The Denver Urban Air Toxics Assessment: Methodology, Results, and Risks

摘要

Hazardous air pollutants have received increased attention over the past decade because of their potential carcinogenic and/or reproductive effects on humans based on long-term exposures to low-level concentrations. In 1999, the Denver Department of Environmental Health began an urban air toxics assessment for the six-county Denver metropolitan region. Emission data from point, area, and mobile sources was collected and processed using existing and newly developed methodologies. A Geographical Information System (GIS) was utilized throughout all phases of the assessment and proved to be an extremely valuable tool for modeling on an urban scale. Recently, DDPHE has worked to verify and refine emission inventories for several air toxics using Mobile 6 as well as developing a fuel-based inventory coupled with remote sensing data collected locally. Processed emissions were run through the Industrial Source Complex air dispersion model (ISC3ST, version 00101) that was enhanced for urban air toxics modeling applications. Model predictions were compared with long-term monitoring data to evaluate model performance and also to judge the relative accuracy of the emission inventories. AERMOD, the next generation dispersion model proposed to replace ISC3, was also run as a check against ISC3ST. Results from the current phase of the assessment indicate mobile source pollutants are the predominant contributors to estimated cancer risks, a result consistent with monitoring data in many urban areas. The most important findings from this assessment indicate that ISCST3 performs very well for urban applications with low-level releases and that care must be taken to refine and improve emission inventories.