Sensitivity of model assessments of high-speed civil transport effects on stratospheric ozone resulting from uncertainties in the NO_x production from lightning

Lightning NO_x production is one of the most important and most uncertain sources of reactive nitrogen in the atmosphere. To examine the role of NO_x lightning production uncertainties in supersonic aircraft assessment studies, we have done a number of numerical calculations with the State University of New York at Stony Brook-Russian State Hydrometeorological Institute of Saint-Petersburg two-dimensional model. The amount of nitrogen oxides produced by lightning discharges was varied within its quoted uncertainty from 2 to 12 Tg N/yr. Different latitudinal, altitudinal, and seasonal distributions of lightning NO_x production were considered. Results of these model calculations show that the assessment of supersonic aircraft impacts on the ozone layer is very sensitive to the strength of NO_x production from lightning. The high-speed civil transport produced NO_x leads to positive column ozone changes for lightning NO_x production less than 4 Tg N/yr, and to total ozone decrease for lightning NO_x production more than 5 Tg N/yr for the same NO_x emission scenario. For large lightning production the ozone response is mostly decreasing with increasing emission index, while for low lightning production the ozone response is mostly increasing with increasing emission index. Uncertainties in the global lightning NO_x production strength may lead to uncertainties in column ozone up to 4%. The uncertainties due to neglecting the seasonal variations of the lightning NO_x production and its simplified latitude distribution are about 2 times less (1.5-2%). The type of altitude distribution for the lightning NO_x production does not significally impact the column ozone, but is very important for the assessment studies of aircraft perturbations of atmospheric ozone. Increased global lightning NO_x production causes increased total ozone, but for assessment of the column ozone response to supersonic aircraft emissions, the increase of lightning NO_x production leads to column ozone decreases in response to aircraft emissions.