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

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Documents

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

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

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


Abstract


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

The relative Importance of sea-salt and nss-sulphate aerosol to the marine CCN Population The relative Importance of sea-salt and nss-sulphate aerosol to the marine CCN Population

Date added: 08/06/1999
Date modified: 07/08/2009
Filesize: 9.2 MB

O'Dowd, C.D., J. Lowe, M.H. Smith and A.D. Kaye, The relative importance of sea-salt and nss-sulphate aerosol to the marine CCN population: An improved multi-component aerosol-droplet parameterisation. Q. J. Roy. Met. Soc., 125, 1295-1313. 1999


Abstract


The effect of sub-cloud aerosol on cloud droplet concentration was explored over the north Atlantic and east Pacific under a variety of low and high wind speed conditions. A relationship of the form of D = 197(1-exp(-6.13 × 10-3 * A)] was found to fit best the relationship between cloud droplet concentration (D; cm-3) and sub-cloud aerosol concentration (A; cm-3) under low to moderate wind conditions. A few noticeable deviations from this relationship were observed which occurred under moderate to high wind speed condition. Under these high wind conditions, sea-salt aerosol provided the primary source of cloud nuclei due to their higher nucleation activity and larger sizes, even under sulphate-rich conditions. Simple model simulations reveal that the activation of sea-salt nuclei suppresses the peak supersaturation reached in cloud, and thus inhibits the activation of smaller sulphate nuclei into cloud droplets. A multi-component aerosol-droplet parametrization for use in general circulation models is developed to allow prediction of cloud droplet concentration as a function of sea-salt and non-sea-salt-(nss) sulphate nuclei. The effects of enhancing an existing nss-sulphate cloud condensation nuclei (CCN) population with sea-salt nuclei are to reduce the number of cloud droplets activated under high (polluted) sulphate conditions and to increase the cloud droplet concentration under low (clean) sulphate conditions. The presence of sea-salt CCN reduces the influence of nss-sulphate CCN on cloud droplet concentrations, and thus is likely to reduce the predicted effect of nss-sulphate indirect radiative forcing.

 

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.

 

Aerosol dynamics in ship tracks Aerosol dynamics in ship tracks

Date added: 08/06/1999
Date modified: 07/23/2009
Filesize: 1.65 MB

Russell, L. M. ; Seinfeld, J. H. ; Flagan, R. C. ; Ferek, R. J. ; Hegg, D. A. ; Hobbs, P. V. ;  Wobrock, W. ;  Flossmann, A. I. ; O'Dowd, C. D. ; Nielsen, K. E. ; Durkee, P. A.  1999 Aerosol dynamics in ship tracks J. Geophys. Res. Vol. 104 , No. D24 , p. 31,077-31096 DOI 10.1029/1999JD900985


Abstract

 

Ship tracks are a natural laboratory to isolate the effect of anthropogenic aerosol emissions on cloud properties. The Monterey Area Ship Tracks (MAST) experiment in the Pacific Ocean west of Monterey, California, in June 1994, provides an unprecedented data set for evaluating our understanding of the formation and persistence of the anomalous cloud features that characterize ship tracks. The data set includes conditions in which the marine boundary layer is both clean and continentally influenced. Two case studies during the MAST experiment are examined with a detailed aerosol microphysical model that considers an external mixture of independent particle populations. The model allows tracking individual particles through condensational and coagulational growth to identify the source of cloud condensation nuclei (CCN). In addition, a cloud microphysics model was employed to study specific effects of precipitation. Predictions and observations reveal important differences between clean (particle concentrations below 150 cm-3) and continentally influenced (particle concentrations above 400 cm-3) background conditions: in the continentally influenced conditions there is a smaller change in the cloud effective radius, drop number and liquid water content in the ship track relative to the background than in the clean marine case. Predictions of changes in cloud droplet number concentrations and effective radii are consistent with observations although there is significant uncertainty in the absolute concentrations due to a lack of measurements of the plume dilution. Gas-to-particle conversion of sulfur species produced by the combustion of ship fuel is predicted to be important in supplying soluble aerosol mass to combustion-generated particles, so as to render them available as CCN. Studies of the impact of these changes on the cloud's potential to precipitate concluded that more complex dynamical processes must be represented to allow sufficiently long drop activations for drizzle droplets to form.

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

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

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


Abstract


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

 

Modelling OH, HO2, and RO2 radicals in the marine boundary layer 2. Mechanism reduction and unce Modelling OH, HO2, and RO2 radicals in the marine boundary layer 2. Mechanism reduction and unce

Date added: 08/06/1999
Date modified: 07/23/2009
Filesize: 1.21 MB

Carslaw N., P.J. Jacobs, and M.J. Pilling (1999), Modelling OH, HO2 and RO2 radicals in the marine boundary layer: 2. Mechanism reduction and uncertainty analysis, J. Geophys. Res., 104, 30257-30273.


