Evaluating Ammonia Abatement Measures with the Use of Measurements and Models

Ammonia is one of the most important eutrophying components in the Netherlands. Also, ammonia deposition to the soil may contribute to soil acidification and nitrate leaching. The ammonia deposition accounts for almost 70% of the total nitrogen deposition in the Netherlands. About 75% of the ammonia deposition in the Netherlands arises from agricultural activities. Therefore the reduction of the ammonia emissions is an important national goal as well as subject in international protocols (EU, UN-ECE). Several abatement measures, like development of low emission animal housing systems, coverage of manure storage basins and incorporation of manure into the soil, have been taken since 1990. In the Netherlands the effect of the measures are evaluated using measurements and modeling of the ammonia concentrations.

The National Air Quality Monitoring Network consists of eight locations for measuring ammonia concentrations in air, seven for the ammonium aerosol concentrations and fifteen for the ammonium in precipitation. In the near future two dry deposition locations will also be operative. Ammonia concentrations in ambient air are strongly related to local ammonia emissions and can act as the most direct indicators for spatial emission differences and trends in emissions. Nevertheless, the interpretation of measured time-series in terms of emission trends is not straightforward because year-to-year differences in meteorological factors and systematic changes in the chemical composition of the atmosphere have their impact on the emission-concentration relation. These impacts can be quantified by using a transport and deposition model.

Model calculations of the ammonia concentrations on the basis of emission estimates show that the trend in the measured concentrations as well as the spatial distribution of the concentrations over the Netherlands can be simulated quite well. Conclusions on the basis of this analysis is that the emissions over the last decade have been reduced by about 35%. With the model also the reductions in the different emission categories can be shown. It is found that the emissions of animal housings and so the reductions on them have a much larger effect on the ammonia concentrations than emissions from other sources. The model, however, underestimates the measured concentrations with about 30%. The reason for this difference is not yet clear but probably point to an underestimation of the emissions as well as an overestimation of the dry deposition of ammonia by the model.

*This project is funded by the EPA’s Chesapeake Bay Program