Carbon monoxide (CO)

CAS Number



  • long-lived trace gas
  • colourless, odourless and tasteless

Main sources

  • motorised road transport (incomplete combustion of fuel)
  • wood combustion

Thresholds for the reporting requirement of facilities in accordance with Annex 2 PRTRO

(Ordinance on the Register relating to Pollutant Release and the Transfer of Waste and of Pollutants in Waste Water)

  • Air               500,000 kg/year
  • Water           -
  • Soil               -


  • toxic when inhaled by humans and warm-blooded animals
  • precursor to ozone formation in the upper troposphere
  • contributes to the greenhouse gas effect (greenhouse potential above the potential of carbon dioxide)

Ambient limit values

8 mg/m3 24-h mean value; may be exceeded once per year at most

Status and changes

Carbon monoxide levels no longer pose a direct problem for human health in Switzerland. Health-threatening carbon monoxide emissions reached maximum levels in the mid-1970s. Since then, the emissions have been reduced to less than one-fifth. The limit values under the Ordinance on Air Pollution Control are also met in inner city street canyons. In these areas, carbon monoxide values are highest due to stagnant traffic and poor aeration.

    Last modification 04.07.2018

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