Réalisation de cadastres dynamiques des émissions d'ammoniac liées à la fertilisation azotée aux échelle régionale et nationale. Rapport de fin de projet Cadastre_NH3, Convention ADEME n°1081C0031

Field: Environmental Science (Physical Sciences)

Arable crops are the sources of numerous gaseous components which are expected to have a major threat to the environment and/or on neighboring ecosystems: it is particularly the case of ammonia, originating at 97% from the agricultural and related activities, and for more than one third from field fertilization. Ammonia is recognized to be involved in particulate matter formation which damages air quality and human health (PM2.5), and, after deposition, it contributes to soil acidification, semi-natural ecosystem biodiversity decline and terrestrial aquatic ecosystem eutrophication. Controlling atmospheric ammonia emissions to the troposphere is becoming a major concern at an international level with the currently committed revision of the Gothenburg Protocol (1999) as part of the Geneva Convention on Long-Range Transboundary Air Pollution (1979). This control relies on a better knowledge and quantification of the sources, and of their spatial and temporal variability. Ammonia volatilization is a process which intensity and duration depend on agricultural and environmental conditions. The variability of conditions encountered in agricultural practice makes the quantification of emissions difficult. The use of emission factors allows not allow neither to account for their spatial and temporal variability, nor to assess the abatement potential of recommended measures or changes in emissions due to global changes.Two methodologies are available for the development of emission inventories:•the first type, the so-called "top-down" one, considers the general statistical data and calculate national or regional emissions, based on the use of distribution or disaggregation keys to generate data required for the calculation at a finer scale (Department, Township, or grid scale). This method has generally a low cost in time, and allows many methodological and technical shortcuts; it is used by the air quality models. However, it proved inadequate to the forecast of some particulate pollution events.•the second type, the so-called "bottom-up" one, is based on the collection of data from the thinnest level to the more aggregated one, preferring fine data sources rather than distribution keys. This approach is more costly in time and requires that the data and methodology are adapted one to another to form a coherent model for the estimation of the emissions.We plan to implement a "bottom-up" type approach to build dynamic and spatially-explicit inventories of ammonia emissions from the field. This method is expected to reflect regional or annual specific effects related to climate, cultural practices, soil type, and to assess some scenarios of agricultural practices and climate change. The target spatial scale is regional and national (France). The approach is therefore based on the combination of ammonia volatilization models run and geo-referenced databases.The project focuses on three work-packages:The first work-package concerns the process-base modeling of physical, chemical and biological process at the field scale. It involves the coupling of two models developed at the UMR EGC: Volt'Air, the process-based predictive model of ammonia volatilization on bare soil and SurfAtm, the SVAT model (soil-vegetation-atmosphere transfer) for the description of the exchange of ammonia between the soil, the plant and the atmosphere. The spatialization and initialization of the resulting volatilization model will be provided by coupling it with the agro-ecosystem CERES-EGC model which simulates the global dynamic of water, carbon and nitrogen.The second work-package relates to the implementation of geographical information system (GIS) methods including the crossing of the information layers to map and generate the model inputs. It implies the constitution of several geo-referenced databases: soil, climate, land-use and management. The project will particularly focus on the cultural practice database, as a consequence of the lack of references on organic fertilization practices in France.The last work-package concerns the generation of the dynamic and spatially-explicit emission inventories. A methodological component should allow analyzing to what extent the aggregation and the loss of information related to the change of scale alter the values of the emissions. Finally, we will apply this approach to the prospective study of the effect of the implementation of the policies/guidelines for abating ammonia emissions (annex IX of the Gothenburg Protocol (1999)).