Environmentally Persistent Free Radicals, Reactive Oxygen Species Generation, and Oxidative Potential of Highway PM_2.5

Abstract

In urban environments, vehicle exhaust and nonexhaust emissions represent important sources of fine particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5), which plays a central role in adverse health effects and oxidative stress. We collected PM2.5 filter samples from two highway sites (Anaheim and Long Beach, CA) and an urban site (Irvine, CA) to quantify environmentally persistent free radicals (EPFRs) contained in PM2.5 and the generation of radical forms of reactive oxygen species (ROS) in water using electron paramagnetic resonance spectroscopy. The EPFR concentrations were 36 ± 14 pmol m–3 at highway sites, which were about two times higher than those at the urban site. EPFRs correlate positively well with CO, NOx, and elemental and organic carbon, indicating that EPFRs are emitted from vehicular exhaust. Good correlations of EPFRs and Fe and Cu may indicate that EPFRs are stabilized by Fe and Cu emitted from tire and brake wears. EPFRs are negatively correlated with ozone, suggesting that photochemistry does not play a large role in the formation of EPFRs and possibly also indicating that EPFRs are quenched by ozone. Highway PM2.5 are found to generate mainly OH and organic radicals in the aqueous phase. The generated ROS are correlated with PM2.5 mass concentrations and OH radicals show a good correlation with EPFRs, implying the role of EPFRs in aqueous OH radical generation. The PM2.5 oxidative potentials as quantified with the dithiothreitol (DTT) assay are correlated with ROS, OH, and organic radicals for PM2.5 collected in Anaheim, whereas little correlations are observed for Long Beach. These findings highlight the interplay of various PM redox-active chemical components and complex relationship between ROS formation and DTT activity.

Environmentally persistent free radicals in indoor particulate matter, dust, and on surfaces

“…For example, Borrowman et al 19 reported EPFR formation upon exposing PAH-containing films to ozone, which then decayed via radical–radical recombination or interaction with ozone, and EPFR quenching by ambient ozone was also recently suggested. 62 While similar formation processes may explain the type 1 EPFR increase (Fig. 2), the decay of type 2 EPFR suggests they are sensitive to ozone exposure.…”

“…water-soluble redox activity). 30,35,36,40,[68][69][70] Similarly, recent ndings have shown these radicals could originate from stable oxidized organic species, 26,30 or from EPFR, 30,62 in ambient PM.…”

Mario Molina Memorial Special Issue

“…46 In the Los Angeles area, Hwang and co-workers dig deeper into the health effects of highway fine particulate matter with an aerodynamic diameter of less than 2.5 μm (PM 2.5 ) and the role of environmentally persistent free radicals. 47 Van Rooy et al report observations of how VOC levels changed during the first months of the COVID-19 pandemic. 48,49 Next-generation approaches are presented for monitoring air pollution using low-cost sensors in Ghana 50 and China, 51 and a new aerosol chemical speciation monitor mass spectrometry system was demonstrated in Atlanta, GA. 52 An airborne solar occultation flux instrument measured gases in plumes resulting from biomass burning, which is a major pollution source globally.…”

“…Ultra-high-performance liquid chromatography with tandem mass spectrometry revealed trends in organosulfate and nitrooxy organosulfate formation chemistry in Guangzhou, China . In the Los Angeles area, Hwang and co-workers dig deeper into the health effects of highway fine particulate matter with an aerodynamic diameter of less than 2.5 μm (PM 2.5 ) and the role of environmentally persistent free radicals . Van Rooy et al report observations of how VOC levels changed during the first months of the COVID-19 pandemic. , Next-generation approaches are presented for monitoring air pollution using low-cost sensors in Ghana and China, and a new aerosol chemical speciation monitor mass spectrometry system was demonstrated in Atlanta, GA .…”

Generation of Environmentally Persistent Free Radicals on Metal–Organic Frameworks

“…Environmentally persistent free radicals (EPFRs) are long-lived radicals mainly found in various environmental media such as airborne fine particulate matter (PM) and organic pollutants contaminated soil. − In contrast with other free radicals, they exhibit certain paramagnetic stability, with half-lives usually as long as days or even months in natural condition. , They can not only induce the formation of biologically damaging reactive oxygen species (ROSs) such as •OH, •O 2 – , and H 2 O 2 , but also act as precursors contributing to the formation of environmental hazards like persistent organic pollutants (POPs). − Because of their persistence and radical-type reactivity along with environmental mobility, EPFRs have become one of the important emerging contaminants and caused widespread concerns. ,− …”