Aerosol hygroscopicity is crucial for understanding rolesof aerosol particles in atmospheric chemistry and aerosol climate effects.Light-scattering enhancement factor (RH, ) is one of theparameters describing aerosol hygroscopicity, which is defined as(RH, ) = (RH, )∕(dry, ), where(RH, ) or (dry, ) represents atwavelength under certain relative humidity (RH) or dry conditions.Traditionally, an overall hygroscopicity parameter can beretrieved from measured (RH, ), hereinafter referred to as, by combining concurrently measured particle numbersize distribution (PNSD) and mass concentration of black carbon. In thispaper, a new method is proposed to directly derive based only on measurements from a three-wavelength humidified nephelometersystem. The advantage of this newly proposed approach is that can be estimated without any additional informationabout PNSD and black carbon. This method is verified with measurements fromtwo different field campaigns. Values of estimatedfrom this new method agree very well with those retrieved by using thetraditional method: all points lie near the 1 : 1 line and the square ofcorrelation coefficient between them is 0.99. The verification resultsdemonstrate that this newly proposed method of deriving is applicable at different sites and in seasons ofthe North China Plain and might also be applicable in other regions aroundthe world.
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