OBSERVATIONS AND MODEL-CALCULATIONS OF JET AIRCRAFT EXHAUST PRODUCTS AT CRUISE ALTITUDE AND INFERRED INITIAL OH EMISSIONS

Exhaust emissions of NO, HNO2, and HNO3 in the near-field plume of two B747 jet airliners cruising in the upper troposphere were measured in situ using the research aircraft Falcon of the Deutsches Zentrum fur Luft- und Raumfahrt. In addition, CO2 was measured providing exhaust p lume dilution rates for the species. The observations were used to est imate the initial OH mixing ratio OH0 and the initial NO2/NOx ratio (N O2/NOx)(0) at the engine exit and the combustor exit by comparison wit h calculations using a plume chemistry box model. From the two differe nt plume events, and using two different model simulation modes in eac h case, we inferred OH emission indices EI(OH) = 0.32-0.39 g (kg fuel) (-1) (OH0 = 9.0-14.4 ppmv) and (NO2/NOx)(0) = 0.12-0.17. Furthermore, our results indicate that the chemistry of the exhaust species during the short period between the combustion chamber exit and the engine ex it must be considered with respect to the amount of OH at the engine e xit plane because OH is already consumed to a great extent in this eng ine section because of conversion to HNO2 and HNO3. For the engines di scussed here the modeled OH concentration decreases by a factor of sim ilar to 350 between combustor exit and engine exit, leading to OH conc entrations of 1-2 x 10(12) molecules cm(-3) (= 0.3-0.7 ppmv) at the en gine exit.