celtic Explorer as part of the Marine Aerosol 1 within borne measurements, we report the first observations of purely open 1 for these events.

### Marine organohalogens in the atmosphere over the Atlantic and Southern Oceans

 Date added: 08/06/2003 Date modified: 07/24/2009 Filesize: 564.21 kB

Carpenter, L. J., P. S. Liss, and S. A. Penkett (2003), Marine organohalogens in the atmosphere over the Atlantic and Southern Oceans, J. Geophys. Res., 108(D9), 4256, doi:10.1029/2002JD002769.

Abstract

Reactive halogen species (RHS) such as the halogen oxide radicals IO and BrO influence tropospheric oxidation processes in both polar and temperate regions. Oceanic photolabile halocarbons have been shown to be strong sources of RHS in midlatitudes. However, the global source strengths of these halocarbon precursors and the relative importance of the coastal and pelagic oceans on their concentrations are highly uncertain. Here we present atmospheric measurements of the reactive organic halogens CH3I, CH2I2, CH2ClI, CH2IBr, CHIBr2, CHBr3, CH2Br2, and CHBr2Cl made at Mace Head, Ireland, during the Particle Formation and Fate in the Coastal Environment campaign in September 1998 and at Cape Grim, Tasmania, during the Southern Ocean Atmospheric Photochemistry Experiment 2 campaign in January/February 1999. Mace Head is strongly influenced by local macroalgae, whereas Cape Grim, owing to its cliff-top location, suffers much less impact from seaweeds. The very reactive halocarbons CH2I2, CH2IBr, and CHIBr2 observed at Mace Head were below detection limits at Cape Grim, although CH2ClI was detected at both locations. Mixing ratios of CH3I, CH2ClI, CHBr3, CHBr2Cl, and CH2Br2 at Cape Grim were on average 25–50% of those at Mace Head. Concentrations of the polybromomethanes correlated well at both sites. Using these correlations, we estimate molar source strengths of CHBr2Cl and CH2Br2 to be between 3 and 6% and between 15 and 25% of the global CHBr3 flux, respectively. These values fall within ranges estimated independently from concentration and lifetime data.

### Primary and secondary organic marine aerosol and oceanic biological activity: recent results and new

 Date added: 11/10/2010 Date modified: 11/10/2010 Filesize: 672.69 kB

Rinaldi,M., S.Decesari, E. Finessi, L.Giulianelli, C.Carbone, S.Fuzzi, C.D. O'Dowd, D.Ceburnis and M.C. Facchini, Primary and secondary organic marine aerosol and oceanic biological activity: recent results and new perspectives for future studies, Adv. in Meteorol., Volume 2010, Article ID 310682, doi:10.1155/2010/243701, 2010.

One of the most important natural aerosol systems at the global level is marine aerosol that comprises both organic and inorganic components of primary and secondary origin. The present paper reviews some new results on primary and secondary organic marine aerosol, achieved during the EU project MAP (Marine Aerosol Production), comparing them with those reported in the recent literature.Marine aerosol samples collected at the coastal site ofMaceHead, Ireland, show a chemical composition trend that is influenced by the oceanic biological activity cycle, in agreement with other observations. Laboratory experiments show that seaspray  aerosol from biologically active sea water can be highly enriched in organics, and the authors highlight the need for further studies on the atmospheric fate of such primary organics. With regard to the secondary fraction of organic aerosol, the average  chemical composition and molecular tracer (methanesulfonic-acid, amines) distribution could be successfully characterized by adopting a multitechnique analytical approach.

### Home Environment and Childhood Asthma

 Date added: 07/31/1994 Date modified: 07/02/2009 Filesize: 224.33 kB

Leen, M.G., O'Connor, T.C., Kelleher, C.C., Loftus, B.G. & Mitchell, C. (1994)- Home environment and childhood asthma. The Irish Medical Journal, Vol. 87, No. 5, pp. 142-144.

Abstract

The prevalence of childhood asthma has increased dramatically in the past 20 years. The reasons for the increase are unclear but many authors suggest that changes in the home environment favourable to proliferation of the house dust mite are to blame. Our study aimed to compare home environment of children with asthma and controls. A questionnaire on home environment was administered to the parents of 134 children with asthma and 118 controls. Detailed studies of home temperature, humidity and dust mite allergen (DERpI) levels were performed in 20 homes (10 from each group). The questionnaire response rate was 86%. There were no significant differences between asthma and control homes with respect to social class, type of housing, smoking habits, pets, insulation, home heating, bedding, carpeting and domestic cleaning habits. A first degree family history of atopy wasobtained in 42% of asthmatic families and in 16% of controls. Temperature, humidity and dust mite allergen levels were similar in both groups. The majority gave readings exceeding recommended norms. Values for DERpI were above thresholds by a factor of 5 in 48%. Home environment does not significantly differ in children with or without asthma. The home environment is now generally mite friendly, and large segments of the childhood population are now exposed to high levels of DERpI. This may account for the increasing prevalence as more and more children with an atopic background develop overt symptoms in response to high levels of allergen load.

### Light backscattering and scattering by non-spherical sea-salt aerosols

 Date added: 08/01/2003 Date modified: 07/24/2009 Filesize: 483.03 kB

Chamaillard K., Jennings S.J., Kleefeld C., Ceburnis D. and Yoon Y.J. Light backscattering and scattering by non-spherical sea-salt aerosols. J. of Quantitative Spectroscopy & Radiative Transfer, Vol. 79-80, 577-597, 2003.

Abstract

The scattering coefficient, single-scatter albedo, and up-scatter fraction are key parameters in direct climate forcing by aerosols. Usually the contribution of sea-salt is estimated using Mie theory, assuming that these particles are spherical. The optical properties of particles are known to strongly depend on the shape of the particles. The question of the applicability of using Mie theory in recent studies is mainly devoted to nonspherical dust-like tropospheric aerosols. In this study, we attempt to quantify the relative contribution of nonspherical sea-salt to measured scattering and backscattering coefficients. The shape of nonspherical sea-salt is assumed to be cubic. The discrete dipole approximation model is applied to estimate the optical properties of the nonspherical particles. Measurements are then compared to Mie theory calculations and to DDA cubic calculations. The results are presented for two wavelengths: λ=0.55 μm and 0.7 μm, It is found that the size of particles responsible for scattering is larger than 0.3 μm. The backscattering coefficient, unlike the scattering coefficient, is very sensitive to particle shape. Cubic particles give better agreement to the measurements. Compared to spherical particles, the cubic approach underestimates the backscattering coefficient in contrast to prolate spheroidal calculations.

 Date added: 08/01/2003 Date modified: 07/24/2009 Filesize: 1.51 MB

Mace Head Atmospheric Research Station – characterization of aerosol radiative parameters S. Gerard Jennings, C. Kleefeld, C. D. O'Dowd, C. Junker, T.G. Spain, P. O'Brien, A.F Roddy, and T.C. O'Connor Boreal Environ. Res., 8, 303-314, 2003.

Abstract

A fairly concise description and a short history of the Mace Head atmospheric research station, at 53°N, 10°W, on the west coast of Ireland is reported. The relatively high latitude site is representative of background marine air in the Northern Atlantic on the western periphery of Europe. The site is ideally located to measure the prevailing (about 52% of the time) westerly-southwesterly air from the Atlantic, as well as polluted air under anticyclonic conditions from sources east of the site within Ireland, from the UK and from mainland Europe. Three years of aerosol radiative data, over a period from January 2000 to December 2002, are indicative of the medium to longterm measurement programme at the site. These include aerosol scattering coefficient, aerosol absorption coefficient, aerosol optical depth and single scattering albedo, supported by meteorological and air mass trajectory input. Variability in aerosol parameters are shown to be dependent on air mass origin, season and meteorological conditions. Measurements indicate that the dominant contribution to aerosol optical depth is due to scattering, with single scattering albedo in the range 0.941 to 0.997. Measured aerosol optical depth for marine air over the 3 year period varies between 0.03 and 0.38 with a mean value of 0.11 and standard deviation of ±0.06. These values are in fair agreement with other data for the North Atlantic region.

