The hygroscopic growth of aerosol particles is a key factor of air pollution because it can significantly reduce visibility. In order to better understand the impact of the hygroscopic growth effect on haze events and contributing factors, we made use of rich measurements during an intensive field campaign conducted in Xingtai, Hebei province of China that has suffered from the most serious pollution in the Northern China Plain. Key measurements are from Raman lidar and ground-based instruments such as a GrayWolf 6-channel handheld particle/mass meter for atmospheric particulate matter that have diameters less than 1 μm and 2.5 μm (PM 1 and PM 2.5 , respectively), aerosol chemical speciation monitor (ACSM), and a hygroscopic tandem differential mobility analyzer (H-TDMA). The evolution of PM 1 and PM 2.5 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 particle hygroscopic growth on haze events. The lidar-estimated aerosol hygroscopic enhancement factor during a pollution event (Case II) was greater than that during a relatively clean period (Case I) with similar relative humidity (RH): 80–91 %. The hygroscopic growth was fitted by the Kasten model whose parameter b differ considerably: 0.9346 vs. 0.1000 for cases II and I respectively. The aerosol acidity value of Case II (1.50) was greater than that of Case I (1.35) due to different amounts of inorganics such as NH 4 NO 3 , NH 4 HSO 4 , and (NH 4 ) 2 SO 4 , consistent with the difference in the aerosol hygroscopicity parameter κ calculated from the chemical species of PM 1 obtained by the ACSM. Data from the H-TDMA showed that all of the aerosol particle size hygroscopic growth factors in each particle size category (40, 80, 110, 150, and 200 nm) at different RH (80–91 %) during Case II were higher than those during Case I. Under the same water vapor conditions, aerosol hygroscopic growth was one of the major factors contributing to heavy haze pollution. Concerning aerosol chemical composition, nitrate was the primary component contributing to aerosol hygroscopicity over Xingtai.