Abstract


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

 

An analysis of rapid increases in condensation nuclei concentrations at a remote coastal site i An analysis of rapid increases in condensation nuclei concentrations at a remote coastal site i

Date added: 08/06/1999
Date modified: 07/27/2009
Filesize: 885.01 kB

Grenfell, J.L., R.M. Harrison, A.G. Allen, J.P. Shi, S.A. Penkett, C.D. O'Dowd, M.H. Smith, M.K. Hill, L. Robertson, C.N. Hewitt, B. Davison, A.C. Lewis, D.J. Creasey, D.E. Heard, K. Hebestreit, B. Alicke and J. James, An analysis of rapid increases in condensation nuclei concentrations at a remote site on the West Irish Coast, J. Geophys.Res., 104, 13,771-13,780, 1999, (Ser. No. ACP073).


Abstract


Massive bursts in condensation nuclei (CN) concentration were recorded at a remote site on the west Irish coast during campaigns in summer 1996 and spring/summer 1997. Number concentrations of 3-7 nm diameter CN were observed to rise daily from 102-103 up to ∼105 /cm3 for 1-3 hours. Data were collected as part of the Atmospheric Chemistry Studies in the Oceanic Environment program. In a previous paper the burst phenomenon was linked to the movement of the tide, and it was suggested that enhanced biogenic emissions occurred near low tide with concomitant rapid homogeneous gas phase CN formation. In this paper possible chemical mechanisms for the burst phenomenon are investigated. Two approaches are adopted. First, by assuming a 20:80 sulfate:water molar composition and calculating the number distribution using data from condensation particle counters, the total mass of CN formed during a burst is evaluated. This is compared with that mass of sulfate produced by OH-initiated dimethyl sulfide (DMS) oxidation. The procedure is termed mass balance. Second, a variety of chemical species are coplotted with tidal height. DMS oxidation is not believed to play a major role in CN formation at this site because (1) the mass balance calculations imply ambient DMS concentrations higher than those observed, and (2) gas phase HCI, HNO3. SO2, and NH3 did not exhibit any discernible correlation with tidal height. Further, none of the suite of observed nonmethane hydrocarbons or DMS showed a tidal relation. No mechanism has to date been convincingly identified for the burst phenomenon.

 

Short-lived alkyl iodides and bromides at Mace Head, Ireland Links to biogenic sources and halo Short-lived alkyl iodides and bromides at Mace Head, Ireland Links to biogenic sources and halo

Date added: 08/05/1999
Date modified: 07/23/2009
Filesize: 944.76 kB

Carpenter, L., Hebestreit, K., Sturges, W., Penkett, S., Liss, P., Alicke, B., and Platt, U.: Observation of short-lived alkyl iodides and bromides at Mace Head, Ireland: links to biogenic sources and halogen oxide production, J. Geophys. Res., 104, 1679–1689, 1999. 6080, 6108


Abstract


Automated in situ gas chromatograph/mass spectrometer (GC/MS) measurements of a range of predominantly biogenic alkyl halides in air, including CHBr3, CHBr2Cl, CH3Br, C2H5Br, CH3I, C2H5I, CH2ICl, CH2I2, and the hitherto unreported CH2IBr were made at Mace Head during a 3-week period in May 1997. C3H7I and CH3CHICH3 were monitored but not detected. Positive correlations were observed between the polyhalomethane pairs CHBr3/CHBr2Cl and CHBr3/CH2IBr and between the monohalomethane pair CH3I/C2H5I, which are interpreted in terms of common or linked marine sources. During periods when air masses were affected by emissions from local seaweed beds, the concentrations of CHBr3, CH2ICl, and CH2IBr not only showed remarkable correlation but also maximized at low water. These are the first field observations to provide evidence for a link between the tidal cycle, polyhalomethanes in air, and potential marine production. The calculated total flux of iodine atoms into the boundary layer at Mace Head from organic gaseous precursors was dominated by photolytic destruction of CH2I2. Photolysis of CH3I contributed less than 3%. The calculated peak flux of iodine atoms during the campaign coincided with the highest measured levels of iodine oxide radicals, as determined using Differential Optical Absorption Spectrometry (DOAS).

 

On the photochemical production of biogenic new particles in the coastal boundary layer On the photochemical production of biogenic new particles in the coastal boundary layer

Date added: 08/05/1999
Date modified: 08/05/2008
Filesize: 4.86 MB
O'Dowd, C.D., G. McFiggans, D.J. Creasey, L. Pirjola, C. Hoell, M.H. Smith, B.J. Allan, J.M.C. Plane, D.E. Heard, J.D. Lee, M.J. Pilling, and M. Kulmala, On the photochemical production of biogenic new particles in the coastal boundary layer, Geophys. Res. Lett., 26, 1707-1710, 1999, (Ser. No. ACP072).

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

 

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

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

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


Abstract


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

 

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

 

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

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

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


Abstract


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

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

Measurements of fractionated gaseous mercury concentrations over northwestern and central Europ Measurements of fractionated gaseous mercury concentrations over northwestern and central Europ

Date added: 08/05/1999
Date modified: 07/23/2009
Filesize: 215.76 kB
Sommar, J., Feng, X., Gardfeldt, K. and Lindqvist, O., 1999. Measurements of fractionated gaseous mercury concentrations in northwestern and central Europe, 1995–99. Journal of Environmental Monitoring 1, pp. 435–439.

