IN-SITU OBSERVATIONS OF AIR-TRAFFIC EMISSION SIGNATURES IN THE NORTH-ATLANTIC FLIGHT CORRIDOR

Focussed aircraft measurements have been carried out over the eastern North Atlantic to search for signals of air traffic emissions in the f light corridor region. Observations include NO, NO2, HNO3, SO2, O-3, H 2O, total condensation nuclei (CN), and meteorological parameters. A f light pattern with constant-altitude north-south legs across the major North Atlantic air traffic tracks was flown. Signatures of air traffi c emissions were clearly detected for NOx, SO2, and CN with peak conce ntrations of 2 ppbv, 0.25 ppbv, and 500 cm(-3), respectively, exceedin g background values by factors of 30 (NOx), 5 (SO2), and 3 (CN). The o bserved NOx, SO2, and CN peaks were attributed to aircraft plumes base d on radar observations of the source air traffic and wind measurement s. Major aircraft exhaust signatures are due to relatively fresh emiss ions, i.e., superpositions of 2 to 5 plumes with ages of about 15 min to 3 hs. The observed plume peak concentrations of NOx compare fairly well with concentrations computed with a Gaussian plume model using ho rizontal and vertical diffusivities as obtained by recent large-eddy s imulations, measured vertical wind shear, and the corridor air traffic information. For the major emission signatures a mean CN/NOx abundanc e ratio of 300 cm(-3) ppbv(-1) was measured corresponding to an emissi on index (EI) of about 10(16) particles per 1 kg fuel burnt. This is h igher than the expected soot particle EI of modern wide-bodied aircraf t. For the most prominent plumes no increase of HNO3 concentrations ex ceeding variations of background values was observed. This indicates t hat only a small fraction of the emitted NOx is oxidized in the plumes within a timescale of about 3 hs for the conditions of the measuremen ts.