1. What is Nitrogen Dioxide (NO₂)?

Nitrogen dioxide (NO₂) is one of the nitrogen oxides (NO_x), a group of air pollutants produced from combustion processes.

In urban outdoor air, the presence of NO₂ is mainly due to traffic. Nitric oxide (NO), which is emitted by motor vehicles or other combustion processes, combines with oxygen in the atmosphere, producing NO2. Indoor NO2 is produced mainly by unvented heaters and gas stoves.

NO₂ and other nitrogen oxides are also precursors for a number of harmful secondary air pollutants such as ozone and particulate matter, and play a role in the formation of acid rain. Exposure to NO2 may affect health independently of any effects of other pollutants. However, because its presence is closely linked to the formation or presence of other air pollutants, it is difficult to establish the health effects attributable to NO2 alone. More...