CO concentration is commonly measured in which unit?

CO concentration is commonly measured in which unit?

• A. Parts per Million
• B. Pulses per Minute
• C. Parts per Hundred
• D. Percent

Answer: (A)

Carbon monoxide concentration in air is commonly expressed in parts per million. This unit is used because CO is present in only tiny amounts in typical environments, so expressing it as a fraction of a million air molecules makes readings precise and practical. A reading might be, for example, a few dozen or a few hundred ppm, which is much more informative for ambient air than a percent or any rate. Pulses per minute is a rate, not a concentration, so it doesn’t describe how much CO is present. Parts per hundred is a percent, which would be too coarse for the low levels at which CO is meaningful in most building environments. Percent would imply whole-number percentages and miss the finer distinctions that ppm provides, which is why the standard choice is parts per million.

Carbon monoxide concentration in air is commonly expressed in parts per million. This unit is used because CO is present in only tiny amounts in typical environments, so expressing it as a fraction of a million air molecules makes readings precise and practical. A reading might be, for example, a few dozen or a few hundred ppm, which is much more informative for ambient air than a percent or any rate.

Pulses per minute is a rate, not a concentration, so it doesn’t describe how much CO is present. Parts per hundred is a percent, which would be too coarse for the low levels at which CO is meaningful in most building environments. Percent would imply whole-number percentages and miss the finer distinctions that ppm provides, which is why the standard choice is parts per million.