Abstract


Although it makes up only a few per cent. of total gaseous mercury (TGM) in the atmosphere, the fraction of xidised (divalent) mercury plays a major role in the biogeochemical cycle of mercury due to its high affinity for water and surfaces. Quantitative knowledge of this fraction present in mixing ratios in the parts-per-1015 (ppq) range is currently very scarce. This work is based on #220 data for divalent gaseous mercury (DGM) collected during 1995–99 in ambient air. Over the course of the measurements, the sampling and analytical methods were modified and improved. This is described here in detail and includes transition from wet leaching and reduction procedures to thermo-reductive desorption, the use of annular as well as tubular denuders and adoption of an automated sampling system. The concentration of DGM exhibited a strong seasonal behaviour in contrast to atomic gaseous mercury, with low values in winter and maximum values in summer. The DGM/TGM ratios were frequently found to be below the detection limit (1%) and in the range 1–5%. A trend of diurnal DGM patterns was observed and implies photolytically induced sources. Scavenging of DGM during rain events was also noticed.

 

Intercomparison of measurement methods for black carbon aerosols Intercomparison of measurement methods for black carbon aerosols

Date added: 08/01/1999
Date modified: 07/02/2009
Filesize: 201.1 kB

Hitzenberger, R., Jennings, S.G., Larson, S.M., Dillner, A., Cachier, H., Galambos, Z., Rouc, A. and Spain, T.G. (1999). Intercomparison of measurement methods for black carbon aerosols. Atmos. Environ., 33, 2823-2833.


Abstract


In this study, two method intercomparisons were performed. One thermal and two optical methods for the measurement of black carbon (BC) were applied to laboratory generated aerosols containing only BC. For the optical measurements, an aethalometer (Hansen et al., 1984. Science of Total Environment 36, 191-196) and an integrating sphere technique (Hitzenberger et al., 1996b. Journal of Geophysical Research 101, D14, 19&unknown;601-19&unknown;606) were used. The thermal method was described by Cachier et al. (1989a. Tellus 41B, 379-390). In an additional comparison, the integrating sphere was compared to a thermal optical technique (Birch and Cary, 1996. Aerosol Science Technology 25, 221-241) on ambient aerosol samples. The absorption coefficients were obtained from transmission measurements on filter samples for both the aethalometer and the integrating sphere. The BC mass concentration for the aethalometer was derived from this absorption measurement. The BC mass concentration for the integrating sphere, however, was obtained using an independent calibration curve. The agreement between the absorption coefficient sigmaa obtained for the BC test aerosol on parallel filters with the aethalometer and the integrating sphere was satisfactory. The slope of the regression lines depended on filter type. A comparison between BC mass concentrations, however, showed that the aethalometer values were only 23% of those obtained by the integrating sphere technique indicating that for pure BC aerosols, the standard aethalometer calibration should not be used. Compared to the thermal method, the integrating sphere gave an overestimation of the BC mass concentrations by 21%. For the ambient samples, the integrating sphere and the thermal optical methods for BC mass concentration determination showed agreement within 5% of the 1:1 line, although the data were not so well correlated.

Mace Head Atmospheric Research Station IGActivities Mace Head Atmospheric Research Station IGActivities

Date added: 07/31/1999
Date modified: 07/24/2009
Filesize: 59.08 kB
Jennings, S.G., 1999. Mace Head Atmospheric Research Station. IGACtivities, No. 18, 14-17.

Abstract

 


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

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

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

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

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


Abstract


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

Variations of CN number concentrations with respect to meteorological conditions at Mace Head, Variations of CN number concentrations with respect to meteorological conditions at Mace Head,

Date added: 08/07/1998
Date modified: 07/23/2009
Filesize: 56.9 kB

Kleefeld C.; Geever M.; Jennings S.G.; Maring H.,Variations of CN number concentrations with respect to meteorological conditions at mace head, Ireland,Journal of Aerosol Science, Volume 29, Supplement 1, September 1998 , pp. 203-203(1)


The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baselin The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baselin

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Derwent, RG, Simmonds, PG, O'Doherty, S, et al , The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baseline and European air masses at Mace Head, Ireland over a ten year period from 1987-1996, ATMOS ENVIRON, 1998, Vol: 32, Pages: 3689 - 3702,


Abstract


The international concern following the discovery of Antarctic stratospheric ozone depletion has prompted unprecedented international action by governments to control the production, sales and usage of a range of ozone-depleting chemicals. These international treaty obligations include the Montreal Protocol and its London and Copenhagen Amendments. They address, amongst many halocarbon species, the chlorofluorocarbons: CFC-11, -12 and -113 and the chlorocarbons: carbon tetrachloride and methyl chloroform. These chemicals have been routinely monitored at the remote, baseline monitoring station at Mace Head on the Atlantic Ocean coast of Ireland as part of the GAGE/AGAGE programme. The available monitoring data for the period 1987-1996 are presented here with a view to confirming the extent of compliance with the above Protocols on a global and European basis. Daily wind direction sectors provided by EMEP are used to sort the halocarbon data into northern hemisphere baseline air and European polluted air masses and trends have been determined for each wind direction sector. Evidence of the European phase-out of halocarbon usage is clearly apparent in the sorted halocarbon concentrations. A simple climatological long-range transport and a sophisticated Lagrangian air parcel dispersion model have been used to interpret the Mace Head halocarbon measurements and to derive estimates of European emission source strengths for each year. These emission source strengths confirm that the phase-out of halocarbon manufacture and sales is being followed in Europe.

