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

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

Abstract


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

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

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

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

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


Abstract


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

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

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

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


Abstract


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

 

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

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

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

 


 

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

 

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

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

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

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


Abstract


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

Evaluation of a Lagrangian box model using field measurements from EASE (Eastern Atlantic Summe Evaluation of a Lagrangian box model using field measurements from EASE (Eastern Atlantic Summe

Date added: 08/07/2000
Date modified: 07/24/2009
Filesize: 696.19 kB

Evans, M.J., D.E. Shallcross, K.S. Law, J.O.F. Wild, P.G. Simmonds, T.G. Spain, P. Berrisford, J. Methven, A.C. Lewis, J.B. McQuaid, M.J. Pilling, B.J. Bandy, S.A. Penkett, and J.A. Pyle, Evaluation of a Lagrangian box model using field measurements from EASE 1996, Atmos. Environ., 34, 3843-3863, 2000, (Ser. No. ACP048).


Abstract


The Cambridge Tropospheric Trajectory model of Chemistry and Transport (CiTTyCAT), a Lagrangian chemistry model, has been evaluated using atmospheric chemical measurements collected during the East Atlantic Summer Experiment 1996 (EASE '96). This field campaign was part of the UK Natural Environment Research Council's (NERC) Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) programme, conducted at Mace Head, Republic of Ireland, during July and August 1996. The model includes a description of gas-phase tropospheric chemistry, and simple parameterisations for surface deposition, mixing from the free troposphere and emissions. The model generally compares well with the measurements and is used to study the production and loss of O3 under a variety of conditions. The mean difference between the hourly O3 concentrations calculated by the model and those measured is 0.6 ppbv with a standard deviation of 8.7 ppbv. Three specific air-flow regimes were identified during the campaign - westerly, anticyclonic (easterly) and south westerly. The westerly flow is typical of background conditions for Mace Head. However, on some occasions there was evidence of long-range transport of pollutants from North America. In periods of anticyclonic flow, air parcels had collected emissions of NOx and VOCs immediately before arriving at Mace Head, leading to O3 production. The level of calculated O3 depends critically on the precise details of the trajectory, and hence on the emissions into the air parcel. In several periods of south westerly flow, low concentrations of O3 were measured which were consistent with deposition and photochemical destruction inside the tropical marine boundary layer.

 

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

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

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


Abstract


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

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

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

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


Abstract

 

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

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

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

Abstract


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

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

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

Abstract


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

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

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

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


Abstract


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

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

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

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


Abstract


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

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

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

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


Assessment of changing meteorology and emissions on air quality using a regional climate model: Impact on ozone Assessment of changing meteorology and emissions on air quality using a regional climate model: Impact on ozone

Date added: 03/12/2013
Date modified: 03/12/2013
Filesize: 3.64 MB

Coleman, L. , D. Martin, S. Varghese, S.G. Jennings, C.D. O’Dowd, Assessment of changing meteorology and emissions on air quality using a regional climate model: Impact on ozone, Atmos. Environ., http://dx.doi.org/10.1016/j.atmosenv.2012.11.048, 2012


 

Abstract. A regional climate model is used to assess changes in atmospheric ozone for the years 2030, 2050 and 2100 relative to 2006 brought about by changes in meteorology and emissions. The simulations are evaluated against ozone measurements for 2006, exhibiting good agreement between the model-predicted measurements and the measured annual cycles. Under the RCP6 emission scenario used in these simulations, average ozone mixing ratios are set to reduce by 2.0 ppb over domains encompassing Europe and the North East Atlantic between 2006 and 2100 with the most significant decrease occurring after 2050 due to the pattern in changing emissions. Peak reductions of more than 8 ppb are observed during summer time over mainland Europe by 2100. Model output was studied for three relevant subdomains, namely the North East Atlantic, Ireland and Europe. The relative contribution of changes in both emissions and meteorology is assessed. Over the whole domain, changing emissions are predominantly responsible for changes in surface ozone; although over the North East Atlantic domain, the changing emissions do not perturb surface ozone trends and the decrease in 2100 levels is entirely attributable to changing meteorology.

