Global modelling of atmospheric trace gases: Application of a global three dimensional model

Abstract

The global MOGUNTIA model was applied in two studies: ‘Aspects of atmospheric methane’ and ‘Effects of aircraft emissions’. Results of both studies with respect to the ‘European Renaissance’ and a ‘Joint Implementation’ scenarion will be presented. Methane plays a key role in the atmospheric radiative balance and chemistry. Per mass unit it is 58 times more effective than CO2. In a chemical sense is is the primary sink for OH and it therefore determines the oxidising capacity of the atmosphere to a large extent. We studied model result from 3 methane scenarios representing a uniform regional growth, a joint implementation option, and the European Renaissance assumptions. Previous studies on effects of aircraft emissions have indicated an increase in the upper tropospheric ozone concentration of 5–12% due to aircraft emissions. Since ozone at the upper troposphere level is an effective greenhouse gas, the atmospheric radiative balance may be (further) disturbed by this process. The additional amount of ozone at the cruising altitude is modelled to result in a radiative forcing of 0.03–0.07 W/m2. We assessed the importance of homogeneous chemical processes in aircraft plumes before large scale mixing of the emissions occurs. The exhaust-plume-model developed resulted in a parameterisation of the sub-grid plume effects which was finally implemented in the global MOGUNTIA model. The parameterisation is currently a conversion factor showing a 60% conversion of NOx into NOy when the plume reaches the grid dimensions of MOGUNTIA. Preliminary results with the the global model show that this conversion results in a lower ozone production (6%) than due to unconverted emission fields (8%).