Spatio‐Temporal Trends of the Relationships Between Surface PM_2.5 and Its Chemical Constituents Across Three COALESCE Network Locations in India: A Mass Closure Investigation

Abstract

COALESCE, a collaborative network studying the impacts of carbonaceous aerosols, measured PM2.5 mass and its constituents at several regionally representative sites in India. This study reconciles the reconstructed mass (RCM) from PM2.5 chemical constituents with gravimetric PM2.5 mass measured during 2019 at three COALESCE sites (Bhopal, Mesra, and Mysuru). To evaluate the extent of mass closure, the spatiotemporal variability of organic matter/organic carbon (OM/OC), filter sampling artifacts of OC, nitrate, and aerosol liquid water (ALW) were assessed. The annual loss of total particulate OC from Teflon filters varied across Bhopal (0.46–1.35 μg m−3), Mesra (0.30–0.92 μg m−3), and Mysuru (0.16–0.68 μg m−3). Likewise, the range of nitrate volatilization was 0.7–2.7 μg m−3 at Bhopal, 0.5–2 μg m−3 at Mesra, and 1.3–2.2 μg m−3 at Mysuru. Also, the range of ALW mass was 2.6–6.8 μg m−3 at Bhopal, 3.2–9.5 μg m−3 at Mesra, and 0.8–3.8 μg m−3 at Mysuru. Seasonality was observed in the value of OM/OC with an increase during the pre‐monsoon season at all sites viz., Bhopal (2.20), Mesra (1.61), and Mysuru (2.02) compared to their annual averages, suggesting enhanced contribution of secondary organics to OC. The method developed for estimating RCM in this study resulted in better mass closure compared to using conventional RCM algorithms. Overall, this study provides a robust data validation strategy and India‐specific species coefficients for use in the RCM algorithm. The outcomes of this study can guide regional aerosol sampling, chemical analyses, and model–measurement reconciliation efforts.