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

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.