Assessment of stable carbon isotope ratios and source characterization of aerosols in ambient PM from the Indian COALESCE network.

This study explores the potential of stable carbon isotope (δC) composition of ambient carbonaceous aerosols in assessing the nature and apportionment of their sources. As part of the CarbOnaceous AerosoL Emissions, Source apportionment & ClimatE Impacts (COALESCE) network, δC measurements (n = 1120) were conducted on aerosol samples collected from eight key locations spread across India. The δC values of aerosols exhibit distinct spatial/temporal isotopic variabilities between background and polluted (urban) sites, and indicate an origin primarily from C-biomass, fossil fuels, vehicular emission sources, etc. Spatial δC distribution over India shows more negative δC values in all seasons at the north Indian Himalayan (Kashmir) and east Indian sites (Jorhat) compared to other locations, implying that anthropogenic inputs contribute to more isotopic variability and a typical C-rich signature. Our study shows that although δC provides qualitative information on source characteristics, it is not a robust standalone proxy for such applications. We conclude that δC of aerosols could be a robust proxy for quantification studies if the extent of isotopic fractionation involved during aerosol formation/transport processes is well known and if it is assessed with one or more chemical markers like radiocarbon (ΔC), trace elements/organic species, and specific biomarkers (e.g., levoglucosan or K ).