Effects of chemical compositions in fine particles and their identified sources on hygroscopic growth factor during dry season in urban Guangzhou of South China.

Knowledge of aerosol hygroscopicity is essential to assess visibility improvement and aerosol radiative forcing. Aerosol hygroscopicity is highly dependent on emission sources, while the hygroscopicity of different sources remains largely unexplored. In the current study, the hygroscopic growth factor (i.e., f(RH)) and relevant chemical compositions (e.g., water-soluble inorganic ions, carbonaceous fractions and elements) in fine particles were synchronously measured for nearly 3 months within 2019-2020 in an urban site of Guangzhou. The mean value (± standard deviation) of f(RH) at 70% RH was 1.50 (± 0.11). The diurnal cycle in aerosol hygroscopic growth strongly depended on the mass fraction of hydrophilic chemical compositions (e.g., SO42-, NO3- and NH4+) in fine particles and variation in contributions of aerosol sources. A Positive Matrix Factorization model was applied to distinguish the different hygroscopicity of specific source factors in a mixed aerosol. Secondary nitrate and secondary sulfate were more hydrophilic, whereas emissions from primary combustion processes (i.e., ship emission, coal combustion and road traffic) were less hygroscopic. Soil dust was almost insoluble. The hygroscopic growth of each source was parameterized that quantified the emission sources and f(RH) relationship for use of air quality and radiative transfer models either as input or as validation.