Trace Metals Reveal Significant Contribution of Coal Combustion to Winter Haze Pollution in Northern China

While the contribution of coal combustion to atmospheric particulate matter is well-recognized, its specific role in winter haze remains insufficiently explored. In this study, we elucidate the quantitative effect of coal combustion on winter haze pollution based on high temporal resolution measurements of trace metals in PM2.5. We identified arsenic (As) and selenium (Se) as reliable indicators of coal combustion, with their enrichment factors exceeding 104. The significant increase in As and Se concentrations (9.6-fold and 7.1-fold increase) during severe haze episodes underscores the enhanced contribution of coal combustion to winter haze pollution. Chemical mass closure results indicate that primary emissions from coal combustion contribute 15% to PM2.5, with its proportion in primary PM2.5 mass reaching 42% and 57% during non-haze and haze episodes, respectively. Simulations utilizing the multiphase chemical model (RACM-CAPRAM) indicate that transition metal-catalyzed oxidation is responsible for 68% of secondary sulfate formation, with the aqueous phase and surface catalysis contributing 59% and 9%, respectively. Excluding coal combustion-emitted SO2, Mn, and Fe results in a 49% reduction in secondary sulfate production. This research presents a comprehensive assessment of the impact of coal combustion on winter haze in northern China, offering vital insights for formulating effective pollution control strategies in the future.