Effects of Sea Salt Aerosol Emissions for Marine Cloud Brightening on Atmospheric Chemistry: Implications for Radiative Forcing

• Published in: Geophysical Research Letters
• Main Authors: Horowitz, Hannah M., Holmes, Christopher, Wright, Alicia, Sherwen, Tomás, Wang, Xuan, Evans, Mat, Huang, Jiayue, Jaeglé, Lyatt, Chen, Qianjie, Zhai, Shuting, Alexander, Becky
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Wiley Periodicals, Inc. 2020
• Subjects: atmospheric chemistry; marine cloud brightening; geoengineering; reactive halogens; sea salt aerosols; Geological Sciences; Science; Arctic
• Online Access: https://hdl.handle.net/2027.42/154513; https://doi.org/10.1029/2019GL085838

Marine cloud brightening (MCB) is proposed to offset global warming by emitting sea salt aerosols to the tropical marine boundary layer, which increases aerosol and cloud albedo. Sea salt aerosol is the main source of tropospheric reactive chlorine (Cly) and bromine (Bry). The effects of additional sea salt on atmospheric chemistry have not been explored. We simulate sea salt aerosol injections for MCB under two scenarios (212–569 Tg/a) in the GEOS‐Chem global chemical transport model, only considering their impacts as a halogen source. Globally, tropospheric Cly and Bry increase (20–40%), leading to decreased ozone (−3 to −6%). Consequently, OH decreases (−3 to −5%), which increases the methane lifetime (3–6%). Our results suggest that the chemistry of the additional sea salt leads to minor total radiative forcing compared to that of the sea salt aerosol itself (~2%) but may have potential implications for surface ozone pollution in tropical coastal regions.Plain Language SummaryIn light of global warming, hypothetical geoengineering methods have been proposed to try to counteract rising temperatures. One involves spraying sea salt particles into the air above the oceans in the tropics. This would reduce temperatures by reflecting sunlight away from the Earth. Sea salt particles can also release halogens to the air. Their resulting chemical reactions affect the amount of ozone and methane, both greenhouse gases, which may further impact temperatures. We investigate this for the first time using a computer model of the atmosphere and its chemistry. We find that additional sea salt for geoengineering would reduce ozone, especially at the surface where it is an air pollutant, while increasing methane. Overall, these results suggest that the net effect of the sea salt chemistry on the energy balance of the Earth is near zero, but it may have potential implications for air quality.Key PointsSea salt aerosol emissions for Marine Cloud Brightening geoengineering are implemented in a global chemical transport modelThis ...