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# Journal Publications

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

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## Documents

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### Optical and Thermal Measurements of Black CArbon Aerosol Content.....of the Specific Attenuation Cross-section, Sigma. Jennings, Liousse, Cachier

 Date added: 07/31/1993 Date modified: 07/03/2009 Filesize: 2.92 MB

Louisse, C., Cachier, H., and Jennings, S.G. (1993). - Optical and thermal measurements of black carbon aerosol contents in different environments: variation of the specific attenuation cross-section. Atmos. Environ., 27A, 1203 - 1211.

Abstract

In optical analysers devoted to the analysis of atmospheric black carbon concentration, the specific attenuation cross-section, a is the factor used to convert the attenuation of a light beam due to the absorption of aerosols deposited on a filter into their black carbon content. We have tried to gain further insight for a suitable choice of sigma value, using both optical analysis (with an aethalometer) and thermal analysis of black carbon aerosols and comparison of the two sets of results. Samples which were investigated originate from varying environments, including suburban areas, tropical areas where biomass buming was prevalent and from more remote locations. In a given type of atmospheric environment, a values are found to be constant

### Optical properties of the atmospheric aerosol at mace head

 Date added: 08/07/1999 Date modified: 07/23/2009 Filesize: 118.21 kB

O'Reilly S.; Kleefeld C.; Jennings S.G.,Optical properties of the atmospheric aerosol at mace head  ,Journal of Aerosol Science, Volume 30, Supplement 1, September 1999 , pp. 631-632(2)

Abstract

The atmospheric aerosol is known to cause cooling of the earth's climate through radiative forcing. This forcing is comparable but of opposite sign to the radiative forcing due to greenhouse gases [1PCC, 1995]. However, unlike greenhouse gases, the atmospheric aerosol is not uniformly distributed about the globe. It is found to vary significantly both spatially and temporally. Therefore, an analysis of global radiative forcing due to the atmospheric aerosol requires an estimation of forcing on a regional scale. Characterisation of the optical properties of the local atmospheric aerosol forms an integral part of such an estimation. The scattering coefficient, Osp, and absorption coefficient, (Yap, of the atmospheric aerosol are basic input parameters to radiative forcing models. These parameters have been measured since 1996 and 1989, respectively, at the Global Atmospheric Watch (GAW/WMO) atmospheric research station at Mace Head (53°19'N, 9°54'W), located on the west coast of Ireland. The results of measurements from 7 th January 1997 to 12 th June ! 997 are presented. The scattering measurements were conducted with a TSI Model 3563 Integrating Nephelometer, operating at three wavelengths (450nm, 550nm and 700nm). It also had the
capability of measuring aerosol hemispheric backscatter coefficient from 90 ° to 180 °. Black carbon mass concentrations were measured using a Magee Scientific Model AE9 Aethalometer. The absorption coefficient for each wavelength was obtained by dividing black carbon mass concentrations by a constant, C; C(~=450nm)=1.5, C()~=550nm)=1.9 and C(L=700nm)=2.4 [Bodhaine, 1995], in order to compare with the aerosol scattering coefficients at these wavelengths. The scattering coefficient, Osp, for ~.=550nm ranged from 7 to 280 Mm -1 with an average and standard deviation of 76 + 49 Mm "l (geometric mean of 60 + 2 Mmt). The corresponding hemispheric backscattering coefficient, Cbsp, measurements were about an order of magnitude lower than (ysp ranging from 0.9 to 35 Mm "1 (geometric mean of 7 + 2 Mm-I). This results in a hemispheric backscattered fraction, b, of 0.12 + 0.01 (geometric mean of 0.12). The AngstrOm exponent, describes the dependence of the aerosol scattering coefficient on wavelength, )~. The red-blue Angstr6m exponent (Ll=700nm, ~2=450nm) was found to range from -1.9 to 0.15 with an average of-0.66 + 0.7 (geometric mean of-0.69). The absorption coefficient, aap, for ~.=550nm ranged from 0.12 to 22 Mm "l and averaged 1.7 Mm "1 (geometric mean of 0.9 Mm'l). This results in an extinction coefficient, (yext, averaging 77.7Mm "1 (geometric mean of 53+2Mm'l). The scattering and absorption coefficients areused to calculate the single-scattering albedo, which describes the relative contributions of scattering and absorption to the total light extinction. The calculated albedo values ranged from 0.9 to 0.998 and averaged 0.97 + 0.02 (geometric mean of 0.97), indicating a highly scattering aerosol. The single scattering albedo exhibits a logarithmic correlation (R2=0.55, significant at a 99% confidence level) with black carbon concentrations. As black carbon levels increase, the albedo values can be seen to decrease  The scattering time series obtained were found to change with impact of different types of air mass (continental, marine and polar). The influence of synoptic meteorology on the scattering coefficient at Mace Head will be quantified by combining the pattern recognition capabilities of cluster analysis with air mass back-trajectory data.

### Optical properties of the atmospheric aerosol at mace head

 Date added: 08/07/1999 Date modified: 09/11/2009 Filesize: 118.21 kB

O'Reilly S.; Kleefeld C.; Jennings S.G.,Optical properties of the atmospheric aerosol at mace head  ,Journal of Aerosol Science, Volume 30, Supplement 1, September 1999 , pp. 631-632(2)

