Nitrous Oxide: Air Pollutant Or Not?

Nitrous oxide (N2O) is a greenhouse gas with significant anthropogenic sources contributing to its worldwide abundance. It is a climate threat due to its role in depleting the ozone layer and its heat-trapping power, which is 265 times that of carbon dioxide. In 2022, nitrous oxide accounted for 6% of all US greenhouse gas emissions from human activities, with agriculture, fuel combustion, wastewater management, and industrial processes being the primary sources. While nitrous oxide is a concern, it is important to note that other pollutants, such as nitrogen dioxide (NO2), also contribute to air pollution and have harmful effects on human health.

Nitrous oxide is a greenhouse gas

Nitrous oxide (N2O) is a greenhouse gas with a significant human-induced contribution to its worldwide abundance. It is emitted from a range of human activities, including agriculture, fuel combustion, wastewater management, and industrial processes. In 2022, nitrous oxide accounted for 6% of all US greenhouse gas emissions from human activities.

Nitrous oxide has about 300 times the heat-trapping power of carbon dioxide and can remain in the atmosphere for an average of 114 to 121 years. Its impact on warming the atmosphere is substantial, with one pound of N2O having 265 times the impact of one pound of carbon dioxide. This makes it a potent climate pollutant, despite not being included in the Montreal Protocol, an international treaty aimed at restoring the ozone layer.

Agriculture is a major source of nitrous oxide emissions, with microbes in fertilized soils and animal manure contributing significantly. The application of synthetic and organic fertilizers, the management of manure, and the burning of agricultural residues are all part of agricultural soil management, which was the largest source of N2O emissions in 2022. Forest and grassland fires, as well as the application of synthetic nitrogen fertilizers to urban soils, also contribute to emissions.

Fuel combustion is another significant source of nitrous oxide emissions. The burning of fuels, such as fossil fuels like coal, oil, methane gas, and diesel, releases nitrous oxide. The amount emitted depends on the type of fuel, combustion technology, maintenance, and operating practices. Transportation, including vehicles, aircraft, and power plants, contributes to these emissions.

Wastewater management and industrial processes also generate nitrous oxide. The treatment of domestic wastewater during nitrification and denitrification processes releases nitrous oxide. Additionally, it is produced as a byproduct during the manufacturing of certain chemicals, such as nitric acid for fertilizers, and adipic acid for synthetic products like nylon.

It is a product of human activity

Nitrous oxide (N2O) is a greenhouse gas with significant anthropogenic sources contributing to its worldwide abundance. In 2022, it accounted for 6% of all US greenhouse gas emissions from human activities. Globally, 40% of total N2O emissions come from human activities.

Human activities such as agriculture, fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere. Agriculture is the largest source of N2O emissions. It is emitted from agricultural soil management activities, such as the application of synthetic and organic fertilizers, other cropping practices, the management of manure, or the burning of agricultural residues.

N2O is also emitted when fuels are burned, although the amount depends on the type of fuel and combustion technology used. It is produced as a byproduct of chemical production, such as nitric acid (used for fertilizer) or adipic acid (used to make nylon and other synthetic products).

The treatment of domestic wastewater can also generate nitrous oxide. During nitrification and denitrification processes, N2O is typically produced from the nitrogen present in the form of urea, ammonia, and proteins.

In addition to the above, forest and grassland fires, and the application of synthetic nitrogen fertilizers to urban soils (e.g. lawns, golf courses) also contribute to N2O emissions.

It is emitted during fuel combustion

Nitrous oxide (N2O) is a greenhouse gas that is emitted during fuel combustion. It is formed from nitrogen-containing species by nitric oxide (NO) reacting with a radical derived from either hydrogen cyanide (HCN) or ammonia (NH3). The amount of N2O emitted depends on the type of fuel, combustion technology, maintenance, and operating practices. Fluidized bed coal combustors, for example, yield N2O levels of around 50ppm in their off-gases. The gas-phase reactions of N2O in flames are typically very reactive and are quickly destroyed before being emitted. The removal of N2O is most efficient at high temperatures and in fuel-rich systems with a high relative presence of free hydrogen atoms.

N2O is also produced during the combustion of fossil fuels and solid waste, as well as through the treatment of wastewater. The combustion of fuels such as coal, natural gas, and oil contributes to carbon dioxide emissions, which, along with methane, are significant contributors to the global climate crisis. However, N2O should not be overlooked as it is a potent greenhouse gas with around 300 times the heat-trapping power of carbon dioxide. It absorbs radiation and traps heat in the atmosphere, where it remains for an average of 114 years.

