Ammonia pollution in Europe is persistent and deadly

Ammonia contributes to 50% of fine particulate matter in Europe. But it also has independent health effects, such as an association with early-onset asthma in children under six.

Ammonia pollution is one of Europe’s most pressing air pollutants. Not only has ammonia pollution stayed persistently high despite other air pollutant concentrations falling, it continues to be particularly persistent despite inclusion in regulations. The main source of ammonia pollution in Europe is from agriculture, and the impacts of ammonia pollution span human, animal and environmental health, and well as contributing significantly to secondary PM_2.5 formation. More stringent control is needed as ammonia remains a stubborn pollutant which exacts a heavy toll on health and environment in Europe and is one of the leading precursor causes related to air pollution deaths.

Ammonia (NH₃) is a nitrogen-based compound which has a significant pollutant effect in Europe, and globally. In Europe, and globally, the primary source of ammonia pollution is from agriculture; up to 81% of ammonia pollution globally related to animal farming, manure and soil fertilisers [1]. Many different systems and sources lead to this pollution, including waste from the animals in farming, and how the waste is treated, stored, and applied to land, the biochemical environmental conditions where the animals live, the application of nitrogenous fertilisers to soil, and modified by the surrounding atmospheric and climatic conditions [1]. Cattle farming is particularly predominant, just over half (51%) of all Europe’s ammonia pollution is linked to cattle [2]. Other sources include biomass and industrial processes, including those that produce fertilisers.

Once volatile ammonia becomes airborne, a number of different reactions can take place. Ammonia gas can adhere to surfaces, such as those of plants, and become deposited through dry deposition [1], having a local effect on the organic environment. Otherwise, the ammonia can undergo chemical transformation particularly when coming into contact with acidic compounds containing sulphuric, nitric [1] or hydrochloric acids, to form ammonium sulphate, nitrate and chloride respectively. Once transformed, these compounds can be dissolved into rain and deposited through wet deposition. Ammonia gas can also react with water in certain climatic and acidic conditions to form reactive ammonium and hydroxide. Of note, these reactions can also occur in other mediums, such as when ammonia becomes dissolved in water in soil.

When ammonia, sulphur dioxide, and nitrogen oxides react in the atmosphere they form solid (particulate) ammonium sulphates and nitrates, so called secondary inorganic aerosols. The equilibrium between particulate NH₄–NO₃–SO₄ and gaseous HNO₃ and NH₃ has been subject to many studies. All these forms of ammonia pollution have incredibly important and significant effects on the environment [1]. However, when these ammonium salts aren’t immediately deposited through rain or another medium, they can become a pollutant of great importance to public health: fine particulate matter (PM_2.5). This is why ammonia becomes so critical for air pollution in Europe, and why it is such a vital point of intervention. Up to 50% of all particulate matter in Europe is related to secondary inorganic aerosols [1]. Ammonia has become the most significant precursor of secondary PM_2.5 in Europe, surpassing NOx and SO₂ [1].

Several studies have made estimates of premature mortality attributable to ammonia pollution. A 2021 study looking at data from 2019 put this figure globally at 9%, again with wide variations across different countries, with estimates between <5% and up to 30% for different European countries [3]. Looking at the impact of agriculture emissions on PM_2.5, the study found that two-thirds of premature mortality impact of agricultural PM2.5 emissions was from ammonia pollution, and for Western Europe, this figure was as high as 79% [3]. A study of PM_2.5 emissions in the USA from 2022 found agricultural emissions to be the third leading sector in terms of associated premature mortality through PM2.5 pollution, and attributed ammonia to just over 17% of this mortality [4]. A 2015 global study, based on 2010 figures, attributed just over 20% of all global PM_2.5 mortality to agricultural sources [5]. These figures differed depending on location with PM_2.5-related premature deaths from outdoor air pollution with agricultural origin being about 29% in Turkey, and up to 45% in Germany, and 52% in Ukraine [5].

