EAGER: Airborne Investigation of the Chlorine Mediated Mineral Dust Sea Spray Aerosol (MDSA) Mechanism in the Western Atlantic

The goal of this EAGER project is to investigate a chemical mechanism that can utilize naturally generated chlorine from sea-spray aerosol and iron from Saharan dust over the tropical Atlantic Ocean to oxidize and remove methane from the atmosphere. It recently has been suggested that the artificial introduction of chlorine into the atmosphere to remove methane might be a viable option for mitigating the climate impacts of greenhouse gas emissions. While limited laboratory studies have shown the potential for such a mechanism to remove methane, there is essentially little understanding of the viability of the method and its potential for causing harmful impacts. The MDSA (mineral dust-sea spray aerosol) mechanism depends on the recycling of hydrogen chloride by the methane and chlorine (CH4 + Cl) reaction. Establishing the catalytic efficiency of the process with respect to iron and chlorine under different atmospheric conditions is the key goal of this project. An aircraft campaign will be conducted near Barbados over a 6-week period during June/July 2024 in conjunction with MAGPIE (Moisture and Aerosol Gradients/Physics of Inversion Evolution), a dynamical meteorology project funded by the US Navy and NOAA. Measurements will be made of aerosol load and size distribution, and concentrations of atmospheric carbon monoxide, carbon dioxide, methane, water vapor, and hydrogen chloride, as well as 3-D wind speed and direction and temperature. Air samples will be collected for subsequent analysis of delta 13C in CO and CH4 as this data will validate the existence of the chlorine-hydrogen abstraction mechanism from atmospheric methane, believed to yield highly depleted 13CO in the summertime. This project to evaluate the viability of adding chlorine to the atmosphere to remove methane has high societal relevance for mitigating climate change. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.