Abstract

The goal of our research effort is to derive the vertical and horizontal structure of aerosol scatter in the lower marine boundary layer. Our approach is to use a multi-wavelength 3-D scanning lidar to measure the aerosol backscatter. Realistic aerosol size distributions are assumed in order to derive the wavelength dependent aerosol scattering and backscattering coefficient. At the same time we use an instrumented aircraft to simultaneously measure in situ aerosol size distributions for validation purposes. Both coarse mode sea salt and accumulation mode sulfate aerosols contribute to the atmospheric scatter in the marine boundary layer. Typically sea salt dominates under clean conditions but sulfate rapidly becomes the major scatterer as polluted conditions are approached. On average, the accumulation mode aerosols are well mixed with altitude and sea salt variations cause the vertical gradients in atmospheric scatter. Models of the average sea salt size distribution have been made (Porter and Clarke, 1996; Garthman, 1983; Woodcock, 1953) but the vertical gradients remain insufficiently well characterized. Vertical profiles of the total salt aerosol mass remains equally uncertain. Although vertical profiles of salt concentration have been measured successfully, natural atmospheric dynamics cause a wide range of vertical and horizontal variability. Measurements of sea salt vertical concentration have been measured using both kites and aircraft (Blanchard et al., 1984; Daniels, 1989; Woodcock, 1953). On average these measurements show a strong gradient in the lowest 30 m and a gradual decrease above that. Individual measurements show strong variability with altitude with pronounced maxima and minima. While these studies provide us with an initial idea of the structure of sea salt in the marine boundary layer, they do not provide a large enough data set from which to make statistical inferences.

© 1997 Optical Society of America