text: Radon concentration in the atmosphere is usually measured in becquerels per cubic meter (Bq/m), which is an SI derived unit. As a frame of reference, typical domestic exposures are about 100 Bq/m indoors and 10–20 Bq/m outdoors. In the US, radon concentrations are often measured in picocuries per liter (pCi/L), with 1 pCi/L = 37 Bq/m.
  The mining industry traditionally measures exposure using the working level (WL) index, and the cumulative exposure in working level months (WLM): 1 WL equals any combination of short-lived  progeny (, , , and ) in 1 liter of air that releases 1.3 × 10 MeV of potential alpha energy; one WL is equivalent to 2.08 × 10 joules per cubic meter of air (J/m). The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m). One WLM is equivalent to 3.6 × 10 J·h/m. An exposure to 1 WL for 1 working month (170 hours) equals 1 WLM cumulative exposure.
  A cumulative exposure of 1 WLM is roughly equivalent to living one year in an atmosphere with a radon concentration of 230 Bq/m.
  The radon () released into the air decays to  and other radioisotopes. The levels of  can be measured. The rate of deposition of this radioisotope is dependent on the weather.