Size segregated mass concentration and size distribution of near surface aerosols over a tropical Indian semi-arid station, Anantapur: impact of long range transport

Abstract

Regular measurements of size segregated as well as total mass concentration and size distribution of near surface composite aerosols, made using a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor during the period of September 2007-May 2008 are used to study the aerosol characteristics in association with the synoptic meteorology. The total mass concentration varied from 59.70 ± 1.48 to 41.40 ± 1.72 μg m^-3, out of which accumulation mode dominated by ~50%. On a synoptic scale, aerosol mass concentration in the accumulation (submicron) mode gradually increased from an average low value of ~26.92 ± 1.53 μg m^-3 during the post monsoon season (September-November) to ~34.95 ± 1.32 μg m^-3during winter (December-February) and reaching a peak value of ~43.56 ± 1.42 μg m^-3 during the summer season (March-May). On the contrary, mass concentration of aerosols in the coarse (supermicron) mode increased from ~9.23 ± 1.25 μgm^{- 3}during post monsoon season to reach a comparatively high value of ~25.89 ± 1.95 μg m^-3 during dry winter months and a low value of ~8.07 ± 0.76 μg m^-3 during the summer season. Effective radius, a parameter important in determining optical (scattering) properties of aerosol size distribution, varied between 0.104 ± 0.08 μm and 0.167 ± 0.06 μm with a mean value of 0.143 ± 0.01 μm. The fine mode is highly reduced during the post monsoon period and the large and coarse modes continue to remain high (replenished) so that their relative dominance increases. It can be seen that among the two parameters measured, correlation of total mass concentration with air temperature is positive (R²=0.82) compared with relative humidity (RH) (R²=0.75).