Impact of Coupled NOx/Aerosol Aircraft Emissions on Ozone Photochemistry and Radiative Forcing.

Three global chemistry-transport models (CTM) are used to quantify the radiative forcing (RF) from aviation NO_x emissions, and the resultant reductions in RF from coupling NO_x to aerosols via heterogeneous chemistry. One of the models calculates the changes due to aviation black carbon (BC) and sulphate aerosols and their direct RF, as well as the BC indirect effect on cirrus cloudiness. The surface area density of sulphate aerosols is then passed to the other models to compare the resulting photochemical perturbations on NO_x through heterogeneous chemical reactions. The perturbation on O₃ and CH₄ (via OH) is finally evaluated, considering both short- and long-term O₃ responses. Ozone RF is calculated using the monthly averaged output of the three CTMs in two independent radiative transfer codes. According to the models, column ozone and CH₄ lifetime changes due to coupled NO_x/aerosol emissions are, on average, +0.56 Dobson Units (DU) and -1.1 months, respectively, for atmospheric conditions and aviation emissions representative of the year 2006, with an RF of +16.4 and -10.2 mW/m² for O₃ and CH₄, respectively. Sulphate aerosol induced changes on ozone column and CH₄ lifetime account for -0.028 DU and +0.04 months, respectively, with corresponding RFs of -0.63 and +0.36 mW/m². Soot-cirrus forcing is calculated to be 4.9 mW/m². [ABSTRACT FROM AUTHOR]