T. Iida

Modeling radon flux density from the earth's surface

In order to make the idealized model for predicting soil radon flux more practically and accurately, two central variables (radon emanation power and soil water content) controlling the amount of radon transportation in soil were formulated. The reformulated model for predicting radon flux density was verified by the field measurements carried out in 10 different sites. The result indicates that the reformulated model is useful for improving the prediction feasibility and accuracy of radon flux density from the earths surface.

A case study of radon-222 transport from continental North-East Asia to the Japanese islands in winter by numerical analysis

A case study of the regional transport ( approximately 3000 km) of radon-222 ((222)Rn) from continental North-East Asia to the Japanese islands was performed by numerical analysis using five separate source areas (South, Middle and North China, Russia and Korea), while a seasonal northwest wind blew over the Japan Sea. The results for three periods (Term I: 16-18, Term II: 22-25 and Term III: 27-28 in December 1990) were compared with concentrations measured at the Kanazawa site (near the coast of the Japan Sea facing the seasonal wind) and the Nagoya site (overland and downwind on the shores of the Pacific Ocean). Most of the (222)Rn at the Kanazawa site was calculated to come from North China and Korea in Term I, Middle China, North China, and Korea in Term II, and Russia and Korea in Term III. The considerable differences in the origins of (222)Rn emanated from the continent were estimated between Terms I, II and III, even though the similar northwest wind was dominant over the Japan Sea. A contour line analysis indicated movement of (222)Rn emanated from Middle China in a northerly direction first and then a southeasterly direction, resulting from low pressure. The results suggest that the low-pressure systems play an important role in the transport of (222)Rn in North-East Asia.

The diurnal change in the vertical distribution of atmospheric 222Rn due to the growth and rise of the stable stratification height in the atmospheric boundary layer

Publisher Summary This chapter analyzes the time-change of 222 Rn vertical distribution in the atmospheric boundary layer, 222 Rn was continuously measured at 3 different heights—30, 150 and 520 m—within a 6-km radius. The air temperature was synchronously observed at 4 different heights—1, 33, 160 and 520 m—at the same site and then the vertical distribution of temperature lapse rates calculated from these measurements. The time-change of 222 Rn vertical distribution could be attributed to the time-change of the vertical distribution of the temperature lapse rate. On the basis of this relationship, the mechanism of 222 Rn vertical mixing has been generalized as a mixing model in the atmospheric boundary layer. The chapter concludes with discussion that the periodic changes of the time-change of 222 Rn vertical distribution and the vertical distribution of temperature lapse rate are the diurnal change and an annual change.

A study of atmospheric radon transport as a tracer of pollutants over the Japan Sea

Publisher Summary This chapter evaluates the ratio of air mass transport quantitatively using radon as a tracer, for Oki and Tonghae. It was found that the contribution of transport from the surface of the continent of China to the surface of Japan reaches 40% under winter monsoon conditions in Japan. In this chapter, some results were presented only for Oki and Tonghae. A similar analysis for Nagoya and Oki was also made. However, 222 Rn concentrations measured at Nagoya are strongly affected by local sources that override the variations in the continental component. This makes the correlation coefficient between Nagoya and Oki much poorer than that between Tonghae and Oki. It was found that diurnal variations were clearer at Tonghae than Oki. By comparing the baseline trends, that are day-to-day trends of daily minima at these two stations, pollutants in the continental air mass were found to be diluted to 40% during their transport over the Sea of Japan in the winter season.

A new method for supplying low radon air by using a hollow fiber module

Publisher Summary This chapter develops a new technique for supplying air with low radon concentration by applying the method of membrane permeation using a hollow fiber module. This method is applicable to reduce high radon levels in indoor air. Two hollow fiber set-ups were tested: a MERASILOX-S module made of silicon rubber membrane and a MHF module made of thin segment polyurethane membrane. If radon containing air is forced through these filters, output air may have an up to 40% reduced radon concentration. These results suggest that it is possible, with the application of this technology, to substantially reduce radon concentrations indoors. The dilution ratios obtained by these experiments agree well with the ratios calculated by modeling radon permeation through a membrane. Following this evaluation of the MHF module radon removal capacity from air, it is estimated that the radon concentration in a 50 m 3 room, as elevated as 1000 Bqm −3 , could be reduced below about 20 Bqm −3 using a hollow fiber module of moderate dimensions.