Source apportionment of fine particulate matter in middle Indo-Gangetic Plain by coupled radiocarbon –molecular organic tracer method

Abstract

Despite significant emissions of fine particulate matter (FPM) from the Indo-Gangetic Plain (IGP) that affect the climate and air quality in the region, the sources of these emissions are not adequately addressed. This research uses a combined radiocarbon-molecular organic tracer technique to investigate the degree of contamination, seasonal fluctuations, and contribution of FPM in the middle IGP (Patna), India. The findings indicated levoglucosan (L) as the single primary BB tracer chemical, ranging from 149 ng/m³ to 490 ng/m³ (median 282 ng/m³). Winter (median 462 ng/m³) showed a 2–3 times higher level of L than the monsoon season (median 180 ng/m³). A significant association of L with other organic tracers such as galactosan (G), mannosan (M), vallinic acid, syringic acid, p-hydroxybenzoic acid (pHA) and dehydroabietic acid (DHAA)(r = 0.53 to 0.89, p < 0.05), and moderate connection with Cl⁻ (r = 0.21, p < 0.05), SO₄²⁻ (r = 0.29, p < 0.05), and NO₃- (r = 0.22, p < 0.05) indicated significant BB contribution. However, non-sea salt (nss-K⁺) was not related to L. Based on seven days of air mass back trajectories and MODIS active fire counts analysis, we conclude that OAs composition is not the local origin but is also impacted by long-range atmospheric transport from Pakistan/Afghanistan, followed by the Bay of Bengal and the Arabian Sea. Chemical analysis of organic tracers and positive matrix factorization (PMF) modeling study identified three unique sources, i.e., biomass burning, secondary aerosols formation, and mixed type (fossil fuels and construction dust) as the primary source of FPM in Patna, accounted for 46.1 %, 28.9 %, and 24.9 %, of total emissions, respectively. The radiocarbon (¹⁴ C) analysis of total carbon (TC) samples further supported this conclusion. The results of ^{the 14} C study indicated that emissions from BB, such as wood and stubble, were responsible for 57% of the TC concentration.