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

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Documents

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

Perfluorodecalin global warming potential and first detection in the atmosphere 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.

 

Particle size dependent response of aerosol counters 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.

Particle mobility size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions 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 mobility size spectrometers: harmonization of technical standards and data structure to fac 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 deposition in ventilation duct onto three-dimensional roughness elements 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 counting and numerical models: Effect of instrumental size resolution and particle shapes o 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.

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

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

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


Abstract


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

 

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

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

Organic matter contribution to marine aerosols and cloud condensation nuclei 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.

Organic aerosol formation via sulphate cluster activation 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.

 

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

Optical properties of the atmospheric aerosol at mace head 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 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.

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

Opendda: a Novel High-Performance Computational Framework for the Discrete Dipole Approximation Opendda: a Novel High-Performance Computational Framework for the Discrete Dipole Approximation

Date added: 02/15/2011
Date modified: 02/15/2011
Filesize: 1.26 MB

James Mc Donald, Aaron Golden, and S. Gerard Jennings

Opendda: a Novel High-Performance Computational Framework for the Discrete Dipole Approximation.  International Journal of High Performance Computing Applications, February 2009 23: 42-61, doi:10.1177/1094342008097914, 2009

This work presents a highly optimized computational framework for the Discrete Dipole Approximation, a numerical method for calculating the optical properties associated with a target of arbitrary geometry that is widely used in atmospheric, astrophysical and industrial simulations. Core optimizations include the bit-fielding of integer data and iterative methods that complement a new Discrete Fourier Transform (DFT) kernel, which efficiently calculates the matrix— vector products required by these iterative solution schemes. The new kernel performs the requisite 3-D DFTs as ensembles of 1-D transforms, and by doing so, is able to reduce the number of constituent 1-D transforms by 60% and the memory by over 80%. The optimizations also facilitate the use of parallel techniques to further enhance the performance. Complete OpenMP-based shared-memory and MPI-based distributed-memory implementations have been created to take full advantage of the various architectures. Several benchmarks of the new framework indicate extremely favorable performance and scalability.

 

 

 


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

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

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


Abstract


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

On the spatial distribution and evolution of ultrafine aerosols in Barcelona On the spatial distribution and evolution of ultrafine aerosols in Barcelona

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.29 MB

Dall'Osto, M., X. Querol, A. Alastuey, C. O'Dowd, R. M. Harrison, J. Wenger, and F. J. Gómez-Moreno, On the spatial distribution and evolution of ultrafine aerosols in Barcelona, Atmos. Chem. Phys. 13, 741–759, 2013, doi:10.5194/acp-13-741-2013.


Abstract. Sources and evolution of ultrafine particles were investigated both horizontally and vertically in the large urban agglomerate of Barcelona, Spain. Within the SAPUSS project (Solving Aerosol Problems by Using Synergistic Strategies), a large number of instruments was deployed simultaneously at different monitoring sites (road, two urban background, regional background, urban tower 150m a.s.l., urban background tower site 80m a.s.l.) during a 4 week period in September–October 2010. Particle number concentrations (N>5nm) are highly correlated with black carbon (BC) at all sites only under strong vehicular traffic influences. By contrast, under cleaner atmospheric conditions (low condensation sink, CS) such correlation diverges towards much higher N/BC ratios at all sites, indicating additional sources of particles including secondary production of freshly nucleated particles. Size-resolved aerosol distributions (N10−500) as well as particle number concentrations (N>5 nm) allow us to identify three types of nucleation and growth events: (1) a regional type event originating in the whole study region and impacting almost simultaneously the urban city of Barcelona and the surrounding urban background area; (2) a regional type event impacting only the regional background area but not the urban agglomerate; (3) an urban type event which originates only within the city centre but whose growth continues while transported away from the city to the regional background. Furthermore, during these clean air days, higher N are found at tower level than at ground level only in the city centre whereas such a difference is not so pronounced at the remote urban background tower. In other words, this study suggests that the column of air above the city ground level possesses the optimal combination between low CS and high vapour source, hence enhancing the concentrations of freshly nucleated particles. By contrast, within stagnant polluted atmospheric conditions, higher N and BC concentrations are always measured at ground level relative to tower level at all sites. Our study suggests that the city centre of Barcelona is a source of non-volatile traffic primary particles (29–39% of N>5nm), but other sources, including secondary freshly nucleated particles contribute up to 61–71% of particle number (N>5nm) at all sites. We suggest that organic compounds evaporating from freshly emitted traffic particles are a possible candidate for new particle formation within the city and urban plume.

 

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

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

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


Abstract.  

