Aerosol transport and dispersion measurements in the near surface boundary layer

Date of Completion

January 2006

Keywords

Engineering, Agricultural|Physics, Atmospheric Science|Atmospheric Sciences|Environmental Sciences|Engineering, Environmental

Degree

Ph.D.

Abstract

The studies presented in this dissertation present new techniques for measuring aerosols in the atmosphere, and the application of these techniques to three different aerosol sources. A methodology for measuring dispersion parameters based on lidar images, which can be used as an efficient way to remotely monitor time variations of plume dispersion parameters, is presented. Lidar images of a smoke plume cross-section over a forest canopy during nighttime conditions are analyzed to estimate vertical dispersion parameters and vertical meander of the plume centerline in the near field. Dispersion parameters 60 meters downwind are found to have a median value of 2.31 meters. Measurements of these parameters have not previously been made outside the restraints of a wind tunnel experiment. ^ A second technique to measure in-plume concentrations based on single wavelength lidar images is also presented. A field study of aerial spray movement and dispersion was used to determine in-plume spray concentrations of very fine droplets applied during calm, stable atmospheric conditions. Supporting meteorology and air turbulence measurements were made simultaneously with 3-D sonic anemometers. The amount of spray material remaining in the air decreased rapidly for 1--2 minutes, and thereafter remained nearly constant and drifted as a definable plume with the slight air currents. ^ Finally, these two techniques are applied to measure near-field spatial dynamics, spread and concentrations of dust plumes emitted during tilling and harvesting of an irrigated cotton field. Combined lidar images are used to form three-dimensional plumes. Plume dynamics and suspended aerosol concentrations are found. Dust plume dynamics varied with atmospheric stability. In particular, plume maximum height was significantly lower during stable conditions. Plume tracking indicated little change in plume cross-sectional area with height under unstable conditions and plume movement depended on wind speed and direction. Horizontal spread rate of the plumes, determined from lidar measured Gaussian dispersion parameters, was less than expected by a factor of seven. Thus, in-plume downwind concentrations were higher than expected. Vertical dispersion was dependent on the rise of "cells" of sensible heat rising from the soil surface.^

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