Outside of formation of PM_2.5, ammonia has been independently associated with morbidity. Toxic exposures due to chemical exposure or industrial accident can cause respiratory and mucosal membrane irritation, along with other generalised toxic effects such as diarrhoea [1], but these are now rare. However, a study in Denmark found an association between residential? ammonia pollution and early-onset asthma in under 6-year-old children [6]. This association was not negligible, with an adjusted hazard ratio of 1.74 between the children with the highest decile of exposure as compared to those with the lowest exposure [6]. Similar results were found for ammonium. Interestingly, no association was shown for PM_2.5, indicating effects outside of PM_2.5-related air pollution. This study isn’t a standalone, other studies have made similar suggestions [1].

Interventions to reduce ammonia pollution can have a significant positive effect on public health, and this needs to be a target area for the EU. As we reported in the previous issue of Acid News, ammonia pollution levels have not really changed since 2005, while other pollutants monitored such as PM_2.5, SO₂ and NOx have seen marked reductions [7]. This is a cause for concern, given the health effects and contribution to PM_2.5 pollution, but also because some evidence points to a differential toxicity between other precursors of PM_2.5 and ammonia, with suggested greater associations with both emergency hospital visits for haemorrhagic stroke, and for general mortality [8]. There is also a strong case for rapid action in the face of climate change; warming has been correlated to increased ammonia emission, threatening that efforts to reduce pollution could be undone with higher ambient temperatures [1].

Tackling agricultural ammonia emissions will be a cornerstone to action on air pollution in Europe. As a large contributor to air pollution, the agricultural sector should institute policies and plans to reduce emissions. Modelling in 2017 showed that a 50% reduction in agricultural emissions in Europe could reduce mortality related to air pollution by 19% into the future (and much more globally) [9]. Specifically, ammonia pollution reduction has been modelled to have great potential to reduce air pollution, with one study showing that reducing ammonia emissions would be the single most effective intervention in reducing PM2.5 in Europe [10]. The effects from just reducing ammonia could be up to a 15% reduction in PM_2.5 levels in summer in Central and Western Europe, and 10% in winter [10]. This represents a crucial opportunity for action to protect health and environment, a key part of the European Green Deal, as well as Ambient Air Quality Directive 2024 and the currently being reviewed National Emissions Ceiling Directive. Action on reducing ammonia pollution is an important pillar in creating a healthier future for Europe.

References:
[1] Wyer, K. E. et al. Ammonia emissions from agriculture and their contribution to fine particulate matter: A review of implications for human health. Journal of Environmental Management. 2022.
[2] CLRTAP. Assessment Report on Ammonia – 2020. 2020.
[3] Malley, C. S. et al. Integrated assessment of global climate, air pollution, and dietary, malnutrition and obesity health impacts of food production and consumption between 2014 and 2018. Environment Research Communications. 2021.

[4] Thakrar, S. K. et al. Reducing Mortality from Air Pollution in the United States by Targeting Specific Emission Sources. Environmental Science and Technology Letters. 2020.
[5] Lelieveld, J. et al. The contribution of outdoor air pollution sources to premature mortality on a global scale. Nature. 2015.
[6] Holst, G. et al. Ammonia, ammonium, and the risk of asthma: A register-based case–control study in Danish children. Environmental Epidemiology. 2018.
[7] European Commission, Directorate-General for Environment. Report from the Commission to the Council and the European Parliament on the progress made on the implementation of Directive (EU) 2016/2284 on the reduction of national emissions of certain atmospheric pollutants. EUR-Lex. 2024
[8] Brunekreef, B. et al. Reducing the health effect of particles from agriculture. Lancet Respiratory Health. 2015.
[9] Pozzer, A. et al. Impact of agricultural emission reductions on fine-particulate matter and public health. Atmospheric Chemistry and Physics. 2017.
[10] Megaritis, A. G. Response of fine particulate matter concentrations to changes of emissions and temperature in Europe. Atmospheric Chemistry and Physics. 2013.