### Production Of Cn by Gaseous Reactions

 Date added: 08/07/1963 Date modified: 07/23/2009 Filesize: 4.02 MB
Tom OConnor ,Production Of Cn by Gaseous Reactions, Journal de Recherches Atmospherique, pg 127 - 133 (1963)
Abstract

The production of condensation Nuclei as a result of gaseous reactions is discussed.  A Portable nucleus counter used to investigate sources of nuclei in the littoral zone is described. Laboratory experiments show that decaying seaweed emits a gas which forms condensation nuclei on irradiation with ultra violet or sunlight. It also emits H2S and the significance of this in the natural cycle of sulphur in the atmosphere is considered. Electrically heated wires produce very small condensation nuclei and also NO2.

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

 Date added: 08/06/2003 Date modified: 07/27/2009 Filesize: 184.19 kB
W. J. Bloss, T. J. Gravestock, D. E. Heard, T. Ingham,G. P. Johnson and J. D. Lee, "Application of a compact all solid-state laser system to the in situ detection of atmospheric OH, HO2, NO and IO by laser-induced fluorescence", Journal of Environmental Monitoring., 5, 21-28 (2003).

Abstract

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

### On the representativeness of coastal aerosol studies to open ocean

 Date added: 02/12/2010 Date modified: 02/13/2010 Filesize: 1.01 MB

Rinaldi, M., M. C. Facchini, S. Decesari, C. Carbone, E. Finessi, M. Mircea, S. Fuzzi, D. Ceburnis, M. Ehn, M. Kulmala, G. de Leeuw and C. D. O’Dowd, On the representativeness of coastal aerosol studies to open ocean studies: Mace Head – a case study, Atmos. Chem. & Phys., 9, 9635-9646, 2009

Abstract.

A unique opportunity arose during the MAP project to compare open ocean aerosol measurements with those undertaken at the Mace Head Global Atmosphere Watch Station, a station used for decades for aerosol process research and long-term monitoring. The objective of the present study is to demonstrate that the key aerosol features and processes observed at Mace Head are characteristic of the open ocean, while acknowledging and allowing for spatial and temporal gradients. Measurements were conducted for a 5-week period at Mace Head and offshore, on the Research Vessel Celtic Explorer, in generally similar marine air masses, albeit not in connected-flow scenarios. The results of the study indicate, in terms of aerosol number size distribution, higher nucleation mode particle concentrations at Mace Head than offshore, pointing to a strong coastal  source of new particles that is not representative of the open ocean. The Aitken mode exhibited a large degree of similarity, with no systematic differences between Mace Head and the open ocean, while the  zcumulation mode showed averagely 35% higher concentrations at Mace Head. The higher accumulation mode concentration can be attributed equally to cloud processing and to a coastal enhancement in concentration. Chemical analysis showed similar or even higher offshore concentrations for dominant species, such as nss-SO
2 4 , WSOC, WIOC and MSA. Sea salt concentration differences determined a 40% higher supermicron mass at Mace Head, although this difference can be attributed to a higher  wind speed at Mace Head during the parison period.        Moreover, the relative chemical composition as a function of size illustrated remarkable  similarity. While differences to varying degrees were observed between offshore and coastal  measurements, no convincing evidence was found of local  coastal effects, apart from nucleation mode aerosol, thus confirming the integrity of previously reported marine aerosol characterisation studies at Mace Head.

### Evasion of mercury from coastal and open waters of the Atlantic Ocean and the Mediterranean Sea

 Date added: 08/07/2003 Date modified: 07/24/2009 Filesize: 240.1 kB

Gardfeldt, K., Sommar, J., Ferrara, R., Ceccarini, C., Lanzillotta, E., Munthe, J., Wangberg, I., Lindqvist, O., Pirrone N., Sprovieri, F., Pesenti, E. (2003)   Evasion of mercury from coastal and open waters of the Atlantic Ocean and the Mediterranean Sea. Atmospheric Environment. Vol. 37-S1, 73-84.

Abstract

Dissolved gaseous mercury (DGM) was measured in coastal Atlantic seawater and in the Mediterranean Sea. The Atlantic measurements were performed during September 1999 at the Mace Head Atmospheric Research Station, situated on the Irish west coast. The measurements in the Mediterranean Sea were made along a 6000 km cruise path from 14 July to 9 August 2000 in the framework of the Med-Oceanor project. Total gaseous mercury (TGM) concentrations in air were continuously measured with a 5 min time resolution using an automated mercury analyser (Tekran 2537A) during both expeditions. Paired TGM and DGM samples from all campaigns showed that the surface water was supersaturated with elemental mercury. The mercury evasion was estimated using a gas exchange model (J. Geophys. Res. 97 (1992) 7373), which uses salinity, wind speed and water temperature as independent parameters. The predicted average mercury evasion from the coastal Atlantic water was 2.7 ng m-2h-1 implying that the concentration of TGM in the Atlantic air is enhanced by mercury evasion from the sea. Measurements in different regions of the Mediterranean Sea showed spatial variations in DGM concentrations. The highest DGM concentration (∼90 pg l-1) was observed at a location in the Strait of Sicily (37° 16N 11° 52E). The mercury evasion in the eastern sector of the Mediterranean Sea (area: 32-36°N, 17-28 E) was generally higher (7.9 ng m-2h-1) than that observed in the Tyrrhenian Sea (4.2 ng m-2h-1) or in the western sector (2.5 ng m-2h-1) (areas: 38-42°N, 8-13°E and 38-41°N, 7-8°E, respectively). Estimations of mercury evasion were also made at Mediterranean coastal sites using a dynamic chamber technique. In addition, a newly developed method making continuous in situ DGM measurements possible was tested.

### 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.

### On the production of Aitken nuclei by sunlight in st. Moritz

 Date added: 08/07/1962 Date modified: 07/15/2009 Filesize: 4.41 MB
C. Mc Greevy & TC O Connor, On the production of Aitken nuclei by sunlight in st. Moritz, (1962) Geofisica E Meteorologia

Abstract

It has been found by VERZAR & al. that the concentration of Aitken nuclei in atmospheric air increased from sunrise until  mid-day and decreased again in the afternoon. This effect occurred over the ordinary ground, in a city and also over snow. A similar effect had been reported by MCLAUGHLIN in Paris in 1926 '). It seemed likely that irradiation by the sun caused the increase in the numher of condensation nuclei. In order to study this ii suneffect ), V E R ~&~ RKU NZa nd VERZAR& EVANS  investigated nucleus-free atmospheric air stored in a polyethylene balloon and showed that the same effict took place when the air in the balloon was exposed to direct and scattered sunlight ("5). As a result of their researches and from the findings of other investigators (C.'.'") it was considered a reasonable hypothesis that trace gases in the air were partly responsible for nucleus prduction when irradiation by the sun took place. It was suggested that the production of nuclei by sunrays was due to a photochemical reaction of some impurity in the air. Suspected impurities were SO,, H,S, NH, and ozone. The amount of these contaminants in ordinary atmospheric air has
been discussed by JUNGE( 9.In support of the above hypothesis it was found that when traces of SO, or H,S or NH, were added to nucleus-free atmospheric air in such polyethylene hallons a striking increase in the number of nuclei
produced by sun irradiation occurred over the nnmher produced by irradiation when no traces were added (9. The sun-effect also took place when industrial oxygen or nitrogen replaced the nucleus-free air in the balloons. This also could he due to impurities present in the oxygen or nitrogen. In order to show quite definitely that traces of impurity
gases were partly the cause of nucleus-production in atmospheric air we decided to eliminate the suspected trace gases by filling the balloons with atmospheric air through chemicals which would absorb these trace gases or at least reduce their concentration. In this way it was hoped to he able to discover what trace gases were partly responsible for nucleus production in the sun-effect.

### AGAGE Observations of Methyl Bromide and Methyl Chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998–2001

 Date added: 08/01/2004 Date modified: 06/30/2009 Filesize: 593.54 kB

Simmonds, P.; Derwent, R.; Manning, A.; Fraser, P.; Krummel, P.; O'Doherty, S.; Prinn, R.; Cunnold, D.; Miller, B.; Wang, H.; Ryall, D.; Porter, L.; Weiss, R.; Salameh, P. ,AGAGE Observations of Methyl Bromide and Methyl Chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998–2001, Journal of Atmospheric Chemistry, pg 1573-0662

Abstract

In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998–2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr−1 (CH3Br) and 2.6% yr−1 (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr−1 and 1.5% yr−1, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH3Br) and 541.3 ± 1.1 ppt (CH3Cl). Although CH3Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).

