Validation of aerosol low-level activities by comparison with a deep underground laboratory

•LARA laboratory in Barcelona validated measurements of 40K and 137Cs in air filters.•Validation by an exchange programme with an underground laboratory.•Baselines activities of 40K and 137Cs in Barcelona air of 2005–2010 are presented.

The activities on air filters of the radionuclides 40K and 137Cs were measured in an above ground laboratory and compared with the activities measured in an underground laboratory. The average relative differences were lower than 20% for 137Cs and 40K. The temporal series of these radionuclides in the period 2006–2010 are also presented. These results form the baseline of these radionuclides in the studied period, and are particularly interesting because they correspond to the radioactive background in Barcelona before the Fukushima accident.