Investigation On The Vertical Structure And Interaction Of Fine Particulate Matter And Ozone

Air pollution has become increasingly significant with the accelerating urbanization and industrialization process in China.As the major atmospheric pollutants in urban area,fine particulate matter(FPM,i.e.PM_2.5)and ozone have drawn much attention in recent years for their climate effect and adverse effects on human health and crop growth.In recent decades,a decreasing trends in PM_2.5concentrations in China can be observed due to the emission controls,while the concentration of tropospheric ozone has increased.Therefore,conducting research on the vertical structure and interaction of atmospheric fine particles and ozone is important for understanding the pollution formation.In this paper,the vertical distribution and correlation of FPM and ozone have been investigated through different types of observation.The chemical interactions between FPM and ozone has been studied by using a regional atmospheric chemistry model.An Earth system model has also been applied to evaluate the effects that involve aerosol influences on the radiation balance and on planetary boundary layer development,which can impact ozone concentration.The main results were shown as follows:Firstly,based on the surface observations,ground-based atmospheric ozone lidar observations and atmospheric Raman lidar observations,the variation characteristics,vertical distribution characteristics and the correlations of FPM and ozone in Nanjing have been studied.In 2017,the annual average surface ozone concentration in Nanjing was 36.09 ppb.The average ozone concentration within a range of 2 km generally increased with height,and the ozone concentration at different height showed a typical seasonal variation trend with maximum in summer and minimum in winter.The annual average surface PM_2.5 concentration in Nanjing was 49.81?g m^-3.PM_2.5 concentration was higher in winter(60.97?g m^-3)and lower in summer(18.57?g m^-3).Within 2 km,the extinction coefficient of particles decreased with height,and the change rate of extinction coefficient with height was the largest in winter,followed by spring,and the smallest in summer.In 2017,PM_2.5 and O₃ in Nanjing showed a negative correlation,however,the correlations were different in different seasons:PM_2.5 and O₃ showed a significant positive correlation in summer,and a significant negative correlation in spring,autumn and winter.When considering different heights,in spring and winter,PM_2.5 and ozone were negatively correlated at lower levels,and positively correlated at higher levels.The negative correlation was strongest at 300 m,and the correlation coefficients were-0.32 and-0.47 in spring and winter,respectively.The positive correlation was strongest at around 1500 m,and the correlation coefficients were 0.31 and 0.55 in spring and winter,respectively.In summer,the correlation between PM_2.5 and ozone was positive throughout the entire 2km.The correlation between PM_2.5 and ozone was related to the meteorological feedback of the planet boundary layer(PBL)and the extinction effect of particulate matter.The correlation coefficient between PM_2.5 and planet boundary layer height(PBLH)was about-0.70.The negative correlation between atmospheric visibility and PM_2.5 was also found in this study,with a correlation coefficient of-0.57.Secondly,based on the three-dimensional regional model WRF-Chem,the chemical interaction between FPM and ozone in the Yangtze River Delta(YRD)region was quantitatively evaluated,that is,the influence of photochemical reaction process and heterogeneous reaction process.The simulation shows that the extinction of FPM can weaken solar radiation,increase optical thickness,and lead to the decrease of the surface photolysis rates J_NO2 and J_O1D,which reduced the ozone concentration by 1.3?3.2 ppb.The reduction in ozone concentration also affects the oxidation of the atmosphere and indirectly reduces the concentration of secondary particles.However,the scattering aerosols can increase photolysis rates above PBL and lead to slight ozone increase at higher altitudes.The heterogeneous reactions can directly consume ozone,as well as H_xO_y and ozone precursor NO_x,thereby affecting the ozone concentration.Heterogeneous reactions result in a decrease in surface ozone concentration in YRD in spring,autumn and winter.In summer,the southern YRD is the NO_x-control area,in which the decrease of NO_x leads to a decrease in ozone concentration.While the northern YRD is the VOC-control area,in which the decrease of NO_x leads to a decrease in ozone concentration.Heterogeneous reactions can also affect the formation of secondary aerosols,such as sulfate and nitrate,resulting in increased PM_2.5.Under the combined influence of the two chemical interactions,in the urban areas of YRD,the changes in ozone concentration in spring,summer,autumn and winter were-7.57%,-3.96%,-6.33%,-18.7%,respectively,and the annual average ozone concentration reduced by about 9%.The changes of PM_2.5in spring,summer,autumn and winter were 1.95%,6.47%,-2.57%,and 2.15%respectively,and the annual average concentration increased by about 2%.Finally,based on the global earth system model UKESM1-AMIP,the impact of FPM on ozone through radiation-meteorological feedback was quantitatively evaluated.By comparing the simulations,we found that aerosols direct radiative effect reduced the shortwave radiation by 11%in China,and consequently led to lower turbulent kinetic energy(reduced by 16.7%),weaker horizontal winds and a shallower boundary layer(with a maximum of 22.01%reduction in north China).On the one hand,the suppressed boundary layer limited the export and diffusion of pollutants,and increased the concentration of CO,SO₂,NO,NO₂,PM_2.5 and PM₁₀ in the aerosol rich regions.The NO/NO₂ ratio generally increased and led to more ozone depletion.On the other hand,the boundary layer top acted as a barrier that trapped moisture at lower altitudes and reduced the moisture at higher altitudes.Due to reduced water vapor,fewer clouds were formed(the annual average cloud amount was reduced by 4%),and more sunlight reached the surface,so the photochemical production of ozone increased.Under the combined effect of the two meteorology feedback methods,the annual average ozone concentration in China declined by6.2%.In summary,through the data analysis and numerical simulation research,the vertical distribution and correlation of FPM and ozone,as well as the chemical interactions and meteorological feedback interactions between FPM and ozone were found.FPM affects the photochemical reaction of ozone by increasing atmospheric extinction,weakening ultraviolet radiation,and reducing photolysis rate.FPM directly consumes ozone,atmospheric oxides and ozone precursors through heterogeneous reactions,thereby affecting the concentration of ozone.Through direct radiative effects,FPM affects the radiation balance,weakens the development of the boundary layer,affects the transmission and diffusion of pollutants and water vapor,and causes changes in ozone concentration.The interaction processes generally lead to a decrease in the ozone in the VOC-control regions,and a slight increase in the ozone in the NO_x-control region.These interactions processes generally lead to an increase in PM_2.5.The results in this dissertation are important in fully understanding the interaction between FPM and ozone in China,and provide scientific foundation for controlling PM_2.5 and ozone pollution.