### Hygroscopic and CCN properties of aerosol particles in boreal forests

 Date added: 07/31/2001 Date modified: 07/02/2009 Filesize: 498.17 kB
Hämeri, K. J.M. Mäkelä, L. Pirjola, M. Väkevä, P. Aalto, P. Miikkulainen, and C.D. O'Dowd, Hygroscopic properties of boreal forest aerosol during nucleation events. Tellus B, 53, 359-378, 2001

Abstract

The measurements of the hygroscopic and cloud condensation nuclei (CCN) properties of submicrometer atmospheric aerosol particles were performed with two tandem differential mobility analysers (TDMA) and a CCN counter at the Hyytia¨ la¨ forest field station in south-central Finland during the BIOFOR campaign. The TDMAs were used to measure hygroscopic diameter growth factors of individual aerosol particles in the dry particle diameter range 10–365 nm when taken from the dry state (relative humidity RH<5%) to RH=90%. The CCN counter was used to study the activation of aerosol particles when exposed to supersaturated conditions. The measurements show clear diurnal pattern of particle solubility. The pattern was strongest for particles in nucleation and Aitken modes. The lowest growth factor (soluble fraction) values were detected during late evening and early morning and the maximum was observed during noon–afternoon. The highest soluble fractions were determined for nucleation mode particles. The response of hygroscopic growth to changes of relative humidity suggests that the soluble compounds are either fully soluble or deliquescent well before 70% RH. The hygroscopic growth was investigated additionally by a detailed model using the size-resolved composition from the impactor samples. The comparison between different instruments shows good consistency. We found good agreement for the 20 nm growth factors measured with two TDMAs, not only on average but also regarding the temporal variation. The similar conclusion was drawn for comparison of TDMA with CCNC for Aitken mode particles with dry sizes 50 and 73 nm. Differences between wet and dry spectra measured using APS and CSASP spectrometer probes were used to derive growth factors for coarse mode particles. Growth factors for coarse mode particles (Dp ca. 2 mm) ranged between 1.0 and 1.6. Agreement between the evolution of growth factors with time for both accumulation and coarse modes was observed regularly. However, similar portions of the data set also indicated clear differences and consequently different chemical compositions between both modes. When the differences between both modes were observed, the coarse mode always behaved in a less hygroscopic manner, with growth factors near one.

### Iodine Oxide Homogeneous Nucleation An Explanation for Coastal New Particle Production

 Date added: 07/31/2001 Date modified: 07/24/2009 Filesize: 423.83 kB

Hoffmann, T, CD O'Dowd, JH Seinfeld, Iodine oxides and new particle formation, Geophys. Res. Letts., 27, 1949-1952, 2001.

Abstract

A series of laboratory experiments on the chemical composition of aerosol particles formed after photodissociation of CH2I2, a major volatile alkyl halide released from macroalgae, have been performed in a laboratory scale reaction chamber using on-line atmospheric pressure chemical ionization mass spectrometry (APCI/MS). Based on the mass spectrometric results and the molecular properties of iodine oxides, we suggest that the self-nucleation of iodine oxides provides an efficient source of natural condensable material in coastal environments and discuss this concept focusing on OIO as one potential key species for new particle formation. The presented hypothesis not only fits the measured enrichment of iodine species in submicrometer particles, but also can explain the frequently observed nucleation bursts in the coastal boundary layer.

### Modelling of indoor exposure to nitrogen dioxide in the UK

 Date added: 08/31/2001 Date modified: 07/03/2009 Filesize: 346.84 kB

Dimitroulopoulou, C., Ashmore, M.R., Byrne, M.A. and Kinnersley, R.P. Modelling of indoor exposure to nitrogen dioxide in the UK. Atmos. Environ., 35, 269-279, 2001.

Abstract

A dynamic multi-compartment computer model has been developed to describe the physical processes determining indoor pollutant concentrations as a function of outdoor concentrations, indoor emission rates and building characteristics. The model has been parameterised for typical UK homes and workplaces and linked to a time-activity model to calculate exposures for a representative homemaker, schoolchild and office worker, with respect to NO2. The estimates of population exposures, for selected urban and rural sites, are expressed in terms of annual means and frequency of hours in which air quality standards are exceeded. The annual mean exposures are estimated to fall within the range of 5-21 ppb for homes with no source, and 21-27 ppb for homes with gas cooking, varying across sites and population groups. The contribution of outdoor exposure to annual mean NO2 exposure varied from 5 to 24%, that of indoor penetration of outdoor air from 17 to 86% and that of gas cooking from 0 to 78%. The frequency of exposure to 1 h mean concentrations above 150 ppb was very low, except for people cooking with gas.

### International field intercomparison measurements of atmospheric mercury species at Mace Head, Ireland

 Date added: 07/31/1999 Date modified: 07/24/2009 Filesize: 195.51 kB

Ebinghaus, R., Jennings, S.G., Schroeder, W.H., Berg, T., Donaghy., Guentzel, J., Kenny, C., Kock, H.H., Kvietkus, K., Landing, W., Munthe, J., Prestbo, E.M., Schneeberger, D., Slemr, F., Sommar, J., Urba, A., Wallschlager, D. & Xiao, Z. 1999. International field intercomparison measurements of atmospheric mercury species at Mace Head, Ireland. Atmos. Environ., 33, 3063-3073.

Abstract

Eleven laboratories from North America and Europe met at Mace Head, Ireland for the period 11-15 September 1995 for the first international field intercomparison of measurement techniques for atmospheric mercury species in ambient air and precipitation at a marine background location. Different manual methods for the sampling and analysis of total gaseous mercury (TGM) on gold and silver traps were compared with each other and with new automated analyzers. Additionally, particulate-phase mercury (Hgpart) in ambient air, total mercury, reactive mercury and methylmercury in precipitation were analyzed by some of the participating laboratories. Whereas measured concentrations of TGM and of total mercury in precipitation show good agreement between the participating laboratories, results for airborne particulate-phase mercury show much higher differences. Two laboratories measured inorganic oxidized gaseous mercury species (IOGM), and obtained levels in the low picogram m-3 range.

### Primary Marine Organic Aerosol: A Dichotomy of Low Hygroscopicity and High CCN Activity

 Date added: 11/17/2011 Date modified: 11/17/2011 Filesize: 532.27 kB

Ovadnevaite, J., D. Ceburnis, J. Bialek, C. Monahan, G. Martucci, M. Rinaldi, M.C. Facchini, H. Berresheim, D. R. Worsnop and C. O’Dowd. Primary Marine Organic Aerosol: A Dichotomy of Low Hygroscopicity and High CCN Activity, Geophys. Res. Letts, 38, L21806, doi:10.1029/2011GL048869., 2011

Abstract. High-time resolution measurements of primary marine organic sea-spray physico-chemical properties reveal an apparent dichotomous behavior in terms of water uptake: specifically sea-spray aerosol enriched in organic matter possesses a low hydroscopic Growth Factor (GF~1.25) while simultaneously having a cloud condensation nucleus/condensation nuclei (CCN/CN) activation efficiency of between 83% at 0.25% supersaturation and 100% at 0.75%. In contrast, the activation efficiency of particles dominated by non-sea-salt (nss)-sulfate ranged between 48-100% over supersaturation range of 0.25%-1%. Simultaneous retrieval of Cloud Droplet Number Concentration (CDNC) during primary organic aerosol plumes reveals CDNC concentrations of 350 cm-3 for organic mass concentrations 3-4 mg m-3. It is demonstrated that the retrieved high CDNCs under clean marine conditions can only be explained by organic sea-spray and corroborates the high CCN activation efficiency associated with primary organics. It is postulated that marine hydrogels are responsible for this dichotomous behavior.

