Detection of aerosol mass concentration profiles using single-wavelength Raman Lidar within the planetary boundary layer

Abstract

Considering the importance of the aerosol optical parameters detection for environmental monitoring, a method of converting single-wavelength Raman lidar backscattered echoes to aerosol mass concentrations is proposed to obtain a high-resolution vertical distribution of particulate matter (PM) mass concentrations. PMx (x = 1, 2.5, 10) mass concentrations and extinction coefficients at 355 nm and 532 nm were obtained using a combination of a colocated visibility meter and wide-range particle spectrometer (WRAS), and parameterized equations between the aerosol extinction coefficient and mass concentration at different levels of relative humidity (RH) were established (the sample datasets included different seasonal and weather pollution conditions in Xi'an, China, for 2018 and 2019). The results demonstrate that parametric analysis of sample datasets at three levels of RH (RH < 60%, 60% ≤ RH < 75%, and RH ≥ 75%) can better reflect the long-term variation characteristics of aerosols: the aerosol extinction coefficients show an exponential relationship with PM1 and PM2.5 mass concentrations, and the correlation coefficients are both above 0.965 even at different levels of RH, while the correlation with PM10 is 0.808. The extinction coefficient and RH profiles can be retrieved using single-wavelength Raman lidar, and then the aerosol mass concentration distribution can be calculated by combining parameterized equations. The deviation of mass concentration profiles between 355 and 532 nm Raman lidar was analyzed, and it is a constraint that the calculation of the PM mass concentration profile is made in the planetary boundary layer (PBL). The derivation uncertainty of PMx and the limitations of the method are also discussed. Finally, cases of vertical distribution and variations in PMx on pollution-free and hazy days are presented.