A parameterization of low visibilities for hazy days in the North China Plain

J Chen,P Yan,C S Zhao,T Göbel,X J Zhou,L Ran,P F Liu,Z Z Deng,H J Liu,Z Liang,E Hallbauer,W Y Xu,A Wiedensohler,N Ma

doi:10.5194/acp-12-4935-2012

Abstract

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 of light extinction (Kex) for low visibilities 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 of Kex is developed on the basis of aerosol volume concentrations and RH, taking into accounts the sensitivity of visibility to the two factors and the availability of corresponding data. The extinction coefficients calculated with the parameterization schemes agree well with the directly measured values.

Highlights

Visibility degradation is a pervasive environmental problem in China (Anderson et al, 2003; Quinn et al, 2003; Zhao et al, 2006b; Hoyle et al, 2009)
Kex at different relative humidity (RH) and aerosol volume concentrations can be theoretically obtained by using averaged particle number size distribution (PNSD) and the Mie Model, in which aerosol hygroscopic growth has been taken into account
Most of the low visibility conditions (VIS

Summary

Introduction

Visibility degradation is a pervasive environmental problem in China (Anderson et al, 2003; Quinn et al, 2003; Zhao et al, 2006b; Hoyle et al, 2009). Annual average (2005∼2006) of PM2.5 in Beijing was 118.5±40.6 μg m−3 (Yang et al, 2011) It greatly exceeded the recently revised ambient air quality standard of China (GB3095-2012) for PM2.5 (35 μg m−3, Grade II) and was at least 10 times those (5∼10 μg m−3) measured in the eastern US (Hidy et al, 2009). Intensive aircraft observations in Beijing showed that the average aerosol number concentration near surface level (1419 m above the ground) was about 6600 cm−3, with the highest value over 10 000 cm−3 (Zhao et al, 2006a; Deng et al, 2009; Liu et al, 2009). High daily mean values, 150 μg m−3 (Shen et al, 2009), of PM1 (particulate matter less than 1 μm diameter) were reported in

Methods

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Conclusion