Abstract

The atmospheric aerosol is known to cause cooling of the earth's climate through radiative forcing. This forcing is comparable but of opposite sign to the radiative forcing due to greenhouse gases [1PCC, 1995]. However, unlike greenhouse gases, the atmospheric aerosol is not uniformly distributed about the globe. It is found to vary significantly both spatially and temporally. Therefore, an analysis of global radiative forcing due to the atmospheric aerosol requires an estimation of forcing on a regional scale. Characterisation of the optical properties of the local atmospheric aerosol forms an integral part of such an estimation. The scattering coefficient, Osp, and absorption coefficient, (Yap, of the atmospheric aerosol are basic input parameters to radiative forcing models. These parameters have been measured since 1996 and 1989, respectively, at the Global Atmospheric Watch (GAW/WMO) atmospheric research station at Mace Head (53°19'N, 9°54'W), located on the west coast of Ireland. The results of measurements from 7 th January 1997 to 12 th June ! 997 are presented. The scattering measurements were conducted with a TSI Model 3563 Integrating Nephelometer, operating at three wavelengths (450nm, 550nm and 700nm). It also had the
capability of measuring aerosol hemispheric backscatter coefficient from 90 ° to 180 °. Black carbon mass concentrations were measured using a Magee Scientific Model AE9 Aethalometer. The absorption coefficient for each wavelength was obtained by dividing black carbon mass concentrations by a constant, C; C(~=450nm)=1.5, C()~=550nm)=1.9 and C(L=700nm)=2.4 [Bodhaine, 1995], in order to compare with the aerosol scattering coefficients at these wavelengths. The scattering coefficient, Osp, for ~.=550nm ranged from 7 to 280 Mm -1 with an average and standard deviation of 76 + 49 Mm "l (geometric mean of 60 + 2 Mmt). The corresponding hemispheric backscattering coefficient, Cbsp, measurements were about an order of magnitude lower than (ysp ranging from 0.9 to 35 Mm "1 (geometric mean of 7 + 2 Mm-I). This results in a
hemispheric backscattered fraction, b, of 0.12 + 0.01 (geometric mean of 0.12). The AngstrOm exponent, describes the dependence of the aerosol scattering coefficient on wavelength, )~. The red-blue Angstr6m exponent (Ll=700nm, ~2=450nm) was found to range from -1.9 to 0.15 with an average of-0.66 + 0.7 (geometric mean of-0.69). The absorption coefficient, aap, for ~.=550nm ranged from 0.12 to 22 Mm "l and averaged 1.7 Mm "1 (geometric mean of 0.9 Mm'l). This results in an extinction coefficient, (yext, averaging
77.7Mm "1 (geometric mean of 53+2Mm'l). The scattering and absorption coefficients areused to calculate the single-scattering albedo, which describes the relative contributions of scattering and absorption to the total light extinction. The calculated albedo values ranged from 0.9 to 0.998 and averaged 0.97 + 0.02 (geometric mean of 0.97), indicating a highly scattering aerosol. The single scattering albedo exhibits a logarithmic correlation (R2=0.55, significant at a 99% confidence level) with black carbon concentrations. As black carbon levels increase, the albedo values can be seen to decrease  The scattering time series obtained were found to change with impact of different types of air mass (continental, marine and polar). The influence of synoptic meteorology on the scattering coefficient at Mace Head will be quantified by combining the pattern recognition capabilities of cluster analysis with air mass back-trajectory data.

### Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements

 Date added: 08/05/2007 Date modified: 07/23/2009 Filesize: 683.98 kB
Xiao, X., et al. (2007), Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements, J. Geophys. Res., 112, D07303, doi:10.1029/2006JD007241.

Abstract

Hydrogen (H2), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts. The magnitudes and seasonal cycles of the major (presumably microbial) soil sink of hydrogen have been estimated from high-frequency in situ AGAGE H2 observations and also from more geographically extensive but low-frequency flask measurements from CSIRO and NOAA-GMD using the Kalman filter in a two-dimensional (2-D) global transport model. Hydrogen mole fractions exhibit well-defined seasonal cycles in each hemisphere with their phase difference being only about 3 months. The global production rate of H2 is estimated to be 103 ± 10 Tg yr−1 with only a small estimated interannual variation. Soil uptake (84 ± 8 Tg yr−1) represents the major loss process for H2 and accounts for 81% of the total destruction. Strong seasonal cycles are deduced for the soil uptake of H2. The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere. Oxidation by tropospheric OH (18 ± 3 Tg yr−1) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere. The calculated global burden is 191 ± 29 Tg, indicating an overall atmospheric lifetime of 1.8 ± 0.3 years. Hydrogen in the troposphere (149 ± 23 Tg burden) has a lifetime of 1.4 ± 0.2 years.

### Organic aerosol formation via sulphate cluster activation

 Date added: 08/06/2004 Date modified: 07/03/2009 Filesize: 667.33 kB

Kulmala, M., V.-M. Kerminen, T. Anttila, A. Laaksonen, and C. D. O'Dowd (2004), Organic aerosol formation via sulphate cluster activation, J. Geophys. Res., 109, D04205, doi:10.1029/2003JD003961.

Abstract

The formation of aerosols, and subsequent cloud condensation nuclei, remains one of the least understood atmospheric processes upon which global climate change critically depends. Under atmospheric conditions, the process of homogeneous nucleation (formation of stable clusters ∼ 1 nm in size), and their subsequent growth into new particles (>3 nm), determines the aerosol and cloud nuclei population, yet, hitherto, no theory has elucidated the new particle formation phenomenon in detail. In this study, we present a new theory which provides a mechanistic explanation for new particle formation via activation of stable inorganic clusters by organic vapors. The new nano-particle activation theory is analogous to Köhler theory which describes cloud formation in a supersaturated water vapor field but differs in that it describes the activation of inorganic stable nano-clusters into aerosol particles in a supersaturated organic vapor which initiates spontaneous and rapid growth of clusters. Inclusion of the new theory into aerosol formation models predicts that increases in organic vapor densities lead to even greater increases in particle production, which, in turn, will influence the global radiative cooling effect of atmospheric aerosols.

### Organic matter contribution to marine aerosols and cloud condensation nuclei

 Date added: 09/23/2008 Date modified: 07/23/2009 Filesize: 158.68 kB

Baerbel Langmann, Claire Scannell, Colin O'Dowd, New Directions: Organic matter contribution to marine aerosols and cloud condensation nuclei, Atmospheric Environment, Volume 42, Issue 33, October 2008, Pages 7821-7822, ISSN 1352-2310, DOI: 10.1016/j.atmosenv.2008.09.002.

Abstract

Aerosols in the marine atmosphere influence solar irradiation over the world's ocean directly by backscattering incoming solar radiation and indirectly, by forming cloud condensation nuclei (CCN) thereby affecting the cloud albedo. Charlson et al. (1987) suggested the existence of a feedback mechanism between climate change and the flux of oceanic dimethyl sulfide (DMS), commonly known as the CLAW hypothesis after the four founding authors. According to this hypothesis, DMS produced by marine phytoplankton is ventilated into the marine boundary layer (MBL) and ultimately oxidised to sulfate aerosol which form CCNs.

The change in cloud albedo results in a global temperature perturbation affecting the productivity of the marine biosphere and hence the concentration of oceanic DMS. The authors assumed that non-sea salt (nss) sulfate aerosol as oxidation product of DMS is the major source of CCN over the oceans thereby disregarding the potential of other chemical components of the submicron marine aerosol like sea salt and water soluble and water insoluble organic carbon (OC) to form CCNs. Since the publication of the CLAW hypothesis it has been difficult to prove or disprove the idea, however several studies (e.g. Woodhouse et al., 2008) have elucidated that DMS flux in the MBL alone cannot explain new particle and CCN formation.

In recent years, the role of natural organic aerosol in the marine environment has received increasing attention. Measurements indicate that the increase of the marine biological activity is accompanied by a considerable increase of the contribution of OC to the submicron marine aerosol (e.g. O'Dowd et al., 2004) exceeding the mass fraction of nss sulfate by a factor of more than two. OC aerosols are partly primary aerosols (POC) which are directly released from the ocean and partly secondary aerosols (SOC) which form in the atmosphere through chemical reactions of reactive gases released at the ocean surface. CCNs formed from POC and reactive gases like isoprene should be available much closer to areas with increased marine biological activity than CCNs formed from nss sulfate. Meskhidze and Nenes (2006) argued that SOC aerosols can act as efficient CCNs in the Southern Ocean, even though the authors had to revise their estimates of oceanic isoprene fluxes. Roelofs (2008) showed in a global model study that OC aerosols significantly contribute to marine cloud optical properties and seasonality by estimating a global annual flux of marine organic matter of about 75 Tg C yr−1 (corresponding to 90–135 Tg OC yr−1 depending on the applied conversion factor) whereas Spracklen et al. (2008) provide a global annual oceanic OC emission estimate of around 8 Tg OC yr−1. The very different approaches used by the authors lead to a one order of magnitude difference in the marine OC emissions estimates. As measurements are generally limited spatially and temporally and are only available for selected gases or aerosols, globally, the role of the ocean as a source of photochemical active gases and aerosols remains unclear.

