The Role of Natural Halogens in Global Tropospheric Ozone Chemistry and Budget Under Different 21st Century Climate Scenarios

Abstract

Abstract: Tropospheric ozone ( O 3 ) is an important greenhouse gas and a surface pollutant. The future evolution of O 3 abundances and chemical processing are uncertain due to a changing climate, socioeconomic developments, and missing chemistry in global models. Here, we use an Earth System Model with natural halogen chemistry to investigate the changes in the O 3 budget over the 21st century following Representative Concentration Pathway (RCP)6.0 and RCP8.5 climate scenarios. Our results indicate that the global tropospheric O 3 net chemical change (NCC, chemical gross production minus destruction) will decrease ∼ 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 with stringent abatements in O 3 precursor emissions. Water vapor and iodine are found to be key drivers of future tropospheric O 3 destruction, while the largest changes in O 3 production are determined by the future evolution of peroxy radicals. We show that natural halogens, currently not considered in climate models, significantly impact on the present‐day and future global O 3 burden reducing ∼ 30–35 Tg (11–15 % ) of tropospheric ozone throughout the 21st century regardless of the RCP scenario considered. This highlights the importance of including natural halogen chemistry in climate model projections of future tropospheric ozone.