In situ measured seasonal characteristics of near-surface aerosols over Bay of Bengal and MODIS-retrieved columnar properties: A multicampaign analysis

Seasonal changes in near‐surface aerosol mass loading and their chemical characteristics over the marine environment of Bay of Bengal (BoB) have been investigated, based on the ship‐based experiments carried out as part of three major field campaigns in premonsoon, winter, and monsoon seasons. These spatiotemporal properties of in situ measured near‐surface aerosols were compared with the columnar aerosol optical depth (AOD), Angstrom exponent, effective radius, mass concentration, fine‐mode AOD, and large‐mode AOD retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS). The spatial heterogeneity in the chemical nature of aerosols for the three contrasting seasons has been addressed. In all the seasons, BoB is found to be polluted by anthropogenic aerosols as revealed by their chemical composition. North BoB exhibits highest near‐surface aerosol loading, columnar AOD, and aerosol mass concentration irrespective of the season. While the high AOD in winter is due to fine‐mode anthropogenic aerosols, that in monsoon is due to large‐sized sea‐salt aerosols. The fine‐mode AOD over BoB contributes 45% in monsoon, 69% in premonsoon, and 73% in winter. The column AOD in winter and premonsoon is ~50% of its monsoonal value. The e‐fold scale distances of total aerosol mass loading and those of various chemical species over BoB are also investigated. The column mass concentration has been estimated from the in situ measured near‐surface aerosol mass loading and compared with that retrieved from MODIS. Regions where low near‐surface aerosol mass loading was observed; the satellite‐retrieved columnar loading was found to be overestimated suggesting seasonal and regional differences in scale height. Key Points Near‐surface aerosol characteristics are correlated with columnar parameters Scale distance of total mass loading/species concentration is high in winter Fine‐mode AOD is 45% of total AOD in monsoon, 69% in premonsoon, and 73% in winter