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

This study assesses daytime and nighttime atmospheric abundance and molecular distribution of dicarboxylic acids (DCA: C-2-C-10) and biomass burning tracers (levoglucosan and biomass burning derived potassium: K-BB(+) ) in PM10 (particulate matter with aerodynamic diameter <= 10 mu m) 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 175-388 mu g m(-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 (R-2 >= 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 (Sigma C-2-C-10 ) showed pronounced diurnal variability with a higher concentration during nighttime (2510 +/- 1025 ng m(-3) ) as compared to that in daytime (1499 +/- 562 ng m(-3) ). Concentrations of oxalic acid (C-2 ), succinic acid (C-4 ) and malonic acid (C-3 ) were predominantly high as compared to other congeners of DCA (C-2-C-10 ) over central IGP. Relatively higher mass fraction (73.4%) of C-2 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 C-2 with C-3 and C-4 plausibly suggest that C-2 can have predominant formation pathways via decomposition of higher congeners of DCA. Overall, strong linear correlations of C-2 with levoglucosan and sulphate suggest that biomass burning emission and secondary transformations are predominant sources of DCA over IGP during wintertime. (C) 2017 Elsevier B.V. All rights reserved.