Emissions of multiple metals from vehicular brake linings wear in China, 1980-2020.

Metals emitted from brake linings wear have adverse effects on air quality and human health due to their toxicity and reactivity. However, complexities of factors affecting brake like conditions of vehicles and roads hinder the accurate quantification. Here, we established a comprehensive emission inventory for multi-metals from brake linings wear in China during 1980-2020, based on metals contents in well-representative samples, the wear of brake linings before replacement, vehicle populations, fleet composition, and vehicle-kilometers travelled (VKT). We show that with the boom of vehicle population, the total emissions of studied metals have surged from 3.7 × 106 g in 1980 to 4.9 × 1010 g in 2020, which mainly concentrated in coastal and eastern urban areas while grown significantly in the central and western urban areas in recent years. Therein, Ca, Fe, Mg, Al, Cu, and Ba were the top six metals emitted, together responsible for >94 % of the mass total. Jointly determined by brake linings especially metals contents thereof, VKTs, and vehicle populations, heavy-duty trucks, light-duty passenger vehicles, and heavy-duty passenger vehicles were the top three contributors in metals emissions, together accounting about 90 % of the total. Moreover, more precise description on real-world metals emissions from brake linings wear are still urgently needed, considering the increasingly significant role it has been playing on worsening air quality and public health.