Mid-21st century ozone air quality and health burden in China under emissions scenarios and climate change
Despitemodest emissions reductions of air pollutants in recent years, China still suffers frompoor air quality, and the outlook for future air quality inChina is uncertain.We explore the impact of two disparate 2050 emissions scenarios relative to 2015 in the context of a changing climate with the Geophysical FluidDynamics Laboratory AtmosphericModel version 3 (GFDL-AM3) chemistryclimatemodel.We impose the same near-term climate change for both emission scenarios by setting global sea surface temperature (SST) and sea ice cover (SIC) to the average over 2010–2019 and 2046–2055, respectively, from a three-member ensemble of GFDL coupled climatemodel simulations under the RCP8.5 (Representative Concentration Pathway) scenario. By the 2050s, annualmean surface ozone increases throughout China by up to 8 ppbv from climate change alone (estimated by holding air pollutants at 2015 levels while setting SIC and SST to 2050 conditions in themodel) and by 8–12 ppbv in a scenario inwhich emissions of ozone precursors nitrogen oxides (NOx) and anthropogenic volatile organic compounds (VOCs) increase by∼10%. In a scenario inwhichNOx and anthropogenic VOC emissions decline by 60%, annualmean surface ozone over China decreases by 16–20 ppbv in the 2050s relative to the 2010s. The ozone increase from climate change alone results in an additional 62 000 premature deaths inChina as compared to 330 000 fewer premature deaths by the 2050s under a strong emissionsmitigation scenario. In springtime over SouthwesternChina in the 2050s, themodel projects 9–12 ppbv enhancements to surface ozone from the stratosphere (diagnosed with amodel tracer) and from international anthropogenic emissions (diagnosed by differencing AM3 simulations with the same emissions withinChina but higher versus lower emissions in the rest of theworld). Ourfindings highlight the effectiveness of emissions controls in reducing the health burden inChina due to air pollution, and also the potential for climate change and rising global emissions to offset, at least partially, some of the ozone decreases attainedwith regional emission reductions inChina.