Ammonia Pollution: Key Facts and Insights You Should Know

Following the government’s recent statement of committing to building 1.5 million homes and delivering 150 major infrastructure projects, with an overall objective of addressing the worsening of nature whilst simultaneously tackling the challenges posed by housing and infrastructure shortages.

One such airborne pollutant of concern is ammonia (NH₃), which can have significant effects on both human health and the natural environment. Its emissions negatively affect biodiversity, with certain species and habitats particularly susceptible to ammonia pollution. Ammonia is produced both by natural processes, such as decomposition of organic matter, as well as anthropogenic sources, including fertiliser used in agriculture, industrial processes such as anaerobic digesters used in the waste industry and vehicle emissions.

Human-produced ammonia emissions stem from agricultural activities, accounting for 86% of UK emissions in 2016. Other sources include industrial processes and vehicle emissions, though the latter contribute less substantially. In areas with intensive agriculture, background ammonia levels can overshadow contributions from road traffic, posing challenges for air quality assessments.

Impacts of Ammonia Pollution

Inhalation of ammonia can irritate the respiratory system, with long-term exposure potentially leading to conditions like chronic bronchitis or asthma. Environmentally, ammonia contributes to eutrophication, altering plant communities by favouring nutrient-loving species over sensitive ones. It also has toxic effects on certain invertebrates, fungi, and lichens, and can lead to soil acidification, impacting vegetation indirectly.

It is important to note that the extent of ecological ammonia impacts is still not completely understood since much of the existing evidence on biodiversity impacts relates to all nitrogen pollution rather than just ammonia. There is also considerably less evidence of the impact of ammonia on animal species and the wider ecosystem. However, indirect impacts can occur for animal species which depend on plants as a food source, making herbivorous animals susceptible to the effects of ammonia pollution. Ammonia can similarly affect freshwater ecosystems through agricultural run-off, resulting in toxic effects on aquatic animals that often have thin and permeable skin surfaces. However, more research is needed to understand the extent of ammonia pollution in wider ecosystems.

The recent update to the planning policy now includes permission for development on ‘grey belt’ land, which includes previously developed sites located in the green belt. This change aims to utilise underused land for housing and other developments. Given that this land is within the green belt, the development of these areas is likely to be in proximity to sensitive ecological sites, therefore, there may be a greater need for assessment of associated emissions.

Assessment

When it comes to assessing the impacts of ammonia emissions, there are several repositories for guidelines which air quality experts like those in Temple’s air quality & climate team can consider. These include guidance documents published by the Institute of Air Quality Management (IAQM), Design Manual For Roads and Bridges (DMRB) and Natural England’s guidance on assessing emissions under the habitat regulations.

Describing the impacts of ammonia emissions on ecological receptors typically involves comparing the quantities of ammonia being generated by the source being assessed to threshold values which are derived from the aforementioned guidance documents. These act as benchmarks for assessing the risk of air pollution impacts on ecosystems, where significant adverse effects on receptors may occur if they are exceeded. These can be broadly split into two types: Critical Levels and Critical Loads.

• Critical Level – refers to the threshold level for ambient ammonia concentrations in the air
• Critical Load – refers to the threshold level for the quantity of deposited ammonia from the air to the ground

The concept of these Critical Levels/Loads were originally introduced by the United Nations Economic Commission for Europe (UNECE) and can be accessed via APIS Air Pollution and Information System (APIS). The deposition of ammonia is most likely to specifically affect vegetation (this happens indirectly through changes to soil properties), whilst ambient ammonia can affect both ecological and human receptors.

The critical levels are dependent on the habitat being impacted. For example, the annual critical level of ammonia for less sensitive higher plants is 3 µg/m³ but is reduced to 1 µg/m³ for more sensitive lower plants (such as lichens and bryophytes).

Mitigation

The application of these various assessment methods helps inform the decision-making process when it comes to mitigating any potentially significant impacts associated with ammonia emissions. The specific mitigation recommended depends on the ammonia-generating activity taking place:

• Agriculture: Emissions from livestock farming and fertiliser use are the dominant sources of ammonia. To mitigate emissions, farmers can implement low-emission slurry spreading techniques, such as trailing shoes and injection methods, which minimise ammonia volatilisation. Additionally, covering manure and slurry storage facilities can significantly reduce emissions by limiting ammonia escape. The use of urease inhibitors in fertilisers is another effective mitigation approach, preventing the rapid release of ammonia into the atmosphere.
• Industrial Processes: Sources such as anaerobic digestion plants and biomass combustion facilities can adopt ammonia scrubbing technology to remove ammonia from exhaust gases before they are released into the air. These scrubbing systems use acid-based solutions to neutralise ammonia gas, converting it into ammonium salts, which can then be safely handled.
• Development and Construction: In cases where new developments are located near sensitive ecological sites, developers can incorporate green infrastructure, such as buffer zones of vegetation that help absorb and neutralise ammonia before it reaches receptor sites. Additionally, sustainable drainage systems (SuDS) can be designed to prevent ammonia-laden runoff from construction sites from entering water bodies, protecting aquatic ecosystems.
• Regulatory Compliance: Following the best available techniques (BAT) guidelines ensures compliance with emission standards. Developers working with ammonia-emitting industries must adhere to established regulatory limits, often enforced by agencies such as the Environment Agency. Monitoring strategies, including continuous emissions measurement and dispersion modelling, can help quantify emissions and inform mitigation decisions.

Implication

Recent planning policy updates permit development on ‘grey belt’ land—previously developed sites within the green belt. These areas are often near sensitive ecological sites, necessitating thorough assessments of potential emissions. Additionally, the introduction of the Nature Restoration Fund signifies a shift from project-specific environmental assessments to a more strategic, landscape-scale approach. Developers can now contribute to a centralised fund, supporting broader nature restoration initiatives. This approach aims to streamline development processes while ensuring substantial environmental benefits.

The evolving planning policies underscore the importance of integrating environmental considerations into development projects. Understanding ammonia’s impacts and adhering to updated assessment and mitigation guidelines are crucial for sustainable development. Specialist consultants, like Temple’s air quality & climate team, play a vital role in navigating these complexities, ensuring that development aligns with both regulatory requirements and environmental preservation goals.