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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, meer
Peer reviewed article  
Beschikbaar in  Auteurs 
Author keywords
    methane removal; tropospheric chlorine; chemistry–climate; aerosol chemistry; isotope modeling
Auteurs  Top 
  • 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.
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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