Atmospheric Chemistry and Physics | 2019
Aerosol hygroscopic growth, contributing factors, and impact on haze events in a severely polluted region in northern China
Abstract
Abstract. This study investigates the impact of the aerosol hygroscopic\ngrowth effect on haze events in Xingtai, a heavily polluted city in the\ncentral part of the North China Plain (NCP), using a large array of instruments\nmeasuring aerosol optical, physical, and chemical properties. Key instruments\nused and measurements made include the Raman lidar for atmospheric water\nvapor content and aerosol optical profiles, the PC-3016A GrayWolf six-channel\nhandheld particle and mass meter for atmospheric total particulate matter (PM)\nthat has diameters less than 1 and 2.5\u2009 µ m (PM 1 and\nPM 2.5 , respectively), the aerosol chemical speciation monitor (ACSM) for\nchemical components in PM 1 , and the hygroscopic tandem differential\nmobility analyzer (H-TDMA) for aerosol hygroscopicity. The changes in\nPM 1 and PM 2.5 agreed well with that of the water vapor content due\nto the aerosol hygroscopic growth effect. Two cases were selected to further\nanalyze the effects of aerosol hygroscopic growth on haze events. The\nlidar-estimated hygroscopic enhancement factor for the aerosol backscattering\ncoefficient during a relatively clean period (Case\xa0I) was lower than that\nduring a pollution event (Case\xa0II) with similar relative humidity (RH) levels\nof 80\u2009%–91\u2009%. The Kasten model was used to fit the aerosol optical\nhygroscopic growth factor (GF) whose parameter b differed considerably between\nthe two cases, i.e., 0.1000 (Case\xa0I) versus 0.9346 (Case\xa0II). The aerosol\nacidity value calculated from ACSM data for Case\xa0I (1.35) was less than that\nfor Case\xa0II (1.50) due to different amounts of inorganics such as\n NH4NO3 , NH4HSO4 , and (NH4)2SO4 . Model\nresults based on H-TDMA data showed that aerosol hygroscopic growth factors\nin each size category (40, 80, 110, 150, and 200\u2009nm) at different RH levels\n(80\u2009%–91\u2009%) for Case\xa0I were lower than those for Case\xa0II. For similar\nambient RH levels, the high content of nitrate facilitates the hygroscopic\ngrowth of aerosols, which may be a major factor contributing to heavy haze\nepisodes in Xingtai.