 

Observation and interpretation of the seasonal cycles in the surface concentrations of ozone an Observation and interpretation of the seasonal cycles in the surface concentrations of ozone an

Date added: 08/07/1998
Date modified: 07/23/2009
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Derwent, RG, Simmonds, PG, Seuring, S, et al , Observation and interpretation of the seasonal cycles in the surface concentrations of ozone and carbon monoxide at Mace Head, Ireland from 1990 to 1994, ATMOS ENVIRON, 1998, Vol: 32, Pages: 145 - 157, ISSN: 1352-2310


Abstract


In this study, three independent methods have been applied to the sorting of the daily and hourly mean concentrations of ozone and carbon monoxide measured at Mace Head, Ireland. From the entire 1990-1994 dataset, 61% of the hourly data points have been assigned to Northern Hemisphere mid-latitude background air. The mean ozone and carbon monoxide concentrations in these air masses have been estimated as 35±4.3 and 125±27 ppb, respectively. We have characterised the seasonal variations of ozone and carbon monoxide in these air masses and found them to exhibit spring-time maxima and summer-time minima in monthly mean concentrations. Similar seasonal cycles have been found in the monthly mean concentrations of a number of trace gases in Northern Hemisphere mid-latitude background air at Mace Head, in addition to ozone and carbon monoxide. The occurrence of spring-time maxima is not unique to ozone and spring-time maxima are observed for many trace gases whether or not they have stratospheric sources.

 

European source strengths and Northern Hemisphere baseline concentrations of radiatively active European source strengths and Northern Hemisphere baseline concentrations of radiatively active

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Derwent, RG, Simmonds, PG, O'Doherty, S, et al , European source strengths and northern hemisphere baseline concentrations of radiatively active trace gases at Mace Head, Ireland, ATMOS ENVIRON, 1998, Vol: 32, Pages: 3703 - 3715, ISSN: 1352-2310


Abstract


Greenhouse gas measurements have been made continuously with high frequency and precision at the remote baseline monitoring station at Mace Head on the Atlantic Ocean coastline of Ireland since 1987. By using three independent methods, the two-hourly observations have been sorted by air mass origins into those from unpolluted' or Northern Hemisphere baseline air masses and those from polluted European air masses. Northern Hemisphere baseline methane, nitrous oxide and carbon dioxide concentrations have risen throughout the 10 year period and their respective mid-1996 levels are the highest mid-year levels recorded so far. For ozone, the mid-1996 annual mean concentrations was within 0.1 ppb of the highest mid-year level. The elevated greenhouse gas concentrations found in polluted air masses provide clear evidence for the presence of substantial emission sources in Europe. Using a simple climatological long-range transport model and a sophisticated Lagrangian dispersion model, it has been possible to estimate the magnitudes of the greenhouse gas emissions required to support the observations. Estimates of European source strengths of methane, nitrous oxide, carbon monoxide and halocarbons agree well with the available emission inventories. Using the Mace Head observations, significant additional contributions to global climate change have been identified from the trace gases: methane, nitrous oxide and tropospheric ozone, over and above that driven by carbon dioxide. The radiative forcing consequences of a range of HCFCs and HFCs will only become of significance should their emissions grow to become comparable with those of the CFCs that they have replaced.

 

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
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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

Atmospheric carbon dioxide and its stable isotope ratios, methane, carbon monoxide, nitrous oxi Atmospheric carbon dioxide and its stable isotope ratios, methane, carbon monoxide, nitrous oxi

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Francey, R.J., L.P. Steele, R.L. Langenfelds, C.E. Allison, L.N. Cooper, B.L. Dunse, B.G. Bell, T.D. Murray, H.S. Tait, L. Thompson and K.A. Masarie, Atmospheric carbon dioxide and its stable isotope ratios, methane, carbon monoxide and hydrogen from Shetland Isles, Atmos. Environ., Vol. 32, No. 19, 3331-3338, 1998.


