Nature of the problem • Observations of atmospheric reactive nitrogen (Nr) deposition are severely restricted in spatial extent and type. The chain of processes leading to atmospheric deposition emissions, atmospheric dispersion, chemical transformation and eventual loss from the atmosphere is extremely complex and therefore currently, observations can only address part of this chain. Approaches: • Modelling provides a way of estimating atmospheric transport and deposition of Nr at the European scale. A description of the different model types is provided. • Current deposition estimates from models are compared with observations from European air chemistry monitoring networks. • The main focus of the chapter is at the European scale; however, both local variability and and intercontinental Nr transfers are also addressed. Key findings/state of knowledge: • Atmospheric deposition is a major input of Nr for European terrestrial and freshwater ecosystems as well as coastal sea areas. • Models are key tools to integrate our understanding of atmospheric chemistry and transport, and are essential for estimating the spatial distribution of deposition, and to support the formulation of air pollution control strategies. • Our knowledge of the reliability of models for deposition estimates is, however, limited, since we have so few observational constraints on many key parameters. • Total Nr deposition estimates cannot be directly assessed because of a lack of measurements, especially of the Nr dry deposition component. Differences among European regional models can be significant, however, e.g. 30% in some areas, and substantially more than this for specific locations. Major uncertainties/challenges • There are very few measurements of many of the key compounds (e.g. gaseous HNO3 , coarse-nitrate, NH3 ), which are needed to enable comprehensive model evaluation. Data on all compounds should be available at the same site if the mass-balance of Nr is to be assessed, pointing to the need for integrated site measurements in air monitoring networks. • The main needs for oxidised Nr compounds are to evaluate how well the models capture the partitioning between gaseous HNO3 and either fine or coarse nitrate aerosol. For reduced Nr compounds, better estimates of NH3 emissions are needed, and how these are affected by meteorological factors as well as agricultural practices, coupled with an understanding of biosphere–atmosphere exchange. • Dry deposition of particles, sub-grid fluxes of NHx compounds, and effects of topography on wet deposition are especially difficult to parameterise properly. Recommendations • There is a significant need for studies to constrain uncertain model parameters. This includes measurements of both the gas and particle phases of Nr compounds, and of atmosphere–biosphere fluxes of Nr compounds over sensitive ecosystems. • A balanced programme of observations and models is needed and is critical to future understanding of atmospheric transport and deposition of Nr containing pollutants at local to global scales.

SIMPSON David;  AAS W.;  BARTNICKI Jerzy;  BERGE Haldis;  BLEEKER Albert;  CUVELIER Cornelis;  DENTENER Franciscus;  DORE Tony;  ERISMAN J.W.;  FAGERLI H.;  FLECHARD C.;  HERTEL O;  VAN JAARSVELD Hans;  JENKIN M.E.;  SCHAAP Martijn;  SEMEENA V.S.;  THUNIS Philippe;  VAUTARD R.;  VIENO Massimo; 

2011-06-14

Cambridge University Press

JRC65127

978-1-107-00612-6,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC65127,