Methanol is the second-most abundant organic gas in the remote atmosphere after methane, but its sources are poorly understood. Here, we report a global budget of methanol constrained by observations from the ATom aircraft campaign as implemented in the GEOS-Chem global atmospheric chemistry model. ATom observations under background marine conditions can be fit in the model with a surface ocean methanol concentration of 61 nM and a methanol yield of 13% from the newly implemented CH3O2 + OH reaction. While terrestrial biogenic emissions dominate the global atmospheric methanol budget, secondary production from CH3O2 + OH and CH3O2 + CH3O2 accounts for 29% of the total methanol source, and makes up the majority of methanol in the background marine atmosphere sampled by ATom. Net emission from the ocean is comparatively minor, particularly because of rapid deposition from the marine boundary layer. Aged anthropogenic and pyrogenic plumes sampled in ATom featured large methanol enhancements to constrain the corresponding sources. Methanol enhancements in pyrogenic plumes did not decay with age, implying in-plume secondary production. The atmospheric lifetime of methanol is only 5.3 days, reflecting losses of comparable magnitude from photooxidation and deposition. GEOS-Chem model results indicate that methanol photochemistry contributes 5%, 4%, and 1.5% of the tropospheric burdens of formaldehyde, CO, and ozone, respectively, with particularly pronounced effects in the tropical upper troposphere. The CH3O2 + OH reaction has substantial impacts on radical budgets throughout the troposphere and should be included in global atmospheric chemistry models.
Bibliographical noteFunding Information:
This work was supported by the US NSF Atmospheric Chemistry Program, by the NASA Atmospheric Composition Modeling and Analysis Program, and by the US EPA Science to Achieve Results Program. We thank Bruce Daube and Kathryn McKain for their contribution to the collection of CO data on ATom. K. H. B. acknowledges additional support from the Harvard University Center for the Environment and the National Oceanic and Atmospheric Administration’s Climate and Global Change Fellowship programs. D. B. M., X. C., and K. C. W. acknowledge support from the NASA Atmospheric Composition Campaign Data Analysis and Modeling (ACCDAM) program (Grant no. NNX14AP89G). This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. All ATom data used in this study can be accessed via https://daac.ornl.gov/ATOM/campaign/ .
© 2021. The Authors.
Copyright 2021 Elsevier B.V., All rights reserved.
- air-sea exchange
- atmospheric tomography
- chemical transport modeling