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

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

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

Abstract

 

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


On the Photochemical production of new particles in the coastal boundary layer On the Photochemical production of new particles in the coastal boundary layer

Date added: 09/11/1999
Date modified: 07/13/2009
Filesize: 420.57 kB

O’Dowd, C., et al. (1999), On the Photochemical Production of New Particles in the Coastal Boundary Layer, Geophys. Res. Lett., 26(12), 1707–1710.


Abstract


Concurrent measurements of ultra-fine (r<5 nm) particle (UFP) formation, OH and SO2 concentrations in the coastal environment are examined to further elucidate the processes leading to tidal-related homogeneous heteromolecular nucleation. During almost daily nucleation events, UFP concentration approached ≈300,000 cm−3 under conditions of solar radiation and low tide. Simultaneous measurements of OH illustrate that, as well as occurring during low tide, these events occur during conditions of peak OH concentration, suggesting that at least one of the nucleating species is photochemically produced. Derived H2SO4 production also exhibited remarkable coherence, although phase-lagged, with UFP formation, thus suggesting its involvement, although binary nucleation of H2SO4 and H2O can be ruled out as a plausible mechanism. Ternary nucleation involving NH3 seems most likely as a trigger mechanism, however, at least a fourth condensable species, X, is required for growth to detectable sizes. Since UFP are only observed during low tide events, it is thought that species X, or it’s parent, is emitted from the shore biota - without which, no nucleation is detected. Species X remains to be identified. Model simulations indicate that, in order to reproduce the observations, a nucleation rate of 107 cm−3 s−1, and a condensable vapour concentration of 5 × 107 cm−3, are required.

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

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

On The Occurrence of Open Ocean Particle Production Events On The Occurrence of Open Ocean Particle Production Events

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 603.03 kB

O’Dowd, C.D, C. Monahan and M. Dall’Osto, On The Occurrence of Open Ocean Particle Production Events, Geophys. Res. Letts., 37, L19805, doi:10.1029/2010GL044679,  2010.


We present new results from the Mace Head coastal station illustrating that open ocean new particle production and growth events occur frequently during periods of high oceanic productivity over the N.E. Atlantic. For the first time, we report events during which a recently 

formed nucleation mode (15 nm diameter) is detected and is observed to grow into an Aitken mode (50 nm diameter) over periods up to 48 hours. A growth rate of 0.8 nm hour1 is estimated in a typical case study, pointing to a source region 700 km offshore. The duration of the growth also suggests the particle production events are occurring over large spatial scales. Analysis of seven yearsof data show occurrence of extended growth events (lasting at least 24 hours) from March to September, with a peak occurrence in May. The events suggest that secondary marine boundary layer aerosol formation contributes to the marine aerosol population.

On the formation, growth and composition of nucleation mode particles On the formation, growth and composition of nucleation mode particles

Date added: 08/06/2001
Date modified: 07/03/2009
Filesize: 428.69 kB

Kulmala, M.,M. Dal Maso, J.M. Mäkelä, L. Pirjola, M. Väkevä, P. Aalto, P. Miikkulainen, K. Hämeri and C.D. O'Dowd, On the Formation, growth and composition of nucleation mode particles, Tellus B, 53, 479-490,, 2001


Abstract


Taking advantage of only the measured aerosol particles spectral evolution as a function of time, a new analytical tool is developed to derive formation and growth properties of nucleation mode aerosols. This method, when used with hygroscopic growth‐factors, can also estimate basic composition properties of these recently‐formed particles. From size spectra the diameter growth‐rate can be obtained, and aerosol condensation and coagulation sinks can be calculated. Using this growth‐rate and condensation sink, the concentration of condensable vapours and their source rate can be estimated. Then, combining the coagulation sink together with measured number concentrations and apparent source rates of 3 nm particles, 1 nm particle nucleation rates and concentration can be estimated. To estimate nucleation rates and vapour concentration source rates producing new particle bursts over the Boreal forest regions, three cases from the BIOFOR project were examined using this analytical tool. In this environment, the nucleation mode growth‐rate was observed to be 2–3 nm hour−1, which required a condensable vapour concentration of 2.5–4×107 cm−3 and a source rate of approximately 7.5–11×104 cm−3 s−1 to be sustained. The formation rate of 3 nm particles was ≈1 particle cm−3 s−1 in all three cases. The estimated formation rate of 1 nm particles was 10–100 particles cm−3 s−1, while their concentration was estimated to be between 10,000 and 100,000 particles cm−3. Using hygroscopicity data and mass flux expressions, the mass flux of insoluble vapour is estimated to be of the same order of magnitude as that of soluble vapour, with a soluble to insoluble vapour flux ratio ranging from 0.7 to 1.4 during these nucleation events.

