Sources of Oxidative Potential (OP) of Ambient Fine Particulate Matter in the Midwestern United States

Haoran Yu, Yixiang Wang, Joseph V. Puthussery, VISHAL VERMA, University of Illinois Urbana-Champaign

     Abstract Number: 638
     Working Group: Health-Related Aerosols

Abstract
Although oxidative potential (OP) of ambient fine particulate matter (PM_2.5) has been widely recognized as a more health-relevant indicator compared to PM_2.5 mass concentration, multiple previous studies observed different spatiotemporal patterns of different OP endpoints, indicating the importance of measuring multiple endpoints to obtain a comprehensive assessment of PM-associated oxidative stress. In this study, we analyzed water-soluble OP of PM_2.5 samples (N > 200) collected from five sites in the Midwestern US throughout an entire year (2018 – 2019) with five acellular OP endpoints [consumption of ascorbic acid (AA) and glutathione (GSH) in a surrogate lung fluid (SLF), OP^AA and OP^GSH; depletion of dithiothreitol (DTT), OP^DTT; and generation of ∙OH in SLF and DTT, OP^OH-SLF and OP^OH-DTT]. Detailed chemical composition of these PM_2.5 samples, including inorganic ions, carbonaceous species, and water-soluble trace elements were also measured. Our results showed strong correlations between multiple OP endpoints and OC and several transition metals (i.e., Cu, Fe, Mn, and Zn) at various sites, which are attributed to the high redox activity of these components. Some other species, including EC and K, were also moderately correlated with most OP endpoints at all sites during winter, implying the significance of their associated sources, e.g., biomass burning to OP. Source apportionment results obtained from the positive matrix factorization (PMF) model found very different profiles of the identified sources for their contribution to OP vs. PM_2.5 mass concentration. Anthropogenic sources, including industrial emissions, vehicular-associated emissions at urban sites, and agricultural emissions at rural sites, although accounted marginally for PM_2.5 mass (6.1 – 20.8 %), had significant contributions to various endpoints (17.4 – 64.3 %). In contrast, bulk sources like biomass burning and secondary nitrate, although accounting largely for PM_2.5 mass (16.4 - 27.4 %), contributed lesser to many OP endpoints (<20 %) compared to their mass fractions. Essentially these results indicate that the contribution of various emission sources to the PM_2.5 mass may not necessarily equate with their contribution to PM_2.5 overall health risks, and thus demonstrate the need of developing alternative metrics to control PM_2.5 emissions.