Insights into size-segregated particulate chemistry and sources in urban environment over central Indo-Gangetic Plain

Size-segregated airborne fine (PM2.1) and coarse (PM>2.1) particulates were measured in an urban environment over central Indo-Gangetic plain in between 2015 and 2018 to get insights into its nature, chemistry and sources. Mean (+/- 1 sigma) concentration of PM2.1 was 98 (+/- 76) mgm(-3) with a seasonal high during winter (DJF, 162 +/- 71 mu gm(-3)) compared to pre-monsoon specific high in PM>2.1 (MAMJ, 177 +/- 84 mgm(-3)) with an annual mean of 170 (+/- 69) mgm(-3). PM2.1 was secondary in nature with abundant secondary inorganic aerosols (20% of particulate mass) and water-soluble organic carbon (19%) against metal enriched (25%) PM>2.1, having robust signature of resuspensions from Earth's crust and road dust. Ammonium-based neutralization of particulate acidity was essentially in PM2.1 with an indication of predominant H2SO4 neutralization in bisulfate form compared to Ca2+ and Mg2+-based neutralization in PM>2.1. Molecular distribution of n-alkanes homologues (C-17-C-35) showed C-max at C-23 (PM2.1) and C-18 (PM>2.1) with weak dominance of odd-numbered n-alkanes. Carbon preference index of n-alkanes was close to unity (PM2.1: 1.4 +/- 0.3; PM>2.1: 1.3 +/- 0.4). Fatty acids (C12-C26) were characterized with predominance of even carbon with Cmax at n-hexadecanoic acid (C-16:0). Low to high molecular weight fatty acid ratio ranged from 2.0 (PM>2.1) to 5.6 (PM2.1) with vital signature of anthropogenic emissions. Levoglucosan was abundant in PM2.1 (758 +/- 481 ngm(-3)) with a high ratio (11.6) against galactosan, emphasizing robust contribution from burning of hardwood and agricultural residues. Receptor model resolves secondary aerosols and biomass burning emissions (45%) as the most influential sources of PM2.1 whereas, crustal (29%) and secondary aerosols (29%) were found responsible for PM>2.1; with significant variations among the seasons. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study found that size-segregated fine and coarse particulates in an urban environment have different sources and properties, with PM2.1 being dominated by secondary aerosols and PM>2.1 being enriched in metals. The neutralization of particulate acidity by ammonium showed different characteristics in the two particulate types, with significant seasonal variations.