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    Critical review of slurry storage ammonia emissions and their mitigation


    We carried out this critical review for the Environment Agency to better understand the factors that control release of ammonia from stored slurry and opportunities for reducing emissions during storage.


    In the UK, the agriculture sector is the main source of ammonia emissions, accounting for 88%, of emissions in 2016. One of the main concerns resulting from ammonia emissions is the impact on human health. Ammonia, is a key component of smog, with approximately three-quarters of the particles made up of ammonium nitrate. This particulate matter has significant health impacts including cardiovascular and respiratory disease.  

    Ammonia deposited to land or waters can also harm natural ecosystems, through eutrophication and acidification. Moreover, ammonia emissions can contribute to climate warming because some of the ammonia deposited on land or water will be transformed into N2O and emitted to the atmosphere.

    The Clean Air Strategy, published by Defra in January 2019, sets out the government actions to reduce ammonia emissions from farming. The government has agreed to reduce ammonia emissions by 16% in 2030, when compared to 2005 levels. To achieve this, the Strategy contains a series of specific proposals for reducing emissions from agriculture including the requirement for all slurry stores to be covered by 2027.

    A wide range of factors influence the release of ammonia from stored slurry including but not limited to, temperature in the surface of the liquid manure, wind, slurry pH, ammonium concentration, occurrence of a natural crust and covering slurry (e.g. with a lid, plastic, straw or granulates).

    Quick Scoping Review methodology was used to gather published and grey literature to better understand the factors that control release of ammonia from stored slurry and opportunities for reducing emissions during storage via covering or the use of slurry treatments (e.g. slurry acidification). Expert opinion and knowledge were also used to inform the review findings. Gaps in the current knowledge base were identified and suggestions for research priorities made.

    Funding Body

    Environment Agency

    Lead Organisation

    Harper Adams University


    Bern University; Aarhus University; Stockholm Environment Institute at York University; Heathside Consulting

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