Runsheng Gao

Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere

Emission indices of reactive gases and particles were determined from measurements in the exhaust plume of a Concorde aircraft cruising at supersonic speeds in the stratosphere. Values for NOx (sum of NO and NO2) agree well with ground-based estimates. Measurements of NOx and HOx indicate a limited role for nitric acid in the plume. The large number of submicrometer particles measured implies efficient conversion of fuel sulfur to sulfuric acid in the engine or at emission. A new fleet of supersonic aircraft with similar particle emissions would significantly increase stratospheric aerosol surface areas and may increase ozone loss above that expected for NOx emissions alone.

In situ observations of NOy, O3, and the NOy/O3 ratio in the lower stratosphere

Extensive in situ measurements of reactive nitrogen (NO y ) and ozone (O 3 ) were made in the lower stratosphere over a broad latitude range (60°N-70°S) during two different seasons (March and October) in 1994. Both NO y and O 3 mixing ratios show a strong latitude dependence, with values increasing toward the poles. The NO y /O 3 ratio reveals a high-gradient region near the tropics that is not well-represented in standard 2-D photochemical transport models. Improving the representation by changing the horizontal eddy-diffusion coefficients near the tropics has important implications for the predicted impacts of aircraft emissions on stratospheric O 3 .

Observations of large reductions in the NO/NOy ratio near the mid-latitude tropopause and the role of heterogeneous chemistry

During the 1993 NASA Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE), anomalously low nitric oxide (NO) was found in a distinct sunlit layer located above the mid-latitude tropopause. The presence of a significant amount of reactive nitrogen (NO_y) in the layer implies the systematic removal of NO, which is without precedent in stratospheric in situ observations. Large increases in measured chlorine monoxide (ClO) and the hydroperoxyl radical (HO_2) also were observed in the layer. Heterogeneous reaction rate constants of chlorine nitrate (ClONO_2) with hydrogen chloride (HCl) and H_2O to form nitric acid (HNO_3) on sulfate aerosol are enhanced in the NO removal layer by local increases in H_2O and aerosol surface area. The associated conversion of NO_x (= NO + NO_2) to HNO_3 is the most likely cause of the observed low NO and NO_x/NO_y values and high ClO values.

The role of HOx in super‐ and subsonic aircraft exhaust plumes

The generation of sulfuric acid aerosols in aircraft exhaust has emerged as a critical issue in determining the impact of supersonic aircraft on stratospheric ozone. It has long been held that the first step in the mechanism of aerosol formation is the oxidation of SO2 emitted from the engine by OH in the exhaust plume. We report in situ measurements of OH and HO2 in the exhaust plumes of a supersonic (Air France Concorde) and a subsonic (NASA ER-2) aircraft in the lower stratosphere. These measurements imply that reactions with OH are responsible for oxidizing only a small fraction of SO2 (2%), and thus cannot explain the large number of particles observed in the exhaust wake of the Concorde.