1Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
2Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China
3Leibniz Institute for Tropospheric Research, Leipzig, Germany
*now at: Meteorological Observation Centre, China Meteorological Administration, Beijing, China
Abstract. Visibility degradation is a pervasive and urgent environmental problem in China. The occurrence of low visibility events is frequent in the North China Plain, where the aerosol loading is quite high and aerosols are strongly hygroscopic. A parameterization scheme for low visibility conditions on hazy days is proposed in this paper, based on visibility, relative humidity (RH), aerosol hygroscopic growth factors and particle number size distributions measured during the Haze in China (HaChi) Project. Observational results show that a high aerosol volume concentration is responsible for low visibility at RH < 90%; while for RH > 90%, decrease of visibility is mainly influenced by the increase of RH. The parameterization scheme is developed on the basis of aerosol volume concentrations and RH, taking into accounts the sensitivity of visilibity to the two factors and the availability of corresponding data. The extinction coefficients calculated with the parameterization scheme agree well with the measured values.