02 Jun 2021

02 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Spatiotemporal Variability in the Oxidative Potential of Ambient Fine Particulate Matter in Midwestern United States

Haoran Yu, Joseph Varghese Puthussery, Yixiang Wang, and Vishal Verma Haoran Yu et al.
  • Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States

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

Haoran Yu et al.

Status: open (until 14 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-376', Anonymous Referee #2, 21 Jun 2021 reply

Haoran Yu et al.


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Short summary
We assessed the oxidative potential (OP) of ambient PM2.5 collected from five sites in the Midwest US. Compared to the homogeneously distributed PM2.5 mass, OP showed high spatiotemporal variation. Weak correlations for the regression between mass and OP indicated a limited role of mass in determining the OP. Moreover, the intercorrelations among different OP endpoints were not strong, justifying the need for using multiple assays for determining the oxidative levels of the particles.