COMPRESSED-AIR SAMPLE TECHNOLOGY FOR ISOTOPIC ANALYSIS OF ATMOSPHERICCARBON-MONOXIDE

A methodology for the collection of large ( 1000 L) air samples for is otopic analysis of atmospheric carbon monoxide is presented. A low-bac kground, high-pressure, high-flow sampling system with a residual back ground of less than 2 ppbv CO has been built and employed for collecti on of samples both from the ground and from an aircraft platform. The time required for obtaining a 1000-L sample pressurized to 600 psi was approximately 30 min on the ground, and 75 min at 8-km altitude. Foll owing collection, samples were analyzed for CO concentration, C-13 O-1 8, and C-14 using cryogenic vacuum extraction followed by stable isoto pe ratio mass spectrometry and accelerator mass spectrometry. Standard deviation for delta C-13 is 0.2 per mil, for delta O-18 0.8 per mil, and for CO-14 0.5 molecules per cubic centimeter (STP).