| dc.description.abstract | A new simplified photochemistry scheme for urban areas has been developed and implemented in EPISODE 3.0.The scheme is based on the comprehensive EMEP mechanism, but contains only 45 compounds and about 70 reactions, the minimal number essential for a city or urban atmosphere. The new scheme can be run with reasonable CPU time and use of memory on a standard Windows based PC. All reaction coefficients are updated according to the latest IUPAC 2001 survey. The resulting nonlinear system of ordinary differential equations (stiff ODEs) is solved using state-of-the-art numerical methods, based on fast Gauss-Seidel iterative techniques, with numerical error control and restart in case of detected numerical inaccuracies. The new scheme has successfully been run in a standalone version of EPISODE 3.0 for the city of Berlin, as part of the City Delta model intercomparison study. The calculations were performed for a total simulation period of 6 months. The new scheme has also been compared with the complete EMEP photochemistry scheme. The latter study show that the scheme retains the essential aspects of photochemical reactions in an urban atmosphere with good accuracy. The new scheme has so far only been implemented in EPISODE 3.0. Further development is needed in order to run the photochemistry scheme as part of the AirQUIS system. | |