We would like to contribute to an improved understanding of marine OC emissions by presenting a global annual marine OC flux estimate based on a different approach. A combined organic–inorganic submicron sea–spray source function (O'Dowd et al., 2008) is applied globally, where we make use of chlorophyll-a concentration obtained from MODIS Aqua and Terra satellite and wind speed obtained from SeaWinds on QuikSCAT as monthly average input information. The only difference to O'Dowd et al. (2008) is the use of a revised relationship between organic mass and chlorophyll concentration in the current estimate (organic mass [%] = 49.129 × chlorophyll [mg m−3]) because of recent corrections of the chemical analysis. The resulting marine flux of submicron OC aerosols is 2.3 Tg OC yr−1 for 2003 and 2.8 Tg C yr−1 for 2006, with a spatial distribution as shown in Fig. 1. As the submicron OC aerosols are likely internally mixed with sea-salt and therefore are already hygroscopic, they can act as sites for biogenic SOC condensation making them more active as CCN. Estimates for the very high latitudes should be regarded with caution because the satellite sensors have a large margin of errors in these regions. Our estimate of the global annual marine OC flux is in the range of that published by Spracklen et al. (2008), but approximately a factor of 3 lower as only submicron particles are considered here. The global distribution of the marine OC flux by Spracklen et al. (2008) follows the global distribution of chlorophyll-a, whereas high wind speed in the approach presented here leads to increased marine OC emissions in particular in the region of the Antarctic circumpolar current, the North Atlantic and the North Pacific Ocean and considerably lower emissions in the tropics and subtropics where wind speed is generally lower. Further measurements preferably in remote oceanic regions, and measurements and modelling studies on the mechanisms of marine OC production are needed to illuminate the nature and role of marine OC aerosols and their potential to act as CCNs.

### Overview of the international project on biogenic aerosol formation in the boreal forest

 Date added: 07/31/2001 Date modified: 07/22/2009 Filesize: 727.68 kB

Kulmala, M., K. Hämeri, P.P. Aalto, J.M. Makela, L. Pirjola, E.D. Nilsson, G. Buzorius, U. Rannik, M. Dal Maso, W. Seidl, T. Hoffmann, R. Janson, H-C. Hansson, Y. Viisanen, and A. Laaksonen, C.D. O'Dowd, Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR), Tellus B, 324-343, 2001.

Abstract

Aerosol formation and subsequent particle growth in ambient air have been frequently observed at a boreal forest site (SMEAR II station) in Southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest has focused on: (a) determination of formation mechanisms of aerosol particles in the boreal forest site; (b) verification of emissions of secondary organic aerosols from the boreal forest site; and (c) quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. The approach of the project was to combine the continuous measurements with a number of intensive field studies. These field studies were organised in three periods, two of which were during the most intense particle production season and one during a non-event season. Although the exact formation route for 3 nm particles remains unclear, the results can be summarised as follows: Nucleation was always connected to Arctic or Polar air advecting over the site giving conditions for a stable nocturnal boundary layer followed by a rapid formation and growth of a turbulent convective mixed layer closely followed by formation of new particles. The nucleation seems to occur in the mixed layer or entrainment zone. However two more prerequisites seem to be necessary. A certain threshold of high enough sulphuric acid and ammonia concentrations is probably needed as the number of newly formed particles Was correlated with the product of the sulphuric acid production and the ammonia concentrations No such correlation was found with the oxidation products of terpenes. The condensation sink, i.e., effective particle area, is probably of importance as no nucleation was observed at high values of the condensation sink. From measurement of the hygroscopic properties of the nucleation particles it was found that inorganic compounds and hygroscopic organic compounds contributed both to the particle growth during daytime while at night time organic compounds dominated. Emissions rates for several gaseous compounds was determined. Using four independent ways to estimate the amount of the condensable vapour needed for observed growth of aerosol particles we get an estimate of 2-10 × 107 vapour molecules cm-3. The estimations for source rate give 7.5-11 x 104 cm-3 s-1. These results lead to the following conclusions: The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia). After nucleation, growth into observable sizes (≥3 nm) is required before new particles appear. The major part of this growth is probably due to condensation of organic vapours. However, there is lack of direct proof of this phenomenon because the composition of 1-5 nm size particles is extremely difficult to determine using the present state-of-art instrumentation.

### Overview of the synoptic and pollution situation over Europe during the EUCAARI-LONGREX field campai

 Date added: 02/07/2011 Date modified: 02/07/2011 Filesize: 2.98 MB

Hamburger, T., G. McMeeking, A. Minikin, W. Birmili, M. Dall’Osto, C. O’Dowd, H. Flentje, B. Henzing, H. Junninen, A. Kristensson, G. de Leeuw, A. Stohl, J. F. Burkhart, H. Coe, R. Krejci, and A. Petzold

Abstract. In May 2008 the EUCAARI-LONGREX aircraft field campaign was conducted within the EUCAARI intensive observational period. The campaign aimed at studying the distribution and evolution of air mass properties on a continental scale. Airborne aerosol and trace gas measurements were performed aboard the German DLR Falcon 20 and the British FAAM BAe-146 aircraft. This paper outlines the meteorological situation over Europe during May 2008 and the temporal and spatial evolution of predominantly anthropogenic particulate pollution inside the boundary layer and the free troposphere. Time series data of six  selected ground stations are used to discuss continuous measurements besides the single flights. The observations encompass total and accumulation mode particle number concentration (0.1–0.8 μm) and black carbon mass concentration as well as several meteorological parameters. Vertical profiles of total aerosol number concentration up to 10 km are compared to vertical profiles probed during previous studies.During the first half of May 2008 an anticyclonic blocking event dominated the weather over Central Europe. It led to increased pollutant concentrations within the centre of the high pressure inside the boundary layer. Due to long-range transport the accumulated pollution was partly advected towards Western and Northern Europe. The measured aerosol number concentrations over Central Europe showed in the boundary layer high values up to 14 000 cm−3 for particles in diameter larger 10 nm and 2300 cm−3 for accumulation mode particles during the high pressure period, whereas the middle free troposphere showed rather low concentrations of particulates. Thus a strong negative gradient of aerosol concentrations between the well mixed boundary layer and the clean middle troposphere occurred.

