Characteristics, sources, and health risks of fine particulate matter in Wuhan subway, China

The concentrations and characteristics of PM_2.5-bound metals in subway station atmosphere change in time and location within subway stations, which can intensely influence the health of subway workers and passengers. Therefore, this study aimed to reveal the characteristics and distribution of PM_2.5-bound metals in subway stations and across subway stations, further identify the possible sources and perform health risk assessment by integrating source apportionment with element-specific health risk analysis. The PM_2.5 samples were collected from entrances and platforms in seventeen subway stations in Wuhan, China. Fifteen metals in PM_2.5 from subway stations were detected. Enrichment factors (EFs) and the positive matrix factorization (PMF) model were applied to identify potential sources. Non-carcinogenic and carcinogenic health risks to subway workers and passengers were conducted. The most abundant metallic element in PM_2.5 at subway stations was Fe. The annual mean concentrations of Fe at subway station entrances and platforms were respectively 1898.29 ± 1554.66 ng/m³ and 6615.43 ± 6515.85 ng/m³, which is significantly higher than the other metals. Six sources of metallic elements in PM_2.5 were identified at entrances and platforms in four seasons. Although there were seasonal and spatial differences of the six sources, anthropogenic sources consistently dominated PM_2.5-bound metals in subway stations. Rails and wheels were the most predominant source in subway stations. Cr(VI) and As had carcinogenic risks to subway workers. In conjunction with source apportionment with element-specific health risk analysis, rails and wheels mainly contributed carcinogenic risks to subway workers, followed by coal burning. This study provides basic data for source control and mitigation measures to protect subway workers' health.