Nitrogen dioxide is a highly reactive gas formed by emissions from motor vehicles, industry, unflued gas-heaters and gas stove tops. High concentrations can be found especially near busy roads and indoors where unflued gas-heaters are in use.

Other indoor sources can be from cigarette smoke or from cooking with gas. Outdoors, nitrogen dioxide contributes to the formation of ground-level ozone (O3) as well as particulate matter pollution. Nitrogen dioxide is a respiratory irritant and has a variety of adverse health effects on the respiratory system.

• Increased susceptibility to lung infections in people with asthma
• Increased susceptibility to asthma triggers like pollen and exercise
• Worsened symptoms of asthma – more frequent asthma attacks
• Airway inflammation in healthy people
  

To learn more, visit our section ‘Who is affected by air pollution’ and ‘Simple steps to protect your health’.For further information on unflued gas heaters, please see our section on air quality factsheets.