Quantifying vehicle restriction related PM_2.5 reduction using field observations in an isolated urban basin

Abstract

Vehicle (related particulate matter) emissions, including primary vehicle (related particulate matter) emissions, secondary nitrate, and road dust, have become an important source of fine particulate matter (PM2.5) in many cities across the world. The relationship between vehicle emissions and PM2.5 during vehicle restrictions has not yet been revealed using field observational data. To address this issue, a three-month field campaign on physical and chemical characteristics of PM2.5 at hourly resolution was conducted in Lanzhou, an urban basin with a semi-arid climate. The Lanzhou municipal government implemented more strict vehicle restriction measure during the latter part of field campaign period. The concentration of nitrogen oxides (NO x ) and PM2.5 decreased by 15.6% and 10.6%, respectively during the strict vehicle restriction period. The daily traffic fluxes decreased by 11.8% due to the vehicle restriction measure. The vehicle emission reduction led to a decrease of 2.43 μg·m−3 in PM2.5, including the decrease of primary vehicle emissions, secondary nitrate, and road dust. The contribution of vehicle emissions to PM2.5 decreased by 9.0% based on the results derived from a positive matrix factorization model. The sources other than vehicle emissions increased by 0.2 μg·m−3. Combining all evidence from the observations, the reduction of vehicle emissions is almost equal to the observed reduction in PM2.5. A further extrapolation that 9.0% reduction in vehicle emissions led to the observed reduction in PM2.5 (2.32 μg·m−3). This study clearly quantifies the vehicle restriction related PM2.5 reduction using field observations. The results provide scientific support for the implementation of effective vehicle emission reduction measures.