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

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

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


Abstract


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

 

Atmospheric Emissions and Trends of Nitrous Oxide Deduced From 10 Years of ALE–GAGE Data Atmospheric Emissions and Trends of Nitrous Oxide Deduced From 10 Years of ALE–GAGE Data

Date added: 08/01/1990
Date modified: 07/27/2009
Filesize: 1.5 MB

R.G. Prinn, D. Cunnold, R. Rasmussen, P. Simmonds, F. Alyea, A. Crawford, P. Fraser, and R. Rosen.  Atmospheric emissions and trends of nitrous oxide deduced from ten years of ALE/GAGE data. J. Geophys. Res., 95, 18369-18385, 1990.


Abstract


We present and interpret long-term measurements of the chemically and radiatively important trace gas nitrous oxide (N2O) obtained during the Atmospheric Lifetime Experiment (ALE) and its successor the Global Atmospheric Gasses Experiment (GAGE). The ALE/GAGE data for N2O comprise over 110,000 individual calibrated real-time air analyses carried out over a 10-year (July 1978-June 1988) time period. These measurements indicate that the average concentration in the northern hemisphere is persistently 0.75+/-0.16 ppbv higher than in the southern hemisphere and that the global average linear trend in N2O lies in the range from 0.25 to 0.31% yr-1, with the latter result contingent on certain assumptions about the long-term stability of the calibration gases used in the experiment. Interpretation of the data, using inverse theory and a 9-box (grid) model of the global atmosphere, indicates that the N2O surface emissions into the 90°N-30°N, 30°N-0°, 0°-30°S, and 30°S-90°S semihemispheres account for about 22-34, 32-39, 20-29 and 11-15% of the global total emissions, respectively.<p>The measured trends and latitudinal distributions are consistent with the hypothesis that stratospheric photodissociation is the major atmospheric sink for N2O, but they do not support the hypothesis that the temporal N2O increase is caused solely by increases in anthropogenic N2O emissions associated with fossil fuel combustion. Instead, the cause for the N2O trend appears to be a combination of a growing tropical source (probably resulting from tropical land disturbance) and a growing northern mid-latitude source (probably resulting from a combination of fertilizer use and fossil fuel combustion). The exact combination of these sources which best fits the data depends on the assumed tropospheric-stratospheric exchange rates for N2O in the northern hemisphere relative to the southern hemisphere. Accepting a theoretically-calculated N2O lifetime of 166+/-16 years due to stratospheric destruction only, we deduce from the ALE/GAGE data a 10-year average global N2O emission rate of (20.5+/-2.4)×1012gN2O yr-1, but with significant year-to-year variations in emissions associated perhaps with year-to-year variations in tropical land disturbance.

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

Date added: 08/07/1998
Date modified: 07/24/2009
Filesize: 339.88 kB

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.

 

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

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

Abstract

 

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

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

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

Abstract

 

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

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

Date added: 08/07/1998
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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.

 

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

Date added: 08/07/2001
Date modified: 07/27/2009
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S.G. Yeatman, L.J. Spokes, P.F. Dennis, T.D. Jickells, Can the study of nitrogen isotopic composition in size-segregated aerosol nitrate and ammonium be used to investigate atmospheric processing mechanisms?, Atmospheric Environment 35 (2001) 1337}1345


Abstract


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

 

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.

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

Date added: 07/31/2001
Date modified: 07/27/2009
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Derwent, R.G., Ryall, D.B., Jennings, S.G., Spain, T.G., and Simmonds, P.G. (2001). Black carbon aerosol and carbon monoxide in European regionally polluted air masses at Mace Head, Ireland during 1995-1998. Atmos. Environ., 35, 6371-6378.


Abstract


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

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

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

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


Abstract


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

 

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

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

Abstract


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

How falling raindrops collide How falling raindrops collide

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

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


Abstract

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

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

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


Abstract


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

 

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

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

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


Abstract


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

Estimating European emissions of ozone-depleting and greenhouse gases using observations and a Estimating European emissions of ozone-depleting and greenhouse gases using observations and a

Date added: 08/07/2003
Date modified: 07/27/2009
Filesize: 1.48 MB

Manning, A. J., D. B. Ryall, R. G. Derwent, P. G. Simmonds, and S. O'Doherty (2003), Estimating European emissions of ozone-depleting and greenhouse gases using observations and a modeling back-attribution technique, J. Geophys. Res., 108(D14), 4405, doi:10.1029/2002JD002312.


