Testing Re-entrained Aerosol Kinetic Emissions from Roads (TRAKER): a new approach to infer silt loading on roadways

PM10 and PM2.5 emissions from roadways are currently estimated using the si lt loading on the road surface as a surrogate for the emissions potential o f road dust. While the United States Environmental Protection Agency prescr ibes this method in AP-42, there is considerable cost associated with silt loading measurements, it is feasible to sample only a small portion of a ro adway network. A new approach for measuring the concentration of suspendabl e PM10 above road surfaces has been developed to obtain a more spatially re presentative estimate of a road's potential to emit dust. The Testing Re-en trained Aerosols Kinetic Emissions from Roads (TRAKER) system uses real-tim e aerosol sensors mounted on a vehicle to measure the concentration of dust suspended from the road while the vehicle is in motion. When coupled with a Global Positioning System (GPS) instrument, TRAKER can be used to efficie ntly survey the changes in the suspendable particle reservoir due to varyin g road conditions over a large spatial domain. In a recent study on paved roads in Las Vegas, the TRAKER system was compar ed with collocated silt loading measurements. The TRAKER system was also us ed to survey the relative amounts of suspendable road dust on approximately 300 miles of paved roads. The system provides a unique perspective on road dust sources and their spatial distribution. Results of this study indicated that the difference of the PM10 concentrati ons measured behind the tire and on the hood is exponentially related to ve hicle speed. This was an interesting finding because current AP-42 road dus t emissions estimation methods do not include vehicle speed as a factor in the emissions calculations. The experiment also demonstrated that the distr ibution of suspendable material on roadways is highly variable and that a l arge number of samples are needed to represent road dust emissions potentia l on an urban scale for a variety of road and activity conditions. (C) 2001 Published by Elsevier Science Ltd.