Interaction Of Black Carbon Aerosol And Boundary Layer And Its Influence On Ozone

The problems of air pollution in China are characterized by regionalization.Interaction between ozone and primary and secondary aerosols poses great challenges for effective treatment of regional pollution.In order to understand the characteristics of current ozone pollution and make policy for effective pollution control in the ozone region,this paper based on the observation data of black carbon aerosol（BC）,ozone（O₃）,particulate matter(PM_2.5),nitrogen oxides（NOx）and sulfu dioxide（SO₂）in 2016-2017 and the relationship between black carbon aerosol and near-surface ozone and seasonal characteristics from the perspective of long-term observation will be discussed.Using the WRF-Chem（December 2017）model and taking Nanjing as the research object to explore the distribution of ground black carbon aerosols in complex wind fields in urban areas.We still explore the short-wave radiation、short-wave radiance attenuation、photolysis rate、pseudo-equivalent temperature change、changes in the physical and chemical processes（advection term ADV,vertical mixing term VMIX,chemical term CHEM,the sum of the three is the net contribution NET）in the vertical direction due to black carbon aerosol.Then we design two groups of individual cases（control test and sensitive test）to analysis of the physical and chemical mechanisms of BC on the near-surface ozone concentration in Nanjing area.The main conclusions are followed:The results showed that the average annual concentration of black carbon aerosol in 2016-2017 was 1.29μg/m³.It was found that the value of O₃ under the influence of high BC（higher than average）was significantly lower than that under the influence of low BC（lower than average）.The correlation coefficients between black carbon aerosol and ozone in four seasons were-0.28,-0.13,-0.16,-0.38 respectively,all of them passed the significance test of 95%confidence interval.The coefficients in winter was higher than that in summer,but the reverse correlation between PM_2.5.5 and O₃ was not significant.The numerical simulation found that the difference between the ground-level ozone concentration（the difference of ozone concentration between the sensitive test and the control test）overlaps with the high-value area and the high-value area of the BC,explaining the impact of BC on negative feedback on ozone concentration and confirming the observations.The negative feedback effect of BC on O₃ was confirmed again.The tropospheric ozone formation process is affected by various physical and chemical processes and the ozone concentration will be directly affected by the changes.The numerical model process analysis proves that the influencing mechanisms following:The photochemical production of ozone was reduced by the accumulation of NOx near the ground（VOCs depended condition）via the interaction between BC and boundary layer;The inhibition of vertical turbulent exchange in boundary layer weakened the vertical transport of ozone from upper layer of boundary layer to surface and finally reduced the concentration of surface ozone;And by reducing the wind speed near the ground to decrease the advection input of O₃from upwind region.The main control factors of the cases are different and should be analyzed in detail.When the presence of high concentration of black carbon aerosol in the atmosphere,the incident short-wave radiation will be attenuated by the absorption of the black carbon aerosol,and other meteorological elements and atmospheric pollutant concentrations and variables will be correspondingly changed.