Which nitrogen oxides contribute to air pollution?

Nitrogen oxides, collectively referred to as NOₓ, are a group of gases that significantly contribute to air pollution. Among these, nitrogen dioxide (NO₂) is of primary concern and is frequently used as an indicator for the broader group of nitrogen oxides.12

These pollutants are primarily formed during the combustion of fossil fuels when high temperatures cause atmospheric nitrogen to react with oxygen. Major sources include stationary facilities like power plants and mobile sources such as gasoline engines.12

The environmental and health impacts of these nitrogen oxides include:

• Photochemical Smog: Nitrogen dioxide plays a key role in the formation of photochemical smog, a reddish-brown haze created by sunlight-promoted reactions in the lower atmosphere that can cause respiratory irritation and exacerbate asthma.12
• Acid Rain: Nitrogen oxides react in the atmosphere to form nitric acid, which contributes to acid rain and the acidification of ecosystems.123
• Eutrophication: The deposition of nitrogen from NOₓ emissions can lead to the over-enrichment of water bodies, causing harmful algal blooms that deplete oxygen and threaten aquatic life.3