A study published in the Proceedings of the National Academy of Sciences explores the effects of Saharan dust clouds on atmospheric methane. Its findings have potentially far-reaching implications for understanding the global methane budget and reasons behind the accelerating increase in atmospheric methane. The study, entitled "Photocatalytic Chlorine Atom Production on Mineral Dust-Sea Spray Aerosols over North Atlantic," incorporates a proposed new mechanism whereby blowing mineral dust mixes with sea-spray to form mineral dust-sea spray aerosol (MDSA).

The results suggest that MDSA is activated by sunlight to produce an abundance of chlorine atoms, which oxidize atmospheric methane and tropospheric ozone via photocatalysis. Largely composed of blowing dust from the Sahara Desert combined with sea salt aerosol from the ocean, MDSA is the dominant source of atmospheric chlorine over the North Atlantic, the study finds.

The study relies on a combination of global modeling and laboratory and field observations, including air samples from Barbados showing seasonal depletion of the stable isotope 13CO, an anomaly which puzzled scientists for 20 years. They knew observed changes in 13CO and C18O were evidence of chlorine atoms reacting with methane, and that carbon monoxide is the first stable product in atmospheric methane oxidation. But the known sources of atmospheric chlorine could not account for the degree of depletion in 13CO, until now.

More information: van Herpen, Maarten M. J. W. et al, Photocatalytic chlorine atom production on mineral dust–sea spray aerosols over the North Atlantic, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2303974120

Journal information: Proceedings of the National Academy of Sciences

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