 

On the contribution of organics to the North East Atlantic aerosol number concentration On the contribution of organics to the North East Atlantic aerosol number concentration

Date added: 03/22/2013
Date modified: 03/22/2013
Filesize: 1.01 MB

Bialek, J. M. Dall’Osto C. Monahan, D. Beddows and C. O’Dowd, On the contribution of organics to the North East Atlantic aerosol number concentration, Environ. Res. Lett. 7, 044013 (7pp) doi:10.1088/1748-9326/7/4/044013, 2012.


 

Abstract. k-means statistical-cluster analysis of submicron aerosol size distributions is combined with coincident humidity tandem differential mobility analyser data, leading to five unique aerosol categories for hygroscopic growth factors (HGFs): low sea-salt background marine, high sea-salt background marine, coastal nucleation, open ocean nucleation and anthropogenically influenced scenarios. When considering only marine conditions, and generic aerosol species associated with this environment (e.g. non-sea-salt sulfate, sea-salt, partly soluble organic matter and water insoluble organic matter), the two-year annual average contribution to aerosol number concentration from the different generic species was made up as follows: 46% (30–54%) of partially modified ammonium sulfate particles; 23% (11–40%) of partially modified sea-salt; and the remaining 31% (25–35%) contribution attributed to two distinct organic species as evidenced by different, but low, HGFs. The analysis reveals that on annual timescales, _30% of the submicron marine aerosol number concentration is sourced from predominantly organic aerosol while 60% of the anthropogenic aerosol number is predominantly organic. Coastal nucleation events show the highest contribution of the lowest HGF mode (1.19), although this contribution is more likely to be influenced by inorganic iodine oxides. While organic mass internally mixed with inorganic salts will lower the activation potential of these mixed aerosol types, thereby potentially reducing the concentration of cloud condensation nuclei (CCN), pure organic water soluble particles are still likely to be activated into cloud droplets, thereby increasing the concentration of CCN. A combination of dynamics and aerosol concentrations will determine which effect will prevail under given conditions.

 

On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to det On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to det

Date added: 08/05/2011
Date modified: 08/05/2011
Filesize: 3.35 MB

Milroy, C., Martucci, S. Lolli,  S. Loaec, L. S. I. Xueref-Remy, J. V. Lavrič, C.D. O’Dowd,  On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to determine boundary-layer structure: intercomparison and comparison with in-situ radiosounding, Atmos. Meas. Tech. Diss.. 1–35, 2011 www.atmos-meas-tech discuss.net/4/1/2011/doi:10.5194/amtd-4-1-2011, 2011

 


 

Twenty-one cases of boundary-layer (BL) structure were retrieved by three co-located remote sensors, one lidar (Leosphere ALS300) and two ceilometers (Vaisala CL31, Jenoptik CHM15K). Data were collected during the ICOS field campaign held at the

GAW Atmospheric Station of Mace Head, Ireland, from 8 to 28 June 2009. The study is a two-step investigation of the BL structure based (i) on the intercomparison of backscatter pofiles from the three laser sensors and (ii) on the comparison of the backscatter profiles with twenty-three radiosoundings performed during the period of 8 to 15 June 2009. The Temporal Height-Tracking (THT) algorithm was applied to the three sensors’ backscatter profiles to retrieve the decoupled structure of the BL over Mace Head. The results of the intercomparisons are expressed in terms of the mean correlation coefficients, mean bias (difference between two sensors’ detections), mean sigma (the standard deviation of the bias) and the consistency, i.e. the percentage of cases where the detections of the intercompared sensors were closer than 200 m.  The ALS300-CHM15K comparison provided the most consistent retrievals amongst the three comparisons with, respectively, the 86.5% and 77.2% of the lower and upper layer detections closer than 200m and with correlation coefficients equal to 0.88 and 0.83 at the lower and upper layer, respectively. The lidar and ceilometers-detected BL heights were then compared to the temperature profiles retrieved by radiosoundings. The most consistent retrievals at the lower layer are from the ALS300 with the 75% of  detections closer than 200m to the radiosoundings’ first temperature inversion. Despite the lower signal-to-noise ratio and R-value compared to the ASL300 and CHM15K, the CL31 is more consistent with  the soundings retrievals at the upper layer with 62.5% of detections closer than 200m to the radiosoundings’ econd temperature inversion. The ALS300 has larger pulse-averaged power compared to the two ceilometers and better ability in detecting fine aerosol layers within the BL. The comparison of remote and in-situ data proved both the veracity of the inherent link between temperature and aerosol backscatter profiles, and the existence of possible limitations in using aerosols as a tracer to detect the BL structure. 

