Compressed air sample technology for isotopic analysis of atmospheric carbon monoxide

A low-background, high-pressure, high-flow sampling system with a residual background of less than 2 ppbv CO has been built and employed for collection of samples both from the ground and from an aircraft platform. The time required for obtaining a 1000-L sample pressured to 600 psi was approximately 30 min on the ground, and 75 min at 8-km altitude. Following collection, samples were analyzed for CO concentration, ¹³C, ¹⁸O, and ¹⁴C using cryogenic vacuum extraction followed by stable isotope ratio mass spectrometry and accelerator mass spectrometry. Standard deviation for δ¹³C is 0.2 per mil, for δ¹⁸O 0.8 per mil, and for ¹⁴CO 0.5 molecules per cubic centimeter (STP). -Authors