Photoinduced formation of persistent free radicals, hydrogen radicals, and hydroxyl radicals from catechol on atmospheric particulate matter

Linjun Qin; Lili Yang; Jiahui Yang; Ralph Weber; Kalina Ranguelova; Xiaoyun Liu; Bingcheng Lin; Cui Li; Minghui Zheng; Guorui Liu

doi:10.1016/j.isci.2021.102193

Photoinduced formation of persistent free radicals, hydrogen radicals, and hydroxyl radicals from catechol on atmospheric particulate matter

iScience. 2021 Feb 16;24(3):102193. doi: 10.1016/j.isci.2021.102193. eCollection 2021 Mar 19.

Authors

Linjun Qin^{1

2}, Lili Yang^{1

2}, Jiahui Yang³, Ralph Weber⁴, Kalina Ranguelova⁴, Xiaoyun Liu^{1

2}, Bingcheng Lin⁵, Cui Li^{1

2}, Minghui Zheng^{1

2

5}, Guorui Liu^{1

2

5}

Affiliations

¹ State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
² College of Resource and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
³ Bruker BioSpin Corp, Shanghai 200233, China.
⁴ Bruker BioSpin Corp, Billerica, MA 01821, USA.
⁵ School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310000, China.

Abstract

Catechol is speculated to be a potential precursor of environmentally persistent free radicals (EPFRs) in the atmosphere. EPFRs absorbed on PM_2.5 have attracted public attention because their toxicity is similar to cigarette smoke. In this study, we found that catechol could produce EPFRs, which were oxygen-centered phenoxy and semiquinone radicals. These free radical species had half-lives of up to 382 days. CaO, CuO, and Fe₂O₃ markedly promoted EPFR formation from catechol. The valence states of Cu and Fe changed during the photochemical reactions of catechol but no valence state changed for Ca. Alkaline nature of CaO is possibly the key for promoting the free radical formations through acid-base reactions with catechol. In addition to hydroxyl free radicals, hydrogen free radicals and superoxide anions formed from the photochemical reactions of catechol were first discovered. This is of concern because of the adverse effects of these free radicals on human health.

Keywords: Chemistry; Environmental Chemical Engineering; Environmental Science; Theoretical Photochemistry.