A study of the direct emission of tire wear particles on different types of roads

In the range of 5-6 Mt/y tire wear particles (TWP) are emitted from vehicles in both developed and emerging countries. In an attempt to reduce these emissions, new regulations will come into force in the EU and USA, although currently no oversight methods are actually in place. This study proposes a method for assessing direct TWP emissions (TWP_D) from vehicles. The method entails labeling the tire with mercury, then collecting and fractionating the particles emitted at the rear of the wheel (RoWP), and lastly analyzing their Hg content in the laboratory using atomic absorption spectroscopy. It provides access to the magnitude, size distribution and factors affecting TWP_D emissions under actual driving conditions. Furthermore, the implementation of desorption and dispersion models allows evaluation of the proportion of TWP_D embedded in tire and road wear particles (TRWP) and estimating the TWP_D contribution to the lower atmosphere PM₁, PM_2.5 and PM₁₀ pollution within the EU-27. A key finding of this research is that ultrafine TWP_D (accounting for 33-260 mg/g of abraded front tire material) account for 30-70 % of total TWP_D emissions (with >93 % being in the form of inclusions), although they make up 0.5-5.7 % of RoWP mass emissions. Our data also draw attention to the magnitude and lower TRWP-embedment of TWP_D emissions in urban areas.