Numerical simulation of IL-8-based relative inflammation potentials of aerosol particles from vehicle exhaust and non-exhaust emission sources in Japan

Spatial distributions of interleukin-8 (IL-8)-based relative inflammation potentials (IP) of PM_2.5 from vehicle exhaust and non-exhaust emission sources in Japan are derived using the meteorology–chemistry model (NHM-Chem) and laboratory experiments. In this study, IP is first defined as multiplying PM_2.5 from different emission sectors by supernatant IL-8 concentrations released using PM_2.5 samples, normalized to that of particle-free controls. The simulated IP of primary exhaust particles IP(E) accounts for 3%–30% of the total vehicle IP (exhaust + non-exhaust, primary + secondary), IP(V), which is low in densely populated regions (3%–15%) and high (5%–30%) in less populated regions, because there are fewer exhaust PM_2.5 emitters (diesel trucks) in more populated regions. The contribution of IP(V) to IP of the total environmental PM_2.5, IP(A), varied substantially in space by approximately 3–5 times (the contributions are greater in larger cities as there is more traffic). In our estimates, IP(V) is approximately one and two orders of magnitude higher than IP(E) and IP(T), the IP of fresh tire wear particles (TWPs), respectively. IP(T) has a minor contribution to IP(V) and IP(A). Recently, however, aged TWPs have been reported to be toxic; thus, the aging process of TWPs needs to be considered in the future.