Measurement of PM10 Emission Factors from Paved Roads Using On-Board Particle Sensors

Based on emission factors derived from the AP-42 algorithm, particulate matter from paved roads has been estimated to be a major source of PM10 of geologic origin. This is an empirical formula based on upwind-downwind measurement of PM10 concentrations and is dependent solely on the silt loading of the pavement and the weight of vehicles. A number of upwind-downwind studies conducted in urban areas to validate this algorithm have been generally unsuccessful because the PM10 concentration difference between upwind and downwind often is within the measurement uncertainty. In the approach presented here PM10 concentrations were measured directly on moving vehicles in order to improve the measurement sensitivity for estimating the emission factors for vehicle on paved roads. Optical sensors were used to measure PM10 concentrations with a time resolution of approximately ten seconds. Sensors were mounted in the front and behind the vehicle in the well-mixed wake. A special inlet probe was designed to allow isokinetic sampling under all speed conditions. As a first approximation the emission factor was based on the concentration difference between upwind and downwind and the frontal area of the test vehicle. The emissions factors for a wide variety of roads in southern California ranged from 64 to 124 mg/km. These are consistent with but generally lower than measurements using upwind-downwind techniques. This technique is useful for quickly surveying large areas and for investigating hot spots on roadways caused by greater than normal deposition of PM10 forming debris.