Rural vehicle emission as an important driver for the variations of summertime tropospheric ozone in the Beijing-Tianjin-Hebei region during 2014-2019

摘要

Tropospheric ozone(O_(3))pollution is increasing in the Beijing-Tianjin-Hebei(BTH)region despite a significant decline in atmospheric fine aerosol particles(PM_(2.5))in recent years.However,the intrinsic reason for the elevation of the regional O_(3)is still unclear.In this study,we analyzed the spatio-temporal variations of tropospheric O_(3)and relevant pollutants(PM_(2.5),NO_(2),and CO)in the BTH region based on monitoring data from the China Ministry of Ecology and Environment during the period of 2014-2019.The results showed that summertime O_(3)concentrations were constant in Beijing(BJ,0.06μg/(m^(3)·year))but increased significantly in Tianjin(TJ,9.09μg/(m^(3)·year))and Hebei(HB,6.06μg/(m3·year)).Distinct O_(3)trends between Beijing and other cities in BTH could not be attributed to the significant decrease in PM_(2.5)(from-5.08 to-6.32μg/(m3·year))and CO(from-0.053 to-0.090 mg/(m^(3)·year))because their decreasing rates were approximately the same in all the cities.The relatively stable O_(3)concentrations during the investigating period in BJ may be attributed to a faster decreasing rate of NO_(2)(BJ:-2.55μg/(m^(3)·year);TJ:-1.16μg/(m^(3)·year);HB:-1.34μg/(m3·year)),indicating that the continued reduction of NOx will be an effective mitigation strategy for reducing regional O_(3)pollution.Significant positive correlations were found between daily maximum8 hr average(MDA8)O_(3)concentrations and vehicle population and highway freight transportation in HB.Therefore,we speculate that the increase in rural NO_(x)emissions due to the increase in vehicle emissions in the vast rural areas around HB greatly accelerates regional O_(3)formation,accounting for the significant increasing trends of O_(3)in HB.