Sources of cellular oxidative potential of water-soluble fine ambient particulate matter in the Midwestern United States.

We investigated the spatiotemporal distribution and sources of cellular oxidative potential (OP) in the Midwest US. Weekly samples were collected from three urban [Chicago (IL), Indianapolis (IN), and St. Louis (MO)], one rural [Bondville (IL], and one roadside site [Champaign (IL)] for a year (May 2018 to May 2019), and analyzed for water-soluble cellular OP using a macrophage reactive oxygen species (ROS) assay. Chemical composition of the samples including several carbonaceous components, inorganic ions, and water-soluble elementals, were also analyzed. The emission sources contributing to water-soluble cellular OP and PM mass were analyzed using positive matrix factorization. The secondary organic aerosols contributed substantially (≥54%) to PM cellular OP at urban sites, while the roadside and rural OP were dominated by road dust (54%) and agricultural activities (62%), respectively. However, none of these sources contributed substantially to the PM mass (≤21%). Other sources contributing significantly to the PM mass, i.e., secondary sulfate and nitrate, biomass burning and coal combustion (14-26%) contributed minimally to the cellular OP (≤13%). Such divergent profiles of the emission sources contributing to cellular OP vs. PM mass demonstrate the need of considering more health-relevant metrics such as OP in the design of air pollution control strategies.