Atmos. Chem. Phys. Discuss., 10, 5185-5231, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Chemically aged and mixed aerosols over the Central Atlantic Ocean – potential impacts
M. Astitha1,2, G. Kallos1, C. Spyrou1, W. O'Hirok2, J. Lelieveld2,3, and H. A. C. Denier van der Gon4
1University of Athens, School of Physics, Division of Environmental Physics-Meteorology, Bldg PHYS-V, 15784, Athens, Greece
2Energy, Environment and Water Research Centre, The Cyprus Institute, Nicosia, Cyprus
3Max Planck Institute for Chemistry, Becherweg 27, 55128 Mainz, Germany
4TNO Built Environment and Geosciences, Princetonlaan 6, P.O. Box 80015, 3584 CB Utrecht, The Netherlands

Abstract. Detailed information on the chemical and physical properties of aerosols is important for assessing their role in air quality and climate. This work explores the origin and fate of continental aerosols transported over the Central Atlantic Ocean, in terms of chemical composition, number and size distribution, using chemistry-transport models, satellite data and in situ measurements. We focus on August 2005, a period with intense hurricane and tropical storm activity over the Atlantic Ocean. A mixture of anthropogenic (sulphates, nitrates), natural (desert dust, sea salt) and chemically aged (sulphate and nitrate on dust) aerosols is found entering the hurricane genesis region, most likely interacting with clouds in the area. Results from our modelling study suggest rather small amounts of accumulation mode desert dust, sea salt and chemically aged dust aerosols in this Atlantic Ocean region. Aerosols of smaller size (Aitken mode) are more abundant in the area and in some occasions sulphates of anthropogenic origin and desert dust are of the same magnitude in terms of number concentrations. Typical aerosol number concentrations are derived for the vertical layers near shallow cloud formation regimes, designating that the aerosol number concentration can reach several thousand particles per cubic centimetre. The vertical distribution of the aerosols indicates that the desert dust particles are often transported near the top of the marine cloud layer as they enter into the region where deep convection is initiated. The anthropogenic sulphate aerosol can be transported within a thick layer and enter the cloud deck through multiple ways (from the top, the base of the cloud and entrainment). The sodium (sea salt related) aerosol is mostly found below the cloud base. The results of this work may provide insights relevant for studies that consider aerosol influences on cloud processes and storm development in the Central Atlantic region.

Citation: Astitha, M., Kallos, G., Spyrou, C., O'Hirok, W., Lelieveld, J., and Denier van der Gon, H. A. C.: Chemically aged and mixed aerosols over the Central Atlantic Ocean – potential impacts, Atmos. Chem. Phys. Discuss., 10, 5185-5231, doi:10.5194/acpd-10-5185-2010, 2010.
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