Sources of Acellular Oxidative Potential of Water-soluble Fine Ambient Particulate Matter in the Midwestern United States

Ambient fine particulate matter (PM2.5) is associated with numerous health complications, yet the specific PM2.5 chemical components and their emission sources contributing to these health outcomes are understudied. Our study analyzes the chemical composition of PM2.5 collected from five distinct locations at urban, roadside and rural environments in midwestern region of the United States, and associates them with five acellular oxidative potential (OP) endpoints of water-soluble PM2.5. Redox-active metals (i.e., Cu, Fe, and Mn) and carbonaceous species were correlated with most OP endpoints, suggesting their significant role in OP. We conducted a source apportionment analysis using positive matrix factorization (PMF) and found a strong disparity in the contribution of various emission sources to PM2.5 mass vs. OP. Regional secondary sources and combustion-related aerosols contributed significantly (> 75% in total) to PM2.5 mass, but showed weaker contribution (43-69%) to OP. Local sources such as parking emissions, industrial emissions, and agricultural activities, though accounting marginally to PM2.5 mass (< 10% for each), significantly contributed to various OP endpoints (10-50%). Our results demonstrate that the sources contributing to PM2.5 mass and health effects are not necessarily same, emphasizing the need for an improved air quality management strategy utilizing more health-relevant PM2.5 indicators. Oxidative potential (OP) has been purported as a health relevant metric of ambient PM2.5, although ambient air quality standards are based only on PM2.5 mass concentrations. Our study investigates the sources of OP of PM2.5 across different sites in the midwest region of US. Local sources such as industrial and parking emissions, and agricultural activities, though contributing marginally to PM2.5 mass, significantly impact OP. These findings highlight the need to develop the emission control strategies which not only manage regional sources of PM2.5 pollution, but also account for the local sources to minimize the overall health effects from PM2.5 pollution.