Secondary inorganic PM.sub.2.5 particles are formed from SO.sub.x (SO2+SO42-), NO.sub.x (NO+NO.sub.2 ), and NH.sub.3 emissions, through the formation of either ammonium sulfate ((NH.sub.4).sub.2 SO.sub.4) or ammonium nitrate (NH.sub.4 NO.sub.3). EU limits and WHO guidelines for PM.sub.2.5 levels are frequently exceeded in Europe, in particular in the winter months. In addition the critical loads for eutrophication are exceeded in most of the European continent. Further reductions in NH.sub.3 emissions and other PM precursors beyond the 2030 requirements could alleviate some of the health burden from fine particles and also reduce the deposition of nitrogen to vulnerable ecosystems. Using the regional-scale EMEP/MSC-W model, we have studied the effects of year 2030 NH.sub.3 emissions on PM.sub.2.5 concentrations and depositions of nitrogen in Europe in light of present (2017), past (2005), and future (2030) conditions. Our calculations show that in Europe the formation of PM.sub.2.5 from NH.sub.3 to a large extent is limited by the ratio between the emissions of NH.sub.3 on one hand and SO.sub.x plus NO.sub.x on the other hand. As the ratio of NH.sub.3 to SO.sub.x and NO.sub.x is increasing, the potential to further curb PM.sub.2.5 levels through reductions in NH.sub.3 emissions is decreasing. Here we show that per gram of NH.sub.3 emissions mitigated, the resulting reductions in PM.sub.2.5 levels simulated using 2030 emissions are about a factor of 2.6 lower than when 2005 emissions are used. However, this ratio is lower in winter. Thus further reductions in the NH.sub.3 emissions in winter may have similar potential to SO.sub.x and NO.sub.x in curbing PM.sub.2.5 levels in this season. Following the expected reductions of NH.sub.3 emission, depositions of reduced nitrogen (NH3+NH4+) should also decrease in Europe. However, as the reductions in NO.sub.x emission are larger than for NH.sub.3, the fraction of total nitrogen (reduced plus oxidised nitrogen) deposited as reduced nitrogen is increasing and may exceed 60 % in most of Europe by 2030. Thus the potential for future reductions in the exceedances of critical loads for eutrophication in Europe will mainly rely on the ability to reduce NH.sub.3 emissions.