### 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.

### 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.

### Quantification of carbon dioxide, methane, nitrous oxide and chloroform emissions over Ireland from atmospheric observations at Mace Head

 Date added: 08/01/2002 Date modified: 07/23/2009 Filesize: 738.69 kB

Biraud, S., Ciais, Philippe, Ramonet, Michel, Simmonds, Peter, Kazan, Victor, Monfray, Patrick, O’Doherty, Simon, Spain, Gerard, and Jennings, S. Gerard. 2002. Quantification of carbon dioxide, methane, nitrous oxide, and chloroform emissions over Ireland from atmospheric observations at Mace Head, Tellus, 54B, pp. 41-60.

Abstract

Flux estimates of CO2, CH4, N2O and CHCl3 over Ireland are inferred from continuous atmospheric records of these species. We use radon-222 (222Rn) as a reference compound to estimate unknown sources of other species. The correlation between each species and 222Rn is calculated for a suite of diurnal events that have been selected in the Mace Head record over the period 1995-1997 to represent air masses exposed to sources over Ireland. We established data selection criteria based on 222Rn and 212Pb concentrations. We estimated flux densities of 12 × 103 kg CH4 km-2 yr-1, 680 kg N2O km-2 yr-1 and 20 kg CHCl3 km-2 yr-1 for CH4, N2O and CHCl3, respectively. We also inferred flux densities of 250 x 103 kg C km-2 yr-1 for CO2 during wintertime, and of 760 x 103 kg C km-2 yr-1 for CO2 during summer night-time. Our CH4 inferred flux compare well with the CORINAIR90 and CORNAIR94 inventories for Ireland. The N2O emission flux we inferred is close to the inventory value by CORINAIR90, but twice the inventory value by CORINAIR94 and EDGAR 2.0. This discrepancy may have been caused by the use of the revised 1996 IPCC guidelines for national greenhouse gas inventories in 1994, which include a new methodology for N2O emissions from agriculture. We carried out the first estimation of CHCl3 emission fluxes over Ireland. This estimation is 4 times larger than the CHCl3 emission fluxes measured close to the Mace Head station over peatlands. Our CHCl3 emission fluxes estimate is consistent with the interpretation of the same data by Ryall (personal communication, 2000), who obtained, using a Lagrangian atmospheric transport model, CHCl3 fluxes of 24 ± 7 kg CHCl3 km-2 yr-1. Our estimates of CO2 emission fluxes during summer night-time and wintertime are close to those estimated from inventories and to one biogeochemical model of heterotrophic respiration.

### An automated system for near-real time monitoring of trace atmospheric halocarbons

 Date added: 08/05/1998 Date modified: 07/27/2009 Filesize: 122.2 kB

An Automated System for Near-Real-Time Monitoring of Trace Atmospheric Halocarbons, Bassford, M.R., Simmonds, P.G., and Nickless, G.,Anal. Chem., 70, 5, 958 - 965, 1998,  10.1021/ac970861z

Abstract

A new gas chromatographic method developed to quantitatively determine important atmospheric halocarbons is described. Target compounds include replacement CFCs, chlorinated solvents, and biosynthesized (naturally produced) organohalogens, all trace gases in the atmosphere at concentrations ranging from 0.1 to 600 pptv (where pptv = 1 part in 10-12 by volume). A combination of ultralow concentrations and relatively small electron attachment cross sections renders these compounds very difficult to routinely measure in the background air typical of remote atmospheric monitoring stations. Detection is achieved by preconcentration of a 200-mL air sample using an adsorbent-filled microtrap and enhancement of electron capture detector response by oxygen doping one of two detectors connected in series. Oxygen doping specifically targets halocarbons with relatively poor electron attachment rate coefficients. The work described here details construction of a novel analytical system, laboratory trials, and optimization followed by an extended field campaign at a remote atmospheric monitoring station, Mace Head, Ireland. A calibration standard or ambient air sample was acquired every hour using a cyclic, automated procedure without employing cryogenic preconcentration or refocusing. Overall precision of the analytical method for the target compounds is between 0.3 and 1.5%.

### Low Molecular Weight Organic Compounds in Maritime Air Recent Results from NAMBLEX Experiment,

 Date added: 08/06/2003 Date modified: 07/24/2009 Filesize: 13.55 kB
Read, K.; Hopkins, J.; Lewis, A., "Low Molecular Weight Organic Compounds in Maritime Air: Recent Results from NAMBLEX Experiment, Mace Head, Ireland", Geophysical Research Abstracts Volume 5, 2003.

Abstract

A dual channel GC-FID for the simultaneous measurement of C2-C7 non-methane hydrocarbons (NMHC), dimethyl sulphide (DMS) and some previously unmeasured oxygenated hydrocarbons (O-VOC) in the atmosphere has been developed and run alongside an established single channel GC-FID measuring NMHC. The instruments were implemented in the field as part of the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign to investigate the role of these trace species in the marine boundary layer. Oxygen containing species such as aldehydes, ketones and alcohols although well known to be highly significant in atmospheric reactions, have in the past been poorly

understood from both distribution and source perspectives. They exist from a combination of both biogenic and anthropogenic emissions together with a secondary source from hydrocarbon oxidation. Under all maritime conditions the organic composition was dominated by acetone, methanol and acetaldehyde with the sum of these compounds contributing up to 85% of the carbon mass of organics in air and up to 80% of the normalised OH radical sink. The relative contribution of NMHC was only comparable when isoprene emissions from terrestrial sources were present. In marine air masses a positive correlation was seen between average zonal surface wind speed and DMS concentration in air in line with previous studies. No equivalent behaviour was recreated for either acetone or acetaldehyde indicating that in this region the ocean is not a significant atmospheric source. These O-VOC compounds appeared to follow the general trends of anthropogenic NMHC tracers such as acetylene indicating a common terrestrial origin for these compounds. Methanol however showed strong anti correlation with averaged wind speed directly indicating that the surface ocean was acting as a sink.

### 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.

### An analysis of condensation nuclei levels at Mace Head, Ireland

 Date added: 07/31/1999 Date modified: 07/27/2009 Filesize: 737.83 kB

Mc Govern, F.M. (1999). An analysis of condensation nuclei levels at Mace Head, Ireland. Atmos. Environ., 33, 1711-1723.

Abstract

Condensation nuclei (CN) concentrations measured at Mace Head between 1990 and 1992 are presented. The background CN concentration was found to typically range from 100 to 700 cm-3. Concentration values were in this range for 55% of the measurement period. No seasonal cycle was observed in the CN concentration values. Concurrent equivalent black carbon (EBC) measurements are used to examine anthropogenic influences on the background CN concentration. Evidence that transatlantic air mass transport influenced the background CN concentration contributing to increased CN and EBC levels, is shown. During polluted conditions the CN concentration was generally higher than 1000 cm-3. The principal source for high pollution levels was European air masses arriving at the site. Very high CN concentrations, greater than 50 000 cm-3, are attributed to local gas-to-particle conversion processes. The characteristics of a number of particle production events are considered. These show that these events are highly photochemical and occur during both clean and polluted conditions. Such production events though infrequent contributed significantly to the total aerosol number concentration.

### Long-term measurements of the concentrations of halocarbons in an urban area of Kraków, Poland

 Date added: 08/07/2003 Date modified: 07/24/2009 Filesize: 210.57 kB

Lasa J., Śliwka I. Long.term measurements of the concentrations of halocarbons in an urban area of Kraków, Poland. Applied Energy, 75 (2003), 155-163.

Abstract

The results of the measurements of the concentrations of freons (F-11 and F-113), chloroform (CHCl3), trichloroethane (CH3CCl3) and carbon tetrachloride (CCl4) in air are presented. The data concern concentration measurements that have been conducted in Krakow since half way through 1997 to the end of 1999. The mean monthly values of these concentrations have been compared with the data from Mace Head, the station situated at a similar longitude as Krakow. It has been concluded that, in the observed period of time, the concentrations of the pollutants in Krakow are higher than in Mace Head. The mean monthly concentrations of F-11 and CCl4 decrease in Krakow faster than in Mace Head (2.5 and 3.3 times, respectively). The concentrations of CHCl3 and CH3CCl3 decrease at both locations, but the change is greater in Krakow. In Krakow, the observed increase of F-113 is 0.13 ppt/month and has an opposite trend than in the same period at Mace Head.

