Optical Remote Sensing of Pristine and Coastal Aerosol Features over the Arabian Sea

This paper purports the results of a comparative study conducted to investigate aerosol optical, microphysical and radiative characteristics over an Exclusive Economic Zone (EEZ) associated with pristine environment, and coastal regions influenced by human activities, during 2009-2011. The measurements over the EEZ of the Arabian Sea (AS) were carried out from Sagar Kanya (SK-226) ship while over the coastal locations (Mumbai and Goa); employing Sun-photometers. The aerosol optical thickness (AOT) at 500 nm was found to be in the range of 0.3-0.45 in the EEZ while it was 0.45-0.75 in the coastal regions. The AOTs at all the three sites showed a good association with concurrent meteorological parameters. Angstrom parameters (alpha and beta, representative of aerosol size distribution and loading, respectively) indicated opposite behavior in the pristine (EEZ) but similar trend in the polluted coastal regions. This feature reveals that the aerosol loading over the EEZ is contributed by coarse-mode particles while the fine-mode particles contribute to the loading over coastal regions. Abundance of fine-mode particles over the coastal regions is also evidenced from the second order polynomial fit coefficients (a1 and a2) of alpha. This aspect corroborates the long-range transport of air-mass over the experimental sites from the western coast India.