An Introduction to Indoor Air Quality: Nitrogen Dioxide (NO2)??

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.


Definition

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 - epa.gov/iris/subst/0080.htm

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).

1) Keep gas appliances properly adjusted.
2) Consider purchasing a vented space heater when replacing an un-vented one.
3) Use proper fuel in kerosene space heaters.
4) Install and use an exhaust fan vented to outdoors over gas stoves.
5) Open flues when fireplaces are in use.
6) Choose properly sized wood stoves that are certified to meet EPA emission
standards. Make certain that doors on all wood stoves fit tightly.
7) Have a trained professional inspect, clean, and tune-up central heating system
(furnaces, flues, and chimneys) annually. Repair any leaks promptly.
8) 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.