Impacts Of Anthropogenic Emission Reduction And Climate Change On Fine Particles And Ozone In China

During the past several years,concentration of air pollutants has been significantly reduced in China owing to the continuous environmental policy restricting anthropogenic emissions.However,the exceedance of PM_2.5 and ozone to national standard is still serious,and long-term emission reductions policy is required in the future.In 2020,China put forward the goal of achieving carbon neutrality by 2060,which may have significant positive effect on air quality during systematical emission reduction.This study produced a WRF/CMAQ regional simulation downscaled from CESM global simulation based on several scenarios in CMIP6,aiming to realize several issues including the improvement of air quality in China around 2060 under the carbon neutral target,the evolution of air pollutants under various emission pathways,and response of PM_2.5 and ozone to anthropogenic emissions and climate change.The main findings are as follows:First of all,air pollutants based during 2056-2060 based on the CMIP6 scenarios was assessed.In the SSP126 scenario with a sustainable development path and similar to the carbon neutral target,the average PM_2.5 concentration will reach 14.7μg/m³,which is 44%less than the historical period,and the number of exceeding days for PM_2.5 is only 2.3%,reduced by 2/3compared to historical period.The average concentration of ozone in China has dropped to 39.8ppbv,23%less than historical period,and the number of days exceeding the standard has been reduced by more than 90%.Then,individual effect of anthropogenic emissions and climate change on PM_2.5 and ozone is isolated under climate change.In regions with relatively high emisisons,the drastic reduction of anthropogenic emissions in the SSP126 scenario dominates the reduction of PM_2.5and ozone concentrations and the number of days exceeding the standard,contributing more than 80%.For SSP585 where the reduction of anthropogenic emissions is medium,climate change has a dominantly negative impact on ozone,leading to the“climate penalty”effect on ozone,which need more effort on reducing anthropogenic emissions than SSP585.Further more,The compound extreme weather from heat wave and stagnation and its non-linear effect on ozone was proposed.Heat wave and stagnation have a significantly positive effect on ozone concentrations.Meanwhile,their compound extreme event has a stronger positive effect on ozone,and the non-linear effect like"1+1>2"exists.The positive non-linear effect tends to occur while the intensity of heat wave during compound extreme event is greater than the intensity of the heat wave as well as high emissions.Finally,the mechanism of ozone response to climate change is analyzed from two perspectives.The importance of temperature higher-orders changes on ozone is firstly revealed.The contribution of high-order changes in temperature to the probability of ozone exceedance during heat waves is 20%and-48%,respectively,indicating climate model need to improve their ability for predicting temperature higher-orders feature in terms of ozone studies.The coupling effect of emissions,temperature,and water vapor on ozone is investifgated.Temperature dominantly has positive effects,and water vapor dominantly generate negative effects on ozone.However,water vapor presents a positive effect under conditions of high emissions,high temperature and high water vapor together.Given large reduction in anthropogenic emissions which may restrict the positive effect of temperature and water vapor,the“climate penalty”effect during global warming may be converted to“climate reward”.