蚌埠市臭氧污染评价及一次持续性污染过程分析

Climatological characteristics and the long-term tendency of surface ozone (O₃) in Bengbu were investigated using air pollutants data and meteorological indices data. Both are obtained from the national monitoring stations over a 4-year period (Jan. 2015-Dec. 2018). By combining the outputs of HYSPLIT Backward Trajectory Model and Weather Research Forecast Model (WRF-Chem), the impacts of air pollutants (excluding O₃), meteorological indices and external transport on the surface O₃ concentration during a continuous event of O₃ pollution were analyzed. Meanwhile, statistical information of Bengbu's air environment during 2015-2017 was used to study the effect of local pollutants emission on the generation of O₃. The results indicate that, during 2015-2018, the 90th percentile of 8-hour average O₃ concentration has increased from 128 μg•m^-3 to 177 μg•m^-3, trending up year by year. The over-standard rate of O₃ has risen from 2.28% to 18.88% and the number of O₃ pollution days from 4.08% to 50.83%. Apparently, O₃ has become one of the major pollutants in Bengbu. Regarding the meteorological indices, most of the time wind speed was 1~3 m•s^-1 when the O₃ pollution event occurred in Bengbu. O₃ concentration was high to over-standard level in wind directions of NNW, E, SE, SSE and S. Besides, O₃ concentration also rose significantly when O₃ pollution occurred over the Yangtze River Delta and meanwhile eastern/southeastern winds were prevailing in Bengbu, or when there was O₃ pollution in Beijing-Tianjin-Hebei and surrounding regions as well as prevailing northwestern winds in Bengbu, indicating an obvious external transport in the study area. During 2015-2017, industries in Bengbu has reduced from 420 to 257, leading to a sharp decrease of air pollutants including dust, NO_x, VOC, etc. However, 107.8 thousand more motor vehicles were introduced into the city and as a consequence, vehicle emission gradually increased and comprised a large proportion of the air pollutants which are important precursors of O₃ pollution. Overall, in view of the above-mentioned facts that O₃ pollution is primarily caused by external transport and vehicle emission precursors, we suggest these two aspects be specially concerned and car usage be properly controlled to mitigate O₃ pollution in Bengbu.