### 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.

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

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

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

Abstract

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

### Particle deposition in ventilation duct onto three-dimensional roughness elements

 Date added: 08/01/2002 Date modified: 07/03/2009 Filesize: 133.69 kB
A.C.K. Lai, M.A. Byrne, A.J.H. Goddard, Particle deposition in ventilation duct onto three-dimensional roughness elements, Building and Environment, 37, No .10, 939-945, 2002.

Abstract

Gaining insights on particle deposition onto ventilation duct has many important applications. One key pathway by which outdoor polluted air enters the indoor environment is through mechanical ventilation ducts. An experimental system was designed for the study of particle deposition on regular arrays of uniform elements (in the form of discrete protrusions) in a turbulent ventilation duct flow using monodisperse tracer small particles, in the range 0.7–7.1 μm. The Reynolds number for the test conditions was 44,000 in the 150 mm square duct. Four different types of uniform roughness elements were tested. Compared to earlier measurements in the same duct system involving smooth or ribbed surfaces, a significant increase (up to 74 times) in deposition velocity onto the regular roughness elements is observed.

### Particle mobility size spectrometers: harmonization of technical standards and data structure to fac

 Date added: 02/15/2011 Date modified: 02/15/2011 Filesize: 2.08 MB

Wiedensohler, A., Birmili, W., Nowak, A., Sonntag, A., Weinhold, K., Merkel, M., Wehner, B., Tuch, T., Pfeifer, S., Fiebig, M., Fjäraa, A. M., Asmi, E., Sellegri, K., Depuy, R., Venzac, H., Villani, P., Laj, P., Aalto, P., Ogren, J. A., Swietlicki, E., Roldin, P., Williams, P., Quincey, P., Hüglin, C., Fierz-Schmidhauser, R., Gysel, M., Weingartner, E., Riccobono, F., Santos, S., Grüning, C., Faloon, K., Beddows, D., Harrison, R. M., Monahan, C., Jennings, S. G., O'Dowd, C. D., Marinoni, A., Horn, H.-G., Keck, L., Jiang, J., Scheckman, J., McMurry, P. H., Deng, Z., Zhao, C. S., Moerman, M., Henzing, B., and de Leeuw, G.: Particle mobility size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions, Atmos. Meas. Tech. Discuss., 3, 5521-5587, doi:10.5194/amtd-3-5521-2010, 2010.

Particle mobility size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide application in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. This article results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research). Under controlled laboratory conditions, the number size distribution from 20 to 200 nm determined by mobility size spectrometers of different design are within an uncertainty range of ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. Instruments with identical design agreed within ±3% in the peak number concentration when all settings were done carefully. Technical standards were developed for a minimum requirement of mobility size spectrometry for atmospheric aerosol measurements. Technical recommendations are given for atmospheric measurements including continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyser. In cooperation with EMEP (European Monitoring and Evaluation Program), a new uniform data structure was introduced for saving and disseminating the data within EMEP. This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.

### Particle mobility size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions

 Date added: 03/19/2013 Date modified: 03/19/2013 Filesize: 1021.65 kB

Wiedensohler, A., Birmili, W., Nowak, A., Sonntag, A., Weinhold, K., Merkel, M., Wehner, B., Tuch, T., Pfeifer, S., Fiebig, M., Fjäraa, A. M., Asmi, E., Sellegri, K., Depuy, R., Venzac, H., Villani, P., Laj, P., Aalto, P., Ogren, J. A., Swietlicki, E., Roldin, P., Williams, P., Quincey, P., Hüglin, C., Fierz-Schmidhauser, R., Gysel, M., Weingartner, E., Riccobono, F., Santos, S., Grüning, C., Faloon, K., Beddows, D., Harrison, R. M., Monahan, C., Jennings, S. G., O'Dowd, C. D., Marinoni, A., Horn, H.-G., Keck, L., Jiang, J., Scheckman, J., McMurry, P. H., Deng, Z., Zhao, C. S., Moerman, M., Henzing, B., and de Leeuw, G.: Particle mobility size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions, Atmos. Meas. Techs., Vol 5 Issue 3 Pages 657-685 DOI: 10.5194/amt-5-657-2012,2012.

Abstract. Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental setup, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30 %, which could not be explained. The network reference mobility spectrometers with identical design agreed within ±4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5 %. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.

### Particle size dependent response of aerosol counters

 Date added: 08/01/2002 Date modified: 07/03/2009 Filesize: 652.99 kB
Ankilov, A., A Baklanov, M. Colhoun, K-H. Enderle, J. Gras, Yu Jualanov, D. Kaller, A. Linder, A.A. Lushnikov, R. Mavliev, F. McGovern, T.C. O'Connor, J. Podzimek, O. Prining, G.P. Reischl, R. Rudolf, G.J. Sem, W.W. Szymanski, E. Tamm, A.E. Vrtala, P.E. Wagner, W. Winklmayr and V. Zagaynov, Particle size dependent response of aerosol particle counters, Atmos. Res., 62, 209-238, 2002.

Abstract

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.

The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.

### Perfluorodecalin global warming potential and first detection in the atmosphere

 Date added: 08/07/2005 Date modified: 07/23/2009 Filesize: 233.75 kB

Shine KP, Gohar LK, Hurley MD, Marston G, Martin D, Simmonds PG, Wallington TJ and Watkins M, 2005: Perfluorodecalin: global warming potential and first detection in the atmosphere. Atmospheric Environment doi:10.1016/j.atmosenv.2005.01.001

Abstract

Perfluorodecalin (C10F18) has a range of medical uses that have led to small releases. Recently, it has been proposed as a carrier of vaccines, which could lead to significantly larger emissions. Since its emissions are controlled under the Kyoto Protocol, it is important that values for the global warming potential (GWP) are available. For a 50:50 mixture of the two isomers of perfluorodecalin, laboratory measurements, supplemented by theoretical calculations, give an integrated absorption cross-section of 3.91×10−16 cm2 molecule−1 cm−1 over the spectral region 0–1500 cm−1; calculations yield a radiative efficiency of 0.56 W m−2 ppbv−1 and a 100-year GWP, relative to carbon dioxide, of 7200 assuming a lifetime of 1000 years. We report the first atmospheric measurements of perfluorodecalin, at Bristol, UK and Mace Head, Ireland, where volume mixing ratios are about 1.5×10−15. At these concentrations, it makes a trivial contribution to climate change, but on a per molecule basis it is a potent greenhouse gas, indicating the need for careful assessment of its possible future usage.

### Performance of a venturi dilution chamber for sampling 3-20 nm particles

 Date added: 08/01/2005 Date modified: 07/23/2009 Filesize: 207.08 kB

Yoon, Y.J., S. Cheevers, S.G. Jennings, C.D. O’Dowd, Performance of a venturi dilution chamber for sampling 3-20 nm particles. J. Aerosol Science, 2005, 36(4), pp 535-540. doi:10.1016/j.jaerosci.2004.10.004

Abstract

The transmission efficiency of a venturi mixing and dilution system was investigated with laboratory generated aerosol by comparison of two condensation particle counters (CPCs). The transmission efficiency exceeded 95% for particle sizes between 3 and 20 nm. The use of the diluter system is demonstrated through comparison with total concentrations derived from a nano-scanning mobility particle sizer (nSMPS) applied to measuring a rapidly changing atmospheric nucleation mode. The study indicates that the diluted-CPC sampler can resolve rapidly changing, and more intense peaks in excess of 106 cm-3, which are otherwise missing or under-sampled by the nSMPS.

