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
To investigate the sources and health risks of heavy metals in PM2.5 during winter in Xi'an, hourly concentrations of eight heavy metals (Cu, Pb, Ni, Cr, etc.) were measured using an Amms-100 online analyzer at the Xi'an International Horticultural Exposition site from November 2024 to March 2025. The positive matrix factorization (PMF) model was applied for source apportionment, and the U.S. EPA health risk assessment model was used to evaluate carcinogenic and non-carcinogenic risks for different populations. Results showed that PM2.5 concentrations varied significantly across pollution levels, with an average of 173.5 μg·m−3 during heavy pollution, 4.1, 1.9, and 1.3 times higher than during non-pollution, light, and moderate pollution periods, respectively. Concentrations of Pb, Mn, and Cu increased with pollution level, indicating a combined effect of coal combustion and unfavorable dispersion. PMF identified five sources during non-pollution periods (industrial metallurgy, crustal dust, metal processing, etc.) but only four during polluted periods, with Cu contribution increasing significantly, suggesting a shift to traffic-related mechanical wear. Health risk assessment indicated that carcinogenic risks were highest in adult males, followed by adult females and children. Non-carcinogenic risks (HQ) for Zn and Cu were below 1, but Pb and Mn posed non-carcinogenic risks, with Mn being significant. The incremental lifetime cancer risks (ILCR) for As and Cr exceeded 10−4, identifying them as primary carcinogenic metals. This study provides scientific evidence for targeted air pollution control in Xi'an, emphasizing the need to strengthen controls on coal combustion, traffic, and industrial emissions during heating periods.