Physico-chemical characterization and sink mechanism of atmospheric aerosols over South-west India

Abstract

The properties of the atmospheric aerosols depend on the source region and on the modifications that occur during their transport in the air. We have studied physical and chemical properties of aerosols along with their sink mechanism over two locations in southwest India, an urban site (Pune) and well-established climate observatory at Sinhagad (SINH), which represents rural and high altitude site. The ground-based measurements of aerosols, together with their radiative properties in this study have provided means to understand the observed variability and the impact on the aerosol radiative properties effectively over this region. The annual mean elemental carbon concentration (3.4 μg m^??3) at Pune was observed about three times higher compared to SINH (1.3 μg m^??3), indicating strong emissions of carbon-rich aerosols at the urban location. Aerosol optical properties were derived using the OPAC model which were used to compute the Aerosol radiative forcing (ARF) over both stations calculated using SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model shows pronounced seasonal variations due to changes in aerosol optical depth and single scattering albedo at both locations. The year-round ARF was 4–5 times higher over Pune (31.4?±?3.5 Wm^??2) compared to SINH (7.2?±?1.1 Wm^??2). The atmospheric heating rate due to aerosols shows a similar pattern as ARF for these locations. The heating was higher in the wintertime, ~?0.9–1.6 K day^??1 at Pune, and ~?0.3–0.6 K day^??1 at SINH. The estimated scavenging ratio was found high for NO₃^? and Ca.²⁺. The wet deposition fluxes of Cl^?, SO₄^2?, Na⁺, Mg²⁺ were observed higher for SINH as compared to Pune, due to the high amount of rain received at SINH.