Spatiotemporal variability in the oxidative potential of ambient fine particulate matter in the Midwestern United States

Abstract. We assessed the oxidative potential (OP) of both water-soluble and methanol-soluble fractions ambient fine particulate matter (PM2.5) in Midwestern United States. A large set PM2.5 samples (N=241) was collected from five sites up different environments, i.e., urban, rural, roadside, Illinois, Indiana, Missouri during May 2018–May 2019. Five acellular OP endpoints, including consumption rate ascorbic acid glutathione a surrogate lung fluid (SLF) (OPAA OPGSH, respectively), dithiothreitol (DTT) depletion (OPDTT), ?OH generation SLF DTT (OPOH?SLF OPOH?DTT, were measured for all samples. mass concentrations US as obtained these spatially homogeneously distributed, while most endpoints showed significant spatiotemporal heterogeneity. Seasonally, higher activities occurred summer water- extracts. Spatially, roadside site highest extracts, only occasional peaks observed at urban OP. Most similar trends between mass- volume-normalized across seasons. Comparisons two solvents (i.e., water methanol) that generally had activity levels than corresponding Site-to-site comparisons stronger correlations compared to OP, indicating better extraction water-insoluble redox-active compounds various emission sources into methanol. found weak correlation inconsistent slope values endpoints. Moreover, poor moderate intercorrelations among indicate mechanisms represented by thus demonstrate rationale analyzing multiple more comprehensive assessment