Factors controlling temporal variability of near-ground atmospheric <sup>222</sup>Rn concentration over central Europe

Abstract

Abstract. Concentration of radon (222Rn) in the near-ground atmosphere has been measured quasi-continuously from January 2005 to December 2009 at two continental sites in Europe: Heidelberg (south-west Germany) and Krakow (southern Poland). The atmosphere was sampled at ca. 30 and 20 m above the local ground. Both stations were equipped with identical instruments. Regular observations of 222Rn were supplemented by measurements of surface fluxes of this gas in the Krakow urban area, using two different approaches. The measured concentrations of 222Rn varied at both sites in a wide range, from less than 2.0 Bq m−3 to approximately 40 Bq m−3 in Krakow and 35 Bq m−3 in Heidelberg. The mean 222Rn content in Krakow, when averaged over the entire observation period, was 30% higher than in Heidelberg (5.86 ± 0.09 and 4.50 ± 0.07 Bq m−3, respectively). Distinct seasonality of 222Rn signal is visible in the obtained time series of 222Rn concentration, with higher values recorded generally during late summer and autumn. The surface 222Rn fluxes measured in Krakow also revealed a distinct seasonality, with broad maximum observed during summer and early autumn and minimum during the winter. When averaged over a 5-year observation period, the night-time surface 222Rn flux was equal to 46.8 ± 2.4 Bq m−2 h−1. Although the atmospheric 222Rn levels at Heidelberg and Krakow appeared to be controlled primarily by local factors, it was possible to evaluate the "continental effect" in atmospheric 222Rn content between both sites, related to gradual build-up of 222Rn concentration in the air masses travelling between Heidelberg and Krakow. The mean value of this build-up was equal to 0.78 ± 0.12 Bq m−3. The measured minimum 222Rn concentrations at both sites and the difference between them was interpreted in the framework of a simple box model coupled with HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) analysis of air mass trajectories. The best fit of experimental data was obtained for the mean 222Rn flux over the European continent equal to 52 Bq m−2 h−1, the mean transport velocity of the air masses within the convective mixed layer of the planetary boundary layer (PBL) on their route from the Atlantic coast to Heidelberg and Krakow equal to 3.5 m s−1, the mean rate constant of 222Rn removal across the top of the PBL equal to the 222Rn decay constant and the mean height of the convective mixed layer equal to 1600 m.

Investigation of the atmospheric boundary layer depth variability and its impact on the 222Rn concentration at a rural site in France

“…In general, during night, strength of the turbulent mixing decreases due to the removal of underlying heat sources. However, since the NBL was frequently lower than 180 m deep, the rapid nocturnal buildup of 222 Rn was not evident in our measurements at 180 m but usually observed at other sites, illustrating the accumulation of 222 Rn in the near‐ground atmosphere during the night [e.g., Zimnoch et al ., ]. Using trace gas measurements (e.g., CO and CO 2 ) on the TRN tower, Schmidt et al .…”

Outdoor 222Rn behaviour in different areas of Slovakia

“…These parameters have a major infl uence on radon behaviour in the atmosphere. This was confi rmed by the measurements carried out by various authors who showed that radon time series are different in urban, suburban and rural environments [7,8].…”

Analysis of ground‐based 222Rn measurements over Spain: Filling the gap in southwestern Europe

“…In addition, a harmonization of the experimental techniques applied for the measurements of atmospheric 222 Rn concentrations and 222 Rn fluxes is needed as suggested by the International Atomic Energy Agency [ International Atomic Energy Agency , ]. European long‐term 222 Rn monitoring stations, in agreement with the published literature, are presented in Figure with black labels [e.g., Chevillard et al ., ; Hatakka et al ., ; Taguchi et al ., ; Belviso et al ., ; Pitari et al ., ; Zimnoch et al ., ; Chambers et al ., ], and the lack of stations over the Mediterranean Basin is noticeable.…”

“…[]. The main aim of this collaboration is to extend the monitoring of atmospheric 222 Rn concentrations carried out in Europe by other research institutes [e.g., Levin et al ., ; Szegvary et al ., ; Belviso et al ., ; Zimnoch et al ., ] offering high‐quality data to the scientific community and working to fill the lack of harmonized 222 Rn data. Three stations: Gredos (GIC3), Delta de l'Ebre (DEC3), and Huelva (UHU), violet filled circles in Figure , are already operative and have been running continuously since December 2012, September 2013, and April 2014, respectively.…”

“…In the first part of the present study the performance of the ARMON detector was evaluated against that of a 222 Rn progeny monitor [e.g., Levin et al ., ] routinely operating in Krakow, Poland [ Zimnoch et al ., ], under a range of high ambient temperature and relative humidity conditions. The short comparison exercise was conducted at two different stations: the Kasprowy Wierch mountain station located in Poland (Figure , KW blue label, black rectangle) and the Delta de l'Ebre coastal station situated in Catalonia, Spain (Figure , DEC3 violet label, black rectangle).…”