Potential Ozone Formation Attributable to Rural Interstate Traffic

The impact of motor vehicle emissions from rural interstate traffic on local ozone formation is investigated. In particular, the interaction between nitrogen oxide and hydrocarbon emissions associated with heavy-duty vehicles and biogenic hydrocarbon emissions is examined. Such interaction is investigated with coupled modeling systems. First, modal emission rate estimates for carbon monoxide, nitrogen oxides, and speciated hydrocarbons are produced for light and heavy-duty vehicles using a freeway operations simulation tool. Second, biogenic hydrocarbon emissions are estimated from forests. Both biogenic and anthropogenic emissions of ozone precursors are then introduced in a photochemical model to describe photochemical processes within and above forests where isoprene is the dominant chemical species. The photochemical mechanism is modified to account for the introduction of anthropogenic species from the interstate traffic into a nitrogen oxide-limited rural environment. A hypothetical interstate is "superimposed" on a remote microclimate removed from anthropogenic sources. Three scenarios are presented for comparison: Scenario 1 (forest, no interstate), Scenario 2 (forest, interstate), and Scenario 3 (no forest, interstate). Several combinations of traffic and roadway factors (e.g.,speeds, traffic volumes, percent heavy-duty vehicles, grade) are evaluated within Scenarios 2 and 3. Results illustrating the potential for ozone formation due to local heavy traffic will be presented and discussed.