On condensation nuclei produced at heated surfaces On condensation nuclei produced at heated surfaces

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

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


Abstract

 

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

Observations on the Aitken nuclei in Atlantic air Observations on the Aitken nuclei in Atlantic air

Date added: 01/01/1961
Date modified: 07/23/2009
Filesize: 796.79 kB

O'Connor, T.C, Sharkey, W.P.F., and Flanagan, V.P. (1961)- Observations on the Aitken nuclei in Atlantic air, Quart. J. R. Met. Soc., 87, pp.105-108.


Abstract

 

The concentration, size and distribution of charges on Aitken nuclei in air from the Atlantic Ocean were measured at a station on the western coast of Ireland where man-made pollution was most unlikely. The results are examined in relation to the meteorological elements and human activities. Some sources of the nuclei observed in maritime air are discussed.

Observations of the evolution of the aerosol cloud and boundary layer ACE2 LE Observations of the evolution of the aerosol cloud and boundary layer ACE2 LE

Date added: 08/06/2000
Date modified: 07/03/2009
Filesize: 1.95 MB

Osborne, S. R., D. W. Johnson, R. Wood, B. J. Bandy, M. O. Andrae, C. D. O'Dowd, P. Glantz and K. Noone (1999). Observations of the evolution of the aerosol, cloud and boundary layer dynamic and thermodynamic characteristics during the second Lagrangian experiment of ACE-2. Tellus. 52B, 375-400, 2000


Abstract


During the 1st Lagrangian experiment of the North Atlantic Regional Aerosol Characterisation Experiment (ACE-2), a parcel of air was tagged by releasing a smart, constant level balloon into it from the Research Vessel Vodyanitskiy. The Meteorological Research Flight's C-130 aircraft then followed this parcel over a period of 30 h characterising the marine boundary layer (MBL), the cloud and the physical and chemical aerosol evolution. The air mass had originated over the northern North Atlantic and thus was clean and had low aerosol concentrations. At the beginning of the experiment the MBL was over 1500 m deep and made up of a surface mixed layer (SML) underlying a layer containing cloud beneath a subsidence inversion. Subsidence in the free troposphere caused the depth of the MBL to almost halve during the experiment and, after 26 h, the MBL became well mixed throughout its whole depth. Salt particle mass in the MBL increased as the surface wind speed increased from 8 m s-1 to 16 m s-1 and the accumulation mode (0.1mum to 3.0 mum) aerosol concentrations quadrupled from 50 cm-3 to 200 cm-3. However, at the same time the total condensation nuclei (>3 nm) decreased from over 1000 cm-3 to 750 cm-3. The changes in the accumulation mode aerosol concentrations had a significant effect on the observed cloud microphysics. Observational evidence suggests that the important processes in controlling the Aitken mode concentration which, dominated the total CN concentration, included, scavenging of interstitial aerosol by cloud droplets, enhanced coagulation of Aitken mode aerosol and accumulation mode aerosol due to the increased sea salt aerosol surface area, and dilution of the MBL by free tropospheric air.

 

Observations of iodine monoxide in the remote marine boundary layer Observations of iodine monoxide in the remote marine boundary layer

Date added: 08/06/2000
Date modified: 07/23/2009
Filesize: 584.58 kB

Allan B. J., G. McFiggans, J. M. C. Plane and H. Coe Observations of iodine monoxide in the remote marine boundary layer. J. Geophys. Res., 105, 14363-14369, 2000.


Abstract


We report measurements of the iodine monoxide (IO) radical in the marine boundary layer at three remote sites: Mace Head (Ireland), Tenerife (Canary Islands), and Cape Grim (Tasmania). IO was observed by long-path differential optical absorption spectroscopy using the A2Π3/2-X2Π3/2 electronic transition between 415 and 450 nm. The daytime IO concentration at these three locations was found to vary from below the detection limit (≤0.2 parts per trillion (ppt)) to a maximum of 4 ppt, with an average of about 1 ppt. Of particular note is that the IO observed off the north coast of Tenerife, which is probably typical of the open ocean sub-tropical North Atlantic, exhibited a distinct diurnal cycle which correlated strongly with the solar actinic flux in the near UV. IO was also observed at Cape Grim to be present at much lower levels (0.3 ppt) in westerly air from the Southern Ocean. As is shown in the companion paper (McFiggans et al., this issue), these measurements of IO are satisfactorily reproduced by a photochemical box model incorporating the recycling of iodine through marine aerosol. This model indicates that the direct iodine-catalyzed destruction of ozone in the boundary layer may well be similar to the losses caused by odd-hydrogen photochemistry and dry deposition. The significance of this work is that IO is probably present in much of the open ocean boundary layer, at levels where it may cause significant depletion of ozone.

