NO2 absorbs sunlight and forms the yellow-brown haze you can see over many cities with high levels of industry. Nitrogen dioxide is extremely volatile and reactive, interacting readily with interior surfaces and furnishings. After interaction, the rate of decay of the gas is dependent on temperature, relative humidity, and the area and materials involved in the reaction process.

Indoor sources for both gases may result from unvented fuel burning appliances (such as kerosene space heaters or gas stoves), back drafting heating appliances, or tobacco smoking. Also, automobiles and industrial furnaces produce high levels of both gases, so residency near an industrial plant or highway may result in nitrogen dioxide exposure.

Exposure to either gas results in high irritation of the skin, eyes, and mucous membranes. If concentrations of the gases are high enough, they may cause throat irritation and a burning cough. Both gases are also involved in bodily functions such as blood clotting and the control of blood pressure, so overexposure may affect balance in either of the aforementioned functions. Nitric oxide also impedes the flow of oxygen to body tissue, and at high concentrations has many of the same harmful effects of carbon monoxide. Nitrogen dioxide, even in low levels, can cause lung irritation and changes in sensory perception. Studies in the medical community have shown that long term exposure to NO2 puts the subject at higher risks of respiratory illness, especially in children. However, these studies have not, as of now, been officially confirmed.

No exposure guidelines are set for nitric oxide since once it is released into the air it quickly oxidizes into nitrogen dioxide. For nitrogen dioxide, the following  acceptable exposure level in residential indoor air is suggested to be:

For short-term exposure (ASTER): 0.25 ppm (parts per million) - one hour average exposure, or less than or equal to 480 micro-grams per cubic metre - one hour average exposure.

For long-term exposure (ALTER): 0.05 ppm (parts per million) or 100 micro-grams per cubic metre.

Nitrogen dioxide exposure can be prevented by making sure all fuel burning home appliances are properly vented, and if necessary provided with adequate combustion and make-up air. Another solution is a balanced, mechanical ventilation system, which works to solve problems with most indoor air pollutants. The ventilation system will help remove both forms of gas and aid in preventing any possible toxic buildup.