An alternative method for estimating hygroscopic growth factor of aerosol light-scattering coefficient: a case study in an urban area of Guangzhou, South China

Abstract. A method was developed to estimate hygroscopic growth factor (f(RH)) of aerosol light-scattering coefficient (b_sp), making use of the measured size- and chemically resolved aerosol samples. In this method, chemical composition of the measured aerosol samples were first reconstructed using the equilibrium model ISORROPIA II. The reconstructed chemical composition, which varies with relative humidity (RH), was then employed to calculate b_sp and hygroscopic growth factor of b_sp (f_sp(RH)) using the Mie model. Furthermore, the calculated f_sp(RH) was fitted with an empirical curve. To evaluate the applicability of f_sp(RH), the curve of f_sp(RH) was used to correct the long-term records of the measured b_sp from the values under comparative dry conditions to the ones under ambient RH conditions. Compared with the original b_sp data, the f_sp(RH)-corrected b_sp had a higher linear correlation with, and a smaller discrepancy from, the b_sp derived directly from visibility and absorption measurements. The f_sp(RH) determined here was further compared with that reported in previous studies. The method described in this manuscript provides an alternative approach to derive credible f_sp(RH) with high accuracy and has many potential applications in aerosol-related research.