Spatial and Temporal Distribution of Highway-Generated Air Pollution in a Residential Urban Neighborhood: Comparison of Monitoring and Dispersion Modeling Results

摘要

Exposure to highway-generated air pollution is associated with elevated risk for adverse health effects. However, quantification of exposures, and hence health risk, is hampered by incomplete knowledge of the spatial and temporal variation of pollutants in near-highway residential areas. As part of a study to determine whether people who live near highways express measurably higher risk factors for cardiovascular disease, we developed a mobile laboratory to measure near-highway air pollution gradients at relatively high temporal resolution. In this paper, we report a subset of measured spatial and temporal variation of fine and ultrafine particles (7-225 nm) in the near-highway urban environment, and we evaluate the ability of the CALINE4 software package to predict ultrafine particle concentrations on an hourly timescale. CALINE4 is a line source Gaussian dispersion model intended for regulatory modeling of pollutants in areas within 400 m of highways. Fine and ultrafine particle monitoring was done within an 8,000 m2 area that straddles the highway. Small-scale spatial and short-term temporal variations were found in both upwind and downwind pollutant levels. Particle number concentration generally decreased with increasing distance from Ⅰ-93, though the slope of the concentration gradient varied with time of day, wind direction, and day of the week. Experimental measurements on a transect perpendicular to Ⅰ-93 were compared to the results from CALINE4 for the morning of January 6, 2010. Using estimated emission factors of 9 x 10~14 to 18 x 10~14 particles (7-225 nm) per vehicle per mile, we achieved the best agreement between the model and the data. These calculated emission factors are consistent with values previously published in the literature. These early results suggest that a more refined model can be developed that estimates concentrations of ultrafine particles over the entire study area.