Future Projection Of Concentrations Of Pm_2.5 And O₃ And The Associated Health Effects In China Under Different Emission Scenarios

With the rapid economic development in the past few decades,China confronts the complex air pollution characterized by fine particulate matter(PM_2.5)and ozone(O₃).Both PM_2.5 and O₃ are harmful to the ecological environment and human health.Therefore,exploring the variation of PM_2.5 and O₃ concentrations in China and the associated health effects under different future scenarios is the basis to formulate medium and long-term plans for the atmospheric environment.We applied a global chemical transport model GEOS-Chem combined with different Shared Socioeconomic Pathways(SSPs)to carry out the following research:(1)GEOS-Chem model was applied to project the concentrations of PM_2.5 and O₃concentrations in China from 2015 to 2050 based on SSP1-1.9,SSP1-2.6,SSP2-4.5,SSP3-7.0and SSP5-8.5 pathways.The model captures the PM_2.5 and the maximum daily 8-h average of O₃(MDA8 O₃)concentrations and variations in China generally well.It is suggested that the annual mean concentrations of PM_2.5 and MDA8 O₃ in China will decrease year by year under SSP1-1.9(SSP1-2.6)scenario from 2015 to 2050 with the percentage reductions of 73.0%(64.4%)and 22.8%(16.2%),respectively.And those under SSP3-7.0 pathway were simulated to increase significantly with the change of+21.2%and+8.3%,respectively.By analyzing the concentrations of PM_2.5 components,it is found that under each scenario,due to the decrease in sulfate concentrations and the increase in NH₃ emissions,controlling nitrate will become the important way to improve PM_2.5 air quality in China in the future(especially in winter)when the organic carbon can't be ignored(especially in Pearl River Delta region(PRD)).It is worth noting that the annual mean MDA8 O₃ concentration in BTH and YRD regions from 2015?2050 will increase by 13.8%and 8.9%under SSP2-4.5 scenario which is close to current development scenario due to the reduction in NO_x under VOCs-limited zone.These results suggest that the synergistic reduction in PM_2.5 and O₃ concentrations in China in the future only can be achieved under SSP1-1.9 and SSP1-2.6 pathways.(2)We further quantitatively esitimated the contribution of transport from SA and SEA to concentrations of PM_2.5 and O₃ in China using GEOS-Chem mode based on emission zero-out sensitivity experiments.The results show that the transport from SA and SEA had a great impact on air quality in China in 2015,which increased the annual mean PM_2.5 and MDA8 O₃concentrations by 1.1?g m^-3(6.3?g m^-3 in Yunnan)and 4.0?g m^-3(19.1?g m^-3 in Yunnan),respectively.The transport from SA and SEA has obvious monthly variation characteristics,and it contributed largest to PM_2.5 concentration in Sichuan Basin(SCB)in March(3.8?g m^-3),followed by PRD in July(1.8?g m^-3)in 2015.And it contributed greatly to the concentration of MDA8 O₃ in YRD and PRD in July with increase of 3 and 14?g m^-3,respectively,and increased that in SCB by 4.6?g m^-3 in April.The impact of pollutant transport from SA and SEA on air quality in China will vary with pollutant concentrations and emissions over there.The influence on the annual mean concentrations of PM_2.5 and MDA8 O₃ in China will decrease year by year under SSP1-1.9 scenario,to 0.5 and 2.4?g m^-3 in 2050,respectively;under SSP3-7.0 pathway,it will rise to 1.5 and 4.9?g m^-3.Moreover,under SSP3-7.0 scenario,the contribution to PM_2.5 concentration in SCB in March 2050 will be 5.1?g m^-3 when the MDA8O₃ concentration in PRD in July 2050 will increase by 15.3?g m^-3 which are quite impressive.It should be considered that the relative contribution from SA and SEA to air quality in typical polluted regions will also gradually increase with the decline in pollutant concentrations in China under SSP1-1.9 scenario.The above results reveal that the transport from SA and SEA has a great impact on the current and future air quality in China.(3)The GEOS-Chem model was used to explore future PM_2.5 and O₃ air quality and the associated health effects in China under carbon neutral(SSP1-1.9)scenario.The environment and health benefits of carbon neutrality will be derived by comparison with the results under SSP5-8.5 scenario(a pathway with high fossil-fuel consumption).Under SSP1-1.9 scenario,from 2015 to 2060,the annual mean PM_2.5 concentrations(90th percentile of MDA8 O₃concentrations)in BTH,YRD,PRD,SCB,Fenwei Plain(FWP)and China will decrease by75.2%(27.6%),74.7%(25.6%),77.0%(33.4%),75.1%(32.2%),74.9%(31.3%)and 72.2%(25.4%),respectively.PM_2.5 and O₃ air quality in above regions will meet the national standard simultaneously by 2040 and 2030,respectively,which wouldn't be achieved by 2060 under SSP5-8.5.Although pollutant concentrations will decrease dramatically,the total number of pollutant-related deaths from 2015 to 2060 will increase from 2.90(95%CI:2.86?3.02)million in 2015 to 4.06(95%CI:3.98?4.13)million(+38.1%)in 2060 due to the deepening of population aging under SSP1-1.9 scenario which will be more significant(+157.8%)under SSP5-8.5 pathway.Therefore,based on the development of the carbon neutrality,relative to SSP5-8.5,about 3.52(95%CI:3.47?3.57)million premature deaths will be avoided in 2060.Decreasing pollutant concentrations under SSP1-1.9 pathway will reduce premature deaths caused by severe aging from 2015 to 2060,and will offset about 5077.6(95%CI:5054.9?5100.1)and 95.0(95%CI:71.0?116.7)thousand deaths related to PM_2.5 and O₃ in 2060,respectively.In contrast,the increase in MDA8 O₃ concentrations under SSP5-8.5 pathway will accelerate the growth of O₃-related deaths in China from 2015 to 2060.These results suggest appreciable enviroment and health benefits to achieve carbon neutrality.