Seasonal variations in concentrations of PM2.5 and tire wear particle of < 2.5 μm (TWP2.5) and polymeric components of PM2.5 at a bus stop

Abstract

Air pollution is a global public health concern. Bus stops have heavy traffic and local emissions. PM2.5 was collected for 2 day at a bus stop each month for one year. Polymeric components in the PM2.5 samples were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Seasonal variations of the polymeric components, PM2.5 concentration, and concentration of tire wear particles <2.5 μm (TWP2.5) were investigated. Various polymeric components were found, including natural rubber (NR) and curing agents from TWPs, bitumen originating from asphalt pavement wear particles (APWPs), plant-related components (PRCs), and poly (ethylene-terephthalate) (PET) from PET fabric lint. The PM2.5 concentrations at the bus stop were 4–124% higher than those in the regional background, and the annual average PM2.5 concentration at the bus stop was more than 1.5 times higher than that in the regional background. Non-exhanst sources such as abrasion of tires, brakes, and asphalt pavements, vehicle exhaust emissions, and road dust resuspension accounted for the high PM2.5 concentrations. The PM2.5 concentrations during winter were higher than those in the other seasons. On average, the additional generation of PM2.5 at the bus stop was approximately 10 μg/m3, while that in the winter was approximately 18 μg/m3. The annual average TWP2.5 concentration at the bus stop was 1.28 μg/m3 (0.7–1.8 μg/m3), and the seasonal order was winter > fall > spring > summer. TWP2.5 is directly generated by the abrasion of tire tread through the friction with the road surface and also is produced from primary TRWPs by pressing and breaking them upon the contact with tires while driving vehicles. The annual average contribution of TWP2.5 to the PM2.5 concentration at the bus stop was 5.5% (1.6–14.0%).