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.  The primary sources indoors are combustion processes, such as unvented combustion appliances

Nitrogen Dioxide (NO2)

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.  The primary sources indoors are combustion processes, such as unvented combustion appliances, e.g. gas stoves, vented appliances with defective installations, welding, and tobacco smoke.



Properties:  A red-brown gas or yellow liquid; becomes colorless solid at -11.2oC, which exists in varying equilibrium with other oxides of nitrogen as the temperature is varied.  A component of automotive exhaust fumes.  M.p. (liquid) -9.3oC; b.p. (gas) 21oC.  Noncombustible.  Derivation: By oxidation of nitric acid, an intermediate stage in the oxidation of ammonia to nitric acid.  Hazard:  Highly toxic; inhalation may be fatal.  Tolerance, 5 ppm in air.  Can react strongly with reducing materials.
Source:  "The Condensed Chemical Dictionary," 9th ed., revised by Gessner G. Hawley, Van Nostrand Reinhold Co., NY, 1977.

Sources of Nitrogen Dioxide

Kerosene heaters, un-vented gas stoves and heaters. Environmental tobacco smoke.

Health Effects Associated with Nitrogen Dioxide

Eye, nose, and throat irritation. May cause impaired lung function and increased respiratory infections in young children.  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 and increased risk of respiratory infections, especially in young children.

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.

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.

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.

Additional Resources

Office of Air and Radiation page - " NOx - How Nitrogen Oxides Affect the Way We Live and Breathe"

Maine's Department of Environmental Protection's BEAM Chemical Fact Sheet on Nitrogen Dioxide exiting epa

What You Should Know About Combustion Appliances and Indoor Air Pollution

Answers commonly-asked questions about the effect of combustion appliances (e.g., fuel-burning furnaces, space heaters, kitchen ranges, and fireplaces) on indoor air quality and human health. Describes other sources of combustion pollutants in and around the home. Suggests ways to reduce exposure to such pollutants and encourages proper installation, use, and maintenance of combustion appliances. This brochure was coauthored with the U.S. Consumer Product Safety Commission and the American Lung Association.  [EPA 400-F-91-100, 1993]

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. Addresses the health problems that may be caused by contaminants encountered daily in the home and office. Organized according to pollutant or pollutant groups such as environmental tobacco smoke, VOCs, biological pollutants, and sick building syndrome, this booklet lists key signs and symptoms from exposure to these pollutants, provides a diagnostic checklist and quick reference summary, and includes suggestions for remedial action. Also includes references for information contained in each section. This booklet was coauthored with the American Lung Association, the American Medical Association, and the U.S. Consumer Product Safety Commission.  [EPA 402-R-94-007, 1994]