Atmospheric HT and HTO: I. Experimental procedures and tropospheric data 1968-72

A technique was developed for direct field sampling of atmospheric HTO and HT. Airborne, portable, and laboratory versions were implemented, and a comprehensive sampling program begun. The air is passed first through Molecular Sieve to adsorb the water, then over palladium carried on Molecular Sieve, which oxidizes atmospheric hydrogen and adsorbs the resulting water in situ. Both samples are subsequently extracted from the adsorbers, and the tritium content measured by internal low-level gas counting. Resolution is 4% of present atmospheric levels. Monitoring of HT and HTO at three stations in the Northern Hemisphere shows that HT does not undergo seasonal fluctuations like HTO, and variations are small around the present mean of about 46 HT molecules per mg air. After the previous rise from pre-nuclear level, the tropospheric HT-inventory has reached a steady state within the past few years. Sampling transects from 40°N to 65°S in 1971 and 1972 show similar HT levels in the Northern and Southern Hemispheres indicating a long residence time of HT (and hydrogen). The HT appears to have its source at ground level, most likely from nuclear fuel element processing, underground nuclear fusion device detonations, and military and civilian handling of tritium gas. In the troposphere, there is now more tritium as gas (HT or T₂) than as HTO (water vapor).