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 NOx emissions, and the resultant reductions in RF from coupling NOx 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 NOx 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 NOx/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