The slide above was part of a presentation delivered by IAEA officials at the Press Briefing of 20 March. The slide displays average air concentrations of certain isotopes measured at four different locations in Japan in the period 15-19 March.
The measurements appearing in the last column were provided by the CTBTO. They come from the CTBTO’s certified radionuclide station in Takasaki, Gunma (RN38).
The measurements from Ibaraki, Tokyo and Chiba were performed by Japanese agencies and were provided to the IAEA by the Ministry of Education, Culture, Sports, Science and Technology of Japan.
As of 18 March the CTBTO has been sharing on a daily basis data and analyses with the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO).
See the entire powerpoint presentation by the IAEA here.
For more background on the CTBTO sharing data with the IAEA and the WHO see the relevant press release here.