 

 

Observations of high concentrations of I2 and IO in coastal air Observations of high concentrations of I2 and IO in coastal air

Date added: 03/03/2010
Date modified: 03/03/2010
Filesize: 299.46 kB

Huang, R.-J., K. Seitz, T. Neary, C. D. O’Dowd, U. Platt, and T. Hoffmann, Observations of high concentrations of I2 and IO in coastal air supporting iodine-oxide driven coastal new particle formation . Geophys. Res. Letts, VOL. 37, L03803, doi:10.1029/2009GL041467, 2010


Abstract.

 Theoretical studies have predicted that concentrations of gaseous I2 and IO of the order of 80–100 ppt and 40–50 ppt, respectively, are required in coastal air to account for photochemically-driven coastal new-particle formation events to occur. However, measurements reported to date  (i.e., 20 ppt I2,  10 ppt IO) have not supported the required model predictions. Here, we present measurements of high concentrations of I2 and IO n N.E. Atlantic marine air on the west coast of Ireland. The maximum mixing ratios of daytime I2 and IO over the seaweed beds during low tide were 302 ppt and 35 ppt, respectively. The I2 distribution=was rather inhomogeneous, even at the inter-tidal zone, but closely related to the macroalgae biomass  bundance. New particle formation bursts were frequently observed during daytime hours with the concentrations up to 4.5  105 particles cm3 during low-tide conditions, and the concentrations of ultra-fine particles were positively correlated with the IO concentrations. Considering the constraints set out in theoretical studies for new particle formation via condensation of condensable iodine oxide vapours, the results reported here clearly demonstrate that the molecular iodine and iodine monoxide concentrations in coastal air are sufficient to meet the theoretical precursor concentrations required to drive intensive coastal newparticle formation from higher order condensable iodine oxides.

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

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

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


Abstract


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

 

Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates

Date added: 08/05/2007
Date modified: 07/23/2009
Filesize: 2.28 MB
Greally, B. R., et al. (2007), Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations in 1994–2004 and derived global and regional emission estimates, J. Geophys. Res., 112, D06308, doi:10.1029/2006JD007527.

Abstract


Ground-based in situ measurements of 1,1-difluoroethane (HFC-152a, CH3CHF2) which is regulated under the Kyoto Protocol are reported under the auspices of the AGAGE (Advanced Global Atmospheric Gases Experiment) and SOGE (System of Observation of halogenated Greenhouse gases in Europe) programs. Observations of HFC-152a at five locations (four European and one Australian) over a 10 year period were recorded. The annual average growth rate of HFC-152a in the midlatitude Northern Hemisphere has risen from 0.11 ppt/yr to 0.6 ppt/yr from 1994 to 2004. The Southern Hemisphere annual average growth rate has risen from 0.09 ppt/yr to 0.4 ppt/yr from 1998 to 2004. The 2004 average mixing ratio for HFC-152a was 5.0 ppt and 1.8 ppt in the Northern and Southern hemispheres, respectively. The annual cycle observed for this species in both hemispheres is approximately consistent with measured annual cycles at the same locations in other gases which are destroyed by OH. Yearly global emissions of HFC-152a from 1994 to 2004 are derived using the global mean HFC-152a observations and a 12-box 2-D model. The global emission of HFC-152a has risen from 7 Kt/yr to 28 Kt/yr from 1995 to 2004. On the basis of observations of above-baseline elevations in the HFC-152a record and a consumption model, regional emission estimates for Europe and Australia are calculated, indicating accelerating emissions from Europe since 2000. The overall European emission in 2004 ranges from 1.5 to 4.0 Kt/year, 5–15% of global emissions for 1,1-difluoroethane, while the Australian contribution is negligible at 5–10 tonnes/year, <0.05% of global emissions.

Observations and modelling of aerosol growth in marine stratocumulus - Case Study Observations and modelling of aerosol growth in marine stratocumulus - Case Study

Date added: 08/31/1999
Date modified: 07/03/2009
Filesize: 364.64 kB

O'Dowd, C.D., J.A. Lowe, and M.H. Smith, Observations and modelling of aerosol growth in marine stratocumulus - Case Study. Atmos. Environ, 33, 3053-3062, 1999.


