Nitrogen Oxide

What is Nitrogen Oxide?

The term “nitrogen oxide” refers to a combination of gases made up of oxygen and nitrogen. The two most common nitrogen oxide (NOx) gases are known as nitrogen monoxide (NO) and nitrogen dioxide (NO2). Nitrogen monoxide is also commonly known as nitric oxide. These two gases are both harmful to human health, and the environment so it is important that we recognize these dangers and do all we can to minimize our nitrogen oxide emissions. Nitrogen oxides also play an important role in the production of other harmful pollutants when they react with other gases in the atmosphere such as ground-level ozone, smog, and acidic rain.


Ontario Nitrogen Oxides Emissions by Sector – 2012 Estimates

Image and Data from the Government of Ontario as posted on June 7, 2019 (

What are the Sources of Nitrogen Oxide?

Nitrogen is all around us and is normally relatively un-reactive in the atmosphere. Nitrogen will only react with oxygen when put under specific conditions to form nitrogen oxides such as nitrogen monoxide, and nitrogen dioxide. The most common method that causes nitrogen and oxygen to react and form nitrogen oxides is by combusting fuel, a process where fuel is burned at high temperatures. As can been seen in Figure 1, our everyday activities such as burning fuel for transportation, or using electricity in our homes produced by burning coal or oil, or in power plants, are all activities that directly or indirectly cause the production of nitrogen oxide emissions.

What are the Health Effects of Nitrogen Oxides?

Small levels of nitrogen oxides can irritate the eyes and/or nose, cause nausea, may cause fluid to form in the lungs, and cause shortness of breath. Exposure to high levels of nitrogen oxides can lead to rapid, burning spasms, cause the throat to swell, reduce oxygen intake, cause a larger build-up of fluids in the lungs, and sometimes even death. Many scientific studies have found a relationship between high levels of nitrogen oxides and sulphur dioxide and increased sickness and premature death from cardiac and respiratory disorders.

Since nitrogen oxides are also associated with ground level ozone, and particulate matter, health affects for these other pollutants should also be observed. For more information about the health effects of ground level ozone and particulate matter, please refer to Factsheet # 1 and Factsheet #2 respectively.

What are the Environmental Effects of Nitrogen Oxide?

The main environmental concern regarding nitrogen oxides is when they combine with sulphur dioxide (SO2) to form acid rain. Acid rain forms when nitric and sulphuric acid reacts with water droplets to form a rain cloud. The precipitation that comes out of this rain cloud will be high in acidity. When acid rain continually falls on the same location, the soil and bodies of water surrounding this area slowly become more acidic as well. This changes the living conditions for many plants and animals living on both the land and in the water. Some plants and animals are not able to adapt to these increased acidic conditions and die. Acid rain also affects infrastructures by corroding cars, buildings, and historical monuments. This costs cities millions of dollars in damages every year!

As mentioned above, nitrogen oxides are associated with ground level ozone, and particulate matter. The environmental impacts of these other pollutants should also be observed. For more information about the environmental effects of ground level ozone and particulate matter, please refer to Factsheet # 1 and Factsheet #2 respectively.

Nitrous Oxide and Climate Change

Nitrous oxide (N2O) is another combination of nitrogen and oxide that the term nitrogen oxide encompasses. Nitrous oxide is know to contribute to climate change. Although the concentration of nitrous oxide (N2O) is lower than the concentration of carbon dioixde (CO2), research shows that the effects of nitrous oxide is 300 times greater!

Did you Know?

According to the Ontario Ministry of the Environment June 2005 Transboundary Air Pollution in Ontario Report, transboundary air pollution contributes to over 2700 premature deaths a year in Ontario, puts approximately 12 000 people in hospitals and causes over $5 billion in damage to the province’s people, economy, and environment.

What is being Done?

Hamilton has a number of air monitors that monitor the air quality including levels of nitrogen oxides in the air.

Since the majority of Hamilton’s nitrogen oxide emissions come from transportation, the City has developed a Transportation Master Plan to develop a transportation network which includes transit, cycling, and walking facilities. The City also hosts annual events to promote alternative modes of transportation such as Commuter Challenge Week.

In Ontario, from 2006-2015 nitrogen oxide emissions decreased by 38%1 and nitrogen dioxide concentrates decreased by 32%. In Hamilton, from 1998-2017 nitrogen dioxide decreased by 54%.

How Can you Help?

Knowing that the most nitrogen oxide emissions are being caused by our everyday activities such as transportation and energy, we can start by reducing our reliance on cars and chose alternative forms of active transportation such as walking, or biking. Hamilton has many walking trails and bike lanes that can be used. In addition, we can all make an effort to conserve energy at home, and at work by doing simple things such as turning of the lights when leaving the room, or setting our computers to automatically go to sleep after a set time.

REDUCE YOUR OWN EMISSIONS: Practice energy conservation and investigate emissions-free energy, such as solar power. Use public transportation, car pool, walk, rollerblade or cycle. If you do drive, keep your car well-maintained.


1Air Quality in Ontario 2015 Report, Ministry of the Environment and Climate Change, The Province of Ontario   (