Modeling and Analysis of Ozone and Nitrogen Oxides in the Southeast United States National Parks

High O3 episodes are observed in several eastern US national parks, among which the Great Smoky Mountains National Park by far of the fastest increase in frequency of exceedance days (days when any 8-hour average O3 concentration exceeding 85 ppbv). It has been well established that the southeast US rural areas are characterized with strong biogenic VOCs emissions and that O3 production in this region is mostly NOx-limited during summer time. Thus, understanding the contribution of nitrogen oxides to O3 formation during transport and for local photochemistry is essential to predict what effects the planned reductions in NOx emissions from large point sources might have on observed O3 concentrations at these southeast national parks. Our specific interests in this study are: 1) to quantify the relative importance of point sources and mobile sources to total nitrogen oxides emissions; 2) to identify origins of air masses associated with high levels of nitrogen oxides and O3; 3) to quantify contributions of individual chemical and physical processes, i.e., chemistry, transport, emission, and deposition, to the budget of production and removal of nitrogen oxides and O3 in the southeast national parks.