Abstract


Airborne measurements of the growth of the marine accumulation mode after multiple cycles through stratocumulus cloud are presented. The nss-sulphate cloud residual mode was log-normal in spectral shape and it's mode radius was observed to progressively increase in size from 0.78 to 0.94 μm over 155 min of air parcel evolution through the cloudy marine boundary layer. The primary reason for this observed growth was thought to result from aqueous phase oxidation of SO2 to aerosol sulphate in activated cloud drops. An aqueous phase aerosol-cloud-chemistry model was used to simulate this case study of aerosol growth and was able to closely reproduce the observed growth. The model simulations illustrate that aqueous phase oxidation of SO2 in cloud droplets was able to provide enough additional sulphate mass to increase the size of activated aerosol. During a typical cloud cycle simulation, ≃ 4.6 nmoles kgair-1 (0.44 μg m-3) of sulphate mass was produced with ≃ 70% of sulphate production occurring in cloud droplets activated upon sea-salt nuclei and ≃ 30% occurring upon nss-sulphate nuclei, even though sea-salt nuclei contributed less than 15% to the activated droplet population. The high fraction of nss-sulphate mass internally mixed with sea-salt aerosol suggests that aqueous phase oxidation of SO2 in cloud droplets activated upon sea-salt nuclei is the dominant nss-sulphate formation mechanism and that sea-salt aerosol provides the primary chemical sink for SO2 in the cloudy marine boundary layer.

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

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

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


Abstract


Observation of diurnal cycles in atmospheric concentrations of reactive alkenes are reported from measurements performed at a North Atlantic coastal site (Mace Head, Eire 53°19'34N; 9°54'14W). Species seen to exhibit distinct cycles included isoprene, ethene, propene, 1-butene, iso-butene and a substituted C6 alkene. Five hundred and thirty air mass classified measurements were performed over a 4 week period at approximately hourly frequency and demonstrate that during periods when air flow resulted from unpolluted oceanic regions a clear daily cycle in concentrations existed, peaking at around solar noon for all species. These observations support the proposed mechanism of production via photochemical degradation of organic carbon in sea water. The observed concentrations showed strong correlation (propene R2 > 0.75) with solar flux, with little relationship to other meteorological or chemical parameters. The species' short atmospheric lifetimes indicate that the source of emission was from local coastal waters within close proximity of the sampling site. At solar noon concentrations of reactive alkenes from oceanic sources were responsible for up to 88% of non-methane hydrocarbon reaction with the hydroxyl radical at this coastal marine site.

 

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

Date added: 08/07/1998
Date modified: 07/23/2009
Filesize: 1.37 MB

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


Abstract


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

 

Number size distributions and seasonality of submicron particles in Europe 2008–2009 Number size distributions and seasonality of submicron particles in Europe 2008–2009

Date added: 08/04/2011
Date modified: 08/05/2011
Filesize: 11.95 MB

Asmi, A.,  A. Wiedensohler, P. Laj, A.-M. Fjaeraa, K. Sellegri, W. Birmili, E. Weingartner, U. Baltensperger, V. Zdimal, N. Zikova, J.-P. Putaud, A. Marinoni, P. Tunved, H.-C. Hansson, M. Fiebig, N. Kivekäs, H. Lihavainen, E. Asmi, V. Ulevicius, P. P. Aalto, E. Swietlicki, A. Kristensson, N. Mihalopoulos, N. Kalivitis, I. Kalapov, G. Kiss, G. de Leeuw, B. Henzing, R. M. Harrison, D. Beddows, C. O'Dowd, S. G. Jennings, H. Flentje, K. Weinhold, F. Meinhardt, L. Ries, and M. Kulmala.

Number size distributions and seasonality of submicron particles in Europe 2008–2009, Atmos. Phys. Chem. 11, 5505-5538, doi:10.5194/acp-11-5505, 2011

 


 

  

