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

点击翻译按钮获取中文摘要

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.