Study of aerosol trace elements over three COALESCE network locations in India: Spatio-temporal variability, dry deposition and health risks

A small fraction (5-10 %) of PM_2.5 (fine particulate matter, with aerodynamic diameter ≤ 2.5 µm) mass constitutes trace elements (TEs) and plays an important role in controlling human health, ecological systems and air quality. TE/groups of TE are used as tracers to identify specific PM sources, predominantly due to their persistence and stability in the atmosphere. As a part of the COALESCE network ambient aerosol measurement campaign, 24-h integrated collocated PM_2.5 filter sampling was carried out for 2019 in all the three distinctly different geographical locations in India, viz., Bhopal, Mesra and Mysuru, and 15 TE concentrations were analyzed using Energy Dispersive X-Ray Fluorescence. For all sites, annual mean sulfur contributed highest (~7 %) to PM_2.5 mass among all analyzed elements followed by silicon (~3 %). Elements from multiple sources exhibited differentiable seasonal variations like crustal origin elements peaked during the pre-monsoon season, while other anthropogenic activities driven elements increased during the winter and post- monsoon seasons. Spatial heterogeneity of elements between the sites was examined using statistical tools like coefficient of divergence and spearman correlation coefficient (SCC), and revealed that they had different sources/source regions or were processed differently in the atmosphere. Further, SCC coupled with hierarchical clustering analysis categorized the data set into three common groups to yield likely sources of TEs that included crustal and mineral dust; biomass burning; non-exhaust traffic emissions and industrial sources, for all three locations. The computed dry deposition flux of both crustal (3377.41 ± 3224.65 µg m^-2 d^-1 to 27.83 ± 21.91 µg m^-2 d^-1) and non-crustal elements (53.47 ± 78.57 µg m^-2 d^-1 to 0.72 ± 0.59 µg m^-2 d^-1) was in compliance with modeled deposition flux for the entire Northern Indian Ocean and were similar to the fluxes over different regions across the globe. The United States Environment Protection Agency health risk assessment method in all sites revealed that the route of exposure of metals was highest via inhalation pathway for both adults and children, followed by dermal contact and ingestion. Total potential non-carcinogenic health risk for all pathways were below safe level (Hazard Quotient < 1) for Bhopal and Mysuru, and above safe level (Hazard Quotient > 1) for Mesra. These findings suggest that the non-carcinogenic adverse effects from multi-elemental exposure to PM_2.5 was greater in Mesra, than other two sites and might be due to influence of elemental pollutants from more dominant sources of agricultural burning and industrial activities in this region (1). On the other hand, the carcinogenic risk of all metal exposure was within acceptable limits (1×10^-6 – 1×10^-4), through all three pathways in all the sites. Overall, the multiple site analysis presented in this study provides information on spatiotemporal patterns, dry deposition fluxes of elements in ambient PM, in addition to potential human health risks upon exposure to these species.

 

1.Maheshwarkar, Prem, et al. "Understanding the influence of meteorology and emission sources on PM2. 5 mass concentrations across India: first results from the COALESCE network." Journal of Geophysical Research: Atmospheres 127.4 (2022): e2021JD035663.