Pastures green and skies of blue? Agriculture’s surprising impact on air pollution worldwide

Cows may seem innocent Cows may seem innocent... USDA / CC BY 2.0

Typically, visions of farming and agriculture can summon idyllic imagery of green, rolling hills, the sweet scents of hay and manure, and earthy labour in harmony with nature’s seasons. However, the agricultural industry has come a long way since Wordsworth’s ‘pastoral farms, / Green to the very door’ at the close of the 18th century. One little-discussed recent development is agriculture’s significant impact on air pollution, on both a local and global scale. So how has farming come to emit numerous pollutants into the air, and why should we worry?

Agriculture’s impact on air pollution

Agriculture’s prominent role in emitting pollutants came to light during recent negotiations in European air quality policy. On 12 July, the Environment Committee of European Parliament voted through new legislation (NECD) imposing more stringent limits pollutant emissions from its member states, with the predicted result of halving the number of premature deaths from air pollution amongst the EU’s 508 million citizens by 2030.

Whilst this sounds like a very positive outcome, the agreed deal could have been much more ambitious in limiting harmful emissions, had it not been for one surprising opponent: the agricultural sector.

Farmer sprays field with fertilizer Farmer sprays crops with fertilizer / Pixabay

In an interview with Alex Keynes, a consultant working on air pollution legislation in European Parliament, we heard that the agricultural lobby campaigned hard for more generous limitations during negotiations, particularly for significant farming pollutants such as ammonia and methane. Moreover, we learned that, consistently with this display of opposition, agriculture is the only polluting sector not to have reduced their pollution in recent times.

A global perspective beyond Europe further reinforces agriculture’s substantial polluting impact. A 2015 study compared premature mortality rates across the globe due to outdoor air pollution (PM2.5 and ozone) from different sectors during 2010, and agriculture ranked shockingly highly. For many countries, agriculture was the leading sector, above others such as the notorious heavyweights of residential energy and power generation. These areas include Europe, Russia, Turkey, Korea, Japan and the Eastern USA. The USA as a whole had power generation rank slimly above agriculture, with 16,929 deaths narrowly exceeding 16,221.

So where exactly is all this farming-related pollution coming from?

Public health threat: ammonia

The generation of PM2.5, the measure of pollution widely judged to be most hazardous to human health, primarily comes from agriculture’s significant ammonia emissions. Ammonia (NH3) is a pungent gas generated chiefly through animal waste and heavy use of fertilizer. Ammonia can be a problematic indoor pollutant, as the gas accumulates in poorly ventilated animal housing, which can negatively affect animal health and production. However, outdoor ammonia emissions are increasingly significant, as they can travel long distances, affecting cities as well as farmland.

Pigs crowded in their barn Ammonia can accumulate in poorly ventilated animal housing.

Ammonia particles react with nitrates and sulphates in the atmosphere, emitted through activities such as fossil fuel combustion in transport and industry, to form ammonium salts, a form of harmful PM2.5 which can penetrate deep into the human system and bloodstream. Alone, ammonia can also cause irritation to people’s eyes, nose and throat. High atmospheric concentrations can also lead to environmental damage, including eutrophication of surface waters, and harm to sensitive crops such as tomatoes and cucumbers.

To curb the negative health impact of agriculture’s ammonia emissions, a decrease in fossil fuel combustion from sectors such as transport would reduce the available atmospheric compounds for ammonia to react with in order to form PM2.5, thus having the potential to render increased fertilizer use less harmful to health. However, whilst a reduction in future combustion levels remains uncertain, steps to reduce ammonia emissions from the source include lowering excess protein in animal feed, which lowers levels of nitrogen in the animal’s waste, and careful use of nitrogen in fertilizers.

Greenhouse gases

Agriculture also contributes significantly to greenhouse gas emissions, with meat production providing the bulk of these within the industry. One source estimates that agriculture, forestry and other land-use make up 24% of the global total of GHG emissions, whilst another asserts that livestock alone contributes 18% of this. One well-known agricultural source is the process of enteric fermentation, more commonly known as livestock farts, which produce large amounts of methane (CH4), notoriously from cows. The management of animal manure also produces methane, along with nitrous oxide (N2O).

Cows graze by a wind turbine Cows graze by a wind turbine. Dirk Ingo Franke / CC BY-SA 2.0

Carbon dioxide (CO2) is also a significant product of agriculture, from fossil fuel combustion for processes such as fertilizer production to grow animal feed; maintenance and transportation of refrigerated products; and change of land use, such as deforestation to clear land for farming. CO2 emissions from livestock make up 9% of the global total. Whilst this may seem a relatively small amount, livestock also produces 65% of global N2O emissions, which have 296 times the global warming potential (GWP) of CO2, and 35% of global methane, with 23 times the GWP of CO2. Thus, industrial agriculture as it stands, particularly meat production, poses a serious challenge to humans trying to mitigate the effects of climate change.

Whilst global food demand continues to rise from a growing population, many favouring a meat-centric diet, it becomes increasingly important for the agricultural sector to take responsibility over its pollution. As awareness of their hefty contribution towards both local and global air pollution grows, perhaps the industry will face sufficient pressure to catch up with other industries’ efforts and start reining in its emissions.

In the meantime, if you feel like helping speed along agriculture’s transition to lower emissions, you can help lower demand for heavily-polluting meat production by eating less meat in your diet. Why not check out some of these meat-free recipes and get inspired?

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