Abstract


Since November 1992, 0.5l glass flasks have been filled approximately monthly with dry marine air from Shetland Isles, Scotland (60.2oN, 1.2oW) and transported to CSIRO, Australia for analyses. The Shetland site is part of a CSIRO global flask network with 10-12 sites, anchored to continuous high precision in situ measurements made at the Australian Cape Grim Baseline Station (40.7oS, 144.7oE), a primary station in the Global Atmosphere Watch programme (GAW) coordinated by the World Meteorological Organisation. The methodology is summarised, and Shetland results for CO2, CH4, N2O, CO, H2 and delta13C, delta18O of CO2 presented for the period 1992-1996. We compare data to available results from surrounding stations of the NOAA cooperative network (in particular Mace Head, Ireland, 53.3oN, 9.9oW), and address issues of both trace species intercalibration and atmospheric spatial gradients. While considerable uniformity of trace-gas composition is evident in oceanic air over a 13o range of latitude, nevertheless anomalies in CO2 concentration and isotopic composition are suggested in samples representing air to the west of Shetland. The potential for remotely monitoring integrated emissions from northern Europe is also identified.

 

The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications f The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications f

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Bassford, M.R., G. Nickless, P.G. Simmonds, A.C. Lewis, M.J. Pilling, and M.J. Evans, The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications for sources of atmospheric methyl iodide, Atmospheric Environment, 33 (15), 2373-2383, 1999.


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 significant 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 flow has elucidated part of the global methyl iodide cycle and provides evidence for two distinct source regions of methyl iodide: I. 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 30-50°N and 20-50°W. 2. Measurements taken under different conditions led us to believe that there was an additional source of methyl iodide that influenced the Mace Head atmosphere, most likely produced by coastal macroalgae which inhabit waters off the western coast of Ireland.

 

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

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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.

 

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

Date added: 08/06/1998
Date modified: 07/24/2009
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B. G. Doddridge, R. Morales-Morales, K. P. Rhoads, J. T. Merrill, P. C. Novelli, R. R. Dickerson, V. S. Connors, and H. G. Reichle, Jr., “Ground-based and airborne observations of carbon monoxide during NASA Measurements of Air Pollution from Satellites (MAPS) missions SRL-1 and SRL-2,” J. Geophys. Res. 103, 19305–19316 (1998).


Abstract


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

 

Comparison of 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.

 

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

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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.

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

Date added: 08/06/1998
Date modified: 07/23/2009
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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.

 

Sub-ppt Atmospheric Measurements Using PTV-GC-FID and realtime Digital Signal Processing Sub-ppt Atmospheric Measurements Using PTV-GC-FID and realtime Digital Signal Processing

Date added: 08/05/1998
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J.B McQuaid, A.C Lewis and K.D Bartle. , Sub-ppt Atmospheric Measurements Using PTV-GC-FID and Real-Time Digital Signal Processing., Journal of High Resolution Chromatography:


Abstract


Automated on-line trace level measurements in the atmosphere have become possible over the past ten years due to developments in large volume injection technology and the increased availability of  non-cryogenic cooling devices using phenomena such as the Peltier effect. The analysis of hydrocarbon (HC) species in the atmosphere is a particularly challenging area where individual
ambient concentrations as low as 1 ppt may be encountered in clean tropical marine air. From measurements of hydrocarbon species taken in clean air it has been demonstrated that small but significant concentrations of some species remain constantly present. The presence of certain reactive alkene species even at levels below 5 ppt may have a significant impact on the oxidative capacity ofthe clean atmosphere. Whilst halogenated species have been routinely measured on-line at sub-ppt levels for several years, the analysis of HC species has been limited by the flame ionisation detector - the most popular detector for field measurements. The limiting parameter in using FID for trace determination is often the noise generated within the FID amplifier electronics rather than by the absolute detection limit of the FID itself.  The flame ionisation detector amplifier uses a high gain transimpedance stage which has three main sources of noise. The feedback resistor generates both Johnson and Shot noise. This noise passes through the output without amplification as the voltage gain of a transimpedance amplifier is essentially unity over the bandwidth of interest. The third source of noise is due to current noise generated within the amplifier input stages. This noise is subsequently amplified along with the signal. Determinations at very low concentrations using automatic peak height or area integration prove difficult to perform with reliability due to a combination of poor signal to noise and transient detector spikes. By increasing data acquisition sampling rates coupled to the application of a digital signal processing algorithm, the electrometer output can be bandwidth limited to a frequency which allows peak information to be accurately represented whilst substantially reducing noise of higher frequencies. The roll off rate of a digital filter is much greater than can be achieved using an analogue filter. A rejection of greater than 150 dB can be achieved with a pass band to stop band delta of a fraction of 1 Hz. The benefit of this is that chromatographic resolution and efficiency are not affected by the process, i.e. the peaks are not broadened. This communication reports a digital signal processing (DSP) unit tested in parallel to standard data capture system coupled to an automated trace analysis field GC instrument. The basic principle of DSP is to convert a dynamic analogue signal into discrete values by sampling at certain intervals, followed by the application of mathematical filter algorithms to remove any interference or noise that may be obscuring the desired signal. Once processed, the discrete signal may then be converted back to analogue if necessary. Comparison of data from both systems demonstrates a large enhancement in minimum detectable amount and improved integration reliability. Use of a DSP unit has resulted in a lowering of detection limits to allow automated sub-ppt measurements to be performed. Comparison of trace level analysis has shown that raw FID output logged straight to PC leads to a consistent overestimation of peak height of the order of 25% at low signal to noise levels. Post processing of chromatograms using enhancement in digital gain has also been performed. This has demonstrated that a significant amount of noise remaining following on-line processing is induced at the analogue input stage to PC data capture system.

