Size fraction of hazardous particulate matter governing the respiratory deposition and inhalation risk in the highly polluted city Delhi

Trace elements in PM2.5 from 2016 to 2021 in Shenzhen, China: Concentrations, temporal and spatial distribution, and related human inhalation exposure risk

The prevalence of trace elements from industrial and traffic activities poses potential health risks through inhalation exposure. Prior studies have focused on trace elements in water, food, and dust, and less attention has been paid to their occurrence in fine particulate matter (PM2.5). In this study, 1424 air samples were collected from three districts (Nanshan, Longgang, and Yantian) in Shenzhen from 2016 to 2021, and we analyzed the concentrations, temporal trends, and spatial distributions of PM2.5 and associated trace elements. Both PM2.5 and trace elements exhibited decreasing trends and similar seasonal variations, with high levels in cold seasons and low levels in warm seasons. In terms of spatial distributions, the concentrations of PM2.5 and trace elements in Nanshan and Longgang were significantly higher than those in Yantian, likely due to the industrial structure and traffic activities. It is worth noting that PM2.5 was identified as a potential mediator of the effect of meteorological parameters on trace element levels. Besides, the values of estimated daily intake (EDI) and uptake (EDU) suggested that infants and young children experienced an elevated risk of exposure to trace elements. While the annual average excess hazard indexes (R) were below the safety threshold (10-6), carcinogenic trace elements like arsenic (As) and chromium (Cr) posed a greater potential threat to human health compared to non-carcinogenic trace elements.

Summertime oxidative potential of atmospheric PM2.5 over New Delhi: Effect of aerosol ageing

Exposure to elevated particulate matter (PM) concentrations in ambient air has become a major health concern over urban areas worldwide. Reactive oxygen species (ROS) generation due to ambient PM (termed as their oxidative potential, OP) is shown to play a major role in PM-induced health effects. In the present study, the OP of the ambient PM2.5 samples, collected during summer 2019 from New Delhi, were measured using the dithiothreitol (DTT) assay. Average volume-normalized OP (OPV) was 2.9 ± 1.1 nmol DTT min-1 m-3, and mass-normalized OP (OPm) was 61 ± 29 pmol DTT min-1 μg-1. The regression statistics of OPv vs chemical species show the maximum slope of OPV with the elemental carbon (EC, r2 = 0.72) followed by water-soluble organic carbon (WSOC, r2 = 0.72), and organic carbon (OC, r2 = 0.64). A strong positive correlation between OPm and secondary inorganic aerosols (SIA, such as NH4+ and NO3- mass fractions) was also observed, indicating that the sources emitting NO2 and NH3, precursors of NO3- and NH4+, also emit DTT-active species. Interestingly, the slope value of OPv vs OC for aged aerosols (OM/OC > 1.7, f44 > 0.12 and f43 < 0.04) was 1.7 times higher than relatively fresh organic aerosols (OA, OM/OC < 1.7, f44 < 0.12, f43 > 0.04). An increase in OPv and OPoc with f44 indicates the formation of more DTT active species with the ageing of OA. A linear increase in OPoc with increasing Nitrogen/Carbon (N/C) ratio suggests that nitrogenous OA have higher OP.