Variation of Concentration, 14C Activity and 13C/12C Ratios of CO2 in Air Samples from Kitt Peak, Arizona

Abstract

Air was sampled with 5L flasks at Kitt Peak (2100m elev) from 1983 through 1984 at approximately monthly intervals, occasionally supplemented with air samples from urban Tucson ca 75km away (760m elev). The Kitt Peak CO2 concentrations, represented by a yield measurement, fluctuated ca 25% over the monitoring period. The delta-13C values (uncorrected for N20) varied from ca -7.6 to -9.0%, with high values (and low CO2 yields) in the late summer consistent with hemispheric seasonal biosphere effects. Tucson air has lower delta-13C values and possibly greater CO2 yield suggesting a local fossil-fuel effect. 14C activity of four Kitt Peak samples range from 1.158 +/- .007 to 1.223 +/- .008 as uncorrected fraction of modern, below free air activity of ca 1.250 for 1984 even after correcting for fractionation. The slightly low 14C activity and delta-13C values suggest the Kitt Peak air is not quite 100% clean and there may be a local/regional fossil-fuel contribution, but CO2 concentrations are similar to background atmospheric values.