Evaluation of ammonia emission abatement on the basis of measurements and model calculations

Since 1990 regulations were implemented in order to decrease the ammonia emissions in the Netherlands. These regulations include the coverage of animal manure storage basins, the prohibition of application of manure in winter and the obligatory incorporation of manure in the soil after application. Furthermore, investments to decrease emission from housing systems are stimulated. As the result of these regulations, it was estimated that the ammonia emissions were decreased by 37% in 1996 relative to 1990. These estimates were based on statistical data and assumptions about the effectiveness of the regulations. Measurements of air concentrations and depositions between 1992 and 1996 and model results were used to evaluate the decrease in emission estimates. The measurements do not show a distinct decrease. Model results based on the estimated emissions show lower concentrations and depositions than the measurements. These differences cannot be attributed to variations in meteorological parameters or uncertainties in model parameters. For the period 1984 to 1985 model calculations agree reasonably well with measurements (with higher uncertainty). In the more recent years, however, the difference between model results and measurements becomes much bigger. It is concluded that the abatement strategies with an assumed decrease in emission of 30-40% were in fact less effective.