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Quantifying the amounts and fate of ammonia in the environment requires measurements at a range of spatial and temporal scales. The measurement task can be distinguished into three levels: 1) Application of low-cost sampling methods for the assessment of spatial patterns and long term trends in NH₃ and NH₄⁺ concentrations, 2) Detailed measurements using basic techniques, including basic monitoring of dry deposition, 3) Process studies on NH₃ and NH₄⁺ concentrations and biosphere-atmosphere exchange. In relation to air concentration monitoring, the emphasis needs to be on Levels 1 and 3. Low-cost denuders and passive sampling at a monthly frequency provide data on spatial patterns and temporal trends cheaply, while expensive continuous monitoring techniques for NH₃ and NH₄⁺ can concentration and/or flux data with a 10-minute to hourly resolution for the investigation of process controls. Conversely, traditional daily sampling using manual methods fails to meet either of these objectives optimally.

Substantial advances in quantifying ammonia interactions have been made in the UK and Europe based on these approaches. While Level 3 measurements have aided the development of bi-direc-tional NH₃ exchange models, and feed into improving the process description in regional emission, dispersion and deposition models, the Level 1 measurements provide a resource to test the NH₃ and NH₄⁺ concentration outputs of the regional models, both spatially and against long term trends. This is demonstrated from a comparison of data from the UK and Dutch national monitoring networks with the respective national models. A key challenge for NH₃ is that of local spatial variability, which leads to serious errors in the national risk assessments of ecological impacts. Here there is an ongoing need for fine scale investigations (e.g. 50 m resolution, within example 5 km grid squares), to better quantify impacts, improve sampling representativity and refine NH₃ abatement strategies.

⁽¹⁾ CEH, Edinburgh, UK
⁽²⁾ RIVM, Bilthoven, NL
⁽³⁾ ECN, Petten, NL

Quantifying Ammonia Concentrations and Exchange Fluxes: Process Interactions and Regional Generalization

M.A. Sutton⁽¹⁾, Y.S. Tang⁽¹⁾, C. Milford⁽¹⁾,
T. Dore⁽¹⁾, E. Nemitz ⁽¹⁾, M.R. Theobald⁽¹⁾, U. Dragosits⁽¹⁾,
D. Fowler⁽¹⁾, A. van Pul⁽²⁾ and J.W. Erisman⁽³⁾

Quantifying Ammonia Concentrations and Exchange Fluxes: Process Interactions and Regional Generalization

M.A. Sutton(1), Y.S. Tang(1), C. Milford(1), T. Dore(1), E. Nemitz (1), M.R. Theobald(1), U. Dragosits(1), D. Fowler(1), A. van Pul(2) and J.W. Erisman(3)

M.A. Sutton⁽¹⁾, Y.S. Tang⁽¹⁾, C. Milford⁽¹⁾,
T. Dore⁽¹⁾, E. Nemitz ⁽¹⁾, M.R. Theobald⁽¹⁾, U. Dragosits⁽¹⁾,
D. Fowler⁽¹⁾, A. van Pul⁽²⁾ and J.W. Erisman⁽³⁾