Temporal trends in atmospheric PM2.5, PM10, elemental carbon, organic carbon, water-soluble organic carbon, and optical properties: Impact of biomass burning emissions in the Indo-Gangetic Plain

Abstract

The first simultaneous measurements and analytical data on atmospheric concentrations of PM2.5, PM10, inorganic constituents, carbonaceous species, and their optical properties (aerosol optical depth, AOD; absorption coefficient, babs; mass absorption efficiency, σabs; and single scattering albedo, SSA) from an urban site (Kanpur) in the Indo-Gangetic Plain are reported here. Significantly high aerosol mass concentration (>100 μg m-3) and AOD (> 0.3) are seen as a characteristic feature throughout the sampling period, from October 2008 to April 2009. The temporal variability in the mass fractions of carbonaceous species (EC, OC, and WSOC) is pronounced during October-January when emissions from biomass burning are dominant and OC is a major constituent (∼30%) of PM2.5 mass. The WSOC/OC ratio varies from 0.21 to 0.65, suggesting significant contribution from secondary organic aerosols (SOAs). The mass fraction of SO42- in PM2.5 (Av: 12.5%) exceeds that of NO3- and NH4+. Aerosol absorption coefficient (@ 678 nm) decreases from 90 Mm-1 (in December) to 20 Mm-1 (in April), and a linear regression analysis of the data for babs and EC (n = 54) provides a measure of the mass absorption efficiency of EC (9.6 m2 g-1). In contrast, scattering coefficient (@ 678 nm) increases from 98 Mm-1 (in January) to 1056 Mm-1 (in April) and an average mass scattering efficiency of 3.0 ± 0.9 m2 g-1 is obtained for PM10 samples. The highest bscat was associated with the dust storm event (April 17, 2009) over northern Iraq, eastern Syria, and southern Turkey; thus, resulting in high SSA (0.93 ± 0.02) during March-April compared to 0.82 ± 0.04 in October-February. These results have implications to large temporal variability in the atmospheric radiative forcing due to aerosols over northern India. © 2011 American Chemical Society.