Nitrogen dioxide
Air quality NO2
Nitrogen dioxide, NO₂, is an air pollutant mainly associated with combustion. Concentrations can be substantially higher near traffic and other emission sources.
What NO₂ means
The molecule contains one nitrogen and two oxygen atoms. Combustion produces nitrogen oxides; some are emitted as NO₂ or converted to it in the air. Engines, heating, power stations and industry can contribute. NO₂ is not ordinary nitrogen, which makes up most of the air.
Why the road matters
Concentrations near a source can exceed those a few streets away. Traffic, wind direction and ventilation between buildings alter the value. Calm, stable air can restrict dilution.
More than one irritating gas
NO₂ can affect the airways. Nitrogen oxides also contribute to ozone and secondary particle formation. A pollutant does not necessarily disappear without consequences merely because a reaction turns it into something else.
Reading measurements and model values
Concentrations are usually in µg/m³. Every number needs a place and averaging period. An hourly mean cannot be compared directly with an annual mean. Models describe broader conditions, while a roadside station measures its particular setting.