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

Abstract

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

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

### Photochemical impact on ozone fluxes in Coastal Waters

 Date added: 03/19/2013 Date modified: 03/19/2013 Filesize: 496.45 kB

Coleman, L., P. McVeigh, H. Berresheim, M. Martino, C.D. O’Dowd, Photochemical impact on ozone fluxes in Coastal Waters, Advances in Meteorology, Volume 2012, Article ID 943785, doi:10.1155/2012/943785, 2012

Abstract. Ozone fluxes, derived from gradient measurements in Northeast Atlantic coastal waters, were observed to depend on both tide height and solar radiation. Peak ozone fluxes of 0.26 ±0.04 μg m2 s1 occurred during low-tide conditions when exposed microalgae fields contributed to the flux footprint. Additionally, at mid-to-high tide, when water surfaces contribute predominantly to the flux footprint, fluxes of the order of 0.12 ±0.03 μg m2 s1 were observed. Considering only fluxes over water covered surfaces, and using an advanced ozone deposition model that accounts for surface-water chemistry enhancing the deposition sink, it is demonstrated that a photochemical enhancement reaction with dissolved organic carbon (DOC) is required to explain the enhanced ozone deposition during daylight hours. This sink amounts to an ozone loss rate of up to 0.6 ppb per hour under peak solar irradiance and points to a missing sink in the marine boundary layer ozone budget.

### Photochemical ozone formation in north west Europe and its control

 Date added: 08/07/2003 Date modified: 07/23/2009 Filesize: 635.36 kB

DERWENT, R.G., Jenkin, M.E., Saunders, S.M., Pilling, M.J., Simmonds, P.G., Passant, N.R., Dollard, G.J., Dumitrean, P. and Kent, A., 2003: Photochemical ozone formation in north west Europe and its control. Atmos Environ, 37, 1,983-1,991.

Abstract

A photochemical trajectory model together with a Master Chemical Mechanism and a highly speciated emission inventory for organic compounds have been used to describe the formation of ozone in north west Europe and to identify the most prolific ozone-forming organic compounds. Observations are reviewed to assess the impact of emission controls on their urban volatile organic compound (VOC) concentration trends with time. The observed trends are then used to deduce the likely trends in episodic peak ozone concentrations and to compare them with observed trends in peak ozone concentrations. It is concluded that it is likely that motor vehicle emission controls have brought about a substantial reduction in episodic peak ozone concentrations in north west Europe during the 1990s.

### 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.

### Physical Characteristic of the Ambient Aerosol At Macehead

 Date added: 07/31/1991 Date modified: 07/23/2009 Filesize: 3.29 MB

Jennings, S.G., O'Dowd, C.D., O'Connor, T.C., and McGovern, F.M (1991). - Physical characteristics of the ambient aerosol at Mace Head. Atmos. Environ., 25A, 557 - 562.

Abstract

This paper describes results of a reasonably extensive series of ambient aerosols measurements conducted for the first time from MAce HEad, on the west coast of Ireland. Aerosol size distributions (0.045 <radius,r, <1.5 micrometres (Um)) And Basic meteorological parameters were measured under both maritime, modified maritime and continental air mass conditions. It was found that the shape of the size distribution spectra is dependent on air mass source

### Physical characterization of aerosol particles during nucleation events

 Date added: 07/31/2001 Date modified: 07/03/2009 Filesize: 435.73 kB

Aalto, P.P., K. Hämeri, E. Becker, R. Weber, J. Salm, J.M. Mäkelä, C. Hoell, C.D. O'Dowd, H. Karlsson, H-C. Hansson, M. Väkevä, I. Koponen, G. Buzorius, and M. Kulmala, Physical characteristics of aerosol particles during nucleation events. in press Tellus B, 53, 344-345,, 2001.

Abstract

Particle concentrations and size distributions have been measured from different heights inside and above a boreal forest during three BIOFOR campaigns (14 April–22 May 1998, 27 July– 21 August 1998 and 20 March–24 April 1999) in Hyytia¨la¨, Finland. Typically, the shape of the background distribution inside the forest exhibited 2 dominant modes: a fine or Aitken mode with a geometric number mean diameter of 44 nm and a mean concentration of 1160 cm−3 and an accumulation mode with mean diameter of 154 nm and a mean concentration of 830 cm−3. A coarse mode was also present, extending up to sizes of 20 mm having a number concentration of 1.2 cm−3, volume mean diameter of 2.0 mm and a geometric standard deviation of 1.9. Aerosol humidity was lower than 50% during the measurements. Particle production was observed on many days, typically occurring in the late morning. Under these periods of new particle production, a nucleation mode was observed to form at diameter of the order of 3 nm and, on most occasions, this mode was observed to grow into Aitken mode sizes over the course of a day. Total concentrations ranged from 410–45 000 cm−3, the highest concentrations occurring on particle production days. A clear gradient was observed between particle concentrations encountered below the forest canopy and those above, with significantly lower concentrations occurring within the canopy. Above the canopy, a slight gradient was observed between 18 m and 67 m, with at maximum 5% higher concentration observed at 67 m during the strongest concentration increases.

### 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.

### Physicochemical properties of atmospheric aerosol at South UIST

 Date added: 08/06/1996 Date modified: 07/03/2009 Filesize: 906.46 kB

J. A. Lowe, M. H. Smith, B. M. Davison, S. E. Benson, M. K. Hill, C. D. O'Dowd, R. M. Harrison, C. N. Hewitt, Physicochemical properties of atmospheric aerosol at South UIST, Atmospheric EnvironmentVolume 30, Issue 22, , November 1996, Pages 3765-3776.

Abstract

Four field campaigns over the period November 1993 to August 1994 were undertaken on the island of South Uist, off the northwest coast of Scotland as part of the BMCAPE project. Measurements were made of the concentration and chemical composition of aerosol particles, utilising a variety of instruments. Sulphur and nitrogen gas species were also measured throughout these campaigns, together with appropriate meteorological parameters. A variety of air mass types were encountered during the campaigns and the relationship between the physical and chemical aerosol properties are discussed in terms of air mass histories and season factors.

### 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.

### 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.

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

 Date added: 08/06/2002 Date modified: 09/11/2009 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.

