What is “Nitrogen Dioxide” (NO2)?
The source document for this Digest states: As for PM and O3, the evidence on NO2 and health comes from different sources of information, including observational epidemiology, controlled human exposures to pollutants and animal toxicology. The observational data are derived from studies outdoors where NO2 is one component of the complex mixture of different pollutants found in ambient air and from studies of NO2 exposure indoors where its sources include unvented combustion appliances. Interpretation of evidence on NO2 exposures outdoors is complicated by the fact that in most urban locations, the nitrogen oxides that yield NO2 are emitted primarily by motor vehicles, making it a strong indicator of vehicle emissions (including other unmeasured pollutants emitted by these sources). NO2 (and other nitrogen oxides) is also a precursor for a number of harmful secondary air pollutants, including nitric acid, the nitrate part of secondary inorganic aerosols and photo oxidants (including ozo
