Air concentrations of krypton-85 in the midwest United States during January–May 1974

Abstract

Twice-daily air samples were collected at thirteen sites in the mid-western U.S. from 24 January to 20 May, 1974 in a study of the long-range transport and dilution of the 85Kr plume emitted at the National Reactor Testing Station (NRTS) in Idaho. The NRTS plume (about 1000 Ci day −1) proved to have very little effect on the 85Kr background concentrations in the midwest (1500–2500 km from the source). The mean concentration during the month prior to the start of emissions was 14.0 compared to 13.8pCi/SCM −1 during the most active emission period. Almost all of the 2500 samples collected had 85Kr concentrations within 5% of the ambient background. Meteorological analysis indicated marked changes in 85Kr concentrations from one air mass to another with relatively little fluctuation within an air mass. Surface dewpoint temperature, a quasi-conservative air mass property, was found to be well correlated with 85Kr fluctuations. Occasional high concentrations of 85Kr at Indianapolis and Detroit were found to be caused by plumes from the Savannah River Plant in South Carolina. Two episodes of anomalously high concentrations at Minneapolis are attributed to unknown local sources.