Abstract


The Numerical Atmospheric Dispersion Modeling Environment (NAME) dispersion model driven by three-dimensional (3-D) synoptic meteorology from the Unified Model has been used to determine the fraction of air arriving at Mace Head, Ireland, from different European regions over a 6-year period. These data, along with observations of pollutants at Mace Head and a best fit algorithm, have been used to derive emission estimates over Western Europe. The algorithm starts from randomly generated emission maps and iterates toward the best solution. Using an idealized case study, it has been shown to be effective at distinguishing between distinct source regions. The technique has been applied to two ozone-depleting gases, CFC-11 and CFC-12, and two greenhouse gases, methane and nitrous oxide. The emissions derived compare favorably with existing inventories. The technique is able to provide information regarding the emission distribution across Europe and to estimate area and country contributions; information that for some species is not readily available by other means. It is a different methodology to those currently used and so is a useful tool in verifying existing inventories.

 

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

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

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

 

  

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

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

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

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

  


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

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

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


Abstract


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

Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades

Date added: 08/01/2001
Date modified: 07/01/2009
Filesize: 1.28 MB

Prinn, R. G.; Huang, J.; Weiss, R. F.; Cunnold, D. M.; Fraser, P. J.; Simmonds, P. G.; McCulloch, A.; Harth, C.; Salameh, P.; O'Doherty, S.; Wang, R. H. J.; Porter, L.; Miller, B. R.,Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades, Science, Volume 292, Issue 5523, pp. 1882-1888 (2001).


Abstract


The hydroxyl radical (OH) is the dominant oxidizing chemical in the atmosphere. It destroys most air pollutants and many gases involved in ozone depletion and the greenhouse effect. Global measurements of 1,1,1-trichloroethane (CH3CCl3, methyl chloroform) provide an accurate method for determining the global and hemispheric behavior of OH. Measurements show that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and then decreased rapidly to levels in 2000 that were lower than the levels when measurements began in 1978. Analysis of these observations shows that global OH levels were growing between 1978 and 1988, but the growth rate was decreasing at a rate of 0.23 +/- 0.18% year-2, so that OH levels began declining after 1988. Overall, the global average OH trend between 1978 and 2000 was -0.64 +/- 0.60% year-1. These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself.

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

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

Abstract


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

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

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

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


Abstract


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

 

Intercomparison Of Formaldehyde Intercomparison Of Formaldehyde

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

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

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


Abstract

 

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

Potential for photochemical ozone formation in the troposphere over the North Atlantic as deriv Potential for photochemical ozone formation in the troposphere over the North Atlantic as deriv

Date added: 08/06/2002
Date modified: 07/23/2009
Filesize: 1.34 MB

Reeves, C. E., et al. (2002), Potential for photochemical ozone formation in the troposphere over the North Atlantic as derived from aircraft observations during ACSOE, J. Geophys. Res., 107(D23), 4707, doi:10.1029/2002JD002415.


Abstract


In this paper, ozone (O3), water vapor (H2O), carbon monoxide (CO), and peroxide concentrations and photolysis rates measured in the troposphere over the North Atlantic during two Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) aircraft field campaigns are used to calculate the concentration of nitric oxide (NO) required for net photochemical O3 production (nPO3) to be positive (NOcomp). NOcomp tended to show a decrease with altitude, although it was sometimes found to be low in the marine boundary layer (MBL) where H2O concentrations were high and O3 concentrations were low. nPO3 was calculated for the spring when NO data were available and was found to be mostly negative and generally increased from about −0.5 to −0.2 ppbv hr−1 in the MBL to +0.04 ppbv hr−1 at about 7–8 km altitude. The results suggest that much of the lower and middle troposphere over the eastern North Atlantic during spring is in a state of slow net photochemical O3 destruction. However, in the upper troposphere, the system changes to one of net photochemical production, which results from the drier environment and higher NO concentrations. Furthermore, examples of net O3 production were also observed in the lower and middle troposphere associated with either in situ sources of NO or long-range transport of pollution. The paper also illustrates the sensitivity of this O3 production/loss state to H2O and NO concentrations, photolysis rates, and temperatures.

 

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.

 

New Particle Formation from Photooxidation of Diiodomethane (CH2I2) New Particle Formation from Photooxidation of Diiodomethane (CH2I2)

Date added: 08/01/2003
Date modified: 07/03/2009
Filesize: 1.27 MB

Jimenez, J.L., R. Bahreini, D. R. Cocker III, H. Zhuang, V. Varutbangkul, R. C. Flagan, and J. H. Seinfeld, C.D. O'Dowd, T. Hoffmann, New Particle Formation from Photooxidation of Diiodomethane (CH2I2), in press, J. Geophys. Research, 2003.


