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

Size-segregated airborne fine (PM_2.1) 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 (±1σ) concentration of PM_2.1 was 98 (±76) μgm^-3 with a seasonal high during winter (DJF, 162 ± 71 μgm^-3) compared to pre-monsoon specific high in PM_>2.1 (MAMJ, 177 ± 84 μgm^-3) with an annual mean of 170 (±69) μgm^-3. PM_2.1 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 PM_2.1 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 (C₁₇-C₃₅) showed C_max at C₂₃ (PM_2.1) and C₁₈ (PM_>2.1) with weak dominance of odd-numbered n-alkanes. Carbon preference index of n-alkanes was close to unity (PM_2.1: 1.4 ± 0.3; PM_>2.1: 1.3 ± 0.4). Fatty acids (C₁₂-C₂₆) were characterized with predominance of even carbon with C_max 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 (PM_2.1) with vital signature of anthropogenic emissions. Levoglucosan was abundant in PM_2.1 (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 PM_2.1 whereas, crustal (29%) and secondary aerosols (29%) were found responsible for PM_>2.1; with significant variations among the seasons.