Assessing the Ability of Measurements of Carbon-14 of Atmospheric Carbon Monoxide in a Global Network to Improve Understanding of Spatial and Temporal Hydroxyl Radical Variability

该项目将发展和应用利用一氧化碳碳14同位素（14 CO）全球观测的能力，以评估大气中羟基自由基（OH）的全球分布情况。在过去的20年里，甲基氯仿（MCF）的观测一直有效地建立OH的分布，但大气中的丰富的MCF现在已经下降到点，它变得不那么有用。 OH自由基是主要的大气氧化剂，决定了许多重要辐射气体和受管制污染物的寿命。 该项目的第一阶段包括通过在阿拉斯加的巴罗、爱尔兰的梅斯黑德、夏威夷的莫纳罗亚、巴巴多斯的拉格德角、美属萨摩亚、法国的留尼汪岛、美国的西海岸和美国的西海岸，每两周测量一次14 CO，持续一整年，以加强全球观测。新西兰的Baring Head，南极洲的Arrival Heights较少。 作为试点工作的一部分，该项目的主要研究人员开发了一种用于14 CO观测的新方法，该方法将样本量要求降低了一个数量级，从而在不牺牲测量质量的情况下实现了更简单，更便宜的物流。新的14 CO结果将提供一个具有全球代表性的14 CO分布在一整年的过程中，然后可以用来研究OH浓度的空间和季节性变化，在GEOS-Chem化学运输模型的帮助下。还将在GEOS-Chem中开发MCF能力，并将14 CO的OH结果与通过MCF推断的OH进行比较。 MCF和14 CO的模拟将使用GEOS-Chem一起进行，将MCF约束全球平均OH的能力与14 CO推断OH空间结构和季节变化的能力相结合。 OH浓度在空间和时间上的变化会影响全球空气质量和气候变化的速度。 对对流层OH分布和变化的更好理解在大气科学研究界具有广泛的意义。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

This project will develop and apply the capability for using global observations of the carbon-14 isotope of carbon monoxide (14CO) to assess the global distribution of the hydroxyl radical (OH) in the atmosphere. For the past ~20 years, methyl chloroform (MCF) observations have been effective at establishing the OH distribution, but the atmospheric abundance of MCF has now declined to the point where it is becoming less useful. The OH radical is the main atmospheric oxidant and determines the lifetimes of numerous radiatively important gases and regulated pollutants. Knowledge about the abundance and variability of the global distribution of OH is critical for accurately modeling air quality and climate change.The first phase of this project includes enhancing global observations by measuring 14CO once every 2 weeks for 1 full year at Barrow, Alaska; Mace Head, Ireland; Mauna Loa, Hawaii; Ragged Point, Barbados; American Samoa; La R'union Island, France; Baring Head, New Zealand and less frequently at Arrival Heights, Antarctica. As part of a pilot effort, the principal investigators of this project have developed a new method for 14CO observation that reduces the sample size requirement by an order of magnitude, allowing for simpler and less expensive logistics without sacrificing measurement quality. The new 14CO results will provide a globally-representative 14CO distribution over the course of a full year that can then be used to study the spatial and seasonal variability in OH concentrations, with the aid of the GEOS-Chem chemistry-transport model. MCF capability will also be developed in GEOS-Chem, and OH results from 14CO will be compared with OH inferred via MCF. Simulations of both MCF and 14CO will be performed together using GEOS-Chem, combining MCF's power to constrain global mean OH with 14CO's ability to infer OH spatial structure and seasonal changes. Changes in OH concentrations in space and time impact both global air quality and the rate of climate change. An improved understanding of tropospheric OH distribution and variability has significant broad interest within the atmospheric science research community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.