Atmospheric carbon dioxide measurements at Barrow, Alaska, 1973-1979

The U.S. National Oceanic and Atmospheric Administration has operated a program to continuously measure atmospheric CO₂ concentrations at Barrow, Alaska, since July 1973. This report describes the basic operational program and reports the data through 1979. Analysis of the data shows a large-amplitude annual CO₂ cycle of 15.2 p.p.m., which is similar to that at other Northern Hemisphere high-latitude locations. The annual cycle is asymmetric with a maximum in late April and minimum in late August. Largest day-to-day variability of the the full data set occurs during summer. The long-term CO₂ trend is highlighted by a slight (≃0.1 p.p.m.) decrease in absolute concentrations in 1976 compared to 1975; overall, concentrations rose about 4 to 5 p.p.m. Tentative pressure-broadening corrections were applied to express results in mole fractions so that the Barrow measurements could be directly compared to those at Mauna Loa, Hawaii. Referenced to January 1, 1974, CO2 values at Barrow averaged about 2.5 p.p.m. greater than at Mauna Loa. The Barrow-Mauna Loa interstation difference was greatest (more than 6 p.p.m.) during December and January. The difference reverses during summer when it is less than –6 p.p.m. in August. For 1979 CO₂ at Barrow averaged 336.9 p.p.m.