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Indoor Air Quality (IAQ)

Nitrogen Dioxide's Impact on Indoor Air Quality

The two most prevalent oxides of nitrogen are nitrogen dioxide (NO2) and nitric oxide (NO). Both are toxic gases with NO2 being a highly reactive oxidant and corrosive.

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Sources of Nitrogen Dioxide

The primary sources indoors are combustion processes, such as:

  • unvented combustion appliances, e.g. gas stoves
  • vented appliances with defective installations
  • welding
  • tobacco smoke
  • kerosene heaters.

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Health Effects Associated with Nitrogen Dioxide

EPA's Integrated Risk Information System Profile for Nitrogen Dioxide.

  • NO2 acts mainly as an irritant affecting the mucosa of the eyes, nose, throat and respiratory tract.
  • Extremely high-dose exposure (as in a building fire) to NO2 may result in pulmonary edema and diffuse lung injury.
  • Continued exposure to high NO2 levels can contribute to the development of acute or chronic bronchitis.
  • Low level NO2 exposure may cause:
    • increased bronchial reactivity in some asthmatics
    • decreased lung function in patients with chronic obstructive pulmonary disease
    • increased risk of respiratory infections, especially in young children

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Levels in Homes

Average level in homes without combustion appliances is about half that of outdoors. In homes with gas stoves, kerosene heaters or un-vented gas space heaters, indoor levels often exceed outdoor levels.

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Steps to Reduce Exposure

Venting the NO2 sources to the outdoors, and assuring that combustion appliances are correctly installed, used and maintained are the most effective measures to reduce exposures.

(These are the same steps as those used to reduce exposure to carbon monoxide).

  • Keep gas appliances properly adjusted.
  • Consider purchasing a vented space heater when replacing an un-vented one.
  • Use proper fuel in kerosene space heaters.
  • Install and use an exhaust fan vented to outdoors over gas stoves.
  • Open flues when fireplaces are in use.
  • Choose properly sized wood stoves that are certified to meet EPA emission standards. Make certain that doors on all wood stoves fit tightly.
  • Have a trained professional inspect, clean and tune-up central heating system (furnaces, flues and chimneys) annually. Repair any leaks promptly.
  • Do not idle the car inside garage.

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Standards or Guidelines

No standards have been agreed upon for nitrogen oxides in indoor air. ASHRAE and the US. EPA National Ambient Air Quality Standards list 0.053 ppm as the average 24-hour limit for NO2 in outdoor air.

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Additional Resources

Nitrogen Dioxide "Six Common Pollutants" from the Office of Air and Radiation

Indoor Air Pollution: An Introduction for Health Professionals
Assists health professionals (especially the primary care physician) in diagnosis of patient symptoms that could be related to an indoor air pollution problem.

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