Reactive Oxygen Species Generation in Highway PM2.5
Quantifying environmentally persistent free radicals and ROS generation in highway fine particulate matter using electron paramagnetic resonance spectroscopy.
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.
Methodology
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
- Generation of radical forms of reactive oxygen species (ROS) in water
Both measurements were performed using electron paramagnetic resonance spectroscopy.
Key Findings
EPFR Concentrations
The EPFR concentrations were 36 ± 14 pmol m⁻³ at highway sites, approximately two times higher than those at the urban site.
Correlations
- EPFRs correlate positively with CO, NOx, and elemental and organic carbon—indicating emission from vehicular exhaust
- Good correlations of EPFRs with Fe and Cu suggest stabilization by metals from tire and brake wear
- EPFRs are negatively correlated with ozone, suggesting photochemistry does not play a large role in EPFR formation
ROS Generation
Highway PM2.5 generates mainly OH and organic radicals in the aqueous phase. The generated ROS correlate with PM2.5 mass concentrations, and OH radicals show good correlation with EPFRs—implying the role of EPFRs in aqueous OH radical generation.
Conclusion
These findings highlight the interplay of various PM redox-active chemical components and complex relationship between ROS formation and DTT activity.
Published in ACS Earth and Space Chemistry Read the full paper →