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CO (carbon monoxide)

½ hour measurements.

CO is a toxic gas.

The highest concentrations of CO are found in streets with high traffic density. Here, petrol-driven cars are the main source. CO is continuously measured in streets in connection with the national air monitoring program.

Measure method

Carbon monoxide (CO) is measured by absorption of infrared radiation. The air is drawn into a chamber and illuminated with infrared light. CO effectively absorbs light of a certain wavelength in the infrared range. The concentration of CO can therefore be determined by how much of the infrared light is absorbed in the chamber.

Technical description

CO monitors (API M300):

  • Principle: Gas Filter Wheel IR absorption.
  • Measuring range: 0-10 and 0-25 ppm
  • Lower detection limit: 0.1 ppm
  • Precision: better than ±5%
  • Selectivity: Interference from CO2 and water vapour.
  • Routine checks: Once a day automatic zero-point check with "zero gas" from an internal generator (catalytic combustion of atmospheric CO to CO2).
  • Automatic span check every week with 8 or 20 ppm CO in synthetic air.
  • Calibration at the laboratory: Zero against atmospheric air where CO is oxidized to CO2 by catalytic combustion and absorption CO by "Hopcalite" absorber. Span against dilutions of a standard gas with 1000 ppm CO in N2