### European emissions of mercury derived from long-term obsercations at Mace Head, on the western Irish coast

 Date added: 08/01/2006 Date modified: 07/24/2009 Filesize: 185.84 kB

Slemr F, R. Ebinghaus, P.G. Simmonds and S.G. Jennings, European emissions of mercury derived from long-term observations at Mace Head, on the western Irish coast, Atmos. Environ., 40, 6966-6974, 2006.

Abstract

Many emission inventories for mercury have been compiled but rarely constrained using observations of ambient air concentrations with a known quality. In this paper, we derive Hg/CO, Hg/halocarbon, and Hg/CH4 emission ratios from pollution episodes observed during the long-term mercury monitoring at the Mace Head Atmospheric Research Station in Ireland. The average Hg/CO emission ratio from 15 pollution episodes with air originating from the European continent observed between 1996 and 2003 was 0.0050±0.0021 ng m-3 ppbv-1, i.e. (5.5±2.3) x 10-7mol/mol, which is almost identical to the ratio reported recently for the continental plumes of eastern Asia. Mercury correlated also with CFCl3 (CFC-11), CF2Cl2 (CFC-12), CH3CCl3, CCl4, CCl2FCF2Cl (CFC-113), CHCl3, N2O, and CH4 during the pollution episodes. The mercury emissions calculated from the emission ratios and the European emissions of the above gases are in reasonable agreement with the estimated anthropogenic total mercury emissions of 250t/yr in 1995. However, the measurements encompass almost exclusively elemental mercury whose anthropogenic emissions are estimated to be only 152 t yr-1. Several hypotheses are proposed to explain this discrepancy, such as natural sources, underestimation of the emissions of elementary mercury, and erroneous speciation of anthropogenic emissions.

### Marine aerosol chemistry gradients Elucidating primary and secondary processes and fluxes

 Date added: 08/01/2008 Date modified: 07/24/2009 Filesize: 260.53 kB

Ceburnis, D., C. D. O'Dowd, G. S. Jennings, M. C. Facchini, L. Emblico, S. Decesari, S. Fuzzi, and J. Sakalys (2008), Marine aerosol chemistry gradients: Elucidating primary and secondary processes and fluxes, Geophys. Res. Lett., 35, L07804, doi:10.1029/2008GL033462.

Abstract

Production mechanisms of aerosol chemical species, in terms of primary and secondary processes, were studied using vertical concentration gradient measurements at the coastal research station in Mace Head, Ireland. Total gravimetric PM1.0 mass, sea salt and water insoluble organic carbon (WIOC) concentration profiles showed a net production at the surface (i.e. primary production), while nssSO4 and water soluble organic carbon (WSOC) concentration profiles showed a net removal at the surface. These observations indicate that WSOC was predominantly of secondary origin and that WIOC was predominantly of primary origin. Derived PM1 mass fluxes compared reasonably well with those previously obtained from an eddy covariance (EC) technique following a power law relationship with the wind speed (F PM1 = 0.000096*U 4.23). For cases with clear primary organic mass fluxes in the flux footprint WIOM mass fluxes ranged between 0.16 and 1.02 ng m−2 s−1 and WIOM/sea salt mass ratio was 0.34–3.6, in good agreement with previous measurements at Mace Head.

### Hydroxyl Radical Concentrations Estimated from Measurements of Trichloroethylene during the EAS

 Date added: 08/05/1999 Date modified: 07/24/2009 Filesize: 161.63 kB

Derwent, R.G., N. Carslaw, P. G. Simmonds, M. Bassford, S. O’Doherty, D.B. Ryall, M.J. Pilling, A.C. Lewis, and J.B. McQuaid, Hydroxyl radical concentrations estimated from measurements of trichloroethylene during the EASE/ACSOE campaign at Mace Head, Ireland during July 1996, J. Atmos Chem, 34, 185-205, 1999, (Ser. No. ACP107).

Abstract

During the EASE/OXICOA campaign of the NERC ACSOE programme, trichloroethylene and a wide range of man-made halocarbons and radiatively-active trace gases were monitored with high precision and high frequency throughout July 1996 at Mace Head on the Atlantic Ocean coast of Ireland. Trichloroethylene concentrations in concert with many other trace gases became elevated as regionally-polluted and photochemically-aged air masses reached Mace Head. However, as the anticyclonic air masses retreated during 19 and 20 July, trace gas concentrations remained elevated for a significant period. During this 2-4 day period, trichloroethylene concentrations decayed significantly, though the concentrations of the other more chemically-inert trace gases did not. A detailed interpretation of this behaviour using a Lagrangian dispersion model has allowed the estimation of average and peak OH radical concentrations of 3 and 9 × 106 molecule cm-3, respectively, during the travel from the source areas in the U.K. and the low countries out to Mace Head. Using a simple box model, the available Mace Head measurements, when combined into a detailed chemical mechanism, generated OH radical concentrations which peaked at 7 × 106 molecule cm-3, in close agreement with the estimates based on trichloroethylene decay.

### Primary versus secondary contributions to particle number concentrations in the European boundary layer

 Date added: 03/12/2013 Date modified: 03/12/2013 Filesize: 2.77 MB

C.L. Reddington, K.S. Carslaw, D.V. Spracklen, M.G. Frontoso, L.Collins, J. Merikanto, A. Minikin, T. Hamburger, H.Coe, M. Kulmala, P. Aalto, H. Flentje, C. Plass-Dülmer, W. Birmili, A. Wiedensohler, B. Wehner, T. Tuch, A.Sonntag, C. D. O'Dowd, S.G. Jennings, R.Dupuy, U. Baltensperger, E. Weingartner, H.-C. Hansson, P. Tunved, P. Laj, K. Sellegri, J. Boulon, J.-P. Putaud, C. Gruening, E. Swietlicki, P. Roldin, J. S. Henzing, M. Moerman, N. Mihalopoulos, G. Kouvarakis, V. Ždímal, N. Zíková, A. Marinoni, P. Bonasoni, and R. Duchi,Primary versus secondary contributions to particle number concentrations in the European boundary layer, Atmos. Chem. Phys., 11, 12007-12036, 2011, www.atmos-chem-phys.net/11/12007/2011/ doi:10.5194/acp-11-12007-2011

Abstract. It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2 >0.8) and the normalised mean bias (NMB) was also small (18% for N50 and 1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias R2 >0.8, NMB =52% and 29 %), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the “effective emission size” and composition of primary particles appropriate for different resolution models.

### On condensation nuclei produced at heated surfaces

 Date added: 08/31/1959 Date modified: 07/03/2009 Filesize: 1.59 MB

O'Connor, T.C, Sharkey, W.P.F., and O Brolchain, C. (1959)- On condensation nuclei produced at heated surfaces, Geofisia pura e applicata, 42, 109-116.

Abstract

An investigation of heated surfaces of glass, metal and oil as sources of condensation nuclei is reported. Below a certain transition temperature the nucleus production is of a temporary nature and decreases to zero with the continued heating of the surface. Above this temperature, however, the nucleus production does not change with time. The transition temperature varies with the material of the surface and is not always associated with the onset of incandescence. The nuclei produced at the lower temperatures have a radius of about 10–5 cm and, on production, are mainly uncharged. Electric light bulbs can produce appreciable numbers of these nuclei.

### New Particle Formation Nucleation Rates and Spatial Scales in the Clean Coastal Environment

 Date added: 08/06/1998 Date modified: 07/23/2009 Filesize: 492.74 kB

O’Dowd, C. D., M. Geever, M. K. Hill, M. H. Smith, and S. G. Jennings (1998), New Particle Formation: Nucleation Rates and Spatial Scales in the Clean Marine Coastal Environment, Geophys. Res. Lett., 25(10), 1661–1664.

Abstract

Nucleation of new, ultra-fine, aerosol particles has been observed in the clean marine coastal atmosphere under a variety of conditions. These nucleation events were observed to occur frequently over spatial scales of 10’s-100’s of metres and temporal scales of seconds to minutes. Two conditions appeared to be necessary for nucleation event to occur: low tide and solar irradiation. The requirement of low tide conditions suggests that the exposed shore area provides the source of new particle precursors. It is speculated that VOC and/or alkyl halide derivatives contribute to nucleation under these conditions. Nucleation rates were calculated to be ≈ 10³ −104 cm−3 s−1, suggesting that the coastal zone is an important source of atmospheric nuclei.

