Analysis of motor vehicle emissions during the Nashville/Middle Tennessee Ozone Study

On-road gasoline and diesel-powered Vehicle emissions in Nashville, Tenness ee, were characterized using fuel sales as a measure of vehicle activity, a nd emission factors derived from infrared remote sensing, ambient air conce ntration ratios, and roadway tunnel measurements. On-road vehicle emissions of carbon monoxide (CO), nonmethane hydrocarbons (NMHC), and oxides of nit rogen (NOx) on weekdays during summer 1995 were estimated to be 270 +/- 60, 43 +/- 13, and 53 +/- 9 metric tons per day, respectively. Diesel engines were a minor source of CO and NMHC, but were responsible for similar to 50% of NOx emissions from on-road vehicles. The Environmental Protection Agenc y's MOBILE 5B emission model predictions were similar to fuel-based estimat es for ail pollutants, except for NOx where the MOBILE model predicted a sm aller contribution to total on-road vehicle emissions from diesel engines. Chemical composition profiles for hydrocarbon emissions were developed base d on tunnel air and fuel samples collected in Nashville during summers 1995 and 1999. More than half of the tunnel NMHC mass was liquid fuel that esca ped combustion; the remaining mass came from products of incomplete combust ion such as ethane, acetylene, C-2-C-4 alkenes, and 1,3-butadiene. No major changes in the composition of vehicle-related NMHC emissions were observed between 1995 and 1999 in Nashville.