Frohn, L.M., Brandt, J., Christensen, J.H., Geels, C., Hertel, O., Skjøth, C.A., Ellermann, T. NERI Technical Report No. 621, 33 pp.
Summary
The Lagrangian model ACDEP which has been applied in BOP/-NOVA/NOVANA during the period 1995-2004, has been replaced by the more modern Eulerian model DEHM. The new model has a number of advantages, such as a better description of the three-dimensional atmospheric transport, a larger domain, a possibility for high spatial resolution in the calculations and a more detailed description of photochemical processes and dry deposition.
In advance of the replacement, the results of the two models have been compared and evaluated using European and Danish measurements. Calculations have been performed with both models applying the same meteorological and emission input, for Europe for the year 2000 as well as for <st1:country-region w:st="on"><st1:place w:st="on">Denmark</st1:place></st1:country-region> for the period 2000-2003. The spatial resolution in the calculations performed for this comparison with the DEHM model (50 km x 50 km) is more coarse than the resolution applied in the ACDEP model (16.67 km x 16.67 km).
The European measurements applied in the present evaluation are obtained through EMEP. Using these measurements DEHM and ACDEP have been compared with respect to daily and yearly mean concentrations of ammonia (NH3), ammonium (NH+4), the sum of NH3 and NH+4 (SNH), nitric acid (HNO3), nitrate (NO-3), the sum of HNO3 and NO-3 (SNO3), nitrogen dioxide (NO2), ozone (O3), sulphur dioxide (SO2) and sulphate (SO2-4) as well as the hourly mean and daily maximum concentrations of O3. Furthermore the daily and yearly total values of precipitation and wet deposition of NH+4, NO-3 and SO2-4 have been compared for the two models. The statistical parameters applied in the comparison are correlation, bias and fractional bias.
The result of the comparison with the EMEP data is, that DEHM achieves better correlation coefficients for all chemical parameters (16 parameters in total) when the daily values are analysed, and for 15 out of 16 parameters when yearly values are taken into account. With respect to the fractional bias, the results obtained with DEHM are better than the corresponding results obtained with ACDEP for 11 out of 16 chemical parameters.
On the basis of the EMEP measurements it can be concluded that DEHM provides significantly better results than ACDEP with respect to the reproduction of the temporal as well as the spatial variability for the majority of the chemical parameters applied in the evaluation. Despite the difference in resolution of the meteorology and emission input, the DEHM model provides better results in general when compared to measurements.
The results of the two models have also been compared to measurements of yearly mean concentrations of NH+4, SNH, SNO3, NO2, SO2 and SO2-4 as well as yearly values of wet deposition of NH+4, NO-3 and SO2-4 and precipitation measured at the Danish stations Anholt and Ulborg during the period 2000-2003 (for DEHM the period 1989-2003). The result of this comparison is that both models are in good agreement with measurements.
In general the performance of the DEHM model is at least as good as the performance of the ACDEP model, and for the majority of the chemical parameters the performance of DEHM is better than the performance of ACDEP when model results are compared to measurements. This result is expected since the description of the long-range transport of air pollution, which contributes significantly to the concentration levels in <st1:country-region w:st="on"><st1:place w:st="on">Denmark</st1:place></st1:country-region> , is better in DEHM.
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