ATMOSPHERIC AMMONIA AND AMMONIUM TRANSPORT IN EUROPE AND CRITICAL LOADS - A REVIEW

The atmosphere in Europe is polluted by easily available nitrogen (amm onium and nitrate) mainly from livestock (NH3), traffic (NOx) and stat ionary combustion sources (NOx). The nitrogen emission from various Eu ropean sources decreases in the order: agriculture, road traffic, stat ionary sources and other mobile sources (including vehicular emissions from agriculture), with annual emissions of approximately 4.9, 2.7, 2 .7 and 0.8 Mt N respec tively. The emissions have increased dramatical ly during the latest decades. In the atmosphere the pollutants are oxi dised to more water soluble compounds that are washed out by clouds an d eventually brought back to the earth's surface again. Since ammonia is emitted in a highly water soluble form it will also to a substantia l degree be dry deposited near the source. Ammonia is, however, the do minant basic compound in the atmosphere and will form salts with acidi c gases. These salt particles can be transported long distances especi ally in the absence of clouds. The deposition close to the source is s ubstantial, but hard to estimate due to interaction with other polluta nts. Far from the source the deposition of ammonium is on an annual av erage halved approximately every 400 km. This short transport distance and the substantial deposition near the source makes it possible for countries to control their ammonium deposition by decreasing their emi ssions, provided that there is no country with much higher emission in the direction of the prevailing wind trajectory. When the easily avai lable nitrogen is deposited on natural ecosystems (lakes, forests), ne gative effect can occur. The effect is determined by the magnitude of the deposition and the type of ecosystems (its critical load for nitro gen). In order to reduce the negative effects by controlling the emiss ions in a cost-efficient way it Is necessary to use atmospheric transp ort models and critical loads.