Influence of Natural Halogens on Global Tropospheric Ozone During the 21st Century

Tropospheric ozone (O₃) is an important greenhouse gas relevant for global warming projections as well as secondary pollutant affecting air quality on the regional scale. In this Communication, we use halogen version of the CAM-Chem model to investigate the evolution of the O₃ budget during the 21st century following two different climate scenarios (RCP6.0 and RCP8.5) and halogen emissions. Our results indicate that the global ozone net chemical change (NCC) will decrease by ~50%, notwithstanding increasing or decreasing trends in ozone production and loss. However, a wide range of surface NCC variations (from −60% to 150%) are projected over polluted regions depending on the evolution of anthropogenic O₃ precursor emissions. Most notably, water vapor and iodine are found to be key drivers of future tropospheric O₃ destruction, while the largest changes in O₃ production are determined by the future evolution of peroxy radicals. Overall, future surface ozone destruction due to halogens will become more important moving into the future for both scenarios, reaching a net reduction from −30 to −35 Tg (−11 to −15%) on the global O₃ burden.