Impacts of changes in climate, land use, and emissions on global ozone air quality by mid-21st century following selected Shared Socioeconomic Pathways.

Surface ozone (O) is a major air pollutant and greenhouse gas with significant risks to human health, vegetation, and climate. Uncertainties around the impacts of various critical factors on O is crucial to understand. We used the Community Earth System Model to investigate the impacts of land use and land cover change (LULCC), climate, and emissions on global O air quality under selected Shared Socioeconomic Pathways (SSPs). Our findings show that increasing forest cover by 20 % under SSP1 in East China, Europe, and the eastern US leads to higher isoprene emissions leading 2-5 ppb increase in summer O levels. Climate-induced meteorological changes, like rising temperatures, further enhance BVOC emissions and increase O levels by 10-20 ppb in urban areas with high NO levels. However, higher BVOC emissions can reduce O levels by 5-10 ppb in remote environments. Future NO emissions control reduces O levels by 5-20 ppb in the US and Europe in all SSPs, but reductions in NO and changes in oxidant titration increase O in southeast China in SSP5. Increased NO emissions in southern Africa and India significantly elevate O levels up to 15 ppb under different SSPs. Climate change is equally important as emissions changes, sometimes countering the benefits of emissions control. The combined effects of emissions, climate, and land cover result in worse O air quality in northern India (+40 %) and East China (+20 %) under SSP3 due to anthropogenic NO and climate-induced BVOC emissions. Over the northern hemisphere, surface O decreases due to reduced NO emissions, although climate and land use changes can increase O levels regionally. By 2050, O levels in most Asian regions exceed the World Health Organization safety limit for over 150 days per year. Our study emphasizes the need to consider complex interactions for effective air pollution control and management in the future.