Tropospheric Ozone Assessment Report II: Changing health impacts of global ozone exposure

As part of the second Tropospheric Ozone Assessment Report (TOAR-II), we synthesize global observations and observationally constrained estimates of surface-level ozone (O3) with contemporary literature to characterize the global distribution and trends of long-term O3 exposure, focusing on two health-relevant metrics and health impacts attributable to long-term exposure. The highest 2016–2020 surface-level O3 concentrations are observed or estimated in South Asia, eastern China, and parts of the Middle East and North Africa. From 2000 to 2020, O3 declined across southeastern North America and parts of Eastern Europe, while the largest increases occurred in South Asia and Sub-Saharan Africa. Global premature mortality from chronic obstructive pulmonary disease (COPD) attributable to long-term O3 exposure nearly doubled between 2000 and 2020, reaching approximately 500 000 deaths annually. This overall increase obscures decreasing attributable deaths across North America and Europe and increasing deaths across large parts of the Global South. To spur high-quality, robust research on O3 health impacts, we summarize state-of-the-science practices for conducting health impact assessments (HIAs) and characterizing associated uncertainty. We also call for expanded in situ monitoring, improved health datasets and epidemiologic evidence, and sustained precursor emission reductions to clarify and limit the growing global health burden of O3 under climate change and demographic shifts.