Nitrogen dioxide is a reddish-brown gas with a strong, unpleasant odor that causes eyes, nose and throat irritation, impairs lung function, and increases respiratory infections at high concentrations.
There is evidence that high concentrations or continued exposure to low levels of NO2 increases the risk of respiratory infection. There is also evidence from animal studies that repeated exposures to elevated nitrogen dioxide levels may lead, or contribute, to the development of lung disease such as emphysema.
People at particular risk from exposure to nitrogen dioxide include children and individuals with asthma and other respiratory diseases.
The primary sources of NO2 indoors are combustion processes, such as:
Average NO2 levels in homes without gas appliances are about half that of outdoors. In homes with gas stoves, kerosene heaters or unvented gas space heaters, indoor levels often exceed outdoor levels.
No standards have been agreed upon for NO2 in indoor air. ASHRAE and the US EPA National Ambient Air Quality Standards list 0.053 parts per million (ppm) as the average annual limit for NO2 in outdoor air.
Venting the NO2 sources to the outdoors and assuring gas appliances are correctly installed, used, and maintained are the most effective measures to reduce exposures.