With measures aimed at reducing the emission of pollutants such as ammonia, policy makers pay too little attention to the consequences for the emission of other substances. This is revealed in a computer model constructed by Corjan Brink from Wageningen University during his doctoral research. For example, the model shows that reducing the amount of ammonia emitted leads to an increase in the emission of nitrous oxide (laughing gas). The computer model developed by the environmental economist Brink, combined with figures from European agriculture demonstrates that the policy aimed at reducing ammonia emission can lead to an increased emission of nitrous oxide or methane. For example, ammonia-limiting measures such as the introduction of low-emission stables and the low-emission application of manure can lead to a tripling in the emission of nitrous oxide. The results also indicate that a reduction in nitrous oxide or methane results in a reduced emission of ammonia. However, lower nitrous oxide emissions are associated with an increased emission of methane. The outcomes per country differ considerably, dependent on the measures implemented to reduce the emissions. The most important measures which simultaneously ensure a decrease in ammonia, nitrous oxide and/or methane emissions are less nitrogen in the feed, the more efficient use of artificial fertilisers and manure, and modifications to the feed to increase the productivity of the animals. In his doctoral research, Brink concentrated on the emission of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) in European agriculture. These substances contribute to various environmental problems such as acid rain and climate changes, and are largely produced by the same sources. Brink discovered that there are almost no quantitative data concerning the side effects of measures to reduce the emission of these substances. He therefore estimated the side effects for a number of relevant measures. The computer model he developed made it possible to calculate the costs and effects of reduction strategies for different environmental problems in relationship to each other. With this information policy makers can produce cheaper and more effective strategies to reduce the emission of pollutants. The model works for 36 European countries.