Issue 3, 2023

Wildfire particulate matter as a source of environmentally persistent free radicals and reactive oxygen species

Abstract

Wildfires, which have been occurring increasingly in the era of climate change, emit massive amounts of particulate matter (PM) into the atmosphere, strongly affecting air quality and public health. Biomass burning aerosols may contain environmentally persistent free radicals (EPFRs, such as semiquinone radicals) and redox-active compounds that can generate reactive oxygen species (ROS, including ·OH, superoxide and organic radicals) in the aqueous phase. However, there is a lack of data on EPFRs and ROS associated with size-segregated wildfire PM, which limits our understanding of their climate and health impacts. We collected size-segregated ambient PM in Southern California during two wildfire events to measure EPFRs and ROS using electron paramagnetic resonance spectroscopy. EPFRs are likely associated with soot particles as they are predominantly observed in submicron particles (PM1, aerodynamic diameter ≤ 1 μm). Upon extraction in water, wildfire PM mainly generates ·OH (28–49%) and carbon-centered radicals (∼50%) with minor contributions from superoxide and oxygen-centered organic radicals (2–15%). Oxidative potential measured with the dithiothreitol assay (OP-DTT) is found to be high in wildfire PM1, exhibiting little correlation with the radical forms of ROS (r2 ≤ 0.02). These results are in stark contrast with PM collected at highway and urban sites, which generates predominantly ·OH (84–88%) that correlates well with OP-DTT (r2 ∼ 0.6). We also found that PM generated by flaming combustion generates more radicals with higher OP-DTT compared to those by smoldering or pyrolysis.

Graphical abstract: Wildfire particulate matter as a source of environmentally persistent free radicals and reactive oxygen species

Supplementary files

Article information

Article type
Paper
Submitted
02 déc. 2022
Accepted
27 janv. 2023
First published
27 janv. 2023
This article is Open Access
Creative Commons BY-NC license

Environ. Sci.: Atmos., 2023,3, 581-594

Wildfire particulate matter as a source of environmentally persistent free radicals and reactive oxygen species

T. Fang, B. C. H. Hwang, S. Kapur, K. S. Hopstock, J. Wei, V. Nguyen, S. A. Nizkorodov and M. Shiraiwa, Environ. Sci.: Atmos., 2023, 3, 581 DOI: 10.1039/D2EA00170E

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