In situ observations in aircraft exhaust plumes in the lower stratosphere at midlatitudes

Instrumentation on the NASA ER‐2 high‐altitude aircraft has been used to observe engine exhaust from the same aircraft while operating in the lower stratosphere. Encounters with the exhaust plume occurred approximately 10 min after emission with spatial scales near 2 km and durations of up to 10 s. Measurements include total reactive nitrogen, NO y , the component species NO and NO 2 , CO 2 , H 2 O, CO, N 2 O, condensation nuclei, and meteorological parameters. The integrated amounts of CO 2 and H 2 O during the encounters are consistent with the stoichiometry of fuel combustion (1:1 molar). Emission indices (EI) for NO x (=NO + NO 2 ), CO, and N 2 O are calculated using simultaneous measurements of CO 2 . EI values for NO x near 4 g (kg fuel) −1 are in good agreement with values scaled from limited ground‐based tests of the ER‐2 engine. Non‐NO x species comprise less than about 20% of emitted reactive nitrogen, consistent with model evaluations. In addition to demonstrating the feasibility of aircraft plume detection, these results increase confidence in the projection of emissions from current and proposed supersonic aircraft fleets and hence in the assessment of potential long‐term changes in the atmosphere.