### Globally significant oceanic source of organic carbon aerosol

 Date added: 08/06/2008 Date modified: 07/24/2009 Filesize: 1.07 MB

Spracklen, D. V., S. R. Arnold, J. Sciare, K. S. Carslaw, and C. Pio (2008), Globally significant oceanic source of organic carbon aerosol, Geophys. Res. Lett., 35, L12811, doi:10.1029/2008GL033359.

Abstract

Significant concentrations of organic carbon (OC) aerosol are observed at three oceanic surface sites (Amsterdam Island, Azores and Mace Head). Two global chemical transport models (CTMs) underpredict OC concentrations at these sites (normalised mean bias of −67% and −58%). During periods of high biological activity monthly mean concentrations are underpredicted by a factor of 5–20. At Amsterdam Island and Mace Head, observed OC correlates well (R2 = 0.61–0.77) with back-trajectory weighted chlorophyll-a, suggesting an oceanic OC source driven by biological activity. We use a combination of remote sensed chlorophyll-a, back trajectories and observed OC to derive an empirical relation between chlorophyll-a and the total oceanic OC emission flux. Using the GEOS-chem CTM we show a global oceanic OC emission, from primary and secondary sources, of ∼8 Tg/year matches observations. This emission is comparable in magnitude to the fossil fuel OC source and increases the simulated global OC burden by 20%.

### Quantification of Coastal New Ultra-Fine Particles Formation from In situ and Chamber Measurements during the BIOFLUX Campaign

 Date added: 08/01/2005 Date modified: 07/23/2009 Filesize: 1014.54 kB

Sellegri, K., Y. J. Yoon, S. G. Jennings, C. D. O’Dowd, L. Pirjola, S. Cautenet, H. Chen, T. Hoffmann, Quantification of Coastal New Ultra-Fine Particles Formation from In situ and Chamber Measurements during the BIOFLUX Campaign. Environ. Chem. 2, 260. doi:10.1071/EN05074, 2005.

Abstract

Secondary processes leading to the production of ultra-fine particles by nucleation are still poorly understood. A fraction of new particles formed can grow into radiatively active sizes, where they can directly scatter incoming  solar radiation and, if partly water soluble, contribute to the cloud condensation nuclei population. New particle formation events have been frequently observed at the Mace Head Atmospheric Research Station (western Ireland), under low tide and sunny conditions, leading to the hypothesis that new particles are formed from iodo-species emitted from macroalgae.

### Averaging periods for indoor-outdoor ratios of pollution in naturally ventilated non-domestic buildings near a busy road

 Date added: 08/01/2003 Date modified: 06/30/2009 Filesize: 387.68 kB

Ni Riain, C, Mark, D., Davies, M., Harrison, R.M. and Byrne, M.A. Averaging periods for indoor-outdoor ratios of pollution in naturally ventilated non-domestic buildings near a busy road. Atmos Env, Vl 37, pp 4121-4132 , 2003.

Abstract

Continuous measurements of carbon monoxide (CO) and particulate matter (PM10, PM2.5 and PM1) were made inside and outside two naturally ventilated (NV) and two mechanically assisted (MV) spaces overlooking the same six-lane highway in Central London. The indoor/outdoor (I/O) ratio was calculated for each site for the whole monitoring period in the usual way, and then cumulatively at each hourly time-step from the start of monitoring up to the whole period in order to track the evolution of the I/O ratio with length of monitoring or averaging period. Hourly data were also sorted by wind speed and direction and I/O ratios calculated for each direction/speed set from ensemble means. I/O ratios for the whole period were generally lower in the NV spaces than the MV, however, the indoor-outdoor relationship in the NV spaces was found to vary substantially with wind direction. For a constant above-roof wind speed, I/O ratios of CO varied by 50-60% about the mean value with direction, and by 20-30% for particulate matter. Consequently, I/O ratios for NV spaces depended on the distribution of wind direction within the calculation period and, hence, on the length of monitoring period. The I/O ratio in one NV space changed by a factor of three between the early stages and final stages of monitoring, with a stable final value (±5%) achieved after 900 h of monitoring. By contrast, in the MV spaces under constant fan speed, constant values for the I/O ratio were achieved for CO within 4 h of the start of monitoring. It is argued here that field assessments of the filtration performance of naturally ventilated spaces need to consider exposure to and distribution of natural ventilation drivers within the monitoring period in order to draw meaningful comparisons for design and exposure assessment purposes.

### Airborne concentrations and deposition fluxes of major and trace species at marine stations in

 Date added: 08/05/1997 Date modified: 06/30/2009 Filesize: 1.36 MB

Foltescu et al (1996). V.L. Foltescu, E. Selin Lindgren, J. Isakson, M. Oblad, R. Tiede, J. Sommar, J.M. Pacyna and K. Toerseth , Airborne concentrations and deposition fluxes of major and trace species at marine stations in southern Scandinavia. Atmospheric Environment 30 22 (1996), pp. 3857–3872.

Abstract

Extensive measurements of airborne concentrations and deposition fluxes of many major and trace species were performed within the framework of the BMCAPE project (Background Maritime Contribution to Atmospheric Pollution in Europe) at two Scandinavian sites (Saby in Sweden and Lista in Norway) during four seasons in 1993 and 1994. The study focused on gaseous and particulate S-, N- and CI-species.Airborne concentration levels during the different campaigns, seasons and the various air masses encountered are presented for the following gaseous and particulate species: SO2, HCl, NOx, HNO3, NH3, SO2-4, NH+4, NO-3, S, Cl, K, Ca, V, Ni, Zn, Br, Pb and condensation nuclei. In addition, particle concentrations of Ti, Fe, Cu and Mn are discussed in the text. A time series is given for particulate and gaseous Hg. Annual flux estimates for Southern Scandinavia are given for Mn, Fe, Ni, Cu, Zn, Pb, Cl, S, non-sea-salt-sulphate-S, As, Na, K, Ca, Mg, NO-3-N and NH+4-N. Based on direct flux measurements to a water surface, dry deposition velocities are determined for nine elements: Mn, Fe, Ni, Cu, Zn, Pb, Cl, S, Ca.

### Seasonal cycle of N2O Analysis of data

 Date added: 08/06/2007 Date modified: 07/23/2009 Filesize: 599.77 kB

Jiang, X., W. L. Ku, R.-L. Shia, Q. Li, J. W. Elkins, R. G. Prinn, and Y. L. Yung (2007), Seasonal cycle of N2O: Analysis of data, Global Biogeochem. Cycles, 21, GB1006, doi:10.1029/2006GB002691

Abstract

We carried out a systematic study of the seasonal cycle and its latitudinal variation in the nitrous oxide (N2O) data collected by National Oceanic and Atmospheric Administration–Global Monitoring Division (NOAA-GMD) and the Advanced Global Atmospheric Gases Experiment (AGAGE). In order to confirm the weak seasonal signal in the observations, we applied the multitaper method for the spectrum analysis and studied the stations with significant seasonal cycle. In addition, the measurement errors must be small compared with the seasonal cycle. The N2O seasonal cycles from seven stations satisfied these criteria and were analyzed in detail. The stations are Alert (82°N, 62°W), Barrow (71°N, 157°W), Mace Head (53°N, 10°W), Cape Kumukahi (19°N, 155°W), Cape Matatula (14°S, 171°W), Cape Grim (41°S, 145°E) and South Pole (90°S, 102°W). The amplitude (peak to peak) of the seasonal cycle of N2O varies from 0.29 ppb (parts-per-billion by mole fraction in dry air) at the South Pole to 1.15 ppb at Alert. The month at which the seasonal cycle is at a minimum varies monotonically from April (South Pole) to September (Alert). The seasonal cycle in the Northern Hemisphere shows the influence of the stratosphere; the seasonal cycle of N2O in the Southern Hemisphere suggests greater influence from surface sources. Preliminary estimates are obtained for the magnitude of the seasonally varying sources needed to account for the observations.

