Evaluating the impact of a highway corridor proposal on the air quality in the great Smoky Mountain National Park Using the CMAQ modeling system

Abstract

More than 10 million people per year enter the Great Smoky Mountain National Park (GSMNP). Directly north to the park, traffic-congestion is a growing problem on Highways US-411 and US-441 in Sevier County, especially between the towns, Sevierville and Pigeon Forge, TN. A new four-lane connecting highway and the widening of four existing two-lane roadways into a four-lane divided highway are being considered. For passenger cars, light trucks and sport utility vehicles using gasoline as fuel, the highest emissions of NOx and VOC occur at very low vehicle speeds. However, at faster vehicle speeds, these vehicle emissions are effectively much lower. The computer models MOBILE6 and SMOKE were applied to simulate emissions for two conditions, i.e., the effect of high, on-road light-duty gasoline vehicle and truck emissions caused by traffic-congestion on the existing highway system, and the effect of lowering, on-road light-duty gasoline vehicle and truck emissions by increasing vehicle speed resulting from lane widening improvements to the highway system. The CMAQ model was used to evaluate the photochemical effects on the air quality in the GSMNP as simulated by traffic-congestion vs. free-flow traffic. There was slight emission reduction benefit from modifications to the existing roadway system. However, the emission reduction did not contribute to air quality improvements in the GSMNP. The predicted 8-hr O3 concentrations in GSMNP for the selected episode were very close to exceeding the 80 ppb 8-hr national standard for ground-level O3. This is an abstract of a paper presented at the AWMA 97th Annual Conference and Exhibition (Indianapolis, IN 6/22-25/2004).