https://spap.jst.go.jp/other_asia/news/221103/topic_nt_02.html

A research team from Yang-Ming Chiao Tung University (NYCU) and National Taiwan University (NTU) has found that not only the concentration of particulate matter (PM) but also its composition significantly affects health risks. The team monitored air quality near a busy road in Taipei City for one month and found that organic aerosols, iron, manganese, and copper, which are components of PM, increase cellular oxidative potential. In particular, they found that the above-mentioned metallic components were more likely to have been produced by brake pad wear than by vehicle exhaust. Frequent brake use during traffic jams intensifies such wear.