Abstract


Photolysis of CH2I2 in the presence of O3 has been proposed as a mechanism leading to intense new particle formation in coastal areas. We report here a comprehensive laboratory chamber study of this system. Rapid homogeneous nucleation was observed over three orders of magnitude in CH2I2 mixing ratio, down to a level of 15 ppt (∼4 × 108 molec. cm−3) comparable to the directly measured total gas-phase iodine species concentrations in coastal areas. After the nucleation burst, the observed aerosol dynamics in the chamber was dominated by condensation of additional vapors onto existing particles and particle coagulation. Particles formed under dry conditions are fractal agglomerates with mass fractal dimension, D f ∼ 1.8–2.5. Higher relative humidity (65%) does not change the nucleation or growth behavior from that under dry conditions, but results in more compact and dense particles (D f ∼ 2.7). On the basis of the known gas-phase chemistry, OIO is the most likely gas-phase species to produce the observed nucleation and aerosol growth; however, the current understanding of this chemistry is very likely incomplete. Chemical analysis of the aerosol using an Aerodyne Aerosol Mass Spectrometer reveals that the particles are composed mainly of iodine oxides but also contain water and/or iodine oxyacids. The system studied here can produce nucleation events as intense as those observed in coastal areas. On the basis of comparison between the particle composition, hygroscopicity, and nucleation and growth rates observed in coastal nucleation and in the experiments reported here, it is likely that photooxidation of CH2I2, probably aided by other organic iodine compounds, is the mechanism leading to the observed new particle formation in the west coast of Ireland.

Modelling heterogeneous sulphate production in maritime stratiform clouds Modelling heterogeneous sulphate production in maritime stratiform clouds

Date added: 08/06/2000
Date modified: 07/21/2009
Filesize: 1.48 MB

O'Dowd, C. D., J. A. Lowe, N. Clegg, M. H. Smith, and S. L. Clegg (2000), Modelling heterogeneous sulphate production in maritime stratiform clouds, J. Geophys. Res., 105(D6), 7143–7160.


Abstract


A size-resolved droplet physico chemical model linked to a Lagrangian parcel framework was developed and used to study the heterogeneous sulphate production process in marine stratiform clouds. This model study provides a rigorous approach to cloud chemistry processing by treating the effects of non ideal chemistry on both aqueous phase equilibration and droplet growth using the Pitzer method to overcome many of the shortcomings of alternative thermodynamic methods. In addition, the current study uses a multi modal representation of sea-salt aerosol, rather than the single mode used in most previous work. The results of the model simulations showed a distribution of sulphate production across the aerosol size range that was non linear and that a significant fraction (≈75–90%) of the sulphate was produced in droplets formed on sea-salt aerosol particles. The number of sea-salt particles affected both the total amount of sulphate produced and the fraction produced on cloud droplets formed around non-sea-salt sulphate aerosol. Dissolved ozone and hydrogen peroxide were both important as oxidant species, although the ozone-driven oxidation pathway was dominant in droplets formed on sea-salt aerosol particles. The rate of sulphate production was found to be a non linear function of the gaseous sulphur dioxide concentration at cloud base and only very weakly dependent on sulphate nuclei concentration. A comparison of sulphate production in cloud and below cloud indicates that sulphate production in sea-salt nuclei is not limited by the carbonate buffer and that in-cloud production can exceed, many times, that of cloud-free production due to the “virtual” buffering capacity of the cloud. The use of non ideal solution effects appear important, particularly for clean-to-moderately polluted SO2 concentrations (< 500 parts per trillion) and when sea-salt nuclei are present, resulting in at least 40% lower sulphate production when compared to ideal solution simulations.

 

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.