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
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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.


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

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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%.

 

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

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

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


Abstract


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

Wet properties affecting Atmospheric Aerosols Wet properties affecting Atmospheric Aerosols

Date added: 08/01/1998
Date modified: 07/10/2009
Filesize: 6.2 MB
Jennings. S.G, Wet properties affecting Atmospheric Aerosols, 1998, Atmospheric Particles, Pg 476-502, Wiley & Sons

Abstract

 

The origin of atmospheric particles can be either anthropogenic (man-made) or natural. Primary particles are those which are emitted into the atmosphere as particles such as black carbon and organic particles in smoke plumes, soil dust particles, sea spray and volcanic particles, etc Secondary particles are formed from gas-to-particle coversion processes in the atmosphere- such as sulphates(from SO2), Nitreates (from (NOx) and secondary organics (from gaseous hydro-carbons)

Wet properties affecting Atmospheric Aerosols Wet properties affecting Atmospheric Aerosols

Date added: 08/01/1998
Date modified: 09/11/2009
Filesize: 6.2 MB
Jennings. S.G, Wet properties affecting Atmospheric Aerosols, 1998, Atmospheric Particles, Pg 476-502, Wiley & Sons

Abstract

 

The origin of atmospheric particles can be either anthropogenic (man-made) or natural. Primary particles are those which are emitted into the atmosphere as particles such as black carbon and organic particles in smoke plumes, soil dust particles, sea spray and volcanic particles, etc Secondary particles are formed from gas-to-particle coversion processes in the atmosphere- such as sulphates(from SO2), Nitreates (from (NOx) and secondary organics (from gaseous hydro-carbons)

PM10 Concentration Measurements In Dublin City PM10 Concentration Measurements In Dublin City

Date added: 07/31/1998
Date modified: 07/03/2009
Filesize: 4.08 MB

Jennings, S.G. (1998). How dirty is Dublin air? Technology Ireland, 30, 40-43.


Abstract


Mass concentration of ambient particulate matter with an aerodynamic diameter less than 10μm (PM10) are reported for the first time for a range of sites in Dublin City over a 6 month period from January 1st 1996 to June 30th 1996. PM10 gravimetric mass concentration measurements are made with low flow Partisol 2000 air samplers using an impaction type PM10 inlet and 47mm diameter glass fibre filters. In addition, much finer time resolution measurements (minimum sampling frequency of 30 minutes) are made using a tapered element oscillating microbalance (TEOM) PM10 mass monitor. These PM10 mass concentrations methods are also compared with mass concentration inferred using the standard black smoke method. Analysis of the ambient mass concentration data with reference to traffic density and meteorological influences are presented. Results for the first six months of 1996 show that the average PM10 values range from a high of 49 μg/m3 at the Dublin city centre site to 14 μg/m3 at one of the suburban sites. Intercomparison between PM10 and black smoke mass concentrations show that the relationship is site specific. Statistical analysis between PM10 levels and car traffic number show a positive correlation while a weak negative correlation is found between PM10 levels and rainfall amount, wind speed and air temperature.

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

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

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


Abstract


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

A graphical method for determining the dry-depositional component of aerosol samples and their A graphical method for determining the dry-depositional component of aerosol samples and their

Date added: 08/07/1997
Date modified: 07/27/2009
Filesize: 907.95 kB

Huang, S., K. Rahn, and R. Arimoto. 1997. A graphical method for determining the dry-depositional component of aerosol samples and their field blanks. Atmospheric Environment 31:3383-3394.


Abstract


During the Atmosphere/Ocean Chemistry Experiment (AEROCE), field blanks of certain elements in aerosol samples occasionally increased abruptly, always during periods of unusually high atmospheric concentrations. We hypothesized that the anomalous blanks were created by coarse aerosol entering the sampling shelters and depositing onto the blank filters. If so, samples taken nearby should have been similarly affected. To test this hypothesis, we developed a simple graphical method in which elemental masses in field blanks are plotted against elemental masses in pumped samples, and zones of proportionality between the two are sought. Data from Bermuda and Mace Head (coastal western Ireland) confirmed that depositional zones did indeed appear, but only for coarse-particle elements and only under certain conditions. Actual increases of crustal and pollution-derived elements agreed well with values predicted from settling velocities and sampling rates: blanks increased up to an order of magnitude or more but samples by less than 1%. Marine elements behaved like crustal elements in most samples but occasionally were much more enriched: blanks increased up to 30-fold and samples up to about 3%. It thus appears that when coarse-particle elements are present in high concentrations, their field blanks and samples may be measurably affected by dry deposition. Depending on the elements of interest, this dry deposition may have to be measured and the concentrations corrected.

