Isotopic Analysis of Tropospheric Carbon Monoxide

小行星9417525 羟基自由基（OH）是地球大气的主要氧化剂，因此其浓度在很大程度上决定了许多痕量气体的寿命。 一氧化碳（CO）是一种活性物质，它控制着远程大气中许多部分的OH浓度。 大气一氧化碳的同位素可以用来限制OH浓度以及CO的相对源强度。在第一种情况下，测量14 CO来限制OH浓度。 由于14 CO宇宙成因的生产率是已知的，它的损失率，因此，平均OH浓度，可以推导出，如果大气存量确定。 在第二种情况下，测量稳定同位素（13 CO和C18 O）以帮助评估相对源强度，因为某些CO源具有特征同位素特征。 CO的主要来源是甲烷被OH氧化、非甲烷烃被OH氧化、生物质燃烧和化石燃料燃烧。 然而，这些来源的相对重要性知之甚少。 确定大气中一氧化碳同位素的丰度和季节性将提供有关这些来源的相对大小的重要信息。 在20世纪70年代和80年代，CO一直以每年约1%的速度增长，但在过去的三到五年里，这一趋势发生了逆转，全球CO一直以每年6-7%的速度下降。 这些年际变化的原因尚不清楚。 分析CO同位素组成有助于限制相对源率。 PI建议建立一个清洁空气采样系统和低温真空抽取管线，用于收集、分离和分析空气样本中的一氧化碳同位素（14 CO、13 CO和C18 O），然后开始测量从莫纳罗亚天文台收集的空气样本中的这些同位素（与NOAA CMDL合作 设施）和从加州和新西兰之间的飞行中收集的样品。

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.