Ammonia emissions are expected to decrease less than SO_x and NO_x emissions between 2005 and 2030. As the formation of PM_2.5 particles from ammonia depends on the ratio between ammonia on one hand and sulfate (from SO_x) and HNO₃ (from NO_x) on the other hand, the efficiency of particle formation from ammonia is decreasing. Depositions of reduced nitrogen are decreasing much less than oxidized nitrogen. The critical loads for nitrogen deposition will also be exceeded in much of Europe in 2030.