Tuesday, November 6, 2007
231-10
Mapping of Airborne Particulate Matter from Unpaved Road under two Vehicular Speeds.
David Scott Williams1, Manoj K. Shukla2, and Jim Ross2. (1) Plant and Environmental Sciences, New Mexico State University, P O Box 30003, Las cruces, NM 88003, (2) New Mexico State University, MSC 3Q P.O. Box 30003, Las Cruces, NM 88003
The particulate matter emission from unpaved roads starts with the pulverization of surface material by the force of the wheels, and uplifting and exposure of road to strong air currents behind the wheels. In this study we collected dust samples on a sticky tape using a rotorod sampler by erecting a tower across an unpaved road located in Plant Sciences Research Center , Las Cruces . The dust samples were collected at 1.5-, 4.5- and 6- m height above the ground surface on east and west side of the road. An additional rotorod sampler was installed on the middle of road at 6-m height above the ground surface. The objectives of the project were to demonstrate the usefulness of a simple technique involving rotorods and sticky tapes for collecting suspended airborne particulate matter emitted from unpaved road due to vehicular traffic and to carry out the mass accounting of airborne PM at different height and location to determine the particle size and mineralogy of dust collected on sticky tape by using an electron microscope and image processing software. The soil analysis showed that silt content of road dust was 47.6%, clay content was 23% and in situ gravimetric moisture content was 3%. Both silt and clay sized particles were collected by sticky tapes at all the heights, however increasing vehicle speed increased emission of clay sized particles. The dust particles between PM10 and PM2.5 did not correlate with vehicle speed but particles ≤PM2.5 size did. The emission factor estimated for the total suspended PM were 10147 and 11062 g per vehicle kilometer travel at 48 km h-1 and 64 km h-1 vehicle speeds, respectively. The mineralogical analysis of the dust particle showed that predominant minerals present were carbon, aluminum and silica at all three heights. In general, height and width of the dust plume increased with the vehicle speed on the unpaved road.