Charles David Keeling, of Scripps Institution of Oceanography at UC San Diego, was the first person to make frequent regular measurements of atmospheric concentrations in Antarctica, and on Mauna Loa, Hawaii from March 1958 onwards. Keeling had previously tested and employed measurement techniques at locations including Big Sur near Monterey, rain forests of the Olympic Peninsula in Washington state, and high mountain forests in Arizona. He observed strong diurnal behavior of , with excess at night due to respiration by plants and soils, and afternoon values representative of the free atmosphere over the Northern hemisphere.