Hedegaard, G.B., 2007. Research Notes from NERI, 107pp.

 

Summary

 

The fate of a selected number of chemical species is inspected with respect to climate change. The coupled Atmosphere-Ocean General Circulation Model ECHAM4-OPYC3 is providing future meteorology for the Chemical long-range Transport Model DEHM-REGINA. In order to separate out the effect from climate change the anthropogenic emissions are held constant at 1990 level in all simulations with exception of the validation simulations. Three selected periods (1990’s, 2040’s and 2090’s) are inspected.

 

The 1990’s is used as a control and validation period. In this decade an evaluation of the output from the DEHM-REGINA model with ECHAM4-OPYC3 meteorology input data is carried out. The model results are tested against similar model simulations with MM5 meteorology and against observation from the EMEP monitoring sites in <st1:place w:st="on">Europe</st1:place> .

 

The test results from the control period show that the overall mean values and standard deviations are similar for the two simulations, however the model setup with climate input data fails to predict correctly with respect to the timing of the variability in the data as expected. The overall performance of the ECHAM4-OPY3 setup as meteorological input to the DEHM-REGINA model I acceptable according to the ranking method. It is concluded that running a chemical long-range transport model on data from a “free run” climate model is scientifically sound!

 

From the model runs for the three decades, it is found that the trend detected in the evolution of the chemical species, is the same between the 1990 decade and the 2040 decade and between the 2040 decade and the 2090 decade, respectively.

 

The absolute dominating impact from climate change on a large number of chemical species, is found to be the predicted temperature increase. The temperature is by the ECHAM4-OPYC3 model predicted to increase 2-3 Kelvin on a global average with local maxima in the Arctic of 11 Kelvin. As a consequence of this temperature increase, the temperature dependent biogenic emission of isoprene is predicted to increase significantly in concentration over land in the DEHM-REGINA chemistry-transport model. This leads to an increase in the ozone production and in the number of free OH radicals.

 

This again leads to a significant change in the typical life times of many species, since the hydroxyl radicals participating in a large number of chemical reactions. It is e.g. found that more sulphate will be present in the future over the already polluted areas and this increase can be explained by an enhancement in the conversion of sulphur to sulphate.

 

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