Study On The Interactions Of Air Pollution,Vegetation And Carbon Dioxide In China

Carbon dioxide(CO₂)is an important greenhouse gas that can influence regional climate through disturbing radiation balance,and is the main driver of global climate warming.As the raw material required for plant photosynthesis,the change in its concentration can regulate the emission process of biogenic volatile organic compounds(BVOC),thereby affecting the concentration of ozone and particulate matter in the atmosphere.On the other hand,ozone damage to plant cells and the diffuse fertilization effect of particulate matter can influence plant growth and development,thus changing the CO₂ absorption by terrestrial ecosystems.As the world's largest energy consumer and greenhouse gas emitter,China's CO₂concentration is steadily rising in recent years.At the same time,the compound air pollution mainly caused by particulate matter and ozone is causing the air quality worse and threatens to human health,which has attracted more and more scholars'attention.Therefore,studying the interaction between CO₂,ozone,and particulate matter in China is of great significance for mitigating regional climate change and improving future air quality.In this paper,the coupled regional climate,chemistry,and ecosystem model RegCM-CHEM-YIBs is first used to calculate the spatial and temporal distribution of CO₂ concentrations and terrestrial carbon fluxes in China,and assess the effects of terrestrial carbon fluxes to CO₂ concentrations.Then,we estimate the effects of current ozone and particulate matter on terrestrial carbon fluxes and atmospheric CO₂ concentrations.In addition,the impacts of increasing CO₂concentration and global climate change on BVOC emissions,ozone and secondary organic aerosol(SOA)are investigated.Following are the main results of this study.First,the coupled regional climate,chemistry,and ecosystem model RegCM-CHEM-YIBs is developed.We added a new species CO₂ to the original regional climate chemistry model RegCM-CHEM,and coupled the terrestrial ecosystem model YIBs to calculate the CO₂ and BVOC fluxes of terrestrial vegetation.The SOA scheme in the model is improved,and the prescribed CO₂ concentration in the radiation module and the YIBs model is replaced by the calculated CO₂concentration.So,the RegCM-CHEM-YIBs model has the ability to study the interactions among regional climate,atmospheric chemistry,and terrestrial ecosystems.The simulated results are in good agreement with the reanalysis data,site monitoring observation,and satellite products,indicating that the coupling model are reasonable and credible.Secondly,the spatial and temporal distribution of terrestrial carbon fluxes and atmospheric CO₂ concentrations in China are explored.The terrestrial carbon fluxes show an increasing trend from north to south between 2006 and 2015.The absolute values of the net ecosystem exchange(NEE)are higher in the southwest China,with a maximum exceeding 1000 g C m^-2 yr^-1.Additionally,the terrestrial carbon fluxes in different regions show obvious seasonal variations.NEE in summer accounts for about 60%of the annual NEE.NEE is negative in summer,indicating that the terrestrial ecosystem acts as an important CO₂ sink.On the contrary,it is mainly positive in winter.The seasonal variation of NEE shows significant negative correlations with temperature and precipitation,and the correlation with temperature is greater than that of precipitation.The interannual variation of NEE is strongly correlated with the El Ni?o-Southern Oscillation(ENSO)event.The increased temperature and decreased precipitation during the El Ni?o period can weaken the absorption of CO₂ by vegetation.The annual mean growth rate of CO₂ in China is 2.2ppm yr^-1,which is higher than the global average.High levels of CO₂ are located in the urban clusters such as Beijing-Tianjin-Hebei region,Yangtze River Delta,Pearl River Delta and Sichuan Basin,with a maximum exceeding 430 ppm.CO₂concentrations in winter and spring are higher than that in summer and autumn.The peak value appears in February and the valley value in June for southern regions,while for northern areas,the peak value and valley value appear in April and July,relatively.Terrestrial carbon flux is the main factor that causes the seasonal variation of CO₂ concentration.CO₂ concentrations decrease(about 6 to 12 ppm)in summer due to the absorption of CO₂ by vegetation.Thirdly,the effects of ozone and particulate matter on atmospheric CO₂ are assessed.Due to the ozone damage to vegetation,China's annual mean gross primary productivity(GPP)and NEE decrease by 0.76±0.27 Pg C yr^-1 and 112.2±22.5 Tg C yr^-1,respectively.The effects of ozone on vegetation show obvious seasonal variations.The changes of GPP and NEE are much greater from April to September,which account for more than 90%of that during the whole year.The decrease in terrestrial carbon fluxes leads more CO₂ to accumulate in the atmosphere.The annual mean CO₂ concentrations in most parts of China have increased by about 0.7 to 2.5ppm,with a maximum of 6 ppm in some parts of Yunnan and Guizhou provinces.Particulate matter affects terrestrial carbon uptake through diffuse radiation fertilization effect and hydrometeorological feedbacks.The results show that particulate matter can increase GPP and terrestrial carbon flux by about 0.36 Pg C yr^-1(5%)and 0.06 Pg C yr^-1(21%),respectively.The increase of GPP mainly occurs in the southwest,southeast and north China,while the change of terrestrial carbon flux mainly comes from the southwest and central China.The increase in diffuse radiation fraction caused by particulate matter is found to be the dominant contributor to the changes of GPP and NEE,which covers?59–62%of China's land area.Additionally,the national mean CO₂ concentration decreases by about 0.62 ppm in summer due to the influence of particulate matter.The largest decrease is found in the Sichuan Basin,with a maximum of 4 ppm.Finally,the effects of increased regional CO₂ concentration and global climate change on ozone and SOA concentrations are explored.Under the influence of increased regional CO₂ concentration and global climate change,the photosynthesis rate and productivity of terrestrial vegetation in China have increased significantly.The changes of BVOC emission show obvious seasonal variations,which is enhanced in summer and autumn,but decreased in winter and spring.Annual isoprene emissions increase by 1.40 Tg C yr^-1(17%),and monoterpene emissions decreased by 0.14 Tg C yr^-1(5%).Due to the effect of increased regional CO₂concentration and global climate change,ozone and SOA concentrations over China decrease by 0.5 ppb and 0.3?g m^-3,respectively.The influence of global climate change on ozone and SOA is opposite to the effect of increased regional CO₂concentration.Global climate change has led to a significant decrease in ozone and SOA concentrations in North China during summer(maximum reduction 7 ppb and3.4?g m^-3),and a significant increase in southern China(maximum increase 5 ppb and 2.6?g m^-3).Changes in the atmospheric circulation caused by global climate change enhance the transport of pollutants from north to south in summer,and increase the concentration of ozone,SOA and its precursors in southern China.On the contrary,CO₂ fertilization effect will result in an increase of ozone and SOA concentration in North China and a decrease in South China.In North China,the enhanced photosynthesis rate caused by CO₂ fertilization effect plays a leading role in the emission of BVOC,and the increased BVOC emission further promote the formation of ozone and SOA.However,the CO₂ inhibition effect is more important in South China,and the decreased BVOC emission reduces the concentration of ozone and SOA.This study reveals the spatial and temporal distribution of near-surface CO₂concentration and terrestrial carbon fluxes in China in recent years,and shows a comprehensive analysis on the interactions among CO₂,ozone and particulate matter through terrestrial ecosystem.This dissertation is of considerable referential importance in understanding the feedbacks among regional climate,atmospheric chemistry and terrestrial ecosystem,and provides scientific foundation for future climate policy making and air quality management in China.