Aerosol hygroscopic growth, contributing factors, and impact on haze events in a severely polluted region in northern China

Jun Chen,Yele Sun,Haofei Wang,Wei Wang,Maureen Cribb,Zhanqing Li,Min Lv,Xing Yan,Yingjie Zhang,Yuying Wang

doi:10.5194/acp-19-1327-2019

Abstract

Abstract. This study investigates the impact of the aerosol hygroscopic growth effect on haze events in Xingtai, a heavily polluted city in the central part of the North China Plain (NCP), using a large array of instruments measuring aerosol optical, physical, and chemical properties. Key instruments used and measurements made include the Raman lidar for atmospheric water vapor content and aerosol optical profiles, the PC-3016A GrayWolf six-channel handheld particle and mass meter for atmospheric total particulate matter (PM) that has diameters less than 1 and 2.5 µm (PM1 and PM2.5, respectively), the aerosol chemical speciation monitor (ACSM) for chemical components in PM1, and the hygroscopic tandem differential mobility analyzer (H-TDMA) for aerosol hygroscopicity. The changes in PM1 and PM2.5 agreed well with that of the water vapor content due to the aerosol hygroscopic growth effect. Two cases were selected to further analyze the effects of aerosol hygroscopic growth on haze events. The lidar-estimated hygroscopic enhancement factor for the aerosol backscattering coefficient during a relatively clean period (Case I) was lower than that during a pollution event (Case II) with similar relative humidity (RH) levels of 80 %–91 %. The Kasten model was used to fit the aerosol optical hygroscopic growth factor (GF) whose parameter b differed considerably between the two cases, i.e., 0.1000 (Case I) versus 0.9346 (Case II). The aerosol acidity value calculated from ACSM data for Case I (1.35) was less than that for Case II (1.50) due to different amounts of inorganics such as NH4NO3, NH4HSO4, and (NH4)2SO4. Model results based on H-TDMA data showed that aerosol hygroscopic growth factors in each size category (40, 80, 110, 150, and 200 nm) at different RH levels (80 %–91 %) for Case I were lower than those for Case II. For similar ambient RH levels, the high content of nitrate facilitates the hygroscopic growth of aerosols, which may be a major factor contributing to heavy haze episodes in Xingtai.

Highlights

Aerosols, as solid or liquid particles suspended in the air, help regulate Earth’s climate mainly by directly scattering or absorbing incoming radiation, or indirectly changing cloud optical and microphysical properties (IPCC, 2013)
Others have found the same relationship between W in the lower atmospheric layer and the surface mass concentration of PM2.5
As W in the lower atmospheric layer and the surface mass concentrations of PM1 and PM2.5 increases, the proportion of organic aerosols decreases, suggesting that the proportion of hygroscopic aerosols increased. This shows that strong aerosol hygroscopicity may aggravate air pollution conditions over Xingtai

Summary

Introduction

As solid or liquid particles suspended in the air, help regulate Earth’s climate mainly by directly scattering or absorbing incoming radiation, or indirectly changing cloud optical and microphysical properties (IPCC, 2013). Many studies suggest that aerosols have a direct impact on human health (Araujo et al, 2008; Anenberg et al, 2010; Liao et al, 2015; Li et al, 2017). J. Chen et al.: Aerosol hygroscopic growth, contributing factors, and impact on haze events reduce visibility. Poor visibility is detrimental to human health and hazardous to all means of transportation (Zhang et al, 2010, 2018)

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