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Abstract A method to calculate the aerosol hygroscopic growth factor f(RH), defined as the ratio of aerosol scattering coefficient at wet condition to that at dry condition, was proposed. Based on the back trajectory model HYSPLIT, the air masses arriving at Guangzhou in July 2006 were classified into marine, mixed and urban types, respectively. The mean value of aerosol hygroscopic growth factors at 80% RH [f(RH=80%)] in Guangzhou, were 2.04±0.28, 2.29±0.28, and 2.68±0.59 for urban aerosols, mixed aerosols, and marine aerosols, respectively. The relationship between f(RH) and RH was fitted by empirical equations f(RH)=1+a(RH/100)b and the fitting parameter a was 2.06, 3.26 and 4.92 with b being 3.60, 3.85 and 5.04 for urban aerosols, mixed aerosols, and marine aerosols, respectively.
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