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What is nitrogen pollution?

Why too much of nitrogen is a bad thing.

Nitrogen is in the soil under our feet, in the food we eat, and in our DNA, the building blocks of life. Without it, there would be no life on Earth. Nitrogen helps to make croplands fertile and is a key component of protein, which all living organisms need to grow.

Nitrogen is the most abundant element in our atmosphere. Pure nitrogen must be chemically bonded with other elements, either naturally or artificially, for it to be usable for most organisms.

The discovery a century ago of the Haber-Bosch process that converts nitrogen in the air to ammonia made the manufacture of nitrogen fertilizers possible at an industrial scale and was followed by a spectacular increase in global food production.

Although 78 per cent of the atmosphere is nitrogen, this nitrogen exists almost entirely in a form that is unusable by most organisms.

Atmospheric nitrogen can be made usable or ‘reactive’ through natural processes, like nitrogen fixation by legumes, such as soybeans, or artificially through industrial processes.

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Today, nitrogen pollution is one of the most pressing pollution issues facing humanity, threatening our environment, health, climate and ecosystems.

But too much of this reactive nitrogen is being lost to the environment. It is polluting water and air, degrading soils, causing toxic algal blooms and creating (dead zones) in the ocean.

Each year, 200 million tonnes of reactive nitrogen – 80 per cent of the total – is lost to the environment.

It leaches into soil, rivers and lakes and is emitted to the air. In some forms, nitrogen contributes to ozone depletion and climate change.

Humans are responsible for producing most reactive nitrogen that ends up as pollution, yet the full scale of the problem remains largely unknown outside scientific circles.

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There has been limited public discussion about the need to take action to #BeatNitrogenPollution to mitigate climate change. But it's an issue we cannot afford to ignore. If we don't limit nitrogen pollution now, we will face a cascade of negative impacts that jeopardise the environment, the economy, our well-being and livelihoods -- from degraded ecosystems to polluted soil, water and air, and species loss.

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The Science

How did we get here – and what can we do about it?

First the science.

In its pure form, nitrogen is not usable for humans, animals and plants. In its reactive forms however, it becomes accessible and creates impacts at each stage of the nitrogen cycle, moving through the air into the soil and living organisms.

Molecular nitrogen (N2) is made up of two nitrogen atoms tightly bound together. The strong triple bond between the atoms makes it extremely stable and chemically unreactive.

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The Natural Nitrogen Cycle

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By producing fertilizer or ammonia, humans have interfered with the natural nitrogen cycle.

Click below to find out more

This cycle starts with nitrogen fixation - when atmospheric nitrogen, or pure nitrogen, is converted into nitrates which plants use to make proteins that are needed for their healthy growth. In nature, nitrogen fixation is done through lightning and nitrogen-fixing bacteria.

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A small amount of nitrogen fixation can occur naturally through lightning which carries enough electrical energy to break apart N2 molecules, freeing up nitrogen atoms to react with oxygen to produce nitrates.

These seep into the soil in raindrops, providing plants with a form of nitrogen they can absorb via their roots. But most nitrogen fixation in nature occurs through bacteria found in soil and water, or on the roots of legumes, such as beans and peas.

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Animals eat plants, getting their nitrogen from plant proteins. They pass some of it back into the soil as manure or waste by releasing nitrogen in the form of ammonium. Nitrogen is released in the form of ammonium, which is then converted into nitrates by certain types of bacteria – a process called nitrification.

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Denitrification is the last step in the nitrogen cycle. It occurs when nitrogen is restored by bacteria into its pure form and released into the air.

Until a century ago, natural processes of nitrification and denitrification were fairly balanced. But today this balance has been lost, largely a result of human activity, with serious consequences for our planet.

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Human Impact

Humanity’s interference in Earth’s nitrogen balance

Humanity’s knowledge and understanding of nitrogen has improved rapidly over time. We have learned, for instance, how to extract nitrogen from the air and combine it with other elements such as oxygen, hydrogen and carbon into various reactive forms. These compounds were subsequently harnessed for use in industrial and agricultural activities.

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In the early 20th century, two German chemists – Fritz Haber and Carl Bosch – developed a way of converting nitrogen (N2) and hydrogen (H2) into ammonia (NH3), using high heat and pressure. Their discovery spurred the mass production of nitrogen-based fertilizers, helping to boost crop yields and sustain an expanding world population.

The Haber-Bosch process revolutionized farming globally, but it also marked the start of humanity’s long-term interference with Earth’s nitrogen balance.

The amount of reactive nitrogen produced by humans is now greater than the amount created through natural processes. Humans have doubled the rates of nitrogen fixation.

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The Haber-Bosch process revolutionized farming globally, but it also marked the start of humanity’s long-term interference with Earth’s nitrogen balance. The amount of reactive nitrogen produced by humans is now greater than the amount created through natural processes. Humans doubled the rates of nitrogen fixation.

