Columnar aerosol optical depth, water vapor and ozone over a semi-arid urban location of western India: Potential sources and direct radiative effects

Continuous measurements of Aerosol Optical Depth (AOD), columnar water vapor (WV) and Ozone (O3) concentrations were made over a semi-arid urban location Rajkot (22.29 degrees N, 70.74 degrees E, and 142 m AMSL) in the western India. The annual mean values of AOD, WV and O3 were 0.37 +/- 0.15, 1.44 +/- 0.6 gm cm -2 and 243 +/- 18 DU during 2016-2019. AOD showed large seasonal variability mostly dominated by abundant coarse mode aerosols (Angstrom Exponent, AE < 0.65 and AOD -0.37) during pre-monsoon and monsoon, mainly caused by wind-blown and transported dust from nearby Thar and Kutch desert. Mixture of fine and coarse mode aerosols were abundant (AE = 1.13 +/- 0.26) during post-monsoon influenced by both anthropogenic and natural sources. Columnar WV were also higher in pre-monsoon and monsoon seasons. The O3 concentrations is higher during pre-monsoon (247 DU) and lower during monsoon (230 DU). The vertical distribution of aerosol extinction coefficient derived from satellite (CALIPSO) based observations revealed the dominance of dust aerosols (-74 %) in pre-monsoon; smoke and polluted dust in winter and post monsoon period. The trajectory clus-ters and concentration weighted trajectory maps also indicated the combined effect of anthropogenic (especially from the northern part of India) and natural aerosol sources during the post-monsoon period. Associated with the higher anthropogenic components during post-monsoon season, aerosol direct radiative forcing depicted surface dimming as high as -48.7 +/- 12.6 Wm2, resulting in atmospheric forcing of 42.6 +/- 12.5 Wm -2.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.