Dust Generated by Vehicular Traffic on Unpaved Roadways: Sizes and Infrared Extinction Characteristics

Abstract

Measurements of the size distribution, mass concentration, morphology, and infrared extinction coefficient of dust particles generated by vehicular traffic on unpaved roadways in the arid southwestern U.S. are reported. Measurements were made within a few meters of the point of closest approach of the various tracked and rubber-tired vehicles used in the experiment. For sandy soil, all vehicular dust size distributions reveal a bimodal character with mode mass mean radii about 4 μm and 45 μm, regardless of vehicle type and vehicle speed (for speeds ranging from 5 to 12 ms−1). The larger mode of particles appears to be characteristic of the parent soil, but not the smaller mode. The smaller mode likely derives from large soil grains through some process involving disaggregation. A limited number of measurements made in silty soil also display bimodal size distributions, although with slightly larger mean size and broader distribution for the smaller mode. The shapes of the dust particles generated from san...