### Applicability of condensation particle counters to measure atmospheric clusters

 Date added: 09/12/2008 Date modified: 07/10/2009 Filesize: 617.3 kB

Sipilä, M., Lehtipalo, K., Kulmala, M., Petäjä, T., Junninen, H., Aalto, P. P., Manninen, H. E., Kyrö, E.-M., Asmi, E., Riipinen, I., Curtius, J., Kürten, A., Borrmann, S., and O'Dowd, C. D.: Applicability of condensation particle counters to measure atmospheric clusters, Atmos. Chem. Phys., 8, 4049-4060, 2008

Abstract

This study presents an evaluation of a pulse height condensation particle counter (PH-CPC) and an expansion
condensation particle counter (E-CPC) in terms of measuring ambient and laboratory-generated molecular and ion clusters. Ambient molecular cluster concentrations were measured with both instruments as they were deployed in conjunction with an ion spectrometer and other aerosol instruments in Hyyti¨al¨a, Finland at the SMEAR II station between 1 March and 30 June 2007. The observed cluster concentrations varied and ranged from some thousands to 100 000 cm−3. Both instruments showed similar (within a factor of 5) concentrations. An average size of the detected clusters was approximately 1.8 nm. As the atmospheric measurement of sub 2-nm particles and molecular clusters is a challenging task, we conclude that most likely we were unable to detect the smallest clusters. Nevertheless, the reported concentrations are the best estimates to date for minimum cluster concentrations in a boreal forest 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.

### Aircraft Measurements During NAMBLEX (the SNAP campaign)

 Date added: 08/06/2003 Date modified: 07/27/2009 Filesize: 33.65 kB
Purvis R.M., Lewis A.C., McQuaid J.B. & Lee J.D. "Aircraft Measurements During NAMBLEX (the SNAP campaign)." Geophys Res. Abs. 6 (2004):

Abstract

The spatial distribution of a number of trace species has been determined in marine boundary layer (MBL) and free troposphere (FT) air around the Mace Head Atmospheric Research Station, Ireland. CO and ozone measurements were made onboard the NERC Dornier 228-101 research aircraft operated by the Airborne Remote Sensing Facility during the SNAP (Supporting NAMBLEX from an Airborne Platform) campaign in August 2002. High frequency whole air samples taken from onboard the aircraft with ground analysis using GC-FID were used for C2 - C6 hydrocarbons mixing ratios. The campaign was conducted in conjunction with the ground based NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign carried out at Mace Head during the summer of 2002. The distribution of trace species was investigated in both coastal regions and above the deep waters beyond the continental shelf. A vertical gradient in concentration of hydrocarbon and sulphur species with known oceanic sources was observed in the MBL over both oceanic regions when compared to anthropogenic tracers such as acetylene and CO. Under clear sky conditions typical maximum mixing ratios were MBL ethene 78 pptV: FT ethene 10 pptV: MBL DMS: 89 pptV: FT DMS 21 pptV.

Elevated mixing ratios of species with oceanic origin were observed in the lower most  FT in regions experiencing strong convective activity associated with cumulus cells. Vertical profiles centred over the field site showed good agreement between ground based and airborne hydrocarbon measurements taken within the MBL. The MBL upwind of Mace Head appeared well mixed with respect to both NMHCs,CO and ozone. Above 2 km showed distinct layers with free  tropospheric ozone values of 50 ppbV contrasting typical MBL values of less than 30 ppbV. Flights indicate a boundary layer height of approximately 1200 m. The observations confirm that for these species the surface site measurements are generally representative of the marine boundary layer as a whole but not of the air mass above.

### AGAGE Observations of Methyl Bromide and Methyl Chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998–2001

 Date added: 08/01/2004 Date modified: 07/27/2009 Filesize: 593.54 kB

Simmonds, P.; Derwent, R.; Manning, A.; Fraser, P.; Krummel, P.; O'Doherty, S.; Prinn, R.; Cunnold, D.; Miller, B.; Wang, H.; Ryall, D.; Porter, L.; Weiss, R.; Salameh, P. ,AGAGE Observations of Methyl Bromide and Methyl Chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998–2001, Journal of Atmospheric Chemistry, pg 1573-0662

Abstract

In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998–2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr−1 (CH3Br) and 2.6% yr−1 (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr−1 and 1.5% yr−1, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH3Br) and 541.3 ± 1.1 ppt (CH3Cl). Although CH3Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).

### Nitrogen deposition to the eastern Atlantic Ocean The importance of southeasterly flow

 Date added: 08/06/2000 Date modified: 07/23/2009 Filesize: 782.42 kB

Spokes, L.J., Yeatman, S.G., Cornell, S.E. and Jickells, T.D., 2000. Nitrogen deposition to the eastern Atlantic Ocean. The importance of south-easterly flow. Tellus 52B, pp. 37–49.

Abstract

Converting measured concentrations into fluxes and using estimates of biological productivity in the coastal waters of the eastern Atlantic Ocean enables us to determine the role of the atmosphere as a source of biologically essential species, including nitrate and ammonium, to the marine biota. To understand the effects of the atmosphere as a source of nitrogen capable of promoting new production, we need to know both the seasonality of the input as well as the effects of extreme high deposition events which, while small in overall annual budget terms, maybe able to extend, or even promote, phytoplankton growth under nutrient depleted summer conditions. Aerosols and rainwater were collected at both Mace Head and at sea aboard RRS Challenger. Temporal patterns have been interpreted using airmass back trajectories which give the predicted air path prior to arrival at the sampling site. Low levels of both nitrate and ammonium are seen associated with marine westerly flow across the Atlantic and northerly air originating in the Arctic region. As expected, marine derived sodium, chloride, magnesium and seasalt sulphate are high during these periods. High concentration nitrate and ammonium events are seen associated with south-easterly flow where the airmass passes over the UK and northern Europe prior to arrival on the west coast of Ireland. In the polluted atmosphere, nitrate exists as nitric acid and as fine mode (< 1 μm diameter) ammonium nitrate aerosol. In the coastal zone, nitric acid reacts with coarse mode seasalt aerosols to form coarse mode (> 1 μm diameter) sodium nitrate: HNO3(g) + NaCl(s) → NaNO3(s) + HCl(g). This seasalt displacement reaction not only enhances dry nitrate deposition through more efficient gravitational settling of large particles, but also increases the efficiency of precipitational scavenging via inertial impaction. By looking at the size distribution of nitrate, we can see evidence for the seasalt displacement reaction. Under the polluted south-easterly flow, ∼40-60% of the nitrate occurs in the coarse mode fraction. Under clean marine conditions, the seasalt displacement reaction results in almost complete conversion of nitrate from the fine to the coarse aerosol mode. By converting measured wet and dry nitrate, ammonium and organic nitrogen concentrations into fluxes and comparing the data with estimates of biological productivity in the surface waters, our data suggest that ∼ 30% of new production in eastern Atlantic surface waters off Ireland can be supported by atmospheric inputs in May 1997 and that most of the input occurs during short lived, high-concentration, south-easterly transport events.

### 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.

### Gas-to-particle conversion of sulphur and nitrogen compounds as studied at marine stations in N

 Date added: 08/05/1996 Date modified: 07/02/2009 Filesize: 935.92 kB

V. L. Foltescu, E. Selin Lindgren, J. Isakson, M. Oblad, J. M. Pacyna, S. Benson, Gas-to-particle conversion of sulphur and nitrogen compounds as studied at marine stations in Northern Europe, Atmospheric EnvironmentVolume 30, Issue 18, , September 1996, Pages 3129-3140.

