Radon: Units of Measure
A becquerel is a measure of radioactivity. One becquerel (Bq) is equal to one radioactive decay per second.
Radon concentrations in air are usually measured in becquerels per cubic meter (Bq/m3). That’s the amount of radon (becquerels) in a volume of air (cubic metre).
Worldwide, the average radon concentration in outdoor air is around 10 Bq/m3.
Some countries still use older units of picocuries per litre (pCi/L). 10 Bq/m3 = 0.27 pCi/L.
Potential Alpha Energy Concentration
In some circumstances, it’s more important to measure the level of radon progeny instead of the radon itself, specifically the Potential Alpha Energy Concentration (PAEC). This is the sum of the alpha particle decay energy of all the short-lived progeny of radon in a volume of air. The SI unit is joule per cubic metre (J m-3).
Historically, PAEC was measured in units of Working Levels (WL).
If radon progeny are in equilibrium with radon-222 (which is rarely the case):
10 Bq/m3 (radon-222) = 0.27 pCi/L (radon-222) = 5.56 x 10-8 J m-3 (PAEC) = 0.0027 WL (PAEC)
Quotes from ICRP Publications