Dicarboxylic acids and levoglucosan in aerosols from Indo-Gangetic Plain: Inferences from day night variability during wintertime

Abstract

This study assesses daytime and nighttime atmospheric abundance and molecular distribution of dicarboxylic acids (DCA: C2–C10) and biomass burning tracers (levoglucosan and biomass burning derived potassium: K+BB) in PM10 (particulate matter with aerodynamic diameter≤10μm) from an urban location, Kanpur (in central Indo-Gangetic Plain: IGP) during wintertime (December 2015–February 2016). In this study, PM10 varied from 130 to 242 and 175–388μgm−3 during daytime and nighttime, respectively. The average ratios of OC/EC (day: 12.3; night: 9.3) and WSOC/OC (day: 0.74; night: 0.48) were relatively high during daytime (OC: organic carbon; EC: elemental carbon; WSOC: water-soluble organic carbon). Strong linear correlations (R2≥0.6; p<0.05) of OC with levoglucosan and K+BB suggest biomass burning emission as predominant source of organic aerosols over the IGP. The measured concentrations of total DCA (ΣC2–C10) showed pronounced diurnal variability with a higher concentration during nighttime (2510±1025ngm−3) as compared to that in daytime (1499±562ngm−3). Concentrations of oxalic acid (C2), succinic acid (C4) and malonic acid (C3) were predominantly high as compared to other congeners of DCA (C2–C10) over central IGP. Relatively higher mass fraction (73.4%) of C2 in total DCA during nighttime than that in daytime (61.5%) indicates role of secondary organic aerosols (SOAs) formation involving aqueous-phase chemistry. Strong linear correlations of C2 with C3 and C4 plausibly suggest that C2 can have predominant formation pathways via decomposition of higher congeners of DCA. Overall, strong linear correlations of C2 with levoglucosan and sulphate suggest that biomass burning emission and secondary transformations are predominant sources of DCA over IGP during wintertime.