Methodology for the direct measurement of tire emission factors

A reduction in air pollution is an essential step toward decreasing certain health risks in urban area populations. Road traffic is one source of this pollution and can be categorized into exhaust and non-exhaust emissions (NEE). Non-exhaust emissions include, but are not limited to, brake wear particles and Tire Road Wear Particles (TRWP). Emission Factors are often used to assess the share and the amount of vehicle exhaust and non-exhaust particles in the air. In this study, we developed an approach to measure the Emission Factors (EF) of tire Particulate Matter (PM). The approach is based an experimental method allowing for direct measurements in real conditions (on a vehicle on the road). The experimental set-up as well as the measurement protocol lead to a significant reduction in the classical biases of the on-road approach, which usually lead to a large over-estimation of the amount of PM₁₀ and PM_2.5 emitted by the tire. We observed that TRWP emissions correlate in time with the tire solicitation. A careful computation from the PM₁₀ and PM_2.5 collected by a real time particle counter enables an evaluation of the total amount of TRWP contributing to air pollution. The average results indicate an Emission Factor for PM₁₀ 4.5 times lower than the EMEP guidebook value and 42 times lower for PM_2.5. This discrepancy calls for further tests to confirm the results.