What Is Nitrogen Dioxide?
The EPA describes nitrogen dioxide, NO2, as one of a group of highly reactive gases known as nitrogen oxides, and uses it as the indicator for that larger group. It says NO2 gets into the air mainly from burning fuel, forming from emissions from cars, trucks and buses, power plants and off-road equipment.
Gas appliances matter indoors. On its indoor air page, the EPA says that in homes with gas stoves, kerosene heaters or unvented gas space heaters, indoor NO2 levels often exceed outdoor levels. It says breathing air with a high concentration of NO2 can irritate airways, that short exposures can aggravate respiratory diseases, particularly asthma, and that longer exposures to elevated concentrations may contribute to the development of asthma and potentially increase susceptibility to respiratory infections.
Outdoor air has federal limits. On April 6, 2018, the EPA decided to retain its national ambient air quality standards for nitrogen oxides, a 1-hour standard of 100 parts per billion and an annual standard of 53 parts per billion.
Sources checked September 15, 2026. Every point below links the page it came from.
The sources behind this answer
- Government sourceThe EPA describes nitrogen dioxide as one of a group of highly reactive gases known as nitrogen oxides, and uses NO2 as the indicator for that larger group. US EPA ↗
- Government sourceThe EPA says NO2 primarily gets in the air from burning fuel, forming from emissions from cars, trucks and buses, power plants and off-road equipment. US EPA ↗
- Government sourceThe EPA says high concentrations of NO2 can irritate airways, short exposures can aggravate respiratory diseases such as asthma, and longer exposures may contribute to asthma and increase susceptibility to respiratory infections. US EPA ↗
- Government sourceThe EPA says that in homes with gas stoves, kerosene heaters or unvented gas space heaters, indoor NO2 levels often exceed outdoor levels. US EPA ↗
- Regulatory filingOn April 6, 2018, the EPA retained its national ambient air quality standards for nitrogen oxides, a 1-hour standard of 100 ppb and an annual standard of 53 ppb. US EPA ↗
Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.