Below 53ppb

High levels of Nitrogen Dioxide indoors is the  result of outdoor NO2 entering your indoor  environment as well as combustion sources inside  the home / workplace. According to a study  published in the Environmental Research journal,  short-term exposure can irritate airways while  long-term exposure can lead to chronic illness and  respiratory infections with viruses7. Asthmatics  may also experience longer symptomatic periods  and increased medication use for children.

Examples of sources of nitrogen dioxide:  Automobiles from attached garage or near a busy  street, appliances with defective installations, gas  stoves, kerosene heaters, chimneys, etc.