Airborne Tire\nWear Particles: A Critical Reanalysis\nof the Literature Reveals Emission Factors Lower than Expected

Tires are a ubiquitous part of on-road transport systems\nserving\nas the critical connecting component at the interface of the motive\npower and road surface. While tires are essential to automobile function,\nthe wear of tires as a source of particulate air pollution is still\npoorly understood. The variety of reported emissions found in the\nsecondary literature motivated us to summarize all known mass-based\ntire wear emission factors for light-duty vehicles in primary research.\nWhen excluding road wear and resuspension, mean emissions of 1.1 mg/km/vehicle\n(median 0.2 mg/km/vehicle) were found for tire wear PM<sub>10</sub> and mean emissions of 2.7 mg/km/vehicle (median 1.1 mg/km/vehicle)\nwhen including studies with resuspended tire wear. Notably, these\nfactors are substantially lower than broadly cited and accepted factors\nin the secondary literature with mean emissions of 6.5 mg/km/vehicle\n(median 6.1 mg/km/vehicle). As revealed by our analysis, secondary\nliterature reports emission factors systematically higher than those\nof the primary sources on which they are based. This divergence is\ndue to misunderstandings and misquotations that have been prevalent\nsince the year 1995. Currently accepted mass-based emission factors\nfor directly emitted airborne tire wear particles need revision, including\nthose from the United States Environmental Protection Agency and the\nEuropean Environment Agency.