Atmospheric Ammonia

It concludes that threshold levels for ammonia effects have been underestimated and sets new values, it assesses the independent evidence to verify reported reductions in regional ammonia emissions, and it reviews the uncertainties in modelling ammonia, both in "hot spots" and at the regional scale. Atmospheric ammonia is increasingly being recognized as a pollutant of key environmental concern. Ammonia contributes to several environmental problems, including direct toxic effects on vegetation, atmospheric nitrogen deposition, leading to the eutrophication and acidification of sensitive ecosystem, and to the formation of secondary particulate matter in the atmosphere, with effects on human health, atmospheric visibility and global radiative balance. Ammonia emissions are increasing rapidly in many parts of the world, so that these environmental concerns are expected to grow in future. In Europe, efforts are currently being made to reduce ammonia emissions, alongside reductions in other air pollutants, notably sulphur dioxide and nitrogen oxides. However, reducing ammonia emissions has proved uncertain and challenging, with only modest regional reductions achieved to date. As the emissions of sulphur dioxide and nitrogen oxides are reduced, ammonia is therefore increasingly dominating the air pollution climate of Europe and the consequent environmental impacts. It was in this context that the leading international experts met in Edinburgh in December 2006 under the auspices of the UN-ECE Convention on Long Range Transboundary Air Pollution to review the current state of the science of ammonia in the atmosphere. Specifically, the international workshop was a joint effort between several bodies of the Convention: the Ammonia Expert Group, the Working Group on Effects and…