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Nitrogen pollution contributes to the triple planetary crisis of climate change, nature and biodiversity loss, and pollution and waste.

Today, about 80 per cent of reactive nitrogen – estimated to be worth US$200 billion – is lost to the environment every year.

It is therefore critical that governments accelerate actions and legislation to significantly reduce nitrogen waste globally by 2030 and promote sustainable nitrogen management. This could lead to billions of dollars in savings, while benefiting the environment, biodiversity and human health.

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It is therefore critical that governments accelerate actions and legislation to significantly reduce nitrogen waste globally by 2030 and promote sustainable nitrogen management. This could lead to billions of dollars in savings, while benefiting the environment, biodiversity and human health.

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Drivers of Nitrogen Pollution

What are the biggest drivers of nitrogen pollution today?

One of the main drivers of nitrogen pollution has been the rising consumption of nitrogen-based fertilizer, which doubled between 1978 and 2014 globally.

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In Asia alone, this doubling happened in just 27 years, between 1987 and 2014. Today, almost half of the world's population relies on fertilizers for food production.

Nitrogen pollution is also the byproduct of burning fossil fuels to meet growing demands in the agriculture, transport, industry and energy sectors.

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Nitrogen pollution is also the byproduct of burning fossil fuels to meet growing demands in the agriculture, transport, industry and energy sectors.

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Nitrous oxide (N2O) from industry and combustion is a greenhouse gas, 300 times more powerful than carbon dioxide and has been proven to deplete the ozone layer.

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Livestock waste, also contributes to nitrogen pollution. The livestock sector currently emits 65 teragrams (Tg) of nitrogen per year, equivalent to one-third of current human-induced nitrogen emissions. Of that amount, 68 percent is associated with feed production.

Some 50 percent of industrially produced nitrogen is applied to three major cereals:

18 percent

WHEAT

16 percent

MAIZE

16 percent

RICE

These cereals provide the bulk of human food consumed either directly as grain or indirectly through livestock products.

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Wildfires and the burning of forests can also increase emissions of nitrogen oxide (NO), a harmful component of smog, and nitrous oxide (N2O), a potent greenhouse gas, known collectively as NOx.

Wildfire emissions of NOx account for approximately 15 percent of global NOx emissions.

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Forms of Nitrogen

Investigate about the different forms of pollution.

Different forms of reactive nitrogen in the environment

To learn more about the different forms of reactive nitrogen in the environment, click on the white circles.

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Impacts

Impact of nitrogen pollution

Industrial and agricultural activities have more than doubled the amount of reactive nitrogen in the environment, impacting water bodies, biodiversity and humans everywhere.

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Climate change and the ozone layer

When it comes to tackling climate change, most of the world's attention has focused on reducing carbon dioxide emissions - yet nitrous oxide is 300 times more potent. In the past four decades, nitrous oxide emissions have risen by 30 percent.

With an atmospheric lifetime of up to 200 years, nitrous oxide poses a much more long-term threat than other forms of pollutants.

Nitrous oxide is now the dominant ozone-depleting substance emitted through human activities.

Air

Nitrogen oxides are a group of air polluting chemical compounds, including nitrogen dioxide and nitric oxide. They are generated from coal power plants, factory emissions and vehicle exhausts. At high concentrations they can lead to smog - and ground-level ozone.

Reactive emissions can mix with rain to create nitric acid rain, which can damage buildings and sink into the soil harming plants and other living organisms.

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Biodiversity and ecosystems

Together with habitat destruction and climate change, nitrogen pollution is one of the biggest drivers of biodiversity loss on the planet today.

According to a recent study, ecosystems such forests, heaths and surface waters are more sensitive to atmospheric nitrogen pollution than previously thought.

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Land and soil

When nitrogen is deposited on terrestrial ecosystems, a cascade of effects can occur, often resulting in biodiversity declines.

Excess nitrogen causes nitrogen-tolerant species to thrive and outcompete more sensitive wild plants, fungi and aquatic species. It can cause the inadvertent fertilization of trees and grasslands affecting growth rates and nutrient imbalances, which harm ecosystems and biodiversity.

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Water

Excess nitrogen in soil that plants cannot absorb leach into groundwater, contaminating it. This results in the rapid growth of algae which block sunlight to aquatic plants causing them to die. In the decomposition process the plants rob the water of oxygen and the lake, river or stream becomes ultimately lifeless. This eutrophication causes widespread shifts in species and biodiversity loss.

Nitrogen pollution especially impacts in the marine and coastal environments, where excess nitrogen can lead to algae blooms and oceanic dead zones, that are growing both in scale and frequency.

