JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. D2, PAGES 3065-3074, FEBRUARY 20, 1995 In situ observations in aircraft exhaust plumes in the lower stratosphere at midlatitudes D. W. Fahey, 1 ff.•. Keim, 1,2 E. L. Woodbridge, 1,3 R. S. Gao, 1,3 K. A. Boering, 4 B C. Daube, 4 . . Wofsy, 4R. P. Lohmann, 5E. J.Hintsa, 6 A. E. Dessler, 6,7 C. •.Webster, 8 R. D. May, 8 C. A. Brock, 9 J. C. Wilson, 9 R. C. Miake-Lye, 1ø R. . Brown, 10 J.M. Rodriguez, 11 M. Loewenstein, 12 M. H. Proffitt, 1,3 R. M. Stimpfle, 6 S.W. Bowen, 12 and K. R. Chan 12 Abstract. Instrumentation on the NASA ER-2 high-altitude aircrafthasbeenused to observe engine exhaust from the same aircraft while operating in the lower stratosphere. Encounters with theexhaust plume occurred approximately 10 min afteremission with spatial scales near 2 km and durations ofup to 10s. Measurements include total reactive nitrogen, NOy, the component species NO andNO2, CO 2, H20, CO, N20, condensation nuclei, andmeteorological parameters. The integrated amounts of CO2and H20 during theencounters areconsistent with the stoichiometry of fuel combustion (1:1 molar). Emission indices (EI) for NOx (= NO + NO2), CO, andN20 arecalculated using simultaneous measurements of CO2. EI values for NO x near 4 g (kgfuel) ~• are in good agreement with values scaled from limited ground-based tests of theER-2 engine. Non-NOx species comprise less thanabout 20% of emitted reactive nitrogen, consistent with model evaluations. In addition to demonstrating thefeasibility of aircraft plume detection, these results increase confidence in theprojection of emissions from current and proposed supersonic aircraft fleets and hence in theassessment of potential long-term changes in the atmosphere. Introduction The world's aircraft fleet is expectedto undergo changein the future from continuedgrowth in the commercial subsonic fleet and from internationalefforts to build a high-speed civil transport (HSCT). As a result, the effect on ozone (03) and climate of NOx in aircraft engine exhaust is of increasing concern[World Meteorological Organization (WMO), 1992; International Civil Aviation Organization, 1991; Kandebo, 1993; Johnston et al., 1989, 1991; Beck et al., 1992; Ehhalt et al., 1992; Schumann, 1990]. NOx (= NO + NO2) plays an IAeronomy Laboratory, NOAA, Boulder, Colorado. 2Now at NASAAmes Research Center, Moffett Field, California. 3Cooperative Institute for Research in Environmental Science, University of Colorado,Boulder. 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts. 5pratt & Whitney, East Hartford, Connecticut. 6Department of Chemistry, Harvard University, Cambridge, Massachusetts. 7Now at NASA Goddard Space Flight Center, Greenbelt, Maryland. 8jet Propulsion Laboratory, Pasadena, California. 9Department of Engineering, University of Denver, Denver, Colorado. 10Aerodyne Research, Incorporated, Billerica, Massachusetts. 11Atmospheric and Environmental Research, Incorporated, Cambridge, Massachusetts. I2NASA Ames Research Center, Moffett Field, California. This paperis not subject to U.S. copyright. Published in 1995 by the American Geophysical Union. Paper number94JD02298. importantrole in the photochemistry of the upper troposphere and lower stratosphere (UT/LS). In the troposphere, NOx acts as a catalyst to produce 03 in reactions involving the oxidation of methane and other hydrocarbons. In the stratosphere, NO x catalytically destroys 03 in reactions involving O atoms. In additionto 03 changes, the continued global emissions of NOx, carbon dioxide (CO2),andwater vapor (H20) may influence climate [Johnson et al., 1992; Peter et al., !991; Bekki and Pyle, 1993; Kasibhatla, 1993]. Emissions from the subsonicaircraft fleet are projected to increase 220% between 1990 and 2015, with a significant fraction released in the LS [Stolarski and Wesoky, 1993]. Current emissions in the UT are estimated to contribute 5 to 10% of ambient03 at 40øN from an injectionof 2 teragrams (Tg) nitrogen dioxide (NO2)per year [WMO, 1992]. The proposed HSCT fleet would furtherincrease fuel consumption by 20% and release NOx higher in the LS (16-20 km), where NOx more effectively destroys 03. In currentassessments, however,03 changes are predicted to be smallfor the range of NO x emission index (EI) values projected for HSCT fleet engines [Kandebo, 1993;Stolarski and Wesoky, 1993]. The accuracy of these predictions will depend directly on the accuracyof engine emission estimates. Few direct EI measurements for NOx emissions have been reported for subsonic or supersonic aircraft operating at cruise conditions in the UT/LS [Zheng et al., 1994]. An EI measurement downstream of the exhaust exit planerequires an observation of NOx as well as another species, such as CO2, that can be related to the quantity of fuel burned. The instruments providing these measurements must have a sampling rate and sensitivity that can be used on a moving platform to resolve the plume species from backgroun d levels. Without direct atmospheric measurements, EI values for NOx are derived using data from subsonic and supersonic combustor 3065