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 the Task Force on Measurement and Modelling, together with the COST 729 and the NitroEurope Integrated Project. This book reports the underpinning information in the form of several major reviews, combined with supporting chapters on recent research results, to provide an up-to-date scientific synthesis in relation to four key themes:
- Re-evaluation of the critical thresholds for ammonia effects on sensitive plants and habitats
- Review of approaches for downscaling transboundary assessments to deal with ammonia hotspots in relation to operational modelling and monitoring
- Review of regional scale atmospheric transport and chemistry models in relation to their formulation and results for ammonia.
Each of these themes is of fundamental to the quantification of ammonia impacts in the environment and the assessment of possible abatement measures. The reviews highlight how the critical threshold for ammonia concentrations - the "critical level" - has been overestimated in the past, and the book explains the new estimates. Monitoring of atmospheric concentrations and deposition is the only independent way to verify the success of emission abatement policies. The analysis shows how it has been a major challenge to verify the reported reductions in emissions, but that several new datasets now support expected trends in emission reduction, even though total emissions may still be underestimated. Atmospheric models are central to the assessment at both regional and landscape scales. The dynamics within 'ammonia hotspots' are particularly important to understand both the fate of ammonia export from source regions and to assess the local environmental impacts. Similarly, modeling at regional scales forms the basis for transboundary assessment of ammonia emissions and deposition. At both scales, the present assessment shows that quantification of ammonia dry deposition remains a key uncertainty. Cross-cutting analyses in the review addressed the reliability of ammonia emissions data and abatement efficiencies, as well as the agricultural and environmental policy context, considering how scientific understanding can help address the challenges to reduce the adverse effectsof ammonia in the environment.
This book will be valuable to all those interested in the behaviour of ammonia in the environment, as it explains the current state of knowledge, reports new critical level values, and describes the main scientific uncertainties.
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