Nitrogen Oxides, commonly called NOx, are a group of gaseous compounds, all of which contain nitrogen and oxygen in varying amounts. The most common two are nitric oxide (NO) and nitrogen dioxide (NO2). Outdoors, NOx combines with volatile organic compounds (VOCs) to form ozone and smog1. Both NO and NO2 are common in outdoor air, which influences indoor concentrations. About 40% of the changes in indoor NOx concentrations are caused by changes in outdoor concentrations1. In addition, NOx has common indoor sources that strongly influence indoor concentrations2.
How does NOx get in my home?NOx products are formed during combustion reactions. Although the majority of these products are formed outdoors by motor vehicles (Figure 1), these compounds can be formed by combustion reactions indoors. Some examples of indoor NOx emission sources are1:
Exposure to NOx has been shown to cause varying levels of symptoms, depending on the level of exposure. NOx exposure can be particulary harmful to people with asthma, as it may trigger an asthma attack8. If you suspect you have been exposed to harmful amounts of NOx please contact a health care provider immediately.
At low concentrations, NOx has been shown to cause:1
At high concentrations, NOx has been shown to cause:4
Equipment to measure NOx is available, but is typically too expensive and difficult to use for the general public. Homes that are located near busy roadways or coal burning power plants often have higher levels of NOx 1. Smoking tobacco, burning natural gas, kerosene, or wood inside the home increases concentrations of NOx1. Avoiding sources of indoor NOx is often the best way to limit indoor concentrations. Some simple recommendations to reduce exposure include not smoking tobacco inside, limiting the use of gas or kerosene powered space heaters and stoves, and limiting the use of wood burning fireplaces. To limit indoor concentrations, ventilate devices that create NOx directly to the outside.
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