Field intercomparison of diffusive samplers for measuring ammonia

Agricultural production systems are recognised as a major source of atmosph eric ammonia. Deposition of ammonia and ammonium may contribute to undesire d changes in oligotrophic ecosystems. The continuous measurement of atmosph eric ammonia requires expensive and sophisticated techniques and is perform ed only in a very restrict number of ambient air stations in Europe. Theref ore, the application of passive samplers, which have the advantage of being easy to handle and cost-efficient, is useful. In the past the comparabilit y of different passive samplers must be considered as rather scarce. In a j oint European project under the leadership of the GSF-Forschungszentrum fur Umwelt und Gesundheit, Neuherberg, in 1997 a comparison of different passi ve ammonia monitoring methods was carried out in a prealpine rural site nea r Garmisch-Partenkirchen. It was considered valuable to include not only we ll established systems but also methods still being developed. For the comp arative test ten working groups with different methods took part. A wet ann ular denuder system, which has been developed by the Netherlands Energy Res earch Foundation for on-line measurement of atmospheric ammonia, served as reference of passive methods. The experiment, which started in June and fin ished in December. showed that most of the passive samplers fulfil the requ irements and can be recommended for further measurements. Additional measur ements of meteorological parameters were performed to check the influences of different weather conditions on passive sampling.