Temporal Trends in Atmospheric PM_(2.5), PM_(10), Elemental Carbon, Organic Carbon, Water-Soluble Organic Carbon, and Optical Properties: Impact of Biomass Burning Emissions in The Indo-Gangetic Plain

摘要

The first simultaneous measurements and analytical data on atmospheric concentrations of PM_(2.5), PM_(10) inorganic constituents, carbonaceous species, and their optical properties (aerosol optical depth, AOD; absorption coefficient, σ_(abs); mass absorption efficiency, σ_(abs); 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 PM_(2.5) mass. The WSOC/OC ratio varies from 0.21 to 0.65, suggesting significant contribution from secondary organic aerosols (SOAs). The mass fraction of SO_4~(2+) in PM_(2.5) (Av: 12.5%) exceeds that of NO_3~- and NH_4. 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 b_(abs) and EC (n = 54) provides a measure of the mass absorption efficiency of EC (9.6 m~2 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 PM_(10) samples. The highest b_(scat) 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.