Elevated dust layers inhibit dissipation of heavy anthropogenic surface air pollution

Abstract. Persistent winter–time heavy haze incidents caused by anthropogenic aerosols have repeatedly shrouded North China in recent years, while natural dust from west and northwest of China also frequently affects air quality in this region. Through continuous observation by a multi–wavelength Raman lidar, here we found that aerosols in North China are typically characterized by a pronounced vertical stratification, where scattering non–spherical particles (dust or mixtures of dust and anthropogenic aerosols) dominated above the planetary boundary layer (PBL), and absorbing spherical particles (anthropogenic aerosols) prevailed within the PBL. This stratification is governed by meteorological conditions that strong northwesterly winds usually prevailed in the lower free troposphere, and southerly winds are dominated in the PBL, producing persistent and intense haze pollution. With the accumulation of elevated dust, the proportion of aerosol and trace gas at the surface in the whole column increased. Model results show that, besides directly deteriorating air quality, the key role of the elevated dust is to depress the development of PBL and weaken the turbulence exchange, mostly by lower–level cooling and upper–level heating, and it is more obvious during dissipation stage, thus inhibiting the dissipation of heavy surface anthropogenic aerosols. The interactions of natural dust and anthropogenic aerosols under the unique topography of North China increases the surface anthropogenic aerosols and precursor gases, which may be one of the reasons why haze pollution in North China is heavier than that in other heavily polluted areas in China.