Vehicle emissions in a megacity of Xi'an in China: A comprehensive inventory, air quality impact, and policy recommendation

Abstract

Vehicle emissions continue to have a significant impact on urban air pollution in the megacities of China due to the increasing number of vehicles and lagged control policies. This study established a 5-year vehicle emission inventory for carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOX), and particulate matter (PM2.5 and PM10) in the megacity of Xi'an from 2014 to 2018 by using localized emission factors and annual vehicle activity data, explored the relationship between vehicle emissions and air quality using the best available data. Remote sensing and portable monitoring devices were used to detect the in-use social vehicle on-road situation. The results showed that the total 5-year emissions were 592.7 Gg of CO, 826.0 Gg of HC, 266.1 Gg of NOX, 6.9 Gg of PM2.5, and 6.3 Gg of PM10. Small-duty passenger vehicles (SDPVs) and light-duty trucks (LDTs) were the most significant contributors to CO and HC emissions, while heavy-duty trucks (HDTs) and LDTs dominant to NOX and PM2.5, and motorcycles (MCs) for part of CO (8.2%) and HC (11.9%). The study found that vehicle HC and NOX emissions exacerbate the formation of ozone (O3) and nitrogen dioxide (NO2) in the atmosphere. More reliable policies should be proposed to prevent air pollution from vehicle exhaust.