 

Atmospheric mercury distribution in Northern Europe and in Atmospheric mercury distribution in Northern Europe and in

Date added: 08/06/2001
Date modified: 07/27/2009
Filesize: 238.69 kB

I. Wangberg, J. Munthe, N. Pirrone, A. Iverfeldt, E. Bahlman, P. Costa, R. Ebinghaus, X. Feng, R. Ferrara, K. Gardfeldt, H. Kock, E. Lanzillotta, Y. Mamane, F. Mas, E. Melamed, Y. Osnat, E. Prestbo, J. Sommar, S. Schmolke, G. Spain, F. Sprovieri, G. Tuncel, Atmospheric mercury distribution in Northern Europe and in the Mediterranean region, Atmospheric EnvironmentVolume 35, Issue 17, , June 2001, Pages 3019-3025.


Abstract


Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.

 

Modelling the HOx Radicals during the NAMBLEX campaign Modelling the HOx Radicals during the NAMBLEX campaign

Date added: 08/06/2004
Date modified: 09/11/2009
Filesize: 33.16 kB

R. Sommariva, W.J. Bloss , L.J. Carpenter, N. Carslaw, A.-L. Haggerstone, D.E. Heard, A.C. Lewis, G. McFiggans, M.J. Pilling, J.M.C. Plane,MODELLING HOX RADICALS DURING THE NAMBLEX CAMPAIGN, Geophysical Research Abstracts, Vol. 6, 00232, 2004


Abstract

 

The North Atlantic Marine Boundary Layer Experiment (NAMBLEX) campaign took place at the Mace Head Atmospheric Research Station, Ireland, in July-September 2002. An extensive set of measurements was taken during the campaign including NMHCs, NOx, HCHO, peroxides, photolysis rates, aerosols and radical species (OH, HO2, HO2+RO2, NO3, IO and BrO). Several different zero-dimensional box models based on the Master Chemical Mechanism (MCMv3.1) with different levels of chemical complexity have been used to study the HOx radicals chemistry under comparatively unpolluted conditions. The comparison between the model results and the measurements, based on the FAGE (Fluorescence Assay by Gas Expansion) measurements is satisfactory for OH, but HO2 is overestimated by almost a factor of two.
The effect of constraining the models to the measured oxygenates (methanol, acetaldehyde and acetone) and the effect of IO and BrO on HOx chemistry have been investigated. Aerosol uptake treatment for the relevant species has been  improved with respect to previous analyses by using a transition regime expression, which resulted in better agreement between modelled and measured HOx. A detailed study of the radical chemistry on selected days using a rate of production/ destruction analysis, shows the importance of previously unmeasured oxygenated compounds and of halogen chemistry on the HOx budget in the Marine Boundary Layer.

Atmospheric Particles from organic Vapours Atmospheric Particles from organic Vapours

Date added: 08/06/2002
Date modified: 06/30/2009
Filesize: 99.71 kB

O'Dowd, Colin D.; Aalto, Pasi; Hmeri, Kaarle; Kulmala, Markku; Hoffmann, Thorsten, Aerosol formation: Atmospheric particles from organic vapours, Nature, Volume 416, Issue 6880, pp. 497-498 (2002)


Abstract

 

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

Relative contribution of submicron and supermicron particles to aerosol light scattering...boun Relative contribution of submicron and supermicron particles to aerosol light scattering...boun

Date added: 08/06/2002
Date modified: 07/23/2009
Filesize: 399.76 kB

Kleefeld, C., C. D. O'Dowd, S. O'Reilly, S. G. Jennings, P. Aalto, E. Becker, G. Kunz, and G. de Leeuw (2002), Relative contribution of submicron and supermicron particles to aerosol light scattering in the marine boundary layer, J. Geophys. Res., 107(D19), 8103, doi:10.1029/2000JD000262.


Abstract


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

 

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

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

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


Abstract


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

Experimental studies of the effect of rough surfaces and air speed on aerosol deposition in a test chamber Experimental studies of the effect of rough surfaces and air speed on aerosol deposition in a test chamber

Date added: 07/31/2002
Date modified: 07/01/2009
Filesize: 915.07 kB

Lai, A.C.K., Byrne and AJH Goddard. Experimental studies of the effect of rough surfaces and air speed on aerosol deposition in a test chamber. Aerosol Science and Technology, 36: 973-982, 2002.


Abstract

 

Understanding the fate of particles indoors is important for human health assessment because deposited particles, unless resuspended, cannot be inhaled. To complement studies in real buildings, where control of variables is often difficult, an experimental test chamber facility (8 m3) was designed to study particle deposition under well-stirred conditions using monodisperse tracer aerosol particles in the range of 0.7 to 5.4 mum. The use of neutron-activatable tracers facilitated simultaneous surface sampling and aerosol concentration decay measurements.

