VARIATIONS OF AIR QUALITY RADIO-INDICATORS 40K AND 137Cs IN ATMOSPHERIC AEROSOLS IN SEVERAL LOCATIONS IN SPAIN.

Understanding the mechanisms for transport and deposition of pollutants in the atmosphere is essential for the modelling of air quality. Air quality Radio-indicators (or radio-tracers) such as ⁴⁰K and ¹³⁷Cs may be useful to identify and differentiate natural and anthropogenic inputs of pollutants as well as forcing mechanisms (such as dust plumes, nuclear accidents, etc…).  

Spain, due to its proximity to the African continent, is especially affected by African dust plumes which have a remarkable impact on air quality. These events, in addition to large amounts of aerosols, bacteria, virus, seeds, etc.., are usually accompanied by relatively high concentration of ⁴⁰K (t_1/2 = 1.25·10⁹ years) and ¹³⁷Cs, a fission product with a half-live of 30.2 years. The deterioration of the air quality during such events often has large socio-economical and medical implications to the population.

In this work we analyse and discuss the variations of these two radio-indicators in aerosol samples collected at 7 different monitoring stations over a period of 10 years (2009-2018). The monitoring stations were all located in Spain and operated by the Spanish Nuclear Safety Council. These stations were: Tenerife (28º27′18′′N; 16º17′29′′W), Málaga (36º43’40’’N; 4º28’80’’W), Sevilla (37°22′51″N; 5°59′28″O), Cáceres (39°28'36"N; 6°22'06"O), Madrid (40°27′16″N; 3°43′42″W), Barcelona (41°23′12″N; 2°09′50″E) and Bilbao (43°16′07″N; 2°56′16″O).

⁴⁰K and ¹³⁷Cs activity concentrations in atmospheric aerosols were recorded from January 2006 to July 2018. Sampling was carried out weekly using high-flow collectors that operate at about 600 m³/h.  Polypropylene square filters were used to collect atmospheric aerosols. These filters have an efficiency of approximately 96% for the collection of radionuclides.

⁴⁰K activity concentrations were detected between 39% (Tenerife) and 100% (Bilbao and Madrid) of the samples measured. However, ¹³⁷Cs activity concentrations appeared in between 3% (Sevilla) and 19% (Bilbao) of the aerosol samples. The simultaneous detection of both radio-indicators in the monitoring stations located in the south of Spain were mostly linked to African dust plumes.

During the weeks after the Fukushima nuclear power plant accident in 2011, ¹³⁷Cs was detected between 70% (Málaga) and 100% (Madrid, Barcelona and Bilbao) of the samples analyzed. Other fission products such as ¹³¹I and ¹³⁴Cs were also recorded in the same samples during this period.

This work highlights the proper functioning of the Spanish environmental radiological monitoring network but also its usefulness for the study of atmospheric processes impacting air quality such as African dust plumes.

Acknowledgements

This study was supported by the Spanish Nuclear Safety Council (CSN).