Measuring Ammonia Emissions from Agricultural Sources: Technical Possibilities, Applicability in Situ, Benefits and Drawbacks

Ammonia emissions are an important environmental issue and especially in regions with high animal densities (e.g. the Netherlands). Ammonia contributes not only to soil acidification, but it also leads to disruption of the nutrient cycle and disappearance of sensitive natural ecosystems. In order to comply with the ammonia emission reduction assigned to the Netherlands, fast and accurate measurements are necessary to get new estimates of the ammonia emission from each agricultural category. For years, the basic components of emission measurement strategies for mechanically ventilated houses have been based upon a detailed measurement of the ventilation rate using calibrated anemometers (measurement fans), combined with an accurate measurement of the gas concentration in the exhaust air. Naturally ventilated houses were measured using a gas mass balance method, either using a natural (e.g. CO2) or an introduced (SF6) tracer gas to estimate the ventilation rate, combined with a continuous measurement of the NH₃ concentration in the air leaving the building. Although various theoretical possibilities exist for NH₃ emission measurements from non-point sources, like land spread slurry or grazing cattle, full-scale measurements have been limited due to high costs, large labour requirement or insufficient accuracy. Small-scale (micro meteorological mass balance methods, laboratory scale methods) measurements have been conducted on a large scale to yield emission estimates for practical situations.

New insights in measurement equipment for ventilation rate determination, concentration measurement and flux measurements have yielded a basis for new measurement systems and protocols. Statistics and mechanistic models can be promising aspects of these new protocols, aiming at a reduction of the labour and money input, yet maintaining accuracies and offering possibilities for conducting repetitive measurements.

During campaigns to measure emissions from animal houses, it became clear that management is an important factor in determining the emission level. Differences between animal houses of the same type and kind of animal may differ more than the variation in time and season within one animal house. These management related differences in emission factors point at the need of measuring more animal houses. The newly formulated protocols (partly based upon new measurement techniques) can offer possibilities for a more dense data collection, thus leading to a more accurate average emission level per source type (housing system, storage facility, field application of slurry, grazing) and an improved insight in the variation and its influencing factors. This will eventually benefit the development of emission reduction strategies and more accurate legislation.

The paper will focus on developments in the techniques to measure ventilation rates, gas concentrations and fluxes, and on their applicability in practical and research situations. Benefits and drawbacks are highlighted and discussed. Furthermore, the role of models and statistics will be briefly addressed.