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（14CO）的碳-14同位素的全球观测来评估大气中羟基自由基（OH）的全球分布的能力。在过去的20年里，甲基氯仿（MCF）观测在确定OH分布方面是有效的，但MCF的大气丰度现在已经下降到变得不那么有用的程度。OH自由基是主要的大气氧化剂，它决定了许多重要的辐射气体和受控污染物的寿命。了解全球OH分布的丰度和变异性对于准确模拟空气质量和气候变化至关重要。该项目的第一阶段包括加强全球观测，在阿拉斯加巴罗每两周测量一次14CO，持续一年；梅斯黑德，爱尔兰；夏威夷的莫纳罗亚山；巴巴多斯的粗糙点；美属萨摩亚;La R'union岛，法国；秃头，新西兰和较少经常在到达高地，南极洲。作为试点工作的一部分，该项目的主要研究人员已经开发出一种新的14CO观测方法，该方法将样本量要求减少了一个数量级，从而在不牺牲测量质量的情况下实现更简单、更便宜的物流。新的14CO结果将提供一整年具有全球代表性的14CO分布，然后可以在GEOS-Chem化学运输模型的帮助下用于研究OH浓度的空间和季节变化。GEOS-Chem也将开发MCF功能，并将14CO的OH结果与通过MCF推断的OH进行比较。MCF和14CO的模拟将使用GEOS-Chem一起进行，将MCF限制全球平均OH的能力与14CO推断OH空间结构和季节变化的能力结合起来。氢氧根浓度在空间和时间上的变化既影响全球空气质量，也影响气候变化速度。提高对对流层OH分布和变率的认识在大气科学研究界引起了广泛的兴趣。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.