How is nitrogen dioxide (NO2) measured?
Nitrogen dioxide is commonly measured using automatic analysers that run 24 hours a day. The main measuring method is to use a chemiluminescence continuous analyser (chemiluminescence means the emission of light as a result of a chemical reaction). Air is drawn into the analyser where nitrogen monoxide (NO) is made to react with ozone, to give nitrogen dioxide in a reaction that generates light: Nitrogen monoxide + ozone » nitrogen dioxide + oxygen + light emission. This method doesn’t actually measure nitrogen dioxide but calculates the airborne levels of nitrogen monoxide and total oxides of nitrogen (NOx), and then subtracts one reading from the other. The final results are expressed in parts per billion (ppb) or micrograms per cubic metre of air, this is written as µg m-3. Nitrogen dioxide is also measured using diffusion tubes. For more information on this please go to the diffusion tube page.
