Ammonia is the primary gaseous alkaline species in the atmosphere over Europe, neutralising up to 70% of the original acidity in precipitation [Buijsman et al., 1987>. It is directly involved in the conversion of sulphur dioxide and nitrogen oxides into the aerosol phase. Furthermore, ammonium contributes considerably to the nitrogen deposition and soil acidification which causes extensive changes in plant communities in many ecosystems [Moore, 1995; Rohde et al., 1995>. However, in Europe continuous long-term measurements of atmospheric ammonia or ammonium in precipitation are lacking. Here, we present a continuous, high-resolution record of ammonium in precipitation for the time period 1780 to 1980 deduced from an ice core recovered from a high-altitude glacier in the Alps. The ammonium level remained constant from 1780 to 1870 and increased afterwards by a factor of three. This trend shows that ammonia emissions in Europe have substantially increased in the last 100 years. ¿ American Geophysical Union 1996