Evaluating the contribution of the unexplored photochemistry of aldehydes on the tropospheric levels of molecular hydrogen (H2)

Maria Paula Pérez-Peña, Jenny A. Fisher, Dylan B. Millet, Hisashi Yashiro, Ray L. Langenfelds, Paul B. Krummel, Scott H. Kable

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Molecular hydrogen, H2, is one of the most abundant trace gases in the atmosphere. The main known chemical source of H2 in the atmosphere is the photolysis of formaldehyde and glyoxal. Recent laboratory measurements and ground-state photochemistry calculations have shown other aldehydes photodissociate to yield H2 as well. This aldehyde photochemistry has not been previously accounted for in atmospheric H2 models. Here, we used two atmospheric models to test the implications of the previously unexplored aldehyde photochemistry on the H2 tropospheric budget. We used the AtChem box model implementing the nearly chemically explicit Master Chemical Mechanism at three sites selected to represent variable atmospheric environments: London, Cabo Verde and Borneo. We conducted five box model simulations per site using varying quantum yields for the photolysis of 16 aldehydes and compared the results against a baseline. The box model simulations showed that the photolysis of acetaldehyde, propanal, methylglyoxal, glycolaldehyde and methacrolein yields the highest chemical production of H2. We also used the GEOS-Chem 3-D atmospheric chemical transport model to test the impacts of the new photolytic H2 source on the global scale. A new H2 simulation capability was developed in GEOS-Chem and evaluated for 2015 and 2016. We then performed a sensitivity simulation in which the photolysis reactions of six aldehyde species were modified to include a 1 % yield of H2. We found an increase in the chemical production of H2 over tropical regions where high abundance of isoprene results in the secondary generation of methylglyoxal, glycolaldehyde and methacrolein, ultimately yielding H2. We calculated a final increase of 0.4 Tg yr-1 in the global chemical production budget, compared to a baseline production of ∼41 Tg yr-1. Ultimately, both models showed that H2 production from the newly discovered photolysis of aldehydes leads to only minor changes in the atmospheric mixing ratios of H2, at least for the aldehydes tested here when assuming a 1 % quantum yield across all wavelengths. Our results imply that the previously missing photochemical source is a less significant source of model uncertainty than other components of the H2 budget, including emissions and soil uptake.

Original languageEnglish (US)
Pages (from-to)12367-12386
Number of pages20
JournalAtmospheric Chemistry and Physics
Issue number18
StatePublished - Sep 21 2022

Bibliographical note

Funding Information:
This research has been supported by the Australian Research Council (grant no. DE200100549/DP190102013).

Funding Information:
This work was undertaken with the assistance of resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government (project m19). This research was undertaken also with computer time on the computational cluster Katana supported by the Faculty of Science, UNSW Australia. The authors thank Lisa K. Whalley for her help relating to setting up and running the AtChem simulations and providing the information related with the constraints for the London box modeling. Past and present CSIRO GASLAB staff are thanked for their dedication to making high-quality long-term measurements. CSIRO is thanked for the long-term institutional support of GASLAB and the CSIRO global flask network. The Australian Bureau of Meteorology, Australian Antarctic Division, Australian Institute of Marine Science, National Oceanic and Atmospheric Administration, and Environment and Climate Change Canada are gratefully thanked for the long-term support for filling flasks and logistics at the field stations used in the CSIRO flask network. The determination of the dry deposition fields used in this work was supported by MEXT (JPMXP1020200305) as the Program for Promoting Research on the Supercomputer Fugaku (Large Ensemble Atmospheric and Environmental Prediction for Disaster Prevention and Mitigation).

Publisher Copyright:
© 2022 Maria Paula Pérez-Peña et al.


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