A history of atmospheric tritium gas (HT) 1950–2002

Data collected as a part of this study from 1968–2002 and data from other studies from 1950–1967 show that themaximum atmospheric concentration of tritium gas (HT) occurred in the early to mid 1970s, which corresponds to theera of frequent, large underground nuclear tests. These data clearly show that the major source of HT to the atmospherebetween 1962 and the early 1990s was the underground testing of nuclear weapons. Samples collected at both ourAlaska and Miami stations clearly show marked increases in the autumn of each year between 1970 and 1975 that wereassociated with large underground explosions conducted by the former Soviet Union at the Novaya Zemlya test site.Other significant sources of HT include accidental releases of HT used in the manufacture and maintenance of nuclearweapons stockpiles, the reprocessing of spent nuclear fuel rods and emissions from nuclear power plants. Since theearly 1990s, when underground testing largely ceased, emission estimates from our data agree very well with UnitedNations estimates of worldwide releases from fuel reprocessing and nuclear power plants, suggesting that the nuclear power industry is now the major source of HT to the atmosphere.