Investigating the vertical and spatial extent of radon-based classification of the atmospheric mixing state and impacts on seasonal urban air quality.

A recently-developed radon-based method for combined classification of both diurnal and synoptic timescale changes in the atmospheric mixing state is applied to 1-year of observations in Ljubljana (capital of Slovenia). Five diurnal-timescale mixing classes (#1 to #5) were defined for each season along with an additional mixing class (#6) in non-summer months, representative of synoptic-timescale changes of the atmospheric mixing state associated with "persistent temperature inversion" (PTI) events. Seasonal composite radiosonde profiles and mean sea level pressure charts within each mixing class are used to demonstrate the link between prevailing synoptic conditions and the local mixing state, which drives changes in urban air quality. Diurnal cycles of selected pollutants (BC, NO2, CO, PM10, SO2 and O3) exhibited substantial seasonality as a result of changing mixing conditions, source types and strengths. For the more well-mixed conditions (classes #2 to #3), surface wind speeds were 3 times higher than during class #6 (PTI) conditions, resulting in a 3-fold reduction of primary pollutant accumulation. Daily-mean PM10 concentrations only exceeded EU and WHO guideline values in winter and autumn for two of the radon-defined mixing classes: (i) class #5 (strongly stable near-surface conditions associated with passing synoptic anti-cyclone systems), and (ii) class #6 (PTI conditions driven by regional subsidence in the presence of the "Siberian High"). Both mixing states were associated with low mean wind speeds (∼0-0.7 m s-1) and strong thermal stratification, as indicated both by pseudo-vertical temperature gradients (∆T/∆z) and radiosonde profiles. Diurnal ∆T/∆z values indicated limited opportunity for convective mixing of pollutants from the basin atmosphere under these conditions. The demonstrated consistency in atmospheric mixing conditions (vertically and spatially) across the diurnal cycle within each of the defined mixing classes suggests the radon-based classification scheme used in conjunction with 3-D urban sensor networks could be well suited to evaluate mitigation schemes for urban pollution and urban climate.

EFFECTIVE DOSES DUE TO OUTDOOR AND INDOOR RADON AT A MEDITERRANEAN SITE.

A year-long continuous measurement of the radon activity concentration in the outdoor air at a Mediterranean site has shown a range of 2-144 Bq m-3 and annual mean of 18 ± 14 Bq m-3. Seasonal means were: 15 ± 10 Bq m-3 in winter, 15 ± 12 Bq m-3 in spring, 22 ± 19 Bq m-3 in summer and 17 ± 12 Bq m-3 in autumn. In summer, the average radon activity concentration in the daytime (6-22 h) was 15.2 Bq m-3 and in the night-time (22-6 h) 33.4 Bq m-3. The annual effective dose was 1.83 mSv, with 1.66 mSv from indoor and 0.17 mSv (9%) from outdoor radon. The related doses for the summertime were (mSv): 0.29, 0.24 and 0.05 (18%).

Radon-based atmospheric stability classification in contrasting sub-Alpine and sub-Mediterranean environments.

A recently-developed radon-based technique is used to investigate relative changes in summertime atmospheric stability at two sites in Slovenia with contrasting geographical settings. Although atmospheric stability for both sites (50 km apart) was shown to be governed by similar synoptic conditions, their contrasting settings caused differences in mixing conditions for each stability category. At the urban sub-Alpine site Ljubljana, situated within a topographic basin, wind speeds associated with the most stable conditions were 0.2-0.3 m s-1. By comparison, corresponding wind speeds for the near-coastal sub-Mediterranean site Ajdovscina, located at the foothills of the Trnovski gozd barrier, were 0-0.2 m s-1. The wind direction at Ljubljana under stable conditions (∼80°) was consistent with drainage flow into the basin along the Sava River valley. The corresponding wind direction at Ajdovscina was 20-40°, consistent with gentle katabatic drainage from the flanks of the Trnovski gozd barrier. After removing fetch effects on radon variability at each site, a large contrast in local contributions to the radon signal was noted: the diurnal amplitude of the local radon signal increased from ∼24 Bq m-3 at Ljubljana to ∼47 Bq m-3 at Ajdovscina. This difference was attributed to a greater nocturnal radon accumulation rate at Ajdovscina (3.5 Bq m-3 h-1 vs 2.1 Bq m-3 h-1) due to higher radon fluxes from flysch and carbonate rocks compared to the sea and lake sediments in the Ljubljana Basin. The ability of radon to consistently distinguish subtle changes in atmospheric mixing at sites with contrasting topographic settings indicates that it will be a powerful tool for characterising air quality in these complex environments. Specifically, diurnal radon cycles indicate that the capability of the atmosphere to dilute primary pollutants is considerably less in the basin environment.

OCCUPATIONAL EXPOSURE ASSESSMENT AT A THERAPEUTIC RADON SPA FACILITY IN HUNGARY.

In order to estimate occupational exposure of workers in a therapeutic radon spa facility, radon concentration in the workplace air was investigated at Markhot Ferenc Hospital, Eger, Hungary. The investigated balneotherapeutic facility and its natural hot spa water are used for treatments and rehabilitations of rheumatic patients. Radon concentration, radon decay products at a bathhouse, treatment rooms and a consultation room were continuously measured in August and September 2018. In the present study, different levels of radon concentration among the observation sites and its clear temporal variations were found, though radon concentrations in the investigated sites were below 300 Bq m-3. Regarding such radon fluctuation and low equilibrium factor level (0.1), the annual effective doses of workers are estimated to be around 0.5 mSv year-1.

Radon in soil gas in Kosovo.

An assessment of the radiological situation due to exposure to radon and gamma emitting radionuclides was conducted in southern Kosovo. This study deals with sources of radon in soil gas. A long-term study of radon concentrations in the soil gas was carried out using the SSNTDs (CR-39) at 21 different locations in the Sharr-Korabi zone. The detectors were exposed for an extended period of time, including at least three seasonal periods in a year and the sampling locations were chosen with respect to lithology. In order to determine the concentration of the natural radioactive elements 238U and 226Ra, as a precursor of 222Rn, soil samples were collected from each measuring point from a depth of 0.8 m, and measured by gamma spectrometry. The levels (Bq kg-1) of naturally occurring radionuclides and levels (kBq m-3) of radon in soil gas obtained at a depth 0.8 m of soil were: 21-53 for 226Ra, 22-160 for 238U and 0.295-32 for 222Rn. With respect to lithology, the highest value for 238U and 226Ra were found in limestone and the highest value for 222Rn was found in metamorphic rocks. In addition, the results showed seasonal variations of the measured soil gas radon concentrations with maximum concentration in the spring months.