Modeling Concentrations of Air Toxics near Intersections and Freeways in Florida

Abstract

This paper reports on the results of dispersion modeling of mobile source air toxics (MSATs) near seven intersections and seven freeway segments in the state of Florida. Different modeling approaches were used, all with the focus on a hot-spot analysis to obtain the worst-case (highest) 1-h concentration. To accomplish the worst-case modeling, the CAL3QHC model was modified to handle inputs of several individual MSATs and to predict the concentrations of these MSATs around roadways. Real-world data (traffic volumes and site geometry) were gathered, meteorological input data were selected, and mobile source emission factors (EFs) were obtained from the U.S. EPA’s mobile-source emissions model, MOVES2010a. Based on a literature search of short-term effects, maximum acceptable concentrations (MACs) for a 1-h averaging time were proposed for comparison with the modeled results. Results from this study indicate that for all of the intersections and freeway segments, the worst-case 1-h modeled concentrations of the MSATs were several orders of magnitude below the proposed short-term MACs. It is recognized that long-term exposures and chronic health effects are a major concern associated with MSATs. With this in mind, additional modeling (using CAL3QHCR and AERMOD) was conducted to show how the prediction of long-term concentrations could potentially be addressed.