### Primary and secondary marine organic aerosols over the North Atlantic Ocean during the MAP experiment

 Date added: 03/19/2013 Date modified: 03/19/2013 Filesize: 1.9 MB

Decesari, S., E. Finessi, M. Rinaldi, M. Paglione, S. Fuzzi, E. G. Stephanou, T. Tziaras, A.Spyros, D. Ceburnis, C. O'Dowd, M. Dall’Osto, R. Harrison, J. Allan, H. Coe, M. C. Facchini, Primary and secondary marine organic aerosols over the North Atlantic Ocean during the MAP experiment, J. Geophys. Res., 116, D22210, doi:10.1029/2011JD016204, 2011

Abstract.

The organic chemical composition of atmospheric submicron particles in the marine boundary layer was characterized over the northeast Atlantic Ocean in summer 2006, during the season of phytoplankton blooms, in the frame of the Marine Aerosol Production (MAP) experiment. First measurements of water insoluble organic carbon (WIOC) in marine aerosol particles by nuclear magnetic resonance (NMR) spectroscopy showed that it is structurally similar to lipids, resembling the organic fraction of sea spray formed during bubble bursting experiments. The composition of the watersoluble organic carbon (WSOC) fraction was investigated by liquid chromatography mass spectrometry and by 1D and 2DNMR spectroscopy, and showed a less hydrophilic fraction containing traces of fatty acids and rich of alkanoic acids formed by lipid degradation, and a more hydrophilic fraction, containing more functionalized species encompassing short chain aliphatic acids and sulfate esters of hydroxyl carboxylic acids. The more oxidized fraction of WSOC accounts for the oxidized organic aerosol components, which can form by either gastoparticle conversion or extensive chemical aging of lipidcontaining primary particles, as also suggested by the parallel measurements using online mass spectrometric techniques (presented in a companion paper), showing oxidized organic substances internally mixed with sea salt particles. These measurements are also compared with online measurements using an Aerosol TimeOfFlight Mass Spectrometer (ATOFMS) and Aerodyne Aerosol Mass Spectrometer (AMS). Given the large variability in the chemical composition of marine organic aerosol particles, a multitechnique approach is recommended to reduce method dependent categorizations and oversimplifications and to improve the comparability with the results obtained in different oceanic areas.

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

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

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

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

### Primary marine aerosol emissions size resolved eddy covariance measurements with estimates of the sea salt and organic carbon fractions

 Date added: 08/01/2007 Date modified: 07/23/2009 Filesize: 1.75 MB

Nilsson, E.D., E. M. Mårtensson, J. S. Van Ekeren, G. de Leeuw, M. Moerman, and C. O'Dowd, Primary marine aerosol emissions: size resolved eddy covariance measurements with estimates of the sea salt and organic carbon fractions, Atmos. Chem. Phys. Discuss., 7, 13345-13400, 2007

Abstract

Primary marine aerosol fluxes were measured using eddy covariance (EC), a condensation particle counter (CPC) and an optical particle counter (OPC) with a heated inlet. The later was used to discriminate between sea salt and total aerosol. Measurements were made from the 25 m tower at the research station Mace Head at the Irish west coast, May to September 2002. The aerosol fluxes were dominated by upward fluxes, sea spray from bubble bursting at the ocean surface. The sea salt aerosol number emissions increased two orders of magnitude with declining diameter from 1 to 0.1 μm where it peaked at values of 105 to 107 particles m−2s−1. The sea salt emissions increased at all sizes in the wind range 4 to 22 ms−1, in consistency with a power function of the wind speed. The sea salt emission data were compared to three recent sub micrometer sea salt source parameterisations. The best agreement was with Mårtensson et al. (2003), which appear to apply from 0.1 to 1.1 μm diameters in temperate water (12°C) as well as tropical water (25°C). The total aerosol emissions were independent of the wind speed below 10 ms−1, but increased with the wind above 10 ms−1. The aerosol volume emissions were larger for the total aerosol than for the sea salt at all wind speeds, while the sea salt number emissions approached the total number emissions at 15 ms−1. It is speculated that this is caused by organic carbon in the surface water that is depleted at high wind speeds. The data are consistent with an internal aerosol mixture of sea salt, organic carbon and water. Using the aerosol model by Ellison et al. (1999) (a mono-layer of organic carbon surrounding a water-sea-salt brine) we show that the total and sea salt aerosol emissions are consistent. This predict that the organic carbon fraction increase with decreasing diameter from a few % at 1 μm over 50% at about 0.5 μm to about 90% at 0.1 μm, in consistency with simultaneous chemical data by Cavalli et al. (2004). The combined models of Mårtensson et al. (2003) and Ellison et al. (1999) reproduce the observed total aerosol emissions and offer an approach to model the organic sea spray fraction.

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

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

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

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

### Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates

 Date added: 04/08/2009 Date modified: 11/01/2009 Filesize: 220.61 kB
Facchini, M.C.,  M. Rinaldi, S. Decesari, C. Carbone, E. Finessi, M. Mircea, S. Fuzzi, D. Ceburnis, R.  Flanagan, E. D. Nillsson, G.  de Leeuw, M. Martino,  J. Woeltjen and C.D. O’ Dowd, Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates,, Geophys. Res. Letts., doi:10.1029/2008GL034210, 2008.

Abstract

The chemical properties of sea-spray aerosol particles produced by artificially generated bubbles using oceanic waters were investigated during a phytoplankton bloom in the North Atlantic. Spray particles exhibited a progressive increase in the organic matter (OM) content from 3 ± 0.4% up to 77 ± 5% with decreasing particle diameter from 8 to 0.125 mm. Submicron OM was almost entirely water insoluble (WIOM) and consisted of colloids and aggregates exuded by phytoplankton. Our observations indicate that size dependent transfer of sea water organic material to primary marine particles is mainly controlled by the solubility and surface tension properties of marine OM. The pattern of WIOM and sea-salt content in the different size intervals observed in bubble bursting experiments is similar to that measured in atmospheric marine aerosol samples collected during periods of high biological activity. The results point to a WIOM/sea-salt fingerprint associated with submicron primary marine aerosol production in biologically rich waters.

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

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

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

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

### Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter.

 Date added: 08/31/1946 Date modified: 07/22/2009 Filesize: 4.32 MB
P.J Nolan, L.W. Pollack, Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter., Volume L1, Section A, No. 2, 1946

Abstract

Models of nucleus counterm designed to measure photo-electrically the decrease in intensity of a beam of light which has passed one or more times through an artificially produced fog, are described by L.W. Pollak and W.A. Morgan in a paper.

