乌海市臭氧传输特征与潜在源区

Transport characteristics and potential source of ozone in Wuhai

乌海是典型的西北工业城市,O_(3)污染问题突出但缺乏研究.本文基于乌海市环境监测数据、气象数据分析了乌海市O_(3)污染特征.结果表明:乌海市O_(3)日最大8 h平均值(MDA8O_(3))第90位百分数由2015年的131μg·m^(-3)上升至2018年的162μg·m^(-3),超标天数由2015年的8 d上升到2018年的44 d,O_(3)超标日集中出现在4—8月;2018年4—8月乌海市近地面盛行南风,O_(3)浓度在近地面风向位于西南-南、东南、北-东北3个风向区间,风速处于2~7 m·s^(-1)的区间时最高.为进一步研究乌海O_(3)传输特征、潜在源区,本文基于NCEP再分析资料,使用后向轨迹、PSCF方法与CWT方法研究了2018年4—8月O_(3)的传输特征及潜在源区.O_(3)非污染过程中,74%的轨迹来自北方,气团移动速度快且途经的下垫面以沙漠为主,较为清洁.O_(3)污染过程中,来自南方的轨迹占比59%,贡献了76%的污染轨迹,这些轨迹传输距离较短、移动速度较慢且经过的下垫面多为城市及工业园区;PSCF分析与CWT分析的结果较为一致,O_(3)非污染过程的主要源区分布在乌海市以南.O_(3)污染过程的主要源区为鄂尔多斯西部、阿拉善东部、石嘴山、银川、吴忠、榆林西部,WPSCF值均大于0.5,WCWT值均大于120μg·m^(-3).乌海市O_(3)易受区域传输影响,O_(3)污染过程中其主要源区为距乌海400 km以内的上风向城市,O_(3)非污染过程则主要在200 km的范围内.分过程进行气团轨迹聚类分析和潜在源区分析有利于得到更为真实的污染物传输特征和潜在源区.

The O_(3)pollution problem is prominent but lacks of understanding for the cause of formation in Wuhai located in a typical coal chemical industrial area in Northwest China.The characteristics of O_(3)pollution in Wuhai were revealed by statistical analysis methods based on environmental monitoring data,meteorological data in recent years.The result shows that:from 2015 to 2018,the 90 th percentile of MDA8 O_(3)increased from 131μg·m^(-3)to 162μg·m^(-3),the number of O_(3)exceeding standard day increased from 8 d to 44 d.The O_(3)exceeding standard days occurred mainly from April to August.The O_(3)concentration is high when the near-surface wind direction is southwest-south,north-northeast,or southeast,and the wind speed is in the interval of 2~7 m·s^(-1).The southerly wind prevailed near the ground in Wuhai during this period.For further study the cause of transport characteristics and potential source areas of ozone were investigated by using backward trajectories model,PSCF and CWT and NCEP from April to August in 2018.In ozone non-pollution process,74%of air mass trajectories with high moving speed pass over the northern desert area which are relatively clean region.In ozone pollution process,59%of air mass trajectories,which contributed 76%of polluted trajectories,are over southern region of cities and industrial park.These trajectories are of short transmission distance,slow moving speed.The main potential source of O_(3)non-pollution process is located south of Wuhai.The WPSCF value and WCWT value of western Ordos,eastern Alashan,Shizuishan,Yinchuan,Wuzhong and western Yulin,which are the main potential source of Wuhai in ozone pollution process,are greater than 0.5 and 120μg·m^(-3)respectively.The results of PSCF analysis are consistent with that of CWT analysis.The ozone of Wuhai has obvious characteristics of being affected by regional transportation.During the O_(3)pollution process,its main source area is the upwind city within 400 km from Wuhai,and the O_(3)non-pollution process is mainly within a range of 200 km.It is beneficial to obtain more real pollutant transport characteristics and potential source area by distinguishing the ozone pollution and non-pollution processes based on the clustering analysis of air mass trajectory and the analysis of potential source area.