Climate.gov just posted an interesting video on Charles David Keeling and his ground-breaking measurements of CO2 levels in the atmosphere. The observatory was located on Mauna Loa, on top of the second highest peak in the Hawaiian Islands.
The idea behind the site was to keep it far removed from any nearby sources of CO2 resulting from human activity. Because of it’s location and longevity, it is our best measurement of the background CO2 levels in the lower atmosphere. Here is the link to the Mauna Loa Observatory records and trends.
Dr. Keeling received his undergraduate degree here at the University of Illinois in 1948 and his Ph.D. in Chemistry at Northwestern in 1954. There is a brief bio here.