Deposition of acidifying components and base cations in Germany in the period 1987-1995

The basic model used in this study was EDACS. This model calculates dry deposition fluxes on the basis of meteorological data and atmospheric concentrations of relevant species. As such, the project reported here further elaborates the work carried out in a previous project in 1996, with the following additions and/or improvements worked out:

• The distribution of NH₃ concentrations in Germany has now been calculated on a 5×5 km grid using the EUTREND model, while in the previous study these data were taken from the standard EMEP model.
• Possible concepts for introducing cloud deposition into the inferential approach have been investigated, with results for a small study area in southern Germany shown.
• Canopy exchange estimates for forest sites in Germany were related to parameters, also measured at these sites to gain better insight into the parameters controlling canopy uptake and leaching.

SO_x dry deposition fluxes were highest in central-east Germany, NO_y fluxes in central-west Germany and NH_x fluxes in north-west Germany. The highest dry deposition of potential acid (up to 15,000 eq. ha-1 y-1 in 1987) was calculated for 'Bundesland' Sachsen and the highest dry deposition load of nitrogen was calculated for Bremen (up to 2100 eq ha-1 y-1 in 1989). Dry deposition of SO_x, NO_y, NHx and potential acid in the 1993-1995 period decreased by 36%, 13%, 21% and 31%, respectively, compared to the 1987-1989 period The decrease in potential acid was highest in Sachsen (43%) and lowest in Baden-Wittemberg (12%).

Dry deposition of non-sea salt Ca₂⁺, K⁺, Mg₂⁺ and base cations decreased between the two periods by 42%, 24%, 65% and 43%, respectively. Therefore, on average, the modelled dry deposition of NH_x, Mg₂⁺, Ca₂⁺ and K⁺ is not significantly different from measured dry deposition, although a considerable scatter can be observed. The EDACS model tends to overestimate the dry deposition of SO_x, NOy and Na by factors of 2.15, 1.58 and 1.75, respectively. For SOx this can be explained by the modelled air concentrations, which for Germany have been found too high compared with measurements. The calculated SO_x dry deposition was, therefore, corrected on the basis of SO₂ concentration maps interpolated from available measurements.