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

Highlights: • Diurnal variability of DCAs and levoglucosan in PM₁₀ were assessed in winter over IGP. • Biomass burning and secondary transformations appear predominant sources of DCA. • Decomposition of higher congeners of DCA seems to form C₂ diacid. 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 ≤ 10 μm) 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 μg 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 (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 ± 1025 ng m^{− 3}) as compared to that in daytime (1499 ± 562 ng m^{− 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.