### Production Flux of Sea-Spray Aerosol. Rev. of Geophys.,

 Date added: 05/12/2011 Date modified: 05/12/2011 Filesize: 2.68 MB

de Leeuw, G., E. Andreas, M. Anguelova , C. Fairall , E. Lewis , C. O'Dowd , M. Schulz , S. Schwartz , Production Flux of Sea-Spray Aerosol. Rev. of Geophys., doi:10.1029/2010RG000349, 2011

Knowledge of the sizeand compositiondependent production flux of primary sea spray aerosol (SSA) particles and its dependence on environmental variables is required for modeling cloud microphysical properties and aerosol radiative influences, interpreting measurements of particulate matter in coastal areas and its relation to air quality, and evaluating rates of uptake and reactions of gases in sea spray drops. This review examines recent research pertinent to SSA production flux, which deals mainly with production of particles with r80 (equilibrium radius at 80% relative humidity) less than 1 mm and as small as 0.01 mm. Production of sea spray particles and its dependence on controlling factors has been investigated in aboratory studies that have examined the dependences on water temperature, salinity, and the presence of organics and in field measurements with micrometeorological techniques that use newly developed fast optical particle sizers. Extensive measurements show that waterinsoluble organic matter contributes substantially to the omposition of SSA particles with r80 < 0.25 mm and, in locations with high biological activity, can be the ominant constituent. Orderofmagnitude variation  remains in estimates of the sizedependent production flux per white area, the quantity central to formulations of the production flux based on the whitecap method. This variation indicates that the production flux may depend on quantities such as the volume flux of air bubbles to the surfacet hat are not accounted for in current models. Variation in estimates of the whitecap fraction as a function of wind speed contributes additional, comparable uncertainty to production flux estimates.

### Production Of Cn by Gaseous Reactions

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

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

### PRODUCTION OF METHANOL, ACETONE AND. ACETALDEHYDE DURING LONG-RANGE. TRANSPORT

 Date added: 08/07/2003 Date modified: 08/07/2008 Filesize: 32.63 kB
Stanton, J.C.; Pilling, M.J.; Hopkins, J.R.; Lewis, A.C.Production of methanol, acetone and acetaldehyde during long-range transport [EGU04-A-07457].

### Production of peroxy radicals at night via reactions of ozone and the nitrate radical in the ma

 Date added: 08/06/2001 Date modified: 07/23/2009 Filesize: 1.44 MB

Salisbury, G., et al. (2001), Production of peroxy radicals at night via reactions of ozone and the nitrate radical in the marine boundary layer, J. Geophys. Res., 106(D12), 12,669–12,687.

Abstract

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

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

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

Abstract

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

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

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

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

Abstract

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

### Quantification of the carbonaceous matter origin in submicron marine aerosol particles by dual carbo

 Date added: 08/25/2011 Date modified: 08/25/2011 Filesize: 5.12 MB

Ceburnis, A. Garbaras, S. Szidat, M. Rinaldi, S. Fahrni, N. Perron, L. Wacker, S. Leinert, V. Remeikis, M. C. Facchini, A. S. H. Prevot, S. G. Jennings, and C. D. O'Dowd. Quantification of the carbonaceous matter origin in submicron marine aerosol particles by dual carbon isotope analysis,  Atmos. Chem. Phys., 11, 8593–8606, 2011, doi:10.5194/acp-11-8593-2011

Abstract.

Dual carbon isotope analysis of marine aeroso samples has been performed for the first time demonstrating a potential in organic matter apportionment  etween three principal sources: marine, terrestrial (non-fossil) and fossil fuel due to unique isotopic signatures. The results presented here, utilising combinations of dual carbon isotope analysis, provides conclusive evidence of a dominant biogenic organic fraction to organic aerosol over biologically active oceans. In particular, the NE Atlantic, which is also subjected to notable anthropogenic influences via pollution transport processes, was found to contain 80% organic aerosol matter of biogenic origin directly linked to plankton emissions. The remaining carbonaceous aerosol was of terrestrial origin. By contrast, for polluted air advected out from Europe into the NE Atlantic, the source apportionment is 30% marine biogenic, 40% fossil fuel, and 30% continental non-fossil fuel. The dominant marine organic aerosol source in the atmosphere has significant implications for climate change feedback processes.

### Quasi-Lagrangian investigation into dimethyl sulfide oxidation in maritime air using a combinat

 Date added: 08/06/2000 Date modified: 07/23/2009 Filesize: 1.6 MB

James, J. D. ; Harrison, Roy M. ; Savage, N. H. ; Allen, A. G. ; Grenfell, J. L. ; Allan, B. J. ; Plane, J. M. C. ; Hewitt, C. N. ; Davison, B. ; Robertson, L.  2000, Quasi-Lagrangian investigation into dimethyl sulfide oxidation in maritime air using a combination of measurements and model, J. Geophys. Res. Vol. 105 , No. D21 , p. 26,379 (2000JD900375)

Abstract

Using a combination of field measurement data and a modified photochemical box model, strong evidence is presented to suggest that the rate of daytime oxidation of dimethyl sulfide (DMS) by OH radicals is insufficient to describe the measured conversion. Quasi-Lagrangian measurements were made at two sites in the eastern Atlantic (Research Vessel and Mace Head Research Station, Ireland) as part of the Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) program. Periods of connected flow between the two sites were identified, air parcel transit times were estimated, and measurements of the main DMS oxidation products (MSA, SO2, and nss-SO42-) were compared with model predictions to establish whether the model's chemical mechanism could account for observed changes. The main finding was that during daytime periods with maritime air masses, the model failed to predict a sufficient increase in DMS oxidation products during the estimated transit time. This was despite a tendency to overprediction of the progress of nitrogen chemistry during air mass advection, and independent checks on the model estimates of hydroxyl radical concentrations through measurements. In the light of this, the involvement of halogen species (most probably halogen oxides) or heterogeneous oxidation processes is tentatively suggested as the cause of enhanced daytime DMS oxidation in the marine boundary layer (MBL). Increasing the rate constant for the OH + DMS reaction by a factor of 3.3 (as a crude way of simulating parallel channels of DMS oxidation) permitted model results to reproduce the measurements very much more closely.

### Raindrop interactions and rainfall rates within clouds

 Date added: 11/30/1972 Date modified: 07/06/2009 Filesize: 787.75 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J. (1973)- Raindrop interactions and rainfall rates within clouds. Quart. J. Roy. Met. Soc., 99, 260-272.

Abstract

Experiments showed that when a pair of water drops of raindrop dimensions collide and separate in air at their relative terminal velocities satellite drops are generally produced. Although the numbers and sizes of satellites resulting from individual interactions are highly variable a typical event produces about 3 satellites each having a volume of 0.04 ViVj/(Vi + Vj), where Vi and Vj are the volumes of the parent drops.

A full stochastic treatment is presented of the development of rainfall in a volume within a cloud where water is being released by condensation at a constant rate J. The production of satellites and an experimentally verified expression for the coalescence efficiency are incorporated into these calculations. Computations are made of the variation with time of the cloud water content, C, the rainwater content, L, the radar reflectivity, Z, the rainfall rate, P, and the drop-size distribution. The calculations show that the crucial parameter in governing the intensity and duration of rainfall is J, and that the microphysical processes are of secondary importance; C, L and P are all insensitive to and the production of satellite drops. The influence upon rainfall development of the break-up of large raindrops on attaining their maximum size within a cloud is found to be even less than that of the satellites.