 

Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at

Date added: 08/07/1997
Date modified: 07/23/2009
Filesize: 252.17 kB

Simmonds, PG, Seuring, S, Nickless, G, et al , Segregation and interpretation of ozone and carbon monoxide measurements by air mass origin at the TOR Station Mace Head, Ireland from 1987 to 1995, J ATMOS CHEM, 1997, Vol: 28, Pages: 45 - 59, ISSN: 0167-7764


Abstract


Three independent methods have been used to sort the ozone, carbon monoxide, and other radiatively important trace gases measured at Mace Head, Ireland, and thereby distinguish clean air masses transported over the North Atlantic from the more polluted air masses which have recently travelled from the European continent. Over the period April 1987-June 1995 the Northern Hemisphere surface ozone baseline concentrations exhibited a mean concentration of 34.8 ppb, with a small positive trend (+0.19 ppb yr-1), while the corresponding trend in air originating from the polluted European areas was negative (-0.39 ppb yr-1). Carbon monoxide measurements from March 1990 to December 1994 showed negative trends for both the unpolluted (-0.17 ppb yr-1) and polluted data (-13.6 ppb yr-1). Overall the continent of Europe was shown to be a small net sink of 2.6 ppb for all occasions when European air was transported to the North Atlantic.

 

Modeling sea-salt aerosols in the atmosphere 1. Model development Modeling sea-salt aerosols in the atmosphere 1. Model development

Date added: 08/06/1997
Date modified: 07/23/2009
Filesize: 1.25 MB

Gong, S. L., L. A. Barrie, and J.-P. Blanchet (1997), Modeling sea-salt aerosols in the atmosphere 1. Model development, J. Geophys. Res., 102(D3), 3805–3818.


Abstract


A simulation of the processes of sea-salt aerosol generation, diffusive transport, transformation, and removal as a function of particle size is incorporated into a one-dimensional version of the Canadian general climate model (GCMII). This model was then run in the North Atlantic between Iceland and Ireland during the period of January-March. Model predictions are compared to observations of sea-salt aerosols selected from a review of available studies that were subjected to strict screening criteria to ensure their representativeness. The number and mass size distribution and the wind dependency of total sea-salt aerosol mass concentrations predicted by the model compare well with observations. The modeled dependence of sea-salt aerosol concentration in the surface layer (χ, μg m−3) on 10-m wind speed (U 10, m s−1) is given by χ = beaU10 . Simulations show that both a and b change with location. The value a and b range from 0.20 and 3.1 for Mace Head, Ireland to 0.26, and 1.4 for Heimaey, Iceland. The dependence of χ on surface wind speed is weaker for smaller particles and for particles at higher altitudes. The residence time of sea-salt aerosols in the first atmospheric layer (0–166 m) ranges from 30 min for large particles (r = 4–8 μm) to ∼60 hours for small particles (r = 0.13–0.25 μm). Although some refinements are required for the model, it forms the basis for comparing the simulations with long-term atmospheric sea-salt measurements made at marine baseline observatories around the world and for a more comprehensive three-dimensional modeling of atmospheric sea-salt aerosols.

 

Marine aerosol, sea-salt, and the marine sulphur cycle a short review Marine aerosol, sea-salt, and the marine sulphur cycle a short review

Date added: 08/06/1997
Date modified: 07/02/2009
Filesize: 701.66 kB

O'Dowd, C. D., Lowe, J. A. & Smith, M. H. Marine aerosol, sea-salt, and the marine sulphur cycle: A short review. Atmos. Environ. 31, 73−80 (1997)


Abstract


A short review of the marine aerosol size distribution and the contribution of sea-salt to this distribution is presented. The potential role of sea salt in the marine boundary layer sulphur cycle is highlighted.

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

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

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


Abstract


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

 

A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southe A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southe

Date added: 08/06/1997
Date modified: 07/27/2009
Filesize: 1.01 MB

Carpenter, L. J., P. S. Monks, B. J. Bandy, S. A. Penkett, I. E. Galbally, and C. P. (. Meyer (1997), A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southern hemispheres, J. Geophys. Res., 102(D21), 25,417–25,427.


Abstract


Peroxy radicals and other important species relevant to ozone photochemistry, including ozone, its photolysis rate coefficient jO(1 D), NOx (NO + NO2), and peroxides, were measured at the coastal sites of Cape Grim, Tasmania, in January/February 1995 during the Southern Ocean Atmospheric Photochemistry Experiment (SOAPEX 1) and Mace Head, Western Ireland, in May 1995 during the Atlantic Atmospheric Photochemistry Experiment (ATAPEX 1). At both sites it was observed that the relationship between peroxy radical (HO2 + RO2) concentrations and jO(1 D) switched from a square root dependence in clean oceanic or “baseline” air to a first-order dependence in more polluted air. Simple algorithms derived from a photochemical reaction scheme indicate that this switch-over occurs when atmospheric NO levels are sufficient for peroxy radical reaction with NO to compete with radical recombination reactions. At this crucial point, net tropospheric ozone production is expected to occur and was observed in the ozone diurnal cycles when the peroxy radical/jO(1 D) dependencies became first order. The peroxy radical/jO(1 D) relationships imply that ozone production exceeds destruction at NO levels of 55±30 parts per trillion by volume (pptv) at Mace Head during late spring and 23±20 pptv at Cape Grim during summer, suggesting that the tropospheric ozone production potential of the southern hemisphere is more responsive to the availability of NO than that of the northern hemisphere.

