When considering biosphere–atmosphere exchange of trace gases and volatile aerosols, significant advances have been made both from an experimental and modelling point of view and on several scales. This was particularly stimulated by the availability of new datasets generated from improvements in analytical methods and flux measurement techniques. Recent research advances allow us, not only to identify major mechanisms and factors affecting the exchanges between the biosphere and the atmosphere, but also to recognize several gaps in the methodologies used in accounting for emissions and deposition in landscape and global scale models. This work aims at (i) reviewing exchange processes and modelling schemes, parameterisations and datasets, (ii) presenting a common conceptual framework to model soil-vegetation-atmosphere exchange of reactive trace gases and aerosols accounting for in-canopy transfer chemical interactions and (iii) discussing the key elements of the agreed framework.

Anthropogenic emissions of ammonia cause a host of environmental impacts, including loss of biodiversity, soil acidification and formation of particulate matter in the atmosphere. Under the auspices of the UNECE Convention on Long Range Transboundary Air Pollution, around 80 international experts met to review the state of scientific knowledge. This book reports their analysis. 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.