Measurements of scattering and absorption properties of surface aerosols at a semi-arid site, Anantapur

Abstract

Aerosol optical properties are continuously measured at a semi-arid station, Anantapur from June 2012 to May 2013 which describes the impact of surface aerosols on climate change over the region. Scattering coefficient (σsct) and absorption coefficient (σabs) are obtained from integrating Nephelometer and Aethalometer, respectively. Also, the single scattering albedo (ω0), Scattering/absorption Ångström exponents were examined during the period of study. Diurnal variations of σsct and σabs show a bi-peak pattern with two maxima and one minimum in a day. The largest values of σsct and σabs are obtained in winter while the lowest values are measured in monsoon. From the measurements σsct550 and σabs550 are found to be 110 ± 12.23 Mm− 1 and 33 ± 5.2 Mm− 1, respectively during the study period. An analysis of the ω0 suggests that there is a more absorbing fraction in the particle composition over the measurement site. The ω0 obtained in the surface boundary layer of Anantapur is below the critical value of 0.86 that determines the shift from cooling to warming. A relationship between scattering/absorption coefficients and scattering/absorption Ångström exponent and single scattering albedo is further examined. In order to understand the origins of the air masses in the study region, we performed seven-day back trajectory analyses based on the NOAA HYSPLIT model. These trajectories were computed at several altitudes (3000 m, 1500 m, and 500 m) for June 2012 and May 2013. These results put in evidence the need of efforts to reduce absorbing particles (black carbon) emissions to avoid the possible warming that would result from the reductions of the cooling aerosol only.