Nitrous Oxide

Nitrous Oxide (N₂O) is the third most important individual greenhouse gas. Nitrous oxide is approximately 310 times more effective in trapping heat than carbon dioxide on a molecule for molecule basis, and has an atmospheric lifetime of about 114 years. Carbon dioxide has an atmospheric lifetime of 2 to 200 years, depending on sources and sinks, while methane has an atmospheric lifetime of around 14 years.

Even though nitrous oxide is measured in parts per billion (ppb) and would thus appear to have less of a potential impact on climate than carbon dioxide or methane, its long atmospheric lifetime and heat trapping properties mean that it needs to be seriously considered.

The natural nitrous oxide cycle

Nitrogen is removed from the atmosphere by plants and converted into forms such as ammonia, which can then be used by the plants. This is called nitrogen fixation. At the same time, micro-organisms remove nitrogen from the soil and put it back into the atmosphere - denitrification - and this process produces nitrous oxide. Nitrous oxide also enters the atmosphere from the ocean.

Fertilising

This photograph shows the back of a fertiliser. It is spraying fertiliser over the ground. This helps the crops grow better.

Irish Farmers' Journal

Fertilising
Irish Farmers' Journal

Fertilising

This photograph shows the back of a fertiliser. It is spraying fertiliser over the ground. This helps the crops grow better.

Irish Farmers' Journal

Enlarge image

The impact of human activities

Globally, anthropogenic nitrous oxide emissions are primarily from fertiliser use in agriculture. Land use change also contributes to nitrous oxide emissions. Sewage treatment plants may also be a source of this gas.

Since pre-industrial times (1750), the atmospheric nitrous oxide concentration has increased from 270 ppb (parts per billion) to 333.2 ppb in 2020, an increase of over 20% since pre-industrial values.

Due to the long time it spends in the atmosphere, the nitrous oxide that we release today will still be trapping heat well into the next century.