Tire Wear Chemicals\nin the Urban Atmosphere: Significant\nContributions of Tire Wear Particles to PM<sub>2.5</sub>

Tire wear particles (TWPs) containing tire wear chemicals\n(TWCs)\nare of global concern due to their large emissions and potential toxicity.\nHowever, TWP contributions to urban fine particles are poorly understood.\nHere, 72 paired gas-phase and PM<sub>2.5</sub> samples were collected\nin the urban air of the Pearl River Delta, China. The concentrations\nof 54 compounds were determined, and 28 TWCs were detected with total\nconcentrations of 3130–317,000 pg/m<sup>3</sup>. Most p-phenylenediamines\n(PPDs) were unstable in solvent, likely leading to their low detection\nrates. The TWCs were mainly (73 ± 26%) in the gas phase. 2-OH-benzothiazole\ncontributed 82 ± 21% of the gas-phase TWCs and benzothiazole-2-sulfonic\nacid contributed 74 ± 18% of the TWCs in PM<sub>2.5</sub>. Guangzhou\nand Foshan were “hotspots” for atmospheric TWCs. Most\nTWC concentrations significantly correlated with the road length nearby.\nMore particulate TWCs were observed than model predictions, probably\ndue to the impacts of nonexchangeable portion and sampling artifacts.\nSource apportionment combined with characteristic molecular markers\nindicated that TWPs contributed 13 ± 7% of urban PM<sub>2.5</sub>. Our study demonstrates that TWPs are important contributors to\nurban air pollution that could pose risks to humans. There is an urgent\nneed to develop strategies to decrease TWP emissions, along with broader\nurban air quality improvement strategies.