 

Aerosol deposition on both smooth surfaces and regular arrays of three-dimensional roughness elements under 3 different airflow speeds was investigated in the test chamber.It was expected that the texture of the chamber surface would significantly influence particle deposition, but some counterintuitive results were observed: under the lowest airflow condition and for the smallest particle size, particle deposition onto rough samples was found to be less than on the corresponding smooth surfaces.

 

The ratio of particle deposition on rough surfaces relative to smooth surfaces increased with particle size and magnitude of airflow. For the largest particle size and airflow speed, particle deposition on the rough surfaces exceeded that on the smooth surfaces by a factor of 3.

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

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

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


Abstract


 


Modeling heterogeneous sulphate production in maritime stratiform clouds Modeling heterogeneous sulphate production in maritime stratiform clouds

Date added: 08/06/2000
Date modified: 07/03/2009
Filesize: 1.48 MB

O'Dowd, C. D., J. A. Lowe, N. Clegg, M. H. Smith, and S. L. Clegg (2000), Modeling heterogeneous sulphate production in maritime stratiform clouds, J. Geophys. Res., 105(D6), 7143–7160.


Abstract


A size-resolved droplet physico chemical model linked to a Lagrangian parcel framework was developed and used to study the heterogeneous sulphate production process in marine stratiform clouds. This model study provides a rigorous approach to cloud chemistry processing by treating the effects of non ideal chemistry on both aqueous phase equilibration and droplet growth using the Pitzer method to overcome many of the shortcomings of alternative thermodynamic methods. In addition, the current study uses a multi modal representation of sea-salt aerosol, rather than the single mode used in most previous work. The results of the model simulations showed a distribution of sulphate production across the aerosol size range that was non linear and that a significant fraction (≈75–90%) of the sulphate was produced in droplets formed on sea-salt aerosol particles. The number of sea-salt particles affected both the total amount of sulphate produced and the fraction produced on cloud droplets formed around non-sea-salt sulphate aerosol. Dissolved ozone and hydrogen peroxide were both important as oxidant species, although the ozone-driven oxidation pathway was dominant in droplets formed on sea-salt aerosol particles. The rate of sulphate production was found to be a non linear function of the gaseous sulphur dioxide concentration at cloud base and only very weakly dependent on sulphate nuclei concentration. A comparison of sulphate production in cloud and below cloud indicates that sulphate production in sea-salt nuclei is not limited by the carbonate buffer and that in-cloud production can exceed, many times, that of cloud-free production due to the “virtual” buffering capacity of the cloud. The use of non ideal solution effects appear important, particularly for clean-to-moderately polluted SO2 concentrations (< 500 parts per trillion) and when sea-salt nuclei are present, resulting in at least 40% lower sulphate production when compared to ideal solution simulations.

 

Physical and chemical properties of aerosol during the North Atlantic Marine Boundary Layer Exp Physical and chemical properties of aerosol during the North Atlantic Marine Boundary Layer Exp

Date added: 08/07/2003
Date modified: 07/27/2009
Filesize: 32.66 kB
Coe, H.; THE NAMBLEX AEROSOL TEAM Physical and chemical properties of aerosol during the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) [EGU04-A-03236].
Abstract

 

A wide range of particle physical and chemical measurements were made at Mace Head on the Atlantic coast during the North Atlantic Marine Boundary Layer EXperiment during August 2002. The measurements included particle number, and size distribution from 10 nm to 20 um diameter. These data will be used to show how the loss rates of gaseous species with different uptake coefficients to aerosol impacts on the lifetime of species in the MBL and indicates the extent to which aerosol are an effective sink for a range of species. An Aerodyne Aerosol Mass Spectrometer was used to make continuous measurements of sulphate, nitrate and organic mass loading in the submicron size range at high time resolution. These data are compared with the analyses of filters from multi stage impactor sample collections. The air masses sampled during the experiment are characterised in terms of the aerosol physics and chemistry and comparisons between the AMS and the impactor samples will be shown.Westerly winds provide near background concentrations but significant loadings were observed in several air masses. Gas phase VOC data will be used as a guide to the photochemical age of the air and this will be compared with the aerosol components measured by the AMS. Correlations between gas phase oxidised VOC and the organic aerosol loading will be shown.

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