![]() Most recently, continuous measurement of radon was achieved by combining a commercial radon-in-air analyzer RAD7 (Durridge, Inc., USA) with a water/gas exchanger (RAD AQUA) ( Burnett and Dulaiova, 2003). This approach, however, is time consuming and may present numerous logistical difficulties. This method benefits by having maximum measurement efficiencies approaching 300% which was widely used in multiple international research programs including GEOSECS, TTO and GEOTRACES ( Broecker et al., 1967 Key et al., 1979 Xu et al., 2022). For grab samples, the radon in water is traditionally trapped via a radon extraction line system and transferred to Lucas alpha scintillation cells followed by measurement by a counting system after being sealed for 3 hours to allow the 222Rn progenies ( 218Po, 214Po) to reach radioactive equilibrium ( Stinger and Burnett, 2004). Radon isotopes measurement approaches for marine research have been fully developed in the past centuries. Simultaneous measurements of radon and other natural gases (such as CO 2 and CH 4) were used recently to delineate the significance of SGD and thus better understand carbon and nutrient biogeochemical transformations ( Santos et al., 2012 Schubert and Paschke, 2015 Chen et al., 2018b Chen et al., 2022). However, 222Rn (t 1/2 = 3.83 d) is often measured and has been widely employed for studies such as upwelling and downwelling ( Sarmiento et al., 1976), air-sea interactions ( Broecker and Kaufman, 1970 Broecker and Peng, 1971), diffusion from sediments ( Corbett et al., 1998), earthquake prediction ( Kuo et al., 2010 Chen et al., 2018a) and submarine groundwater discharge (SGD) ( Null et al., 2012 Prakash et al., 2018 Santos et al., 2021). Because the half-lives of 219Rn (t 1/2 = 3.96 s) and 220Rn (t 1/2 = 55.6 s) are so short, it is difficult to measure them precisely. Natural radon isotopes can be used as tracers of various chemical and physical processes in the environment. The new system does not rely on drying units, further reducing on-site supervision, which would benefit the researches in submarine groundwater advection and diffusion and ocean-atmosphere gas exchange. The PIC-ORn detector takes advantage of higher efficiency, lower cost, and power consumption, and is less affected by air moisture. Despite low radon-in-water activities, the results obtained by the new PIC-ORn system matched the traditional measurement systems within the estimated uncertainties. The new system was successfully deployed during a cruise to the northwest Pacific Ocean in June 2021. Laboratorial measurements indicated that the new PIC-ORn system responded timely to the change of radon activities in water. We demonstrated that the PIC measurement efficiency is ~2 times higher than a RAD7 and is less affected by relative humidity and produces reliable results. ![]() Here we present the setup and validation of an improved continuous online measurement system (PIC-ORn) to measure dissolved radon in the surface ocean and other water bodies. In the past centuries, radon isotopes measurement approaches for marine research have been fully developed but still suffer limitations. Radon is an excellent natural tracer for studying various geophysical processes. 8College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, China.7Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao, China.6Department of Geological Sciences, University of Alabama, Tuscaloosa, AL, United States.5College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, China.4Laboratory for Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China.3Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao, China.2R & D Center for Marine Instruments and Apparatuses, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China.1College of Information Science and Engineering, Ocean University of China, Qingdao, China.Dimova 6, Tong Yang 1, Wen Liu 3,4,5, Guangquan Chen 7, Huaming Yu 8 and Bochao Xu 3,4* Chunqian Li 1,2†, Shibin Zhao 3,4,5†, Chenglun Zhang 2, Meng Li 1, Jinjia Guo 1, Natasha T.
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