Development of a Compact and Sensitive Electrostatic Radon-222 Measuring System for Use in Atmospheric Observation

Abstract

A new automated 222 Rn measuring system suitable for a wide range of atmospheric observations has been developed. This system comprises a 222 Rn analyzer and an air-sampling unit, along with a pump, drying equipment, and a filter. The operation of this 222 Rn analyzer is based on an electrostatic collection method involving the use of a PIN photodiode to separately detect a particles emitted from 218 Po and 214 Po released from the decay of 222 Rn in a hemispheric air-sample chamber. The response of the 222 Rn analyzer with respect to the applied voltage, chamber volume size, and sample flow rate is investigated to determine the appropriate measuring conditions. With this instrument, the detection limits have improved to 0.16-0.20 Bq m À3 for 1 h. The new 222 Rn analyzer shows several technical advancements over the previous electrostatic collection methods, such as an improved detection limit, higher sensitivity, higher time-resolution analysis, and longer life. During the preliminary observational test, the 222 Rn measuring system was able to detect the diurnal cycle in 222 Rn resulting from the mixing of rapid vertical air in the surface boundary layer. At the Minamitorishima station located far from the continent, very small 222 Rn peaks were clearly detected when long-range transport of polluted air masses from the Asian continent was observed at the station. We demonstrate that our compact 222 Rn measuring system has the potential to be widely used for high time-resolution measurements of low-level 222 Rn.

Characterising terrestrial influences on Antarctic air masses using Radon-222 measurements at King George Island

“…However, for short integration times (e.g. 1 h), the detection limit can be high (160-200 mBq m −3 ; Wada et al, 2010). The direct two-filter dual-flow-loop technique reported in this study is unique with regard to its broad applicability to weather/fetch conditions and its very low detection limit at hourly temporal resolution (see Sect.…”

Evaluation of anthropogenic emissions of carbon monoxide in East Asia derived from the observations of atmospheric radon-222 over the western North Pacific

“…Wada et al (2011) showed that the combustion-related enhancement ratio of CO to CO 2 observed at these sites depended on the emission ratio of CO to CO 2 in East Asia. In addition, Wada et al (2010) demonstrated that the enhanced 222 Rn peaks observed at MNM showed a high correlation with synoptic scale variation of CO observed simultaneously at this station. These results indicated that the emission ratios of the trace gases emitted from East Asia are conserved in the enhancement ratios reflected at these sites.…”

“…The 222 Rn analyzer used in this study was developed by AIST and MRI (Wada et al, 2010) for precise measurements of atmospheric 222 Rn. It is based on the electrostatic collection method that collects positively charged progenies of 222 Rn in the sampling air on the light sensitive photodiode (PIN photodiode) for an alpha particle detector charged high negative voltage.…”

“…Our current sampling method is a commonly used one for greenhouse gas observation, and is described in Wada et al ( , 2010. Air is sampled at the top of a 10 m observational tower.…”

“…The National Institute of Advanced Industrial Science and Technology (AIST) and the Meteorological Research Institute (MRI) have developed a high precision 222 Rn measuring system (Wada et al, 2010) and used it to measure atmospheric concentration of 222 Rn on the ground for more than three years at remote sites in the western North Pacific. In addition, the Japan Meteorological Agency (JMA) has been simultaneously measuring atmospheric concentrations of trace gases such as carbon monoxide (CO), carbon dioxide (CO 2 ), methane (CH 4 ), and ozone (O 3 ) at the same sites for more than a decade (Tsutsumi et al, 2006;Wada et al, 2007Wada et al, , 2011.…”