Dust Emission from Unpaved Roads

摘要

Near-source deposition of vehicle generated dust can reduce the amount of material that is carried high enough into the atmospheric boundary layer to affect regional air quality.The interaction of vehicle dust plumes with vegetation and terrain irregularities has been proposed as as a dust removal mechanism that is not considered in current emission factor based source inventory calculations.Results from two field experiments are presented.Vehicle-generated road dust was measured under stable atmospheric conditions at a flat site in the Utah west desert,and the horizontal flux of the dust was calculated by integration of interpolation functions that are fit to the wind speed and dust concentration measurements at discrete heights.The site contained a uniformly spaced array of 2.5 m high by 2.4 m by 12.2 m roughness elements simulating an urban setting.The horizontal flux of dust decreased to less than 15% of the initial value while traveling between measurement planes 3 and 95 m from the road.This differes from unstable atmosphere dust flux results presented in this conference by some of the coauthors(Paper #69531).Particle deposition from vehicle-generated dust clouds was measured downwind of an unpaved road.The quantity of particles deposited on a surface divided by the concentration of particles in the air,the surface area,and the time,has the dimensions of length/time and is referred to as"deposition velocity."Microscopy counting of particles deposited on flat substrates gave a deposition velocity based on projected area ranging from 0.3 cm/s for submicron particles to 2 cm/s for 3 mm particles.The artificial vegetation suspended above a tub gave a deposition velocity based on horizontal surface area of about 10 cm/s.These measurements made in the impact zone where surfaces intercept the horizontally moving dust cloud are higher than dry deposition velocities calculated for downward transport in the atmosphere.