Source Apportionment and Health Risk Assessment of Heavy Metals in PM2.5 during Winter in Xi'an under Different Pollution Levels Based on the PMF Model

• • Heavy pollution episodes in Xi'an winter saw PM2.5 average concentrations of 173.5 μg·m−3, 4.1 times higher than non-pollution periods, underscoring the need for emergency response during such events. • • PMF analysis revealed that as pollution levels increased, effective source categories decreased from five to four, with Cu contribution rising significantly, indicating a shift to traffic-related mechanical wear, which is critical for targeted emission controls. • • Health risk assessment showed that As and Cr had incremental lifetime cancer risks (ILCR) exceeding 10−4, making them the primary carcinogenic metals, necessitating priority monitoring and regulation. • • Mn posed a significant non-carcinogenic risk (HQ > 1) across all populations, highlighting an often-overlooked metal that requires attention in air quality management.