Two years of harmonized aerosol number size distribution data from 24 European field monitoring sites have been analysed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distribution of aerosols in the particle sizes most important for climate applications are presented. We also analyse the annual, weekly and diurnal cycles of the aerosol number concentrations, provide log-normal fitting parameters for median number size distributions, and give guidance notes for data users. Emphasis is placed on the usability of results within the aerosol modelling community. We also show that the aerosol number concentrations of  Aitken and accumulation mode particles (with 100 nm dry diameter as a cut-off between modes) are related, although there is significant variation in the ratios of the modal number concentrations. Different aerosol and station types are distinguished from this data and this methodology has potential for further categorization of stations aerosol number size distribution types. The European submicron aerosol was divided into characteristic types: Central European aerosol, characterized by single mode median size distributions, unimodal number concentration histograms and low variability in CCN-sized aerosol number concentrations; Nordic aerosol with low number concentrations, although showing pronounced seasonal variation of especially Aitken mode particles; Mountain sites (altitude over 1000ma.s.l.) with a strong seasonal cycle in aerosol number concentrations, high variability, andvery low median number concentrations. Southern and Western European regions had fewer stations, which decreases the regional coverage of these results. Aerosol number concentrations over the Britain and Ireland had very high varianceand there are indications of mixed air masses from several source regions; the Mediterranean aerosol exhibit high seasonality, and a strong accumulation mode in the summer. The greatest concentrations were observed at the Ispra station in Northern Italy with high accumulation mode number concentrations n the winter. The aerosol number concentrations at the Arctic station Zeppelin in Ny-A° lesund in Svalbard have also a strong seasonal cycle, with greater concentrations of accumulation mode particles in winter, and dominating summer Aitken mode indicating more recently formed particles. Observed particles did not show any statistically significant regional work-week or weekday related variation in number concentrations studied.Analysis products are made for open-access to the research

 

 

community, available in a freely accessible internet site. The

results give to the modelling community a reliable, easy-touse

and freely available comparison dataset of aerosol size

distributions.

Novel iodine chemistry in the marine boundary layer Novel iodine chemistry in the marine boundary layer

Date added: 08/07/2004
Date modified: 07/23/2009
Filesize: 189.32 kB

Saiz-Lopez, A., and J. M. C. Plane (2004), Novel iodine chemistry in the marine boundary layer, Geophys. Res. Lett., 31, L04112, doi:10.1029/2003GL019215.


Abstract


The atmospheric chemistry of iodine is important for several reasons, including the influence of iodine oxides on the oxidising capacity of the troposphere, the formation of new particles, and the enrichment of iodine in marine aerosols and the transport of this essential dietary element to the continents. It is shown here that a substantial iodine source is I2, most likely emitted from macro-algae at low tide. This source accounts for the daytime production of new particles in the coastal marine boundary layer, and also explains the discovery of significant night-time levels of iodine oxides.

 

Novel Biogenic Iodine-Containing Trihalomethanes and Other Short-Lived Halocarbons in the Coast Novel Biogenic Iodine-Containing Trihalomethanes and Other Short-Lived Halocarbons in the Coast

Date added: 08/06/2000
Date modified: 07/23/2009
Filesize: 1.05 MB

Carpenter, L. J., G. Malin, P. S. Liss, and F. C. Küpper (2000), Novel Biogenic Iodine-Containing Trihalomethanes and Other Short-Lived Halocarbons in the Coastal East Atlantic, Global Biogeochem. Cycles, 14(4), 1191–1204.


Abstract


Reactive halogen photochemistry and its impact on tropospheric oxidant levels have recently attracted intense research interest following the observation of the iodine oxide radical at midlatitudes. During September 1998, short-lived organoiodines including CH3I, C2H5I, CH2ICl, CH2IBr, CH2I2, and the hitherto undetected CHIBr2, as well as the organobromines CHBr3, CH2Br2, CHBr2Cl, CH3Br, and C2H5Br, were measured in air and seawater at and around Mace Head, on the west coast of Ireland. The release rates of organic bromines and iodines from seaweeds were determined from incubations of 10 species of brown, red, and green macroalgae collected in the intertidal or subtidal zones of the rocky shore. For all the brown algae studied, iodine was released mainly as CH2I2. However, for several seaweeds, the novel iodine-containing trihalomethanes CHIBr2 and CHI2Cl represented a significant fraction of the released organic iodine. The macroalgae incubation experiments as well as monitoring of the in situ concentrations in a rock pool indicated that natural halocarbon production by seaweeds was stimulated by incident light. The halocarbon fluxes derived from the seaweed incubations, coupled with published detailed biomass surveys, enabled coastal organohalogen seawater concentrations to be estimated. The CHBr3, CH2Br2, and CHBr2Cl concentrations calculated by this method compared well with coastal surface seawater measurements, implying that macroalgae were the major sources of the polybromomethanes. Measured CH3Br, CH3I, and CH2ICl levels were higher than calculated, which may be due to the existence of additional sources. CH3Br production by macroalgae accounted for less than 10% of measured levels in coastal waters. Short-lived iodocarbons such as CH2I2 and CHIBr2 were depleted in surface seawater compared to calculated levels, implying their photolytic loss within the upper water column.

