p-Phenylenediamine Antioxidants in PM2.5: The Underestimated Urban Air Pollutants.

The wide use and continuous abrasion of rubber-related products appears to be leading to an incredible release of p-phenylenediamine (PPD) antioxidants in the environment. However, no related research has been conducted on the pollution characteristics and potential health risks of PM2.5-bound PPDs. We report for the first time the ubiquitous distributions of six emerging PPDs and a quinone derivative, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPDQ), in PM2.5 from urban areas of China. Atmospheric contamination levels of PM2.5-bound PPDs were found to be mostly in pg m-3 amounts between 2018 and 2019. Urban vehicle rubber tire abrasion was found to probably contribute to the PPDs in PM2.5 and accounted for their significant spatiotemporal-dependent concentration variations. Furthermore, 6PPDQ, an emerging oxidation product of 6PPD in the environment, was first quantified (pg m-3) with a total detection rate of 81% in the urban PM2.5, demonstrating its broad existence. On the basis of the determined ambient concentrations, the annual intakes of PPDs and 6PPDQ for adults were not low, indicating their possible human health risks induced by long-term exposure. This study confirms the widespread occurrence of PPDs and 6PPDQ in PM2.5, showing that the pollution of such compounds in urban air should not be underestimated.