MCB could reduce the atmospheric lifetime of methane

[Renaud de RICHTER]

Emme, E., Horowitz, H. M., Moon, A. R., & Shah, V. (2026). Particulate Nitrate Photolysis Alters the Atmospheric Chemistry Response to Marine Cloud Brightening Sea Salt Aerosol Emissions.  https://essopenarchive.org/doi/full/10.22541/essoar.15008567/v1

Abstract
Marine cloud brightening (MCB) aims to inject sea salt aerosols (SSA) into the marine boundary layer to increase cloud reflectivity. Previous work showed SSA emissions for MCB could impact tropospheric chemistry, but updates to our understanding of MCB and atmospheric chemistry suggest the need for further investigation. Using the 3-D global atmospheric chemistry model GEOS-Chem, we explore how a range of SSA emissions scenarios for MCB influence tropospheric
reactive halogens (Bry, Cly, and Iy), oxidants (ozone, OH, and NOx), and methane lifetime. Contrary to previous studies, we show enhanced SSA for MCB increases tropospheric oxidant concentrations and shortens methane lifetime (<15%). Sensitivity simulations demonstrate that increased tropospheric oxidant concentrations and decreased methane lifetime is driven by the treatment of particulate nitrate photolysis. However, the particulate nitrate photolysis mechanism remains poorly constrained, highlighting an important source of uncertainty in evaluating the atmospheric chemistry impacts of MCB.

NOTE: In a previous publication it was found that MCB decreases °OH (−3 to −5%), which increases the methane lifetime (3–6%).

Horowitz, H.M., et al. "Effects of sea salt aerosol emissions for marine cloud brightening on atmospheric chemistry: Implications for radiative forcing." Geophysical Research Letters 47.4 (2020): e2019GL085838.  https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085838