Abstract

The present work provides insights into the N- and S-pollution behaviour at rural and remote sites in Northern Europe. Formation of SO42- and NO3- from their precursor gases receives special attention in order to understand the significance of chemical conversion in shaping the distributions of concentration and deposition monitored at our sites : Säby-on the Swedish west coast, Lista-on the Norwegian south coast and South Uist-on the Hebride Islands in Northern Scotland. Owing mainly to the complexity of the problem, the approach is semiquantitative. Concentration patterns of S- and N-compounds for air mass transport between the sites were investigated for 10 periods (13d), within continental(6d) and oceanic (7 d) air masses. The observations spanned over both winter and summer days and conclusions could be drawn in some cases with respect to seasonality. The measurements were performed during the BMCAPE (Background Maritime Contribution to Atmospheric Pollution in Europe) project in 1993 and 1994. S- and N-ratios were used as indicators of air mass age, chemical conversion efficiency and en-route deposition. The S-ratio is defined as the ratio of particulate S (as SO42-) to total S (as SO2 and SO42-). The N-ratio is taken as the ratio of gaseous HNO3-N over particulate NO3--N. S-ratios at Säby and Lista agreed very well in those cases when no or insignificant precipitation occurred. Higher S-ratios and lower N-ratios were typical for conditions of high relative humidity. It is conceivable that condensed phase chemistry was of major importance in the SO2 oxidation and that HNO3 was absorbed onto the wet aerosol particles. Stagnation of the air masses over source regions of high emission densities and rates resulted in accumulation of pollution, the S-ratios in such conditions being high due to the longer transport time. The S-ratios for marine air flow at Säby and Lista no longer agreed (higher at Lista) as in the case of continental air masses. The reason is likely to be the proximity of the Lista station to the sea. Lista was highly affected by sea spray produced by the strong westerly winds. The N-ratio remained very low in the case of maritime air masses due to unexpectedly high NO3- concentrations. It is conceivable that the high load of NO3- is due to sea spray of surface water. More efficient SO2 deposition over land than over sea has been observed in the westerly airflow by the relative loss of SO2 while the flow swept over land.

### An isotopic study of atmospheric sulphur at three sites in Wales and at Mace Head, Eire

 Date added: 08/06/1998 Date modified: 07/27/2009 Filesize: 1.36 MB
McArdle N. ; Liss P. ; Dennis P.  1998, An isotopic study of atmospheric sulphur at three sites in Wales and at Mace Head, Eire, J. Geophys. Res. Vol. 103 , No. D23 , p. 31,079 (98JD01664)

Abstract

Sulphur isotope measurements made on aerosol and precipitation samples collected at three sites in Wales and Mace Head, Eire, between March 1993 and 1994, had highest non-sea-salt sulphate δ34S values, up to 11.9‰ for aerosol and 9.7‰ for precipitation, during the summer months. Aerosol methanesulphonate shows a clear summer peak with values up to 3-4 nmol m-3. Assuming samples contained only sulphur from terrestrial/anthropogenic, sea salt, and marine biogenic (from the oxidation of dimethylsulphide) sources, we used the sulphur isotope values to determine the contribution of dimethylsulphide-derived sulphate to total sulphate. In general the biogenic contribution was small, < 10%, although in samples from marine air masses it was as high as 40%. A comparison of aerosol and precipitation δ34S values found no evidence for large isotopic fractionations during the oxidation of sulphur dioxide.

### Particle counting and numerical models: Effect of instrumental size resolution and particle shapes o

 Date added: 08/05/2006 Date modified: 08/05/2009 Filesize: 245.54 kB

Karine Chamaillard, S.G. Jennings, Particle counting and numerical models: Effect of instrumental size resolution and particle shapes on optical cross-sections, Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 100, Issues 1-3, VIII Conference on Electromagnetic and Light Scattering by Nonspherical Particles, July-August 2006, Pages 64-76, ISSN 0022-4073, DOI: 10.1016/j.jqsrt.2005.11.064.

Abstract

The effect of instrumental size resolution measurements on numerical calculations of optical cross-sections is investigated. The particle counting instruments considered are a FSSP-300, a large scattering angle probe instrument similar to a ASASP-X, and, an aerodynamical system ELPI instrument. The scattering and hemispheric backscattering cross-sections, Csca and Cbk, are calculated on the basis that the full width of the instrumental size bin should be considered in modeling. An average process is applied on these quantities over the full size bin of the instrument; they are then compared to their usual estimation on the single mean diameter Dp per channel. The effect of particle shape is investigated with ellipsoids and spheres. Results show sensitivity of the optical cross-sections to the shape of the particles as well as position of the mean geometrical diameter Dp of the channels within the interferences modes of the scattering efficiencies. The value of the width of the size bins, d log D, of each channel is crucial in the results. This comparison gives a useful estimation of error important in optical particle counting instruments based on inversion process of optical quantities. In addition, accuracy of size distribution measurements is found not to be representative of accuracy in the calculations of optical cross-sections.

### Behavior of ultrafine particles in continental and marine air masses at a rural site in the Uni

 Date added: 08/06/2000 Date modified: 07/09/2009 Filesize: 1.44 MB

Coe H., P. I. Williams, G. McFiggans, M. W. Gallagher, K. M. Beswick, K. N. Bower and T. W. Choularton Behavior of ultrafine particles in continental and marine air masses at a rural site in the United Kingdom. J. Geophys. Res., 105, 26891-26905, 2000

Abstract

Particle size distribution measurements were made at a coastal site in the United Kingdom. These are presented, and the behavior of recently formed ultrafine particles is discussed. No ultrafine particles were observed in maritime air masses; however, 3 to 7 nm particles were frequently observed at enhanced concentrations when the wind direction was from the land. Their formation was favored at lower temperatures, when 1 ppbv or more of SO2 was present and in air masses that had not been aged extensively. On days when enhanced ultrafine particle concentrations were observed, 3 nm particles increased sharply in the morning, approximately 30 to 90 min after the UV solar flux first increased. By early afternoon the ultrafine particle concentration had returned to background levels. Rapid measurements of 5 nm particles showed no correlation with turbulence parameters, although the boundary layer mixing scales were similar to growth times of freshly nucleated particles to 5 nm diameter. However, ultrafine particle concentrations do correlate with the availability of sulphuric acid vapor. A delay of approximately an hour between the increase of H2SO4 in the morning and a large increase in ultrafine particle concentrations is due to the growth of particles to observable sizes, not the nucleation process itself. An analysis of the timescales for growth showed that coagulation may be important immediately after the particles have nucleated but its effectiveness reduces as number concentration falls. Conversely, growth by condensation is initially slow due to the Kelvin effect but increases in importance as the particles reach observable sizes.

 Date added: 08/07/2003 Date modified: 07/23/2009 Filesize: 34.15 kB
Fleming, Z.L.; Monks, P.S.; Rickard, A.R.; Heard, D.E.; Stills, T; Sommariva, R; Brough, N; Penkett, S.A.; Lewis, A.C.; Lee, J.D.Peroxy radical formation at Mace Head during NAMBLEX [EGU04-A-04097].

Abstract

Analysis of peroxy radical (HO$_2$ + $\Sigma$RO$_2$) data taken using the dual inlet Leicester/UEA PEroxy Radical Chemical Amplification (PERCA) instrument during the North Atlantic Marine Boundary Layer Experiment (NAMBLEX 2002) at the Mace Head Atmospheric Research Station in county Galway, on the west coast of Ireland will be presented.
Photolysis rate coefficients of a variety of compounds (including ozone, formaldehyde and nitrous acid), measured using a spectral radiometer were seen to explain to a large extent the shape of the diurnal variation in the peroxy radicals. In the evening, (after the ozone photolysis is no longer significant) on many days there was still a large amount of radical production appearing to come from formaldehyde photolysis. On a minute timescale, NO$\rm _x$ is shown to suppress radical production but for the averaged peroxy radicals versus NO$\rm _x$ the relationship in daylight hours

there is a maximum in radical production at a NO$\rm _x$ level of just less than 0.5 ppbv and a marked shape to these plots. At nighttime, evidence for an increase in radical production with increasing NO$\rm _x$ shows that NO$_3$ chemistry is a contributor to radical production. Net photochemical ozone production and destruction rates were calculated using amongst other measurements, the peroxy radical data and showed that there were few periods during daylight hours when more ozone was destroyed than produced. In general there was usually a small overall production of ozone. The highest ozone producing periods were when the radical concentrations were high and the NO$\rm _x$ relatively low. HO2 data was compared with total peroxy radical data to examine the ratios of organic to hydrogen peroxy radicals. As the NO$\rm _x$ concentration increased, the proportion of HO$_2$ increased. Examining the contribution of a variety of VOCs to radical production (via their reaction with OH) may explain the variation in
the HO$_2$ : RO$_2$ ratio.

### Observation of diurnal cycles in short-lived tropospheric alkenes at a North Atlantic coastal s

 Date added: 08/05/1999 Date modified: 07/22/2009 Filesize: 210.82 kB

A. C. Lewis, J. B. McQuaid, N. Carslaw, M. J. Pilling, Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site, Atmospheric EnvironmentVolume 33, Issue 15, , 1 July 1999, Pages 2417-2422.

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.

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