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

Since 1990 regulations were implemented in order to decrease the ammonia em issions in the Netherlands. These regulations include the coverage of anima l 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 stim ulated. As the result of these regulations, it was estimated that the ammon ia emissions were decreased by 37% in 1996 relative to 1990. These estimate s were based on statistical data and assumptions about the effectiveness of the regulations. Measurements of air concentrations and depositions betwee n 1992 and 1996 and model results were used to evaluate the decrease in emi ssion estimates. The measurements do not show a distinct decrease. Model re sults based on the estimated emissions show lower concentrations and deposi tions than the measurements. These differences cannot be attributed to vari ations in meteorological parameters or uncertainties in model parameters. F or the period 1984 to 1985 model calculations agree reasonably well with me asurements (with higher uncertainty). In the more recent years, however, th e difference between model results and measurements becomes much bigger. It is concluded that the abatement strategies with an assumed decrease in emi ssion of 30-40% were in fact less effective.