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Environmentally persistent free radicals in PM2.5: a review

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Abstract

Environmentally persistent free radicals (EPFRs) are a new class of pollutants that are long-lived in fine particles (PM2.5), i.e., their 1/e lifetime ranges from days to months (or even infinite). They are capable of producing harmful reactive oxygen species such as hydroxyl radicals. The redox cycling of EPFRs is considered as an important pathway for PM2.5 to induce oxidative stress inside the humans, causing adverse health effects such as respiratory and cardiovascular diseases. Consequently, research regarding their toxicity, formation and environmental occurrences in PM2.5 has attracted increasing attentions globally during the past two decades. However, literature data in this field remain quite limited and discrete. Hence, an extensive review is urgently needed to summarize the current understanding of this topic. In this work, we systematically reviewed the analytical methods and environmental occurrences, e.g., types, concentrations, and decay behaviors, as well as possible sources of EPFRs in PM2.5. The types of pretreatment methods, g-values of common EPFRs and categories of decay processes were discussed in detail. Moreover, great efforts were made to revisit the original data of the published works of EPFRs in airborne particulate matter and provided additional useful information for comparison where possible, e.g., their mean and standard deviation of g-values, line widths (∆Hp-p), and concentrations. Finally, possible research opportunities were highlighted to further advance our knowledge of this emerging issue.

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Acknowledgements

This work was supported by the Ningbo Natural Science Foundation (Grant no. 2018A610208) and the National Institute of Environmental Health Sciences (NIEHS) (Grant no. 2P42ES013648). Dr. Mengxia Xu is grateful to Ms. Jing Zhang, Mr. Qingfu Wang and Mr. Liangliang Zhu from Faculty of Science and Engineering, University of Nottingham Ningbo China for their kind help in the research project of EPFRs in PM2.5.

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Authors and Affiliations

  1. Department of Chemical and Environmental Engineering, University of Nottingham Ningbo China, Ningbo, 315100, China

    Mengxia Xu, Tao Wu, Poornima Ramesh Iyer, Dengting Guo, Anran Chen, Miao Lyu, Jinhu Li, Jiaqi Liu, Dan Li, Yuxin Zuo, Shihan Zhang, Yiran Wang, Yining Meng & Fei Qi

  2. New Materials Institute, University of Nottingham Ningbo China, Ningbo, 315100, China

    Mengxia Xu & Tao Wu

  3. School of Geographical Sciences, University of Nottingham Ningbo China, Ningbo, 315100, China

    Yu-Ting Tang

  4. State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, 310027, China

    Tong Chen

  5. Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA

    Lavrent Khachatryan

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  1. Mengxia Xu
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  2. Tao Wu
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Correspondence to Mengxia Xu, Tong Chen or Lavrent Khachatryan.

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Xu, M., Wu, T., Tang, YT. et al. Environmentally persistent free radicals in PM2.5: a review. Waste Dispos. Sustain. Energy 1, 177–197 (2019). https://doi.org/10.1007/s42768-019-00021-z

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