Human health

An estimated 77 per cent of people breathe annual average concentrations of nitrogen dioxide beyond safe levels. Agricultural ammonia emissions combined with pollution from vehicle exhausts can create extremely dangerous particulates in the air, which can exacerbate respiratory diseases. There is also growing evidence of a connection between reactive nitrogen in air and several types of cancer.

Nitrates from wastewater and agricultural sources can also threaten drinking-water quality.

One of the first links between reactive nitrogen and human health was found with high levels of nitrate in drinking water in the 1940s. Infants whose formula was mixed with water containing high concentrations of nitrate had a high risk of developing methemoglobinemia, known as “blue baby syndrome”.

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Food production

Nitrogen is a major growth factor in food production and it therefore plays an important role in global food security.

Long-term application of ammonium-based fertilizers causes soil to become acidic, negatively affecting crop production.

50 per cent of nitrogen fertilizers added to farm fields ends up as pollution. Through denitrification some is turned back to N2.

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Mobilizing a global drive to beat nitrogen pollution

Since it is not nitrogen per se but excessive reactive nitrogen that is a threat, we must urgently improve our management of the nitrogen cycle to avoid inefficiencies and waste.

Political momentum for collective action on nitrogen is increasing. The United Nations Environment Programme (UNEP), the leading environmental authority in the United Nations system, is convening stakeholders to tackle nitrogen pollution globally.

In March 2019, the United Nations Environment Assembly - the world's foremost environmental decision-making body - adopted a resolution calling for sustainable nitrogen management. In March 2022, the Environment Assembly adopted a second resolution on the topic.

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Stakeholder Actions

What actions can be taken?

Sustainable nitrogen management is needed to live in harmony with nature on a planet that is pollution-free and climate-stable. It is essential to achieving the Sustainable Development Goals and securing a cleaner, healthier environment for future generations.

What can governments do?

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Accelerate actions to support the Global Biodiversity Framework Target 7 by reducing excess nutrients lost to the environment by at least half, including through more efficient nutrient recycling and use.

Share information on existing national action plans where available.

Improve reporting and data collection capacity to identify nitrogen pollution and address its sources.

What can the private sector do?

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The agricultural industry could:

Ensure proper disposal of animal waste.

Avoid unnecessary waste of food production.

Improve nutrient management in crop production and in the livestock sector.

Invest in the recovery of nutrients from wastewater and livestock waste to use as fertilizers, closing the circle and promoting the efficient use of fertilizers.

Harness ecological processes to manage soil fertility (for example, through crop rotation) and use methods such as no-till farming to limit the disturbance of natural habitats and processes.

Replace conventional agriculture with agroforestry and agro-ecological practices such as mixed farming to support biodiversity.

The fertilizer industry could:

Improve the recovery of nutrients from wastewater and livestock waste to reuse as fertilizers.

The livestock industry could:

Adapt protein in livestock diets to reduce nitrogen losses through waste.

Invest in air-cleaning systems on pig and cattle farms to tackle nitrogen emissions.

What can banking institutions do?

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Sign up to the 2019 Principles for Responsible Banking; and the 2012; and the 2006 Principles for Responsible Investment.

Recognise sustainability as a strategic priority.

Invest in agro-ecological systems and nature-based solutions.

What can industrial and small-scale farmers do?

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Embrace sustainable agriculture techniques that emulate nature to preserve soil fertility, prevent pollution and protect biodiversity.

Improve nutrient management in crop production and in the livestock sector.

Invest in the recovery of nutrients from wastewater and livestock waste to use as fertilizers, closing the circle and promoting efficient use of fertilizers.

What can the public do?

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Advocate for the reduction of nitrogen pollution.

Alter dietary choices to reduce consumption of meat, dairy and eggs, which would lower ammonia and nitrogen emissions.

Avoid food waste.

Reducing reactive nitrogen would prevent millions of premature deaths, avert debilitating illness, contribute to food security, while helping to protect wildlife and the ozone layer. There is no single solution to reducing nitrogen pollution. But everyone can play a part in stopping it from poisoning our lakes, rivers, air and soil.

Date Published: 28 Sept, 2023

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Every act to #BeatNitrogenPollution big or small matters. Join us today.

Resources

Reports

UNEP Frontiers Report 2018/19Chapter 4: The Nitrogen Fix: From Nitrogen Cycle Pollution to Nitrogen Circular Economy

Reactive Nitrogen in the Environment: Too Much or Too Little of a Good Thing

UNEP Year Book 2014: Emerging Issues in Our Global Environment

Further Resources

Why nitrogen management is key for climate change mitigation

Why South Asia needs to tackle a surge in nitrogen pollution

5 dangerous pollutants you're breathing in every day

Three ways we can better use nitrogen in farming

Nutrient management: the issue Fertilizers: challenges and solutions
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