The drop size distribution after several minutes of growth is insensitive to the initial spectrum but is markedly dependent upon and the production of satellites, which tend eventually to produce a bimodal spectrum. The radar reflectivity increases very rapidly with time (typically by about an order of magnitude every 2 1/2 minutes) and depends quite strongly on , but is unaffected by the production of satellites.

### Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Adv

 Date added: 08/06/2004 Date modified: 07/23/2009 Filesize: 791.05 kB

O'Doherty, S., et al. (2004), Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Advanced Global Atmospheric Gases Experiment (AGAGE) observations at Cape Grim, Tasmania, and Mace Head, Ireland, J. Geophys. Res., 109, D06310, doi:10.1029/2003JD004277.

Abstract

### Recent Tropospheric Growth Rate and Distribution of HFC-134a (CF3CH2F)

 Date added: 08/06/1996 Date modified: 07/23/2009 Filesize: 488.65 kB

Oram, D.E., Reeves, C.E., Sturges, W.T., Penkett, S.A., Fraser, P.J. and Langenfelds, R.L. 1996. Recent tropospheric growth rate and distribution of HFC-134a (CF3CH2F). Geophysical Research Letters 23:1949-1952.

Abstract

Air samples collected at Cape Grim, Tasmania (41°S) between 1978 and 1995, and at Mace Head, Ireland (53°N) between July 1994 and May 1995, have been analysed by GC-MS to determine recent trends of HFC-134a, an important CFC replacement, in the background atmosphere. Until 1990, the concentration of HFC-134a at Cape Grim was below detection limits, the first quantifiable level (0.01 pptv) appearing in May 1990. Between 1992 and mid-1995 the concentration grew exponentially at ∼200 % yr-1 with the concentration at the end of 1994 reaching 0.43 pptv. At Mace Head, HFC-134a grew at a rate of 1.24 ± 0.11 pptv yr-1 between July 1994 and May 1995, with the concentration at the end of 1994 being 1.48 pptv. In the absence of industrial production and release estimates for HFC-134a, the observations have been used in conjunction with a 2-D global model to estimate recent emissions. The model indicates that significant emissions (250 tonnes) began in 1991, increasing rapidly to a level of ∼8 ktonnes in 1994.

### Regional climate model simulations of North Atlantic cyclones frequency and intensity changes

 Date added: 08/01/2008 Date modified: 07/23/2009 Filesize: 4.19 MB
Semmler, T., S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, and C. O'Dowd (2008) 'Regional climate model simulations of North Atlantic cyclones: frequency and intensity changes'. Climate Research, 36 :1-16.

Abstract

Frequency and intensity of cyclones over the North Atlantic are investigated using 2 data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by ECHAM5- OM1 general circulation model data for May to December from 1985 to 2000 and May to December from 2085 to 2100 assuming the SRES-A2 emission scenario. We apply an objective algorithm to identify and track tropical and extratropical cyclones, as well as extratropical transition. The simulation indicates increase in the count of strong hurricanes and extratropical cyclones. Contrasting, and generally weaker, changes are seen for the less extreme events. Decreases of 18% in the count of extratropical cyclones and 13% in the count of tropical cyclones with wind speeds of ≥18 m s–1 can be found. Furthermore, there is a pronounced shift in the tracks of hurricanes and their extratropical transition in November and December—more hurricanes are seen over the Gulf of Mexico, the Caribbean Sea and the western Sargasso Sea and less over the southern North Atlantic.

### Regional climate simulations of North Atlantic cyclones: changes .. in a climate change scenario

 Date added: 08/06/2008 Date modified: 07/23/2009 Filesize: 4.19 MB

Semmler, S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, C. O'Dowd, Regional climate simulations of North Atlantic cyclones: changes in frequency and intensity in a climate change scenario, Climate Res. Vol. 36: 1–16, 2008, doi: 10.3354/cr00732,  2008

Abstract

Frequency and intensity of cyclones over the North Atlantic are investigated using 2 data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by ECHAM5- OM1 general circulation model data for May to December from 1985 to 2000 and May to December from 2085 to 2100 assuming the SRES-A2 emission scenario. We apply an objective algorithm to identify and track tropical and extratropical cyclones, as well as extratropical transition. The simulation
indicates increase in the count of strong hurricanes and extratropical cyclones. Contrasting, and generally weaker, changes are seen for the less extreme events. Decreases of 18% in the count of extratropical cyclones and 13% in the count of tropical cyclones with wind speeds of ≥18 m s–1 can be found. Furthermore, there is a pronounced shift in the tracks of hurricanes and their extratropical transition in November and December—more hurricanes are seen over the Gulf of Mexico, the Caribbean Sea and the western Sargasso Sea and less over the southern North Atlantic.

### Regional model simulation of North Atlantic cyclones Present climate and idealized response to incre

 Date added: 08/01/2008 Date modified: 07/23/2009 Filesize: 2.79 MB
Semmler, T., S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, and C. O'Dowd, Regional model simulation of North Atlantic cyclones: Present climate and idealized response to increased sea surface temperature, J. Geophys. Res., 113, D02107, doi:10.1029/2006JD008213, 2008.

Abstract

The influence of an increased sea surface temperature (SST) on the frequency and intensity of cyclones over the North Atlantic is investigated using two data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by reanalysis data for May to December 1985–2000 at the lateral and lower boundaries, using SST and lateral boundary temperatures. A realistic interannual variation in tropical storm and hurricane counts is simulated. In an idealized sensitivity experiment, SSTs and boundary condition temperatures at all levels are increased by 1 K to ensure that we can distinguish the SST from other factors influencing the development of cyclones. An increase in the count of strong hurricanes is simulated. There is not much change in the location of hurricanes. Generally weaker changes are seen in the extratropical region
and for the less extreme events. Increases of 9% in the count of extratropical cyclones and 39% in the count of tropical cyclones with wind speeds of at least 18 m/s are found.

### Regional model simulation of North Atlantic cyclones...response to increased sea surface temper

 Date added: 08/06/2007 Date modified: 07/06/2009 Filesize: 2.79 MB

Semmler, T., S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, and C. O'Dowd (2008), Regional model simulation of North Atlantic cyclones: Present climate and idealized response to increased sea surface temperature, J. Geophys. Res., 113, D02107, doi:10.1029/2006JD008213.

Abstract

The influence of an increased sea surface temperature (SST) on the frequency and intensity of cyclones over the North Atlantic is investigated using two data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by reanalysis data for May to December 1985–2000 at the lateral and lower boundaries, using SST and lateral boundary temperatures. A realistic interannual variation in tropical storm and hurricane counts is simulated. In an idealized sensitivity experiment, SSTs and boundary condition temperatures at all levels are increased by 1 K to ensure that we can distinguish the SST from other factors influencing the development of cyclones. An increase in the count of strong hurricanes is simulated. There is not much change in the location of hurricanes. Generally weaker changes are seen in the extratropical region and for the less extreme events. Increases of 9% in the count of extratropical cyclones and 39% in the count of tropical cyclones with wind speeds of at least 18 m/s are found.

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

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

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

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

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