Determination of the refractive index of ambient aerosols: Fid-Bau Portal

Determination of the refractive index of ambient aerosols

Zhao, Gang / Li, Fei / Zhao, Chunsheng

Abstract The refractive index of ambient aerosols is one of the most important parameters indicating the scattering and absorption properties of aerosols. We proposed a new method for retrieving the refractive index (RI) of ambient particles. The main advantage of our method is that it assimilates the single particle mixing states measured by a single-particle soot photometer, when compared to the traditional optical method of retrieving the ambient aerosol RI. This method was validated by good consistency between the determined RI with this method and retrieved RI with the method of Zhao et al. (2019c) using datasets from field measurements conducted in East China in June of 2018. The results show that the real part of the refractive index of the black carbon (BC)-free particles ranged between 1.37 and 1.51 and this value changed little across different tested wavelengths. The mean complex refractive index for the refractory BC was 1.67 ± 0.67i at 525 nm. The mean imaginary parts of the other non-BC components were 0.019 and 0.023 at 450 nm and 370 nm respectively. Brown carbon contributed to 5%, 13% and 29% of the ambient aerosol light absorption at 525 nm, 450 nm and 370 nm respectively in East China. This study provides the ability to determine the ambient aerosol complex refractive index and these data can be used in models to reduce the uncertainties in estimating aerosol radiative forcing.

Highlights • A new method for determining the refractive index with assimilating the single-particle mixing states is proposed. •The refractive index of black carbon-free aerosols at the wavelength of 525 nm varied over a wide range between 1.37 and 1.51. •The mean complex refractive index of black carbon was 1.67 ± 0.67i at 525 nm.