Emissions of ammonia from weeping wall stores and earth-banked lagoons determined using passive sampling and atmospheric dispersion modelling
Ammonia emissions from stored farm manures form a small but significant proportion (∼10%) of the total emitted annually from UK sources. These emissions are regulated by factors including: the surface area of the store; the storage method; the physical form of the stored manure and the source of manure. A method was developed to estimate in situ emissions from a range of store types (weeping wall and earth-banked lagoon) that are currently under-represented in UK emissions estimates. Passive diffusion samplers (Willems Badges) were used to determine vertical concentration profiles to a height of 4.5 m at a number of locations around each slurry store. An atmospheric dispersion model was applied to estimate the contribution from emissions from other on-farm ammonia sources to the measured data and also to determine the emission rates from the stored manure. A procedure was applied whereby the emission rates from each source were allowed to vary and a numerical equation solver was applied to backfit the modelled data set to the field measurements. Measurements were collected at four farms on a monthly basis throughout the year, with each dataset being collected over 24 h. The uncertainties in the estimates of emissions from the slurry stores during individual measurement periods typically ranged between 20–40% though higher uncertainties occurred when emission fluxes from the stores were below 0.25 g NH3–N m−2 day−1 and were entrained in the wakes, and mixed with the emissions, of adjacent buildings. The average emission from the farms was 0.6 g NH3–N m−2 day−1 which agrees with other recent data on ammonia emissions from crusted slurry stores and, though it is within the range of data considered in the UK emissions inventory, suggests that emissions from weeping wall stores and earth-banked lagoons may be currently overestimated in national predictions.
KeywordsAir pollution Agriculture Back-calculation Gaussian plume Nitrogen
The authors would like to thank the Department for Environment, Food and Rural Affair (DEFRA) for funding this project (WA0717). The following people have also contributed to this work: Steven Bailey, Helen Clayton, Trevor Cumby, Bob Jackson, Richard Johnson, Nick Nicholson, Elia Nigro, Sheila Royle and Adrian Williams. The authors would like to thank Professor Roger Timmis for helpful comments on an earlier draft of this paper.
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