The primary outdoor source of nitrogen dioxide (NO2), another nitrogen oxide, is road traffic. Cars, trucks, buses, power plants, and off-road equipment emit NO2 during the burning of fuel. While NO2 is the indicator for the larger group of nitrogen oxides, it is a highly reactive gas that can irritate the airways in the human respiratory system. Exposure to high concentrations of NO2 can aggravate respiratory diseases, especially asthma, leading to coughing, wheezing, and difficulty breathing.

In addition to its direct release, indoor combustion sources of NO2 also emit ultrafine particles, which are co-pollutants produced during cooking. High NO2 concentrations are associated with the use of candles, mosquito coils, and incense burning. Tobacco smoke and the burning of gas, wood, oil, kerosene, and coal for appliances such as stoves, ovens, and heaters are also significant indoor sources of NO2. While N2O is not included in the Montreal Protocol, its role in depleting the ozone layer is recognized, and it is subject to intense research due to its increasing atmospheric concentrations.

It is a primary air pollutant

Nitrous oxide (N2O) is a primary air pollutant and a greenhouse gas with significant anthropogenic sources contributing to its worldwide abundance. It has around 300 times the heat-trapping power of carbon dioxide and stays in the atmosphere for an average of 114 to 121 years. The majority of nitrous oxide comes from agriculture, including microbes in fertilised soils, the application of synthetic and organic fertilisers, and animal manure. It is also emitted when fuels are burned, although the amount varies depending on the type of fuel and combustion technology used.

In 2022, nitrous oxide accounted for 6% of all U.S. greenhouse gas emissions from human activities. Globally, 40% of total nitrous oxide emissions come from human activities, with the largest source being agricultural soil management. Other sources include transportation, industry, and wastewater management.

Nitrous oxide emissions in the United States decreased by 3% between 1990 and 2022, with mobile combustion emissions decreasing by 56% due to criteria pollutant emission standards for on-road vehicles. However, emissions from agricultural soils have remained relatively constant during this period.

While nitrous oxide is a significant contributor to air pollution and climate change, it is not the only problem. Carbon dioxide emissions, for example, represent a massive and intractable challenge in the context of the global climate crisis. Nevertheless, nitrous oxide's potent heat-trapping ability and long atmospheric lifespan make it a critical target for emissions reduction efforts.

It has adverse health effects

Nitrous oxide (N2O) is a greenhouse gas with significant anthropogenic sources contributing to its worldwide abundance. It is emitted from a range of human activities, including agriculture, fuel combustion, wastewater management, and industrial processes. These activities increase the amount of N2O in the atmosphere, leading to various adverse health effects.

One of the primary concerns associated with nitrous oxide is its impact on the respiratory system. High concentrations of N2O in the air can irritate the airways and aggravate respiratory diseases, particularly asthma. Prolonged exposure to elevated levels of N2O may even contribute to the development of asthma and increase susceptibility to respiratory infections. People with existing respiratory conditions, such as asthma, are more vulnerable to the harmful effects of this pollutant.

The health risks of nitrous oxide go beyond respiratory issues. According to studies, exposure to high levels of N2O can lead to a range of health problems, including respiratory ailments, hematologic side effects, metabolic disorders, low blood pressure, nausea, vomiting, and diarrhoea. The impact of N2O on the climate and the environment also has indirect health consequences. As a potent greenhouse gas, N2O contributes to global warming and climate change, which pose significant risks to human health and well-being.

In addition to its direct health effects, nitrous oxide also plays a role in the formation of other harmful pollutants. N2O is involved in the chemical reactions that lead to the production of ozone, a highly reactive secondary pollutant. Ozone, at high concentrations, can cause damage to vegetation and have further implications for human health.

While nitrous oxide has a shorter atmospheric lifetime compared to other greenhouse gases like carbon dioxide, it still remains in the atmosphere for an average of 114 to 121 years. During this time, it absorbs radiation and traps heat, contributing to the overall warming of the planet. This prolonged presence of N2O in the atmosphere exacerbates the climate crisis and increases the likelihood of heat-related health issues, such as heat exhaustion and heatstroke.

Frequently asked questions