 

Non-Methane hydrocarbon measurements in Ireland Non-Methane hydrocarbon measurements in Ireland

Date added: 08/06/2003
Date modified: 07/27/2009
Filesize: 32.07 kB
Noone, C A.Non-methane hydrocarbon measurements in Ireland [EGU04-A-05179].

Abstract

 

The measurement of non-methane hydrocarbons (NMHCs) has become increasingly important in recent years in light of their role as precursors in the formation of ozone and their potential impact on human health. In this poster, observations of diurnal and seasonal cycles of NMHCs (C$_2$-C$_8$) are reported for measurements observed at Mace Head, Ireland from 2002-2003. The remote coastal research station of Mace Head, Co. Galway is unique in Europe offering an opportunity to study the Northern Hemispheric background atmosphere, as well as emissions from Europe. Continuous ground-based data collected at Mace Head allows air mass characterisation and model estimates of ozone production with polluted
plumes to be made.

Nolan–Pollak type CN counters in the Vienna aerosol workshop Nolan–Pollak type CN counters in the Vienna aerosol workshop

Date added: 07/31/2002
Date modified: 07/03/2009
Filesize: 321.73 kB

Gras, J.L., J. Podzimek, T.C. O'Connor, K-H Enderle, Nolan-Pollak type CN counters in the Vienna aerosol workshop. Atmos. Res. 62, 239-254, 2002.


Abstract

 

Three standard Nolan-Pollak (N-P) and a modified N-P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N-P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N-P counters, typically better than ± 12% for a range of aerosol sizes and compositions from a minimum diameter of 4 nm. The independently calibrated GIV CNC-440 (modified N-P type counter) also agreed well with the N-P counters. The minimum size sensitivity of the N-P counter was examined showing a lower detection limit for insoluble (Ag) particles of around 2.6 ± 0.3 nm diameter.

Nitrogenated and aliphatic organic vapors as possible drivers for marine secondary organic aerosol growth Nitrogenated and aliphatic organic vapors as possible drivers for marine secondary organic aerosol growth

Date added: 03/13/2013
Date modified: 03/13/2013
Filesize: 1.02 MB

DallOsto, Manuel,Darius Ceburnis, Ciaran Monahan, Douglas R. Worsnop,

Jakub Bialek, Markku Kulmala, Theo Kurtén, Mikael Ehn, John Wenger,

John Sodeau, Robert Healy, and Colin ODowd. (2012), Nitrogenated and aliphatic organic vapors as possible drivers for marine secondary organic aerosol growth, J. Geophys. Res., 117, D12311, doi:10.1029/2012JD017522.


Abstract. Measurements of marine aerosol chemistry, using state-of-the-art mass spectrometry, as well as aerosol microphysics, hygroscopicity and cloud condensation nuclei (CCN) activity were undertaken during new particle growth events. The events were detected in air advecting over North East (NE) Atlantic waters during the EUCAARI Intensive Observation Period in June 2008 at Mace Head, Ireland. During these growth events, the aerosol mass spectrometers illustrated increases in accumulation mode aerosol phase nitrogenated and aliphatic compounds thought to condense from the gas phase. Since the composition changes observed in the accumulation mode occurred simultaneously to the growth of the accumulation, Aitken and nucleation modes, the growth of both the nucleation mode and the Aitken mode is attributed to the condensation of these species. Nitrogenated compounds like amines are also plausible candidates in the nucleation process, as suggested by quantum mechanic calculations. It is also plausible that amides and organic nitrites, also identified by the mass spectrometers, are possible candidate chemical compounds, suggesting that multiple types of chemical species may be contributing. Given that these open ocean aerosol formation and growth events occur in very clean polar marine air masses, we suggest that the organic compounds responsible for particle formation and growth are mainly of biogenic origin. Despite increasing the particle number concentration, the initial effect is to suppress hygroscopicity and CCN activity.

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

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

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


Abstract


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

 

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

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

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


Abstract


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

 

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

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

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


Abstract


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

New Directions: Organic matter contribution to marine aerosols and cloud condensation nuclei New Directions: Organic matter contribution to marine aerosols and cloud condensation nuclei

Date added: 10/01/2008
Date modified: 07/28/2009
Filesize: 178.38 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 CLAWhypothesis 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.

Nature-times Weather Understanding rainfall Nature-times Weather Understanding rainfall

Date added: 08/01/1971
Date modified: 09/11/2009
Filesize: 336.23 kB

Nature-times Weather Understanding rainfall Nature-times Weather Understanding rainfall

Date added: 08/01/1971
Date modified: 08/01/2008
Filesize: 336.23 kB

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

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

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


Abstract


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

 

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