Unexpected catalytic influence of atmospheric pollutants on the formation of environmentally persistent free radicals

Environmentally persistent free radicals (EPFRs) have been recognized as harmful and persistent environmental pollutants. In polluted regions, many acidic and basic atmospheric pollutants, which are present at high concentrations, may influence the extent of the formation of EPFRs. In the present paper, density functional theory (DFT) and ab-initio molecular dynamics (AIMD) calculations were performed to investigate the formation mechanisms of EPFRs with the influence of the acidic pollutants sulfuric acid (SA), nitric acid (NA), organic acid (OA), and the basic pollutants, ammonia (A), dimethylamine (DMA) on alpha-Al2O3 (0001) surface. Results indicate that both acidic and basic pollutants can enhance the formation of EPFRs by acting as bridge or semi-bridge roles by proceeding via a barrierless process. Acidic pollutants enhance the formation of EPFRs by first transferring its hydrogen atom to the alpha-Al2O3 surface and subsequently reacting with phenol to form an EPFR. In contrast, basic pollutants enhance the formation of EPFRs by first abstracting a hydrogen atom from phenol to form a phenoxy EPFR and eventually interacting with the alpha-Al2O3 surface. These new mechanistic insights will inform in understanding the abundant EPFRs in polluted regions with high mass concentrations of acidic and basic pollutants.

Automated summary

This study investigated the influence of acidic and basic pollutants on the formation of EPFRs using DFT and AIMD calculations. The findings showed that these pollutants can enhance the formation of EPFRs through different mechanisms. Acidic pollutants transfer hydrogen atoms to form EPFRs, while basic pollutants extract hydrogen atoms to form phenoxy EPFRs.