 

In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a

Date added: 08/05/1997
Date modified: 07/24/2009
Filesize: 587.14 kB

Lewis, A.C.; Bartle, K.D.; Heard, D.E.; McQuaid, J.B.; Pilling, M.J.; Seakins, P.W. (1997) In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a remote coastal location (Mace Head, Eire) July-August 1996, Faraday Transactions, 93,  pp.2921-2927.


Abstract


Atmospheric non-methane hydrocarbons (NMHC) and dimethyl sulÐde (DMS) have been monitored at a remote coastal location Mace Head, Eire) using adsorption sampling techniques with analysis by in situ gas chromatography as part of the ACSOE OXICOA 1996 campaign. Concentrations varied considerably during the campaign but can be consistently interpreted by consideration of the relevant back-trajectory of the monitored air mass. Isoprene is conÐrmed as the most important NMHC in determining OH removal, contributing to up to 20%. Isoprene shows strong diurnal variations, although the structure of the diurnal pattern depends on the origin of the air mass. In contrast to previous studies, DMS concentrations during the campaign appeared to show no consistent diurnal variation.

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

 

GAGE/AGAGE measurements indicating reductions in global emissions of CCl3F and CCl2F2 in 1992–1994 GAGE/AGAGE measurements indicating reductions in global emissions of CCl3F and CCl2F2 in 1992–1994

Date added: 08/01/1997
Date modified: 07/24/2009
Filesize: 1.36 MB
Cunnold, D. M., R. F. Weiss, R. G. Prinn, D. Hartley, P. G. Simmonds, P. J. Fraser, B. Miller, F. N. Alyea, and L. Porter (1997), GAGE/AGAGE measurements indicating reductions in global emissions of CCl3F and CCl2F2 in 1992–1994, J. Geophys. Res., 102(D1), 1259–1269.

Abstract


Global Atmospheric Gases Experiment/Advanced GAGE (GAGE/AGAGE) observations of CCl3F indicate that global concentrations of this compound reached a maximum in 1993 and decayed slightly in 1994; CCl2F2 concentrations increased approximately 7 ppt in both 1993 and 1994. The observations suggest that world emissions in these two years were smaller than industry production figures would suggest and have decreased faster than expected under the Montreal Protocol and its amendments. An analysis of regional pollution events at the Mace Head site suggest that industry may be underestimating the decline of emissions in Europe. It is argued, however, that the decline in European emissions is not biasing the background Mace Head measurements (or the GAGE global averages). Combining the chlorofluorocarbon measurements, including CCl2FCClF2, with GAGE/AGAGE measured global decreases in CH3CCl3 and CCl4 after 1992 and with Cape Grim archived air measurements of CHClF2, the measurements suggest that anthropogenic atmospheric chlorine loading from these six gases maximized in 1992 at 2.95 ± 0.04 ppb and that it had decreased by 0.02 ± 0.01 ppb by the beginning of 1995.

Microphysical and physico-chemical characterization of atmospheric marine and continental aerosol at mace head Microphysical and physico-chemical characterization of atmospheric marine and continental aerosol at mace head

Date added: 07/31/1997
Date modified: 07/23/2009
Filesize: 1.02 MB

Jennings, S.G., Geever, M. McGovern, F.M., Francis, J., Spain, G. and Donaghy, T. (1997).- Microphysical and physico-chemical characterisation of atmospheric aerosol at Mace Head. Atmos. Environ., 31, 2795-2808.


Abstract


Measurements of the aerosol particle size, aerosol volume distribution and aerosol volatility (diameter range 0.1-3.0 μm), aerosol mass (diameter range 0.06-16.0 μm), condensation nuclei (CN) and cloud condensation nuclei (CCN), and black carbon (BC) mass concentration at Mace Head during the EU project Background Maritime Contribution to Atmospheric Pollution in Europe (BMCAPE), obtained over four intensive campaigns during the period between November 1993 and August 1994, are presented. Marine air was found to possess mean accumulation mode (ACM) aerosol particle number concentration., N, of between 100 and 160 cm-3 for the winter and summer seasons. Marine ACM mass ranged in value from about 0.8 to 6 μg m-3. Marine air was found to contain black carbon with episodic mean mass concentrations generally in the range 5-40 ng m-3. The impact of black carbon on the marine environment is also reflected by the moderately positive correlation (r2 in the range 0.23-0.44) found between marine ACM number concentration and BC mass loading, with a higher correlation (r2 = 0.55) found for winter continental air. Black carbon accounted for between 0.6% and 1.2% of the ACM mass loading for marine aerosol at Mace Head, increasing to between 4% and 6% for continental air. Arithmetic mean values of ACM number concentration N and BC mass concentration agree quite well with results from a few other investigators of marine atmospheric aerosol in the North Atlantic.

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.

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