Isotopic Analysis of Tropospheric Carbon Monoxide

放射状羟基（OH）是地球大气的主要氧化剂，因此它的浓度在很大程度上决定了许多微量气体的寿命。一氧化碳（CO）是一种活性物质，它控制着遥远大气中许多部分的OH浓度。大气一氧化碳的同位素可以用来约束OH浓度以及CO的相对源强度。在第一种情况下，测量14CO来约束OH浓度。由于14CO的宇宙生成速率是已知的，如果确定大气库存量，就可以推断出14CO的损失率和平均OH浓度。在第二种情况下，测量稳定同位素（13CO和C18O）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OH氧化甲烷、OH氧化非甲烷烃、生物质燃烧和化石燃料燃烧。然而，人们对这些来源的相对重要性知之甚少。确定大气中CO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以每年约1%的速度增加，但在过去的三到五年中，这一趋势已经逆转，全球CO以每年6-7%的速度减少。这些年际变化的原因尚不清楚。CO的同位素组成分析有助于限制相对源速率。该项目建议建立一个清洁的空气采样系统和低温真空提取线，用于收集、分离和分析空气样本中的一氧化碳同位素（14CO、13CO和C18O），然后开始从莫纳罗亚天文台（与NOAA CMDL设施合作）收集的空气样本和从加利福尼亚和新西兰之间的飞行中收集的样本中测量这些同位素。

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.