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Hygroscopic growth can significantly affect size distribution and activation of aerosol particles,as well as their effects on human health,atmospheric visibility,and climate.In this study,an H-TDMA (Hygroscopic Tandem Differential Mobility Analyzer) was utilized to measure hygroscopic growth factor and mixing state of aerosol particles at the CAWNET station in Panyu,Guangzhou,China.A statistical analysis of the results show that,at relative humidity (RH) of 90%,for less-hygroscopic particles of 40-200 nm in diameter,the growth factor (gLH) was around 1.13,while the number fraction (NFLH) varied between 1.46 and 1.55 with the average equivalent ammonium sulfate ratio (εAS) ranging from 0.63 to 0.68.The differences in εAS among particle of different sizes reveal that more-hygroscopic inorganic salts,such as ammonium sulfate and ammonium nitrate,are of mor eeffective condensation growth for Aitken mode particles.A combined analysis of the probability density function of growth factor (Gf-PDF) and simul-taneous meteorological data shows that during clean periods with air masses moving from the north,the particles are more likely to have homogeneous chemical composition,while durin gpolluted or pollution accumulation periods,variations in mean number weighted growth factor (gmean) and MFMH become more pronounced,indicating that locally-emitted aerosol particles tend to be in an externally mixed state and contain a certain proportion of less-hygroscopic particles.This study can help improve our understanding of aerosol hygroscopicity and its impact on the atmospheric visibility and environment.