Photocatalytic chlorine atom production on mineral dust–sea spray aerosols over the North Atlantic
van Herpen, M.J.W.; Li, Q.; Saiz-Lopez, A.; Liisberg, J.B.; Röckmann, T.; Cuevas, C.A.; Fernandez, R.P.; Mak, J.E.; Mahowald, N.M.; Hess, P.; Meidan, D.; Stuut, J.-B; Johnson, M.S. (2023). Photocatalytic chlorine atom production on mineral dust–sea spray aerosols over the North Atlantic. Proc. Natl. Acad. Sci. U.S.A. 120(31). https://dx.doi.org/10.1073/pnas.2303974120
In: Proceedings of the National Academy of Sciences of the United States of America. The Academy: Washington, D.C.. ISSN 0027-8424; e-ISSN 1091-6490, more
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| Author keywords |
methane removal; tropospheric chlorine; chemistry–climate; aerosol chemistry; isotope modeling |
| Authors | | Top |
- van Herpen, M.J.W.
- Li, Q.
- Saiz-Lopez, A.
- Liisberg, J.B.
- Röckmann, T.
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- Cuevas, C.A.
- Fernandez, R.P.
- Mak, J.E.
- Mahowald, N.M.
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- Hess, P.
- Meidan, D.
- Stuut, J.-B, more
- Johnson, M.S.
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| Abstract |
Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent 13C depletion in CO in air samples from Barbados, which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde, in addition to explaining the observation of elevated HOCl. Our model finds that 3.8 Tg(Cl) y−1 is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained top–down models fail to allocate 12 Tg y−1 (2% of total methane emissions) to 13C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the 13C isotope of atmospheric CH4, thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere. |
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