Abstract
Abstract. A method was developed to estimate hygroscopic growth factor (f(RH)) of aerosol light-scattering coefficient (bsp), 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 bsp and hygroscopic growth factor of bsp (fsp(RH)) using the Mie model. Furthermore, the calculated fsp(RH) was fitted with an empirical curve. To evaluate the applicability of fsp(RH), the curve of fsp(RH) was used to correct the long-term records of the measured bsp from the values under comparative dry conditions to the ones under ambient RH conditions. Compared with the original bsp data, the fsp(RH)-corrected bsp had a higher linear correlation with, and a smaller discrepancy from, the bsp derived directly from visibility and absorption measurements. The fsp(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 fsp(RH) with high accuracy and has many potential applications in aerosol-related research.
Highlights
Atmospheric aerosols influence the radiation budget of the Atmosphere–Earth system through light scattering and absorption, which impact climate and degrade air visibility (Seinfeld and Pandis, 2006)
The hygroscopic growth factor of bsp (fsp(RH)) could be determined. Thermodynamic equilibrium models such as EAIM (Wexler and Clegg, 2002) and ISORROPIA II (Fountoukis and Nenes, 2007) were developed for the purpose of reconstructing aerosol chemical composition, as well as estimating water content absorbed by aerosols, in various relative humidity (RH) conditions
Measured inorganic ions were needed as model input for ISORROPIA II to reconstruct aerosol chemical composition
Summary
Atmospheric aerosols influence the radiation budget of the Atmosphere–Earth system through light scattering and absorption, which impact climate and degrade air visibility (Seinfeld and Pandis, 2006). The hygroscopic growth factor of bsp (fsp(RH)) could be determined Thermodynamic equilibrium models such as EAIM (Wexler and Clegg, 2002) and ISORROPIA II (Fountoukis and Nenes, 2007) were developed for the purpose of reconstructing aerosol chemical composition, as well as estimating water content absorbed by aerosols, in various RH conditions. These models take advantage of particle size hygroscopic growth factor (Tang, 1996; Tang et al, 1997; Tang and Munkelwitz, 1994) of several pure chemical
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