9417525 Mak Hydroxyl radial (OH) is the primary oxidant of the earth's atmosphere and so its concentration determines, to a large degree, the lifetimes of a host of trace gases. Carbon monoxide (CO) is a reactive species which controls the OH concentration in many parts of the remote atmosphere. The isotopes of atmospheric carbon monoxide can be used to constrain both the OH concentration as well as the relative source strengths of CO. In the first case, 14CO is measured to constrain OH concentrations. Since the 14CO cosmogenic production rate is known, its loss rate, and therefore the average OH concentration, can be deduced if the atmospheric inventory is determined. In the second case, the stable isotopes (13CO and C18O) are measured to help assess the relative source strengths, since certain sources of CO have characteristic isotopic signatures. The main sources of CO are methane oxidation by OH, non- methane hydrocarbon oxidation by OH, biomass burning, and fossil fuel combustion. However, the relative importance of these sources is poorly known. Determining the atmospheric abundance and seasonality of the isotopes of CO will provide important information concerning the relative magnitude of those sources. During the 1970's and 1980's CO has been increasing at a rate of about 1% per year, but for the last three to five years, this trend has reversed direction, and CO has been decreasing globally at a rate of 6-7% per year. The causes of these interannual variations are not known. Analysis of the isotopic composition of CO can help constrain the relative source rates. The PI proposes to build a clean air sampling system and cryogenic vacuum extraction line which will allow for the collection, separation, and analysis of air samples for the isotopes of carbon monoxide (14CO, 13CO, and C18O), and to then begin measurement of these isotopes from air samples collected at the Mauna Loa Observatory (in collaboration with the NOAA CMDL facility) and from samples collected in-flight between California and New Zealand.
