Impact of aerosol liquid water content and its size distribution on hygroscopic growth factor in urban Guangzhou of South China

Abstract

To investigate the dependence of hygroscopic growth factor (f(RH)) on aerosol liquid water content (ALWC) and its size distribution, a comprehensive campaign was carried out in urban Guangzhou in autumn 2015. Major chemical components in bulk as well as size-segregated PM2.5 samples, bulk PM10 mass, aerosol scattering coefficient (bsp) under dry and wet conditions, inline water-soluble inorganic ions (WSIIs) and meteorological parameters were synchronously measured. Mass fractions of hydrophilic chemical composition (e.g. SO42−, NO3− and NH4+) in PM2.5 and their mass median aerodynamic diameters (MMADs) were evidently larger under conditions of ambient relative humidity (RH) >60% than RH <60%. The estimated f(RH) by the revised IMPROVE formula and the Mie model based on filter-collected WSIIs concentrations was higher than and close to the measured ones, respectively, when RH < 60%, but was evidently lower than the measured ones when RH > 60%. A good linear correlation was found between the measured f(RH) and mass ratio of ALWC to PM2.5 when using the inline WSIIs concentrations, suggesting a strong dependence of f(RH) on the mass fraction of ALWC in PM2.5.