Insight Study of Trace Elements in PM2.5 During Nine Years in Delhi, India: Seasonal Variation, Source Apportionment, and Health Risks Assessment

This study investigated the concentrations, seasonal variations, sources, and human health risks associated with exposure to heavy elements (As, Al, Pb, Cr, Mn, Cu, Zn, and Ni) of PM_2.5 at an urban location of Delhi (28° 38′ N, 77° 10′ E; 218 m amsl), India, from January 2013 to December 2021. The average mass concentration of PM_2.5 throughout the study period was estimated as 127 ± 77 µg m⁻³, which is exceeding the National Ambient Air Quality Standards (NAAQS) limit (annual: 40 µg m⁻³; 24 h: 60 µg m⁻³). The seasonal mass concentrations of PM_2.5 exhibited at the order of post-monsoon (192 ± 110 µgm⁻³) > winter (158 ± 70 µgm⁻³) > summer (92 ± 44 µgm⁻³) and > monsoon (67 ± 32 µgm⁻³). The heavy elements, Al (1.19 µg m⁻³), Zn (0.49 µg m⁻³), Pb (0.43 µg m⁻³), Cr (0.21 µg m⁻³), Cu (0.21 µg m⁻³), Mn (0.07 µg m⁻³), and Ni (0.14 µg m⁻³) exhibited varying concentrations in PM_2.5, with the highest levels observed in the post-monsoon season, followed by winter, summer, and monsoon seasons. Six primary sources throughout the study period, contributing to PM_2.5 were identified by positive matrix factorization (PMF), such as dust (paved/crustal/soil dust: 29.9%), vehicular emissions (17.2%), biomass burning (15.4%), combustion (14%), industrial emissions (14.2%), and Br-rich sources (9.2%). Health risk assessments, including hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR), were computed based on heavy elements concentrations in PM_2.5. Elevated HQ values for Cr and Mn linked with adverse health impacts in both adults and children. High carcinogenic risk values were observed for Cr in both adults and children during the winter and post-monsoon seasons, as well as in adults during the summer and monsoon seasons. The combined HI value exceeding one suggests appreciable non-carcinogenic risks associated with the examined elements. The findings of this study provide valuable insights into the behaviour and risk mitigation of heavy elements in PM_2.5, contributing to the understanding of air quality and public health in the urban environment of Delhi.