Portable Cryogenic Collection of Atmospheric Nitrous Oxide and Carbon Monoxide for High-Precision Isotopic Analysis

A portable cryogenic collection system has been constructed for the isolation of atmospheric nitrous oxide (N 2 O) and carbon monoxide (CO). Ambient air enters the system at a rate of 10 L/min, and N 2 O condenses in a specially designed stainless steel ultrahigh-efficiency collection (UHEC) trap. The CO is next oxidized to CO 2 and removed by a second UHEC trap. In conjunction with drying agents, the UHEC traps remove greater than 99.9989% of atmospheric carbon dioxide (CO 2 ) that would otherwise interfere with CO-derived CO 2 analysis. The oxygen in the N 2 O and CO-derived CO 2 samples is subsequently separated for high-precision mass spectroscopic analysis. This system is unique in that it provides for in situ collection and permits simultaneous measurement of the 18 O/ 16 O and 17 O/ 16 O ratios in N 2 O and CO. Results are presented for a series of trials run to determine the ultimate collection efficiency of the UHEC cryogenic traps.