Measurement report: Rapid changes of chemical characteristics and health risks for highly time resolved trace elements in PM2.5 in a typical industrial city in response to stringent clean air actions

Atmospheric trace metals entail significant damages in human health and ecosystem safety, and thus a series of clean air actions have been implemented to decrease the ambient element concentrations. Unfortunately, the impact of these emission control measures on element concentrations in fine particles remains poorly understood. In our study, the random forest (RF) model was applied to distinguish the effects of emission and meteorology to trace elements in PM2.5 in a typical industrial city named Tangshan based on a 3-year (2017-2020) hourly field observation. The result suggested that the clean air actions have facilitated the dramatic decreases of the deweathered concentrations of Ga, Co, Pb, Zn, and As by 72ĝ€¯%, 67ĝ€¯%, 62ĝ€¯%, 59ĝ€¯%, and 54ĝ€¯%, respectively. It is attributable to the strict implementation of "coal to gas"strategies and optimisation of industrial structure and layout. However, the deweathered levels of Ca (8.3ĝ€¯%), Cr (18.5ĝ€¯%), and Fe (23ĝ€¯%) only displayed minor decreases, indicating that the emission control measures for ferrous metal smelting and vehicle emission were not very effective. The positive matrix factorisation (PMF) results suggested that the contribution ratios of biomass burning, non-ferrous metal smelting, coal combustion, ferrous metal smelting, heavy oil combustion, and traffic-related dust changed from 33ĝ€¯%, 11ĝ€¯%, 15ĝ€¯%, 13ĝ€¯%, 3ĝ€¯%, and 25ĝ€¯% to 33ĝ€¯%, 8ĝ€¯%, 8ĝ€¯%, 13ĝ€¯%, 4ĝ€¯%, and 33ĝ€¯%, respectively. To date, no significant non-carcinogenic and carcinogenic risks were observed for all of the elements, while both of As and Pb still showed relatively high health damages. It was proposed to further cut down the combustion-related emissions (e.g. As and Pb) because it showed the highest marginal health benefits. Besides this, the control of traffic-related emissions might be a key abatement strategy to facilitate the reduction of elements in fine particles.