Using a dispersion model to estimate emission rates of particulate matter from paved roads

From January 1996 to June 1997, we carried out a series of measurements to estimate emissions of PM10 from paved roads in Riverside County, California . The program involved the measurement of upwind and downwind vertical prof iles of PM10, in addition to meteorological variables such as wind speed an d vertical turbulent intensity. This information was analyzed using a new d ispersion model that incorporates current understanding of micrometeorology and dispersion. The emission rate was inferred by fitting model prediction s to measurements. The inferred emission factors ranged from 0.2 g VKT-1 fo r freeways to about 3 g VKT-1 for city roads. The uncertainty in these fact ors is estimated to be approximately a factor of two since the contribution s of paved road PM10 emissions to ambient concentrations were comparable to the uncertainty in the mean value of the measurement. At this stage, our b est estimate of emission factor lies between 0.1 and 10 g VKT-1; there is s ome indication that it is about 0.1 g VKT-1 for heavily traveled freeways, and is an order of magnitude higher for older city roads. We found that mea sured silt loadings were poor predictors of emission factors. The measured emission factors imply that paved road emissions may contribut e about 30% to the total PM10 emissions from a high traffic area such as Lo s Angeles. This suggests that it is necessary to develop methods that are m ore reliable than the upwind-downwind concentration difference technique. ( C) 1999 Elsevier Science Ltd. All rights reserved.