Two-wavelength lidar characterization of atmospheric aerosol fields at low altitudes over heterogeneous terrain

Abstract

The possibilities for applying multiwavelength elastic lidar probing of the atmosphere to help monitor air-quality over large industrial and densely populated areas, based predominantly on the use and analysis of commonly obtainable backscatter-related lidar quantities, are examined. Presented are two-wavelength (1064/532 nm ) lidar observations on the spatial distribution, structure, composition, and temporal evolution of close-to-surface atmospheric aerosol fields over heterogeneous orographic areas (adjacent city, plain, and mountain) near Sofia, Bulgaria. Selected winter-time evening lidar measurements are described. Range profiles, histograms, and evolutional range-time diagrams of the aerosol backscatter coefficients, range-corrected lidar signals, normalized standard deviations, and backscatter-related Ångström exponents (BAE) are analyzed. Near-perfect correlation between the aerosol density distribution and orographic differentiation of the underlying terrain is established, finding expression in a sustained horizontal stratification of the probed atmospheric domains. Distinctive features in the spatial distribution and temporal evolution of both the fine- and coarse aerosol fractions are revealed in correlation with terrain's orography. Zonal aerosol particle size distributions are qualitatively characterized by using an approach based on BAE occurrence frequency distribution analysis. Assumptions are made about the aerosol particle type, origin, and dominating size as connected (by transport-modeling data) to local pollution sources.