Jožef Stefan Institute

Jožef Stefan Institute joined EPOS Slovenia in 2016, and it contributes to EPOS ERIC through its National Distributed Centre. 

Contact information

Janja Vaupotič, PhD

Jamova cesta 39, SI-1000 Ljubljana


The main focus of the Jožef Stefan Institute within EPOS Slovenia infrastructure is radon research. Radioactive noble gas radon (222Rn, Rn) originates from the uranium radioactive chain in the Earth’s crust. It emanates from the mineral grains, enters the void space, migrates toward the surface, and eventually exhales into the atmosphere. The level of radon activity concentration in our environment is governed by the three processes mentioned above, which are strongly dependent on the geochemical and geophysical parameters.

Due to its radioactivity, radon is a health hazard and has thus been systematically surveyed in the built environment. It has been recognised as the second leading cause of lung cancer after cigarette smoking. However, for the harmful effects are primarily responsible radon short-lived progeny (RnP: 218Po, 214Pb, 214Bi 214Po) created after the radioactive transformation of Rn,  present ubiquitously in the air. They appear in the air as radioactive 1–10 nm (unattached RnP) and 200–800 nm (attached RnP) aerosol particles. The fraction of the unattached RnP, predominantly governed by the number concentration and size distribution of non-radioactive aerosol particles, plays a crucial role in radon dosimetry.
Rn has unique properties: noble, radioactive, and mobile. It is, therefore, a suitable research tool, used as a tracer for the global and local transport of air masses and thus the transport of pollutants, air movement in karst caves, earthquake occurrence and volcanic eruptions, the identification of active faults, and efficiency of ventilation in buildings.

The EPOS Slovenia infrastructure, based on the new modern devices to monitor several parameters simultaneously and continuously, enables us to perform excellent investigations in the two areas: (i) studying Rn as a health hazard and (ii) the effective research tool.

RI-SI-EPOS project

The radon research at Jožef Stefan Institute within EPOS Slovenia is conducted in two directions (i) radon as a health hazard and (ii) radon as an effective research tool in various research disciplines. 

(i) In the first field, we have been focusing on dwellings and workplaces. The new modern portable monitors are reliable, small and silent, thus not disturbing occupants. They enable us to study several parameters in the indoor air simultaneously.

Recently, we finished two MSc studies. The first, “Optimisation of natural ventilation in a single-family house with high radon concentration”, was focused on two adjacent residential buildings, of which the first was newer and inhabited, with good airtightness of the building envelope, and the second older, unoccupied, with poorer airtightness of the building envelope. In April–December 2021, Rn and CO2 concentrations were monitored continuously in both buildings. By applying simulation of different ventilation scenarios based on measured data, ventilation in a newer building was optimised (Buh, 2022). In the second study, entitled “Risk of radon exposure in elderly care homes”, several premises were selected in three elderly care homes, in which the dynamics of Rn and CO2 in the air were studied as risk factors for health, particularly concerning the location of the building, its construction-technical characteristics and ventilation systems, as well as the specifics of the users. By calculating the effective doses received by exposure to Rn (and its progeny, RnP) in the air, we assessed the impact on the health of employees and residents (Vadnjal, 2022).

(ii) The main requirement for Rn monitors to be successfully used as tracers of air movement in ambient air is a low detection limit. On the other hand, the monitors for very humid karst cave environments must give reliable results. A new EPOS infrastructure guarantees these requirements.

In the MSc study, not finished yet, ventilation influence on Rn and CO2 concentrations have been analysed in a small apartment. A part of this research has already been published; the paper discusses the impact of ventilation on Rn and CO2 concentrations in indoor air. Continuous measurements of Rn and CO2 concentrations, together with basic meteorological parameters, have been carried out in an apartment and outdoor air in Ljubljana. During the experiment, ‘frequent’ ventilation (several times per day), ‘poor’ ventilation (once to twice per day) and ‘no’ ventilation was applied, and the exact type of ventilation and occupancy schedule were recorded. By using transient data analysis with the CONTAM 3.4 program, the impact of ventilation frequency and duration on Rn and CO2 concentrations in indoor air was examined (Dovjak et al., 2022).

Long-term continuous radon monitoring in ambient air is conducted in Ljubljana to study the atmospheric mixing state (‘stability’).

RI-SI-EPOS equipment



DOVJAK, Mateja, VENE, Ožbej, VAUPOTIČ, Janja. Analysis of ventilation efficiency as simultaneous control of radon and carbon dioxide levels in indoor air applying transient modelling. International Journal of Environmental Research and Public Health. [Online ed.]. Febr. 2022, vol. 19, iss. 4, art. 2125, [20] f., ilustr. ISSN 1660 4601.,  DOI: 10.3390/ijerph19042125. [COBISS.SI-ID 97826563]

BUH, Tanja. Optimisation of natural ventilation in a single-family house with high radon concentration: Master Thesis. Nova Gorica: [T. Buh], 2022. XI, 66 str., ilustr. [COBISS.SI-ID 115332611]

VADNJAL, Nina. Tveganje za izpostavljenost radonu v domovih starejših občanov: magistrsko delo = Risk of radon exposure in elderly care homes: Master Thesis. Ljubljana: [N. Vadnjal], 2022. 89 str., [5] str. pril., ilustr. [COBISS.SI- ID 124211971]


FRIDL, Jerneja, ALJANČIČ, Magdalena, RITLOP, Klemen, STOPAR, Bojan, ŠEBELA, Stanka, ŠINIGOJ, Jasna, VAUPOTIČ, Janja, ŠEBELA, Stanka (editor). Končno
 poročilo o zaključku operacije “RI-SI-EPOS”: (sofinancirane iz ESRR). Postojna; Ljubljana: [ZRC SAZU], 2021. 17 str. [COBISS.SI-ID 82069507] 


ŠEBELA, Stanka, COSTA, Giovanni, VAUPOTIČ, Janja, ŽIVČIĆ, Mladen, RAVBAR, Nataša, ALJANČIČ, Magdalena. Postojna Cave as Near Fault Observatory
site in SW Slovenia. In: EGU General Assembly 2020: Online: 4-8 May 2020. [S. l.]: European Geosciences Union, 2020. 2 str.


COSTA,  Giovanni, PAHOR, Jurij, ŠEBELA, Stanka, VAUPOTIČ, Janja, VIČIČ, Blaž, ŽIVČIĆ, Mladen. Postojna Cave as possible Near Fault Observatory mini
site in SW Slovenia = Postojnska jama kot primerna mini lokacija za NFO (observatorij v bližini preloma) v JZ Sloveniji. In: GOSTINČAR, Petra (ed.). Milestones and challenges in karstology: abstracts & guide book, Postojna, 2017 1. izd.  Ljubljana: Založba ZRC, 2017. Str. 19-20. ISBN 978-961-05-0004-9. [COBISS.SI-ID 41747501]