Reduction of atmospheric PM_2.5 level by restricting the idling operation of buses in a busy station

Fine particulate matter (PM_2.5) has been found to be harmful when inhaled by people, which has caused enormous health problems. It is found at high levels at public bus stations, where many passengers and workers may be exposed to PM_2.5 emissions from idling diesel engines. This study evaluated the restriction on idling vehicles as a strategy to control PM_2.5 levels at bus stations by measuring the PM_2.5 and the chemical properties at both upwind and exposure sites for comparable data. The sampling took place on weekends and weekdays and before and after the idling restriction was applied. Originally, the exposure site showed a PM_2.5 level that was 7% higher, non-neutralized nitrate content, anthropogenic metal elements, and higher mobile source contributions, as evaluated by a chemical mass balance model (CMB8.2). After the prohibition on idling heavy-duty diesel vehicles, the PM_2.5 mass concentrations at the exposure site were reduced to levels comparable to those at the upwind site. Additionally, the nitrate content was reduced in the background. Moreover, the contributions of several anthropogenic metals (Zn, Pb, Mn, Cu, Cr, V, Ni, and Ti) in PM_2.5 were reduced while those of crustal elements (Na, Mg, Al, K, and Ca) significantly increased after the restriction. Finally, the mobile contribution decreased to only 33.7–34.5%. Consequently, these findings verify that the prohibition policy on idling vehicles works well as a control strategy to manage the PM_2.5 emissions at local hotspots such as bus stations.