Atmospheric aerosol and particle properties using lidar.

摘要

Characterization of airborne particulate matter, both dust particles and aerosols, has been a major challenge to researchers. Lidar (light detection and ranging) techniques have been used to make remote sensing measurements of the aerosol optical extinction and other properties of optical scattering from the particles in the atmosphere. In this thesis, a range of technologies available in the area of laser remote sensing have been used to study the optical properties of atmosphere, including the techniques of Rayleigh scattering, Mie scattering and Raman scattering.; Algorithms and techniques have been developed for analysis of data to calculate the atmospheric optical extinction in the troposphere using backscatter lidar and Raman lidar instruments, and models are described which have been developed to study the optical extinction and backscatter characteristics. The data obtained by Raman lidar and backscatter lidar during several different campaigns were analyzed. An algorithm for extinction at W wavelengths measured by Raman lidar has been developed in which the molecular scattering and ozone absorption are removed to obtain the aerosol optical extinction profile. The relationships between extinction profiles measured by Raman lidar and particulate matter (PM) mass concentration measurements of the ambient particles using point sensors at the surface are investigated. Model simulations have been developed to explain and quantify the relations between extinction and PM concentration. The ratio of the extinction coefficient profiles at different wavelengths has been analyzed to show unique information on particle sizes, which can not be obtained from a single extinction profile.; Backscatter lidar has been used to study the atmospheric meteorological properties and characterize the fate (deposition and transport) of PM plumes originating from the mechanical disturbance of surface soil in one of our projects. A particle size distribution model has been developed from lidar results and measurements from particle size instruments. Model calculations based on Mie scattering theory have been designed to simulate various features of the optical scattering from the generated dust plumes. Field measurements are used to analyze the inverse problem and describe the particulate matter properties from the scattering profiles.; Several achievements from the research work in this thesis include: (1) The ultraviolet aerosol extinction algorithm and telescope form factor for LAPS are successfully developed. (2) The relationships between Raman lidar extinction, relative humidity and PM mass measurements are quantified and modeled. The results show that we can describe the vertical distribution of the airborne particulate matter using Raman lidar and thereby describe the evolution of air pollution episodes more accurately. (3) The modeling results from California Dust campaign show the rapid deposition of large (PM 10) particles, and the relatively longer residence time of the optical plume associated with small particles (2 mum). The rapid loss of PM mass may have led to overestimates of airborne particle mass in plumes and could explain the major discrepancy between the source estimate and the measured mass of soil particulates that has been recognized in California. (4) The ratio of signal from backscatter lidar and ratio of extinction profiles from Raman lidar at multiple wavelengths are used to demonstrate the unique information that can be obtained on the characteristics of airborne particles in the atmosphere.