Impacts of Marine Cloud Brightening on Atmospheric Chemistry (Invited Presentation)

Anthropogenic emissions of greenhouse gases and aerosols have led to an effective radiative forcing of +2.3 W m^-2 over the industrial era. Marine cloud brightening (MCB) is a potential geoengineering technique meant to offset global warming by releasing an additional flux of sea salt aerosols into the tropical marine boundary layer (MBL). This cools the planet by increasing cloud albedo and scattering light. We explore the implications of MCB for atmospheric chemistry through its effects on reactive halogen chemistry in the troposphere. We simulate a range of MCB sea salt emissions scenarios in the GEOS-Chem global chemical transport model, which includes coupled gas and multiphase bromine, chlorine, and iodine chemistry. Since sea salt aerosol is the main source reactive chlorine and bromine in the troposphere, increasing the flux of sea salt into the tropical MBL leads to an increase in these halogens. Increases in reactive chlorine and bromine abundances result in reductions in the tropospheric abundance of ozone, a greenhouse gas and pollutant. Reductions in tropospheric ozone lead to decreases in tropospheric reactive iodine, as well as the hydroxyl radical (OH). We quantify effects on the lifetime of the greenhouse gas methane due to changes in its major (OH) and minor (Cl atom) oxidants. We will present the magnitude of atmospheric chemistry-driven impacts of MCB on air pollution levels and climate via radiative forcing by ozone, methane, and other aerosols.