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

Abstract

Surface ozone (O₃) 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 O₃ 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 O₃ 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 O₃ levels. Climate-induced meteorological changes, like rising temperatures, further enhance BVOC emissions and increase O₃ levels by 10-20 ppb in urban areas with high NO_x levels. However, higher BVOC emissions can reduce O₃ levels by 5-10 ppb in remote environments. Future NO_x emissions control reduces O₃ levels by 5-20 ppb in the US and Europe in all SSPs, but reductions in NO_x and changes in oxidant titration increase O₃ in southeast China in SSP5. Increased NO_x emissions in southern Africa and India significantly elevate O₃ 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 O₃ air quality in northern India (+40 %) and East China (+20 %) under SSP3 due to anthropogenic NO_x and climate-induced BVOC emissions. Over the northern hemisphere, surface O₃ decreases due to reduced NO_x emissions, although climate and land use changes can increase O₃ levels regionally. By 2050, O₃ 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.

Keywords: Air pollution; Climate change; Emissions control; Greenhouse gas; LULCC; Surface ozone.