Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2

Tropospheric (OO)-O-18-O-18 is an emerging proxy for past tropospheric ozone and free-tropospheric temperatures. The basis of these applications is the idea that isotope-exchange reactions in the atmosphere drive (OO)-O-18-O-18 abundances toward isotopic equilibrium. However, previous work used an offline box-model framework to explain the (OO)-O-18-O-18 budget, approximating the interplay of atmospheric chemistry and transport. This approach, while convenient, has poorly characterized uncertainties. To investigate these uncertainties, and to broaden the applicability of the (OO)-O-18-O-18 proxy, we developed a scheme to simulate atmospheric (OO)-O-18-O-18 abundances (quantified as increment (36) values) online within the GEOS-Chem chemical transport model. These results are compared to both new and previously published atmospheric observations from the surface to 33 km. Simulations using a simplified O-2 isotopic equilibration scheme within GEOS-Chem show quantitative agreement with measurements only in the middle stratosphere; modeled increment (36) values are too high elsewhere. Investigations using a comprehensive model of the O-O-2-O-3 isotopic photochemical system and proof-of-principle experiments suggest that the simple equilibration scheme omits an important pressure dependence to increment (36) values: the anomalously efficient titration of (OO)-O-18-O-18 to form ozone. Incorporating these effects into the online increment (36) calculation scheme in GEOS-Chem yields quantitative agreement for all available observations. While this previously unidentified bias affects the atmospheric budget of (OO)-O-18-O-18 in O-2, the modeled change in the mean tropospheric increment (36) value since 1850 CE is only slightly altered; it is still quantitatively consistent with the ice-core increment (36) record, implying that the tropospheric ozone burden increased less than 40% over the twentieth century.

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Author Yeung, Laurence Y.
Murray, Lee T.
Banerjee, Asmita
Tie, Xin
Yan, Yuzhen
Atlas, Elliot L.
Schauffler, Sue M.
Boering, Kristie A.
Publisher UCAR/NCAR - Library
Publication Date 2021-07-27T00:00:00
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Topic Category geoscientificInformation
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Metadata Date 2023-08-18T18:16:24.603484
Metadata Record Identifier edu.ucar.opensky::articles:24960
Metadata Language eng; USA
Suggested Citation Yeung, Laurence Y., Murray, Lee T., Banerjee, Asmita, Tie, Xin, Yan, Yuzhen, Atlas, Elliot L., Schauffler, Sue M., Boering, Kristie A.. (2021). Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2. UCAR/NCAR - Library. http://n2t.net/ark:/85065/d7js9tzx. Accessed 13 February 2025.

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