A goal of this project was to develop a global emission ocean inventory for two major, naturally occurring ozone-depleting bromocarbons, bromoform (CHBr₃) and dibromomethane (CH₂Br₂). We also developed the framework to project their emissions and resultant impacts on atmospheric concentrations from now to the end of the century. Originally, the focus of the project was on the Southern Ocean but was extended to include the entire globe.  

These bromine containing species (bromocarbons) are part of a group of substances referred to as very short lived species (VSLS) which are, by definition, species that have atmospheric lifetimes of less than 6 months. The VSLS designation is in reference to the much longer-lived chlorine containing chlorofluorocarbons (CFCs) which are well known ozone depleting substances that have been banned through the Montreal protocol. Bromine, like chlorine, is an important ozone depleting substance. The VSLS, which include both bromocarbons and chlorocarbons, are not regulated by the protocol but are emerging as important species to consider when determining the projected recovery date of the ozone layer. This is the date that scientists foresee in which the ozone layer returns to 1980 levels, which is the date just prior to the rapid depletion of the ozone layer from freon (CFC) sources.

The oceanic emissions and climate impacts of VSLS were explored using a bottom-up oceanic emission inventory of VSLS that we developed based on a machine learning approach that coupled the ocean biogeochemistry with VSLS oceanic concentration. A variety of oceanic and atmospheric observations of VSLS were used to develop, test, and refine this new oceanic VSLS inventory. In particular, the 2016 NSF O₂/N₂ Ratio and CO₂ Airborne Southern Ocean Study (ORCAS) field campaign provided a unique opportunity to examine Southern Ocean VSLS emissions, and their impacts from ocean biogeochemistry, meteorology and sea ice conditions.

This work used the NSF/NCAR Community Earth System Model (CESM) with a newly developed online air-sea exchange framework, to evaluate biogeochemical controls first on the marine sources of VSLS in the Southern Ocean and to then to extend that to the global scale.

The oceanic emissions of CHBr₃ and CH₂Br₂ result from their production in the ocean and their subsequent flux to the atmosphere. Their oceanic production is dependent to both biological (e.g., phytoplankton functional types) and physical parameters (e.g., temperature). This project incorporated these factors and estimated the 2010-2100 oceanic concentration and flux of CHBr₃ and CH₂Br₂ in 1 degree horizontal resolution. The emission flux was developed to investigate how  future changes in anthropogenic greenhouse (AGG) gas emissions will impact the oceanic emissions of CHBr₃ and CH₂Br₂, and their corresponding contribution to bromine loading in the Upper Troposphere Lower Stratosphere (UTLS). The results suggest that changes in AGG emissions will increase the oceanic emissions in the future and, therefore, enhance the tropospheric bromine abundance by up to 1.5 ppt in the UTLS region, with larger values during summer and fall. In addition, we have provided climate researchers with the long-term oceanic concentration of CHBr₃ and CH₂Br₂ which enables other climate studies involving the impact of other Earth system components within the CESM framework on the chemistry-climate-ecosystems interactions, and ozone.

Throughout this effort, we also investigated the global chlorinated VSLS distribution using the CESM Earth system model with updated short lived halogen chemistry, and quantified the inter-hemispheric transport of these compounds. We showed that Asia is the predominant source of these ozone depleting substances. The project outcomes of this study demonstrate that human activities can adversely impact the earth ecosystem.  

Last Modified: 12/30/2024
Modified by: Eric C Apel