Dual-wavelength Mie-scattering Scheimpflug lidar system developed for the studies of the aerosol extinction coefficient and the Ångström exponent.

Abstract

A dual-wavelength Scheimpflug lidar system, utilizing a 4-W 808-nm and 1-W 407-nm multimode laser diodes as light sources and two CMOS sensors as detectors, is developed for the studies of the aerosol extinction coefficient and the Ångström exponent. The system performance has been successfully validated by a two-week continuous measurement campaign on a near horizontal path in May 2018 at Dalian, which is a coastal city in Northern China. The aerosol extinction coefficients retrieved by the Fernald method show good correlations with particle concentrations and relative humidities (RHs). It has been found that the enhancement factor of the backscattering coefficient at the short wavelength due to hygroscopic growth is larger than that at the long wavelength for the aerosol particles off the coast of the Yellow Sea. The Ångström exponent obtains from the aerosol extinction coefficients at the two wavelengths, varies between 0 and 2, and is found to relate with the mass concentration fraction of fine mode particles, specifically PM2.5 particles. Moreover, the Ångström exponent has a positive correlation with the RH, implying a bimodal or multimodal size distribution of aerosol particles in the measurement season.