Mark A. Sutton is a leading international expert in the behaviour of nitrogen compounds in the atmosphere and their impacts on terrestrial ecosystems. He has a special interest in interactions of atmospheric ammonia and on development of the science policy interface. He is based at the UK Centre for Ecology & Hydrology (Edinburgh) and is currently Chair of the International Nitrogen Initiative. Kate E. Mason is an information systems professional working at the UK Centre for Ecology & Hydrology (Edinburgh). She has an MScEcon in Archives and extensive experience working in academic libraries and archives. Lucy J. Sheppard has been leading field manipulation experiments into pollution effects on terrestrial ecosystems for nearly 30 years. She has a special interest in effects of different N forms on semi-natural vegetation and carbon cycling in peatlands. She is based at the UK Centre for Ecology & Hydrology (Edinburgh). Harald Sverdrup researches actively into chemical weathering of minerals in soils, and the modelling of soil chemistry and forest and aquatic ecosystems involving population dynamics and nutrient and pollution flows. His research on Critical Loads has been used widely under the UNECE-LRTAP Convention where his team have built and adapted models such as PROFILE, SAFE, FORSAFE, AGRO-SAFE and BigMERK to regional use in Europe. At present he focuses on integrated sustainability assessments and is using biogeochemical models to drive biodiversity models. He has been Professor of Chemical Engineering at Lund University since 1994. Richard Haeuber leads the Assessment and Communications Branch in the Clean Air Markets Division of the US Environmental Protection Agency. He was formerly Associate Director of the Ecological Society of America's Science Programs Office, where he focused on the ecological effects of air pollution on terrestrial, aquatic, and coastal ecosystems. As a Congressional Fellow, he advised US Senate staff on airquality issues and multi-pollutant control legislation. W. Kevin Hicks is a leading researcher with an interest in the transfer of scientific information to the policy process, especially concerning air pollution impacts on terrestrial ecosystems from local to global scales and the linkages between air pollution, climate, biodiversity and ecosystems services. He currently sits on Steering Committee of the European Centre of the International Nitrogen Initiative (INI) and is a Senior Research Fellow at the Stockholm Environment Institute (SEI), Environment Department, at the University of York, UK.