蚌埠市臭氧污染评价及一次持续性污染过程分析

Ozone pollution assessment and a continuous pollution process analysis in Bengbu

利用2015年1月—2018年12月近4年的国控点大气污染物监测数据和同期气象观测数据,分析评价了蚌埠市近地面O_3污染的变化趋势及特征,并结合HYSPLIT后向气流轨迹模式及中尺度天气和预报模式(WRF-Chem)模拟预报结果,探讨了一次持续性O_3污染过程中,其他污染物、气象因素及外来传输对近地面O_3浓度的影响.同时,结合蚌埠市2015—2017年环境统计数据,分析了本地污染物排放对本地生成O_3的影响.结果表明:2015—2018年,蚌埠市近地面O_3-8 h第90百分位数由128μg·m^(-3)增长至177μg·m^(-3),呈逐年上升趋势;O_3-8 h超标率由2.28%增长至18.88%,以O_3为首要污染物的污染天数占全年污染天数的百分比由4.08%增长至50.83%,O_3成为影响蚌埠市环境空气质量的主要污染物之一.O_3污染过程期间,蚌埠市近地面以1～3 m·s^(-1)小风为主,O_3在NNW、E、SE、SSE、S方向超标较为明显.在京津冀及周边区域、长三角的中北部区域出现O_3连片污染的情况下,蚌埠市地面受偏东风、东南风和西北风影响,存在较为明显的外来污染传输过程.2015—2017年,蚌埠市工业企业数量由420家减少至257家,区域废气污染物中氮氧化物、烟(粉)尘和挥发性有机物排放量均大幅减少;机动车净增10.78万辆,机动车源排放在区域污染物排放总量中占比较大,且有逐年增加的趋势.由此可见,区域性的O_3污染及前体物输送是蚌埠市近年来O_3污染持续恶化的最主要原因,而在本地污染物(含前体物)排放量明显减少的情况下,本地机动车源排放量所占比例快速攀升,为本地O_3生成提供了大量前体物.今后,蚌埠市在O_3污染管控工作中应格外关注外源性、事件性的O_3污染及前体物输入,同时还应考虑控制本地机动车规模的快速增长.

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 90 th 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, NOx, 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.