Seasonal trends and sources of dicarboxylic acids in fine aerosol over the Brahmaputra valley, North-East India.

The atmospheric dicarboxylic acids (DCAs) have a significant impact on the climate and indirectly affect human health, making them important organic substances. PM bound DCAs were analysed for Jorhat, India, 2019. In addition to the temporal variability, seasonal variation throughout the year and the impact of varying meteorological factors on DCAs concentration have also been studied. It has been noted that precipitation and ambient air temperature considerably impact DCA concentrations, which affect the type of source contribution of DCAs. The average concentration of all DCAs was 107.04 ± 97.54 ng/m, with a higher prevalence of high molecular weight DCAs than low molecular weight DCAs. Correlation analysis, water-soluble inorganic species, EC-OC ratio and diagnostic ratios of DCAs were employed to determine whether DCAs originate from direct emission and/or from photochemical oxidation of biogenic or anthropogenic precursors. DCAs concentration varied seasonally in decreasing order, with the maximum in the monsoon (144.24 ± 101.62 ng/m) followed by winter (138.36 ± 95.11 ng/m), post-monsoon (80.72 ± 37.27 ng/m), and summer (36.64 ± 34.52 ng/m). Air mass back trajectory and concentration-weighted trajectory (CWT) were used to show both short and long-range air mass transport with moderate to high DCAs contribution regions. Photochemical oxidation of diacids precursors predominates during the monsoon season, whereas in winter, direct anthropogenic emissions account for the majority of DCAs.