Preliminary measurements of fluorescent aerosol number concentrations using a laser-induced fluorescence lidar.

Abstract

A laser-induced fluorescence lidar has been developed for detecting the concentration of fluorescent aerosols in the air. The fluorescence lidar was constructed with a pulsed fourth-harmonic Nd:YAG laser at the ultraviolet wavelength of 266nm with a repetition rate of 10Hz. A 250mm diameter custom telescope was used to collect optical spectra ranging from 260 to 560nm. Fluorescence signals with wavelengths ranging from 310-440nm were extracted, exploring a filter with a bandwidth of 130nm. The preliminary experiments were conducted at the campus of Xi'an University of Technology, in which the fluorescence signals of atmospheric fluorescent aerosols were continuously collected from 20:00 to 23:00 CST on 13 December 2017. Based on the fluorescence lidar equation, the density of fluorescence signals was calibrated using Rayleigh-Mie scattering signals and ozone (O3) concentration data at the ground level. Measured ranges show a strong dependence with the O3 concentrations due to its absorption characteristics at ultraviolet 266nm. Moreover, the concentration of the biogenic particles was also calculated based on the raw data of the fluorescence channel. Obtained results show that the concentration of biogenic particles in the Xi'an area varied greatly, ranging from 3456 particles · m-3 to 8835 particles · m-3 during winter.