Atmos. Chem. Phys. Discuss., 11, 7851-7907, 2011
www.atmos-chem-phys-discuss.net/11/7851/2011/
doi:10.5194/acpd-11-7851-2011
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under the Creative Commons Attribution 3.0 License.
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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.
Extremely large anthropogenic aerosol component over the Bay of Bengal during winter season
D. G. Kaskaoutis1, S. Kumar Kharol2,3, P. R. Sinha4, R. P. Singh5, H. D. Kambezidis6, A. Rani Sharma2, and K. V. S. Badarinath2
1Research and Technology Development Centre, Sharda University, Greater Noida, 201306, India
2Atmospheric Science Section, Oceanography Division, National Remote Sensing Centre, Dept. of Space-Govt. of India, Hyderabad, 500 625, India
3Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
4National Balloon Facility, Tata Institute of Fundamental Research, Hyderabad, 500 062, India
5School of Earth and Environmental Sciences, Schmid College of Science, Chapman University, Orange, CA 92866, USA
6Atmospheric Research Team, Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Nymphon, 11810 Athens, Greece

Abstract. Ship-borne observations of spectral aerosol optical depth (AOD) have been carried out over the entire Bay of Bengal (BoB) as part of the W-ICARB cruise campaign during the period 27 December 2008–30 January 2009. The results reveal a pronounced temporal and spatial variability in the optical characteristics of aerosols mainly due to anthropogenic emissions and their dispersion controlled by local meteorology. The highest aerosol amount, with mean AOD500 over 0.4, being even above 1.0 on specific days, is found close to the coastal regions in the western and northern parts of BoB. In these regions the Ångström exponent is also found to be high (~ 1.2–1.25) indicating transport of strong anthropogenic emissions from continental regions. A very high AOD500 (0.39 ± 0.07) and α380—870 values (1.27 ± 0.09) are found for the first time over the Eastern BoB, which was unexplored in the earlier ICARB-06 campaign. Except from the large α380—870 values, an indication of strong fine-mode dominance is also observed from the AOD curvature, which is negative in the vast majority of the cases, suggesting dominance of an anthropogenic-pollution aerosol type. On the other hand, clean maritime conditions are rather rare over the region, while the aerosol types are further examined through a classification scheme using the relationship between α and dα. It was found that even for the same α values the fine-mode dominance is larger for higher AODs showing the strong continental influence over the marine environment of BoB. Furthermore, there is also an evidence of aerosol size growth under more turbid conditions indicative of coagulation and/or humidification over specific BoB regions. The results obtained using OPAC model show significant fraction of soot aerosols (~ 6–8%) over the Eastern and Northwestern BoB, while coarse-mode sea salt particles are found to dominate in the southern parts of BoB.

Citation: Kaskaoutis, D. G., Kumar Kharol, S., Sinha, P. R., Singh, R. P., Kambezidis, H. D., Rani Sharma, A., and Badarinath, K. V. S.: Extremely large anthropogenic aerosol component over the Bay of Bengal during winter season, Atmos. Chem. Phys. Discuss., 11, 7851-7907, doi:10.5194/acpd-11-7851-2011, 2011.
 
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