Wintertime study on bulk composition and stable carbon isotope analysis of ambient aerosols from North India

Ambient aerosols (PM2.5; particulate matter with aerodynamic diameter ≤ 2.5 µm) collected during wintertime from Kanpur (26.30 °N, 80.14 °E; in Indo-Gangetic Plain: IGP) in December 2014 were studied for their chemical composition [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), major ions] and stable carbon isotope composition (δ13C) of total carbon (TC). Several source samples have also been strategically collected and characterized with δ13C value. Air-mass back trajectories arriving at the receptor site during the study period exhibited predominant influence of north-westerly winds. PM2.5 mass in ambient samples averaged at 240 ± 72 μg m−3 and total carbonaceous aerosols (TCA) concentration averaged at 91 ± 25 μg m−3 in these samples. The OC and EC concentrations contributed nearly 22% and 2%, respectively to the ambient PM2.5 mass. A significant variability in OC/EC ratio (8.7‒14.8; Avg. ± SD: 12 ± 2) and WSOC/OC ratio (0.350.51; 0.43 ± 0.05) has been recorded during the winter season in IGP. The ambient concentrations of secondary inorganic aerosol species (SIA) viz. SO42-, NO3- and NH4+ were 23.5 ± 8.7, 10.5 ± 6.0 and 12.8 ± 4.9 μg m−3, respectively. The δ13C of TC in ambient aerosols varied from −24.5 to −26.2‰. Large scatter between δ13C and TC content in aerosols indicated signature from multiple sources of carbonaceous aerosols due to mixing of air-masses. Future studies with large δ13C data population in conjunction with bulk composition would be required to better characterize the carbonaceous aerosols over the Indian region.