Effects of Initial and Boundary Values of Reactive Nitrogen Compounds and Hydrocarbons on the Ozone Concentration in the Free Troposphere
The initialisation and the treatment of the boundary conditions of a mesoscale chemistry-transport-model, covering a limited area, are of great importance. The choice of the initial and boundary values can significantly influence the results of a simulation, so that they should be determined as well as possible (NAPAP, 1991). For this reason it is important to provide realistic conditions, if possible derived from current measurements. Unfortunately trace species in the troposphere, especially in the middle and upper free troposphere, are not observed continuously so that relatively little is known about background concentrations. Usually there are no current observations available which can be used as input data for episodic simulations. The available measurements show a high variability in the concentrations of the trace species. To analyse and to quantify the effects of a variation of the initial and boundary values for model results sensitivity studies were carried out with the European Air Pollution Dispersion modeling system (EURAD) using different initial and boundary scenarios. Therefore the literature has been reviewed and a set of initial and boundary values were derived based on available observation data. With regard to the formation of ozone the focus was set on reactive nitrogen species and hydrocarbons, which are important photooxidant precursor species. First a set of simulations with different scenarios representing free tropospheric conditions is calculated with a boxmodel version of the EURAD model in order to determine the non-linear dependencies of the gas phase chemistry. Furthermore a sensitivity study with the full three dimensional model is performed for a summersmog episode.
KeywordsOzone Concentration Reactive Nitrogen Species Free Troposphere Organic Nitrate Trace Species
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