Radioactivity in the air (trace measurements)

The Environmental Radioactivity Section (URA) operates six high-volume (HV) aerosol collectors for measuring aerosol-bound
radioactivity in outdoor air.

The air filters are changed weekly and then measured in the laboratory using gamma spectrometry (HPGe). The diagrams below show the measured values of the last few months in micro-becquerels per cubic metre (µBq/m3).

This data on airborne radioactivity is also displayed on the radioactivity portal and can be found as a map on The raw data can be obtained from (information on the data format see under "Documents" below). The metadata are found at and

Beryllium-7 in ground-level air

Beryllium-7 (Be-7) is naturally formed in the upper troposphere and in the stratosphere. Concentrations in ground-level air vary between 1'000 and 8'000 micro-Becquerels per m3 (µBq/m3). Concentrations are higher in summer with an average of 4'500 µBq/m3 than in winter with an average of 2'500 µBq/m3.

Cäsium-137 in ground-level air

Traces of caesium-137 (Cs-137) with values of up to a few µBq/m3 are often found in the HV filter samples. These are resuspensions (stirring up) of old deposits on the soils (e.g. Chernobyl deposits). The detection limit for Cs-137 is typically 0.2 µBq/m3. Values below the detection limit are not shown in the diagram.

Jod-131 in ground-level air

Sometimes traces of up to a few µBq/m3 of J-131 can be detected. These usually originate from the production or combustion of J-131 used for medical applications.

High-volume aerosol sampler

Since 1993, the URA Section has operated a network of high-volume aerosol collectors. Currently, six stations are in operation:

  • HV-POS: Posieux / FR
  • HV-CAD: Cadenazzo / TI
  • HV-GUT: Güttingen / TG
  • HV-CERN: Meyrin / GE
  • HV-KLI: Klingnau / AG
  • HV-LBF: Liebefeld / BE

These devices collect the aerosol particle of the outdoor air on filters of the dimension 40 cm x 40 cm with a flow rate of about 600 m3 air per hour. The filters are changed weekly and analysed in the URA laboratory for 1-2 days on gamma spectrometers (HPGe). Thanks to the large air flow rate, smallest traces of radioactive elements can be detected, as low as one millionth of the immission limit value. For example, in connection with an incident involving the burnup of a caesium source at the Spanish steelworks in Algeciras at the end of May 1998, and also in connection with the events at the Fukushima nuclear power plant in Japan in March 2011, a slight increase in radioactivity was detected by the high-volume sampler dispositivs. Radiologically, these events were not relevant in Switzerland. Similar samplers are also in operation in many other European countries, and these laboratories inform each other in the event of increased readings.

Detectable radionuclides

The largest activities originate from natural beryllium-7. Traces of artificial caesium-137 (a few micro-Bq/m3) indicate that soil dust was stirred up, which still contains caesium-137 from the reactor accident in Chernobyl. Soil dust also contains the natural potassium-40. Sometimes traces of artificial iodine-131 are visible, which was released into the air by burning waste from hospitals. Cobalt-60, another artificial radioisotope, would indicate emissions (e.g.) from nuclear power plants.
Details on the limit values can be found here: Grenzwerte (in German)

Last modification 02.09.2021

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Federal Office of Public Health FOPH
Division of Radiological Protection
Ambient Radioactivity Section
Schwarzenburgstrasse 157
3003 Berne
Tel. +41 58 462 96 14
Fax-Nr +41 58 462 83 83

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