Worldwide nuclear weapons programs and nuclear power generation add ionizing radiation to the atmosphere continuously. NOAA's website offers five different safety programs related to ionizing radiation. But if NOAA (or any other government entity) is measuring ionizing radiation in the atmosphere, that information is not easily found.
What if "National Security" Depends on Citizens' Insecurity?
Search the NOAA website for strontium-90 or cesium-137 (one of the more common and more serious products of the Fukushima meltdowns with a half-life of 30 years) and there is one result, which begins promisingly:
"The Environmental Measurements Laboratory (EML) has maintained a global network of deposition sampling sites for nearly 40 years. Through CMDL support, American Samoa (SMO) and Mauna Loa (MLO) have been a part of this network for many years. This network was initiated to investigate the transport and fate of radioactivity produced from atmospheric testing of nuclear weapons. Strontium-90 was the radionuclide of primary interest due to the relatively high quantity released and its physical and chemical properties that made it a concern to human health."
But this posting dates from 1996 and includes no data later than 1996.
Radiation Dose So Far Not Harmful, U.N. says -- But It's Not Over Yet
In February the World Health Organization (WHO) of the U.N. released an almost 200-page assessment of the health risks from the Fukushima disaster, "the first-ever analysis of global health effects due to radiation exposure" from Fukushima. In a press release issued in Geneva, WHO concluded that: "for the general population inside and outside of Japan, the predicted risks are low and no observable increases in cancer rates above baseline rates are anticipated."
Using preliminary dose estimation data to make its predictions, the WHO report also found "that the estimated risk for specific cancers in certain subsets of the population in Fukushima Prefecture has increased and, as such, it calls for long term continued monitoring and health screening for those people."