title: Impact of the Loess Plateau on the atmospheric boundary layer structure and air quality in the North China Plain: a case study.
abstract: The North China Plain (NCP), to the east of the Loess Plateau, experiences severe regional air pollution. During the daytime in the summer, the Loess Plateau acts as an elevated heat source. The impacts of such a thermal effect on meteorological phenomena (e.g., waves, precipitation) in this region have been discussed. However, its impacts on the atmospheric boundary layer structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the boundary layer structure and ambient concentrations of pollutants over the NCP under certain meteorological conditions. Thus, this study investigates such effect and its impacts using measurements and three-dimensional model simulations. It is found that in the presence of daytime westerly wind in the lower troposphere (~1 km above the NCP), warmer air above the Loess Plateau was transported over the NCP and imposed a thermal inversion above the mixed boundary layer, which acted as a lid and suppressed the mixed layer growth. As a result, pollutants accumulated in the shallow mixed layer and ozone was efficiently produced. The downward branch of the thermally-induced Mountain-Plains Solenoid circulation over the NCP contributed to enhancing the capping inversion and exacerbating air pollution. Previous studies have reported that low mixed layer, a factor for elevated pollution in the NCP, may be caused by aerosol scattering and absorption of solar radiation, frontal inversion, and large scale subsidence. The present study revealed a different mechanism (i.e., westerly warm advection) for the suppression of the mixed layer in summer NCP, which caused severe O3 pollution. This study has important implications for understanding the essential meteorological factors for pollution episodes in this region and forecasting these severe events.
authors.affiliation: Center for Analysis and Prediction of Storms, and School of Meteorology, University of Oklahoma, Norman, OK 73072, USA. Electronic address: xhu@ou.edu.
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Hu
authors.affiliation: Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China. Electronic address: zqma@ium.cn.
authors.forename: ZhiQiang
authors.initials: Z
authors.lastname: Ma
authors.affiliation: Key Laboratory for Atmospheric Chemistry, Center for Atmospheric Watch and Services, Chinese Academy of Meteorological Sciences, Beijing, 100081, China.
authors.forename: Weili
authors.initials: W
authors.lastname: Lin
authors.affiliation: Department of Civil & Environmental Engineering, University of California, Davis, CA 95616, USA.
authors.forename: Hongliang
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Civil & Environmental Engineering, University of California, Davis, CA 95616, USA.
authors.forename: Jianlin
authors.initials: J
authors.lastname: Hu
authors.affiliation: Key Laboratory for Atmospheric Chemistry, Center for Atmospheric Watch and Services, Chinese Academy of Meteorological Sciences, Beijing, 100081, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory for Atmospheric Chemistry, Center for Atmospheric Watch and Services, Chinese Academy of Meteorological Sciences, Beijing, 100081, China.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Xu
authors.affiliation: Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Jose D
authors.initials: JD
authors.lastname: Fuentes
authors.affiliation: Center for Analysis and Prediction of Storms, and School of Meteorology, University of Oklahoma, Norman, OK 73072, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Xue
mesh_terms: D000336:Aerosols; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data*; D001272:Atmosphere / Q000737:chemistry*; D002681:China; D004784:Environmental Monitoring; D008956:Models, Chemical; D010126:Ozone / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D013458:Sulfur Dioxide / Q000032:analysis; D014919:Wind
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D052638:Particulate Matter; D013458:Sulfur Dioxide; D010126:Ozone
keywords: Air pollution; Atmospheric boundary layer; North China Plain; Ozonesonde; WRF/CMAQ; Westerly warm advection