Key Takeaways & Executive Findings
- •• • 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.
Abstract
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.
1. Introduction
Airborne particulate matter (PM2.5) poses significant health risks, particularly in urban areas with heavy industrial and traffic emissions. In Xi'an, a city in northwest China, winter PM2.5 pollution is exacerbated by coal combustion for heating and stagnant meteorological conditions. While previous studies have characterized PM2.5 mass concentrations, source apportionment of heavy metals and their associated health risks under varying pollution levels remains underexplored. This study addresses this gap by employing high-time-resolution monitoring and the PMF model to identify sources and quantify health risks, providing crucial data for targeted pollution control strategies.
Existing commercial monitoring systems often lack the sensitivity to detect trace heavy metals in real time, and traditional filter-based methods are labor-intensive and provide limited temporal resolution. The use of an Amms-100 online analyzer overcomes these limitations, enabling hourly data collection. By integrating PMF source apportionment with health risk assessment, this study offers a comprehensive framework to understand the dynamic sources of heavy metals and their potential health impacts, thereby informing evidence-based policy interventions for winter air quality management.
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GAO Fei, DONG Yawei, TIAN Tian, WANG Yuwei, ZHANG Yu, ZHAO Bei (2026). 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. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2026021202
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Frequently Asked Questions
What are the dominant sources of heavy metals in PM2.5 during different pollution levels in Xi'an winter?
During non-pollution periods, sources are relatively balanced, including industrial metallurgy, crustal dust, and metal processing. As pollution levels increase, the contribution of Cu rises significantly, and the number of effective sources decreases from five to four, indicating a shift to traffic-related mechanical wear, likely due to congestion and brake wear under stagnant conditions.
Which heavy metals pose the highest carcinogenic and non-carcinogenic risks to the population?
As and Cr have incremental lifetime cancer risks (ILCR) exceeding 10−4, making them the primary carcinogenic metals. For non-carcinogenic risks, Pb and Mn have hazard quotients (HQ) greater than 1, with Mn showing significant risk, while Zn and Cu have HQ < 1, indicating negligible non-carcinogenic risk.
How does the PM2.5 concentration vary across different pollution levels, and what are the implications for public health?
PM2.5 average concentrations during heavy pollution are 173.5 μg·m−3, which is 4.1 times higher than non-pollution periods, and 1.9 and 1.3 times higher than light and moderate pollution, respectively. This substantial increase underscores the need for effective early warning systems and public health advisories during severe pollution episodes.
What is the significance of using an online analyzer for heavy metal monitoring in this study?
The Amms-100 online analyzer provides hourly resolution data, capturing rapid changes in heavy metal concentrations that traditional filter-based methods might miss. This high temporal resolution is crucial for accurately identifying source contributions and assessing health risks, especially during pollution episodes when concentrations can spike.
What are the policy implications of this study for winter air pollution control in Xi'an?
The findings highlight the need to strengthen controls on coal combustion, traffic emissions, and industrial activities during the heating period. Specifically, reducing emissions from traffic-related mechanical wear (e.g., brake and tire wear) and industrial metallurgy could significantly lower heavy metal concentrations and associated health risks. Additionally, monitoring and regulating As and Cr should be prioritized due to their high carcinogenic risk.
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