银川都市圈夏季臭氧来源数值模拟分析

Numerical Simulation Analysis on Ozone Source Apportionment in the Yinchuan Metropolitan Area in Summer

在我国当前臭氧和颗粒物复合污染的局面下,位于西北地区的宁夏回族自治区近年来夏季臭氧区域性污染突出,浓度高值区主要分布在银川都市圈(银川市、石嘴山市和吴忠市)。因此利用区域空气质量模式系统RAMS-CMAQ对2019年夏季6月银川都市圈臭氧污染问题开展数值模拟,定量探讨区域传输及垂直输送对O_(3)浓度的贡献,为有效控制当地臭氧污染提供科学依据。结果表明:2019年6月银川都市圈O_(3)浓度北高、中部低,与前体物的分布特征并不完全一致,表明O_(3)的非线性效应以及背景O_(3)传输潜在的贡献。水平方向上,银川都市圈本地排放源对近地面O_(3)的贡献大都在20%~30%,仅灵武达40%以上,外界传输贡献均在30%以上。其中银川本地贡献较弱,相邻区域间存在输送影响,一定程度上减弱了该地区的本地贡献。此外,在夏季整体偏南风的影响下O_(3)有较为明显的由南向北的输送作用。垂直方向上,郊区、城市和工业代表性站点O_(3)浓度的变化趋势基本一致,各过程量贡献有所差异。夜晚O_(3)光化学损耗工业站最大,城市站、郊区站次之,均在近地面最强。白天城市站和工业站O_(3)主要在边界层中上层光化学生成,连同夜间残留层中的O_(3)向地面垂直输送、周围水平输送,同时自由大气还有少量O_(3)向下夹卷到边界层中;郊区站在整个边界层内均有臭氧光化学生成,近地面生成最强,而输送作用相对较弱。

Under the current situation of combined pollution due to ozone and particulate matter in China,regional ozone pollution is prominent in Ningxia,northwestern China,in summer.Thus,the regional air quality modeling system RAMS-CMAQ(Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality)was applied to investigate ozone pollution in the Yinchuan metropolitan area(Yinchuan,Shizuishan,and Wuzhong)in June 2019.The contribution of ozone regional and vertical transmission was quantitatively discussed to provide scientific evidence for effective control of local ozone pollution.The results show that O_(3) concentration was high in the north and low in the middle of the area,which was not completely consistent with the distribution characteristics of ozone precursors,indicating a nonlinear effect of O_(3) and a potential contribution of background O_(3) transmission.In the horizontal direction,the contribution of local emission sources to near-surface O_(3) was mostly between 20%~30%,except in Lingwu,where it reached more than 40%,and the contribution of external transmission was more than 30%.In Yinchuan,the local contribution was relatively weak,and a transport effect occurred between adjacent areas,weakening the local contribution to some certain extent.Moreover,O_(3) was obviously transported from south to north in summer because of overall southerly winds.In the vertical direction,the variation in O_(3) concentration was basically similar to the suburban,urban,and industrial representative sites,while the contribution of each process differed.At night,O_(3) photochemical loss was the largest at industrial sites,followed by urban and suburban sites,and was the strongest near the ground at all sites.During the day,O_(3) was mainly photochemically generated in the upper and middle regions of the boundary layer at urban and industrial sites.Then,together with a remnant in the nocturnal residual layer,O_(3) was transported vertically to the ground and horizontally around.Meanwhile,some O_(3) in the free atmosphere was entrained down into the boundary layer.Conversely,at suburban sites,photochemical ozone generation occurred throughout the boundary layer and was the strongest near the ground,while the transport effect was relatively weak.