Outdoor radon

Radon is formed during the decay of uranium-238, which is present in all soils and rocks. Via pores, fissures and cracks, it is released from soils and rocks.

About one thousandth of the available radon is transferred from the soil or, respectively, the soil air, into the ground-level air. "Ground-level" defines a height of up to 1.5 metres.

Outdoor radon near the soil

In the ground-level air radon mixes very quickly with the ambient air, generally occurring in low concentrations.

How much radon can be released from the subsoil?

The so-called radon exhalation rate indicates how much radon can be released from the subsoil. It quantifies the radioactivity per surface unit and per time unit and depends on how much radon is formed in the ground and how permeable the soil is for radon. In Germany, typical radon exhalation rates for natural grounds range from 0.01 to 0.03 becquerel per square metre and per second.

In Germany, low radon concentrations ranging between 3 and 31 becquerel per cubic metre air were measured in 1.5 metres above the ground at 173 measuring stations. The mean radon concentrations were around 9 becquerel per cubic metre air.

Inhaling radon outdoors leads to a relatively low radiation dose of 0.1 millisievert per year, which is part of the natural radiation exposure and unavoidable.

Radon concentration outdoors depends on region and weather conditions

How much radon is released from the subsoil is also influenced by weather conditions: The outdoor radon exhalation drops with

• Precipitation,
• snow cover,
• ground frost, and
• rising air pressure

and rises with

• high wind and
• high air temperatures.

Weather conditions determine the mixing of the air and thus influence the radon concentration outdoors. This may lead to distinct diurnal and seasonal fluctuations.

The outdoor radon concentration is also regionally different and depends on

• the radon occurrence in the ground,
• the distance from larger sea areas,
• different weather conditions as well as
• the respective local terrain.

In Northern Germany, for example, the influence of the low-radon sea air leads to lower radon levels than in more continental southern Germany.

Human influence on the outdoor radon concentration

In addition to the natural factors governing outdoor radon concentration, human influence may also cause changes in outdoor radon concentration. Typically, this has occurred through mining activities.

Where does radon occur outdoors in Germany?

In Germany, the outdoor radon concentration varies. The Federal Office for Radiation Protection (BfS) has measured the outdoor radon concentration throughout Germany and developed the outdoor-radon map for Germany.