Atmospheric Ammonia in Sweden: Regional Modeling and Assessment of National Emission Reduction Benefits

Ammonia (NH3) is a central component of atmospheric reactive nitrogen, and a precursor gas that forms airborne particulate matter including nitrate and sulfate aerosol. Reducing ammonia emissions, primarily from agriculture, is a major challenge for air pollution mitigation and environmental protection. This work assesses the effects of ammonia emission reductions in Sweden, which is one of the EU Member States that are currently not meeting their emission reduction commitments. We apply the regional chemical transport model MATCH with improved NH3 treatment, and benchmark the updated model setup against surface observations of atmospheric NH3 and other nitrogen species for a large-scale model domain over Europe. We perform high-resolution regional simulations over Sweden, and compare the effects of reducing the emissions of (1) agricultural NH3, and (2) nitrogen oxides (NOx) from road transport, which is the second major nitrogen source in Sweden. The results show the potential of national NH3 emission reductions to mitigate NH3 levels, fine particulate matter (PM2.5) and nitrogen deposition within Sweden. While cutting NOx emissions is important for air pollution abatement through NOx mitigation, in Sweden the reductions have only minor or negligible effects on PM2.5 and nitrogen deposition. This demonstrates the benefits of NH3 reduction for both air quality and environment, and the impact of national abatement actions.