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Scoping the use of process modelling for use in the assessment of ammonia mitigation options - AM0130

Description
The goal of this project is to show how mechanistic modelling can be used to estimate agricultural ammonia (NH3) emissions and ultimately investigate the potential of using mechanistic models to improve the national emissions inventory, including improved assessment of emission abatement measures. Mechanistic modelling has considerable advantages over simplified empirical modelling, since it gives an insight into the individual processes leading to emission and allows the influence to be assessed of key driving factors, such as temperature, wetness, pH, soil type, wind speed etc. Process modelling has significant potential to improve national scale ammonia emissions estimates, since many of the driving factors vary spatially and temporally across the country. The empirical effect of some of the management and environmental interactions is already being considered in the NARSES model. However, before a fuller process-modelling approach can be taken, substantial work is needed to analyse critically the assumptions and structure of existing process models of NH3 emissions.

Models exist for all the dominant agricultural NH3 sources (housing, manure storage, grazing, land spreading, fertilisers and crops), and it is necessary to assess how suitable and consistent these models are for both generalizing ammonia emissions and analysing abatement potential. Each model describes the chemical, biological and physical interactions for each particular context. Despite the wide differences between systems, all ammonia emissions from agriculture (with the exception of particulate ammonium and organic R-NH2 emissions) result from the same fundamental process of volatilisation from aqueous solution. Recognizing this, the present project will establish a unified framework for ammonia models. This will provide a common structure to review the generality and transferability of the different models in terms of the fundamental component processes and (importantly) in a common language that allows easy comparison of process description. In addition, the framework will highlight the multiple influences of key parameters on competing processes (e.g. distinguishing the effects of water that increase emissions from those that decrease emissions), thereby improving the predictability of emissions. At the same time the comparison will be used to discriminate between models and identify those for different systems meriting more detailed assessment.

In order to assess the most important factors governing the emission process, the existing models will be subjected to rigorous sensitivity analyses of each of the processes identified in the unified modelling framework. As well as providing an insight into the dominant factors and processes within the models, these analyses will provide the basis to recommend integrating protocols of required parameters. These are terms that should be measured in all future experiments, which will allow them to be properly interpreted with process models. (This is important, since the absence of key measurements from many past studies makes them nearly worthless from a process modelling perspective.) Based on a review of NH3 emission measurements where the required integrating parameters are available, a database of interpretable measurements will be constructed and used to test the performance, accuracy and applicability of the models.

Mechanistic modelling is a key resource to assess the mitigation potential of NH3 emissions. The first step will be to analyse the abatement techniques within the unified modelling framework. This will provide the basis to review the structure of the different models regarding their potential for incorporating different abatement techniques. For key abatement methods, a sensitivity assessment of abatement potential will be conducted to demonstrate the potential of process models to assess and predict the generality of mitigation potential. Ammonia abatement needs to consider both the direct reduction in emissions and the increase in on-farm recapture of emissions. The available process models that incorporate the recapture of ammonia by vegetation have been developed and applied in the DEFRA-funded AMBER project (Ammonia Mitigation By Enhanced Recapture). The present project will demonstrate how these recapture models fit within the unified framework and can be applied to quantify the mitigation potential of on-farm recapture.

Following the model assessment stage, the project will provide a demonstration of how mechanistic models can be incorporated into the national scale NARSES model. This will involve an investigation into how spatially and temporally variable factors (such as temperature, wind speed, soil type, etc.) affect the modelled emissions and what implications this has for modelling ammonia emissions on a national scale. From this, one model will be selected to demonstrate how a mechanistic modelling approach can be incorporated into the NARSES framework and to show how this advances the empirical treatment that is currently being developed in NARSES.
Objective
The overall objective of this project is to show how mechanistic modelling can be used to estimate agricultural ammonia emissions and ultimately investigate the potential of using process-based models to improve the UK ammonia emissions inventory, including the estimation of emission abatement potential on a national scale.

1. To construct and refine an integrated conceptual framework of nitrogen flows and component ammonia emission processes from agriculture, to which all process based models can be related.

2. To conduct a critical analysis of available ammonia emission process models for agricultural sources (livestock housing, hard-standings, waste storage, land spreading, crops, mineral fertiliser application and grazing).

3. To carry out sensitivity analyses on the process models to identify and prioritise the influence of individual parameters.

4. To construct a database containing data from ammonia emission measurements and use these data to test the performance of each model and its ability to resolve inconsistencies within the measurements.

5. To assess the dependence of modelled emission estimates of agricultural sources with and without the application of abatement techniques on spatially variable parameters such as soil type and climate.

6. To investigate how the modelled emission estimates could be incorporated into the spatial emissions modelling inventory of NARSES.

7. To recommend which process models (or parts therein) are best suited for use within DEFRA’s ‘Ammonia emissions from agriculture’ research programme.

8. To investigate modelling ammonia recapture for different source-receptor configurations (e.g. recapture of land spreading emission by nearby low vegetation and recapture of housing/storage emissions by tree belts.

9. To recommend which variables need to be measured in experiments to enable the results to be best interpreted and used to maximum effect with process models.

Project Documents
• Final Report : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (1081k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (30k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (685k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (592k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (1459k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (891k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (3311k)
• Final Report - Annex : Scoping the use of process modelling for use in the assessment of ammonia mitigation options   (144k)
Time-Scale and Cost
From: 2003

To: 2005

Cost: £149,861
Contractor / Funded Organisations
Centre for Ecology and Hydrology
Keywords
Agri-Environment              
Air Pollution              
Ammonia              
Environmental Protection              
Modelling              
Pollution              
Fields of Study
Environmental Protection - Agriculture