Research On The Air Pollutants And Their Transport In The North China Using Satellite-derived NO_x Emissions

Nitrogen oxides（NOx=NO2+NO）are important pollutants in the tropospheric atmosphere and are also important precursors to secondary pollutants such as ozone（O3）and aerosols.As an important tool for studying NOx emissions,transport and atmospheric chemistry,air quality models often suffer from uncertainty due to the outdated timeliness of traditional bottom-up emissions.Particularly,with the implementation of a series of pollution control measures and the occurrence of special events such as the COVID-19 epidemic,the NOx emission situation in China has changed dramatically in recent years,leading to further uncertainties in the simulation of air quality models.This thesis develops a new method to improve NOx emissions based on high-resolution satellite observations,which significantly improves the accuracy and timeliness of NOx emissions,the accuracy of model simulations.Then,we carried out the study on the spatial-temporal trends and regional transport of air pollutants based on the adjusted NOx emissions.This paper further evaluates the impact of different TROPOMI NO2 retrievals on the estimation of NOx emissions,the accuracy of NO2 and O3 concentration simulations,and their transport quantities.In addition,two autumn and winter seasons in 2018 and 2019（W₂018 and W₂019）were selected to assess the effectiveness of the implementation of emission reduction policies,quantify the relative contributions of local emissions and regional transport to urban NOx pollution,and distinguish the effects of meteorological conditions and emissions changes on the amount of NOx transport.The main findings were as follows:（1）A new algorithm was developed to quantitatively characterize NOx emissions in the North China（NC）,which based on high spatial-temporal resolution TROPOMI tropospheric NO2 vertical column density（VCDs）,optimized WRF-Chem simulations and a priori emissions.Comparison with near-surface concentration observed by the air quality monitoring network of the China National Environmental Monitoring Centre（CNEMC）and VCDs observed by the Multi-Axis Differential Optical Absorption Spectrometer（MAX-DO AS）,which showed that the relative deviation of the simulated NO2 and O3 concentration with the observations were significantly reduced.Therefore,the effectiveness of the satellite-derived NOx emissions was verified.（2）Compared to the Royal Netherlands Meteorological Institute（KNMI）,the TROPOMI NO2 product from the University of Science and Technology of China（USTC）were more consistent with the independent MAX-DOAS measurements.Then,the two TROPOMI products were used to estimate NOx emissions.The results showed that,during the COVID-19 pandemic,the USTC posterior NOx emissions were 17%31%higher than KNMI one in the NC.Further evaluation of their effects on NO2 and O3 simulations.It showed that,compared to the KNMI posterior simulation,the ground NO2 concentration was 9-20%higher and the ground O3 concentration was 6-12%lower in the USTC posterior simulation.Both sets of posterior simulations reproduce a significant decrease in NO2 concentration from P1（before lockdown,from January 1 to 22,2020）to P2（lockdown,from January 23 to February 17,2020）,and a rebound from P2 to P3（recovery,From February 18 to March 31,2020）.However,the variation range of NO2 and O3 concentration in the USTC posterior simulation between adjacent time periods was larger than that in the KNMI one.（3）By comparing the measurements from CNEMC and ground-based MAXDO AS,it was found that the USTC posterior simulations were closer to the observed NO2 and O3 concentration than the KNMI posteriori simulations.The results indicate that the USTC product was more sensitive to the response of NOx emissions during COVID-19 pandemic,and can better improve the performance of NO2 and O3.simulations.Based on the USTC posterior simulations,surface NO2 concentration decreased by 46%from P1 to P2,while surface O3 concentrations increased by 75%.The reduction in NOx emissions led to an increase in O3 concentration,indicating that O3 production was mainly controlled by volatile organic compounds in the NC during the COVID-19 pandemic.（4）Compared to the prior simulations,the USTC posterior simulation found that the NOx emissions decreased by 10.6%and 28.9%in W₂018 and W₂019,respectively,and the NOx emissions in most cities have decreased,indicating that the reduction measures in the past two years have obvious effect.Due to the combined impact of conventional emissions reduction policies and control policies during COVID-19 pandemic,the NOx emissions decreased more significantly in W₂019.（5）A new measurement method of tropospheric NO2 transport based on WRFChem simulation was established.It was found that Baoding,Shijiazhuang,Xingtai,Handan,Anyang and Hebi in the east of Taihang Mountain,as well as Jinan,Zibo and lining in Shandong Province were significant NO2 sources when using the 2017 MEIC emissions.Those cities output NO2 to the surrounding grid at a rate of over 360 g/s,while the output intensity in these cities was reduced after the TROPOMI observational constraint.This result indicating that the NOx reduction was significant under the joint impact of pollution control measures and the lockdown policy.However,compared to the prior simulation,Taiyuan,Changzhi and Jincheng in Shanxi Province shows an increase output using TROPOMI posterior simulation,which due to the NOx emissions in W₂018 and W₂019 were higher than those in 2017.This finding indicated that emission control measures in these three cities need to be strengthened.（6）A measurement method for the inter-city transport of air pollutants has been constructed.USTC posterior simulation shows that the contribution rate of local emissions and external transport to NOx concentration in Beijing is about 60%and 40%,respectively.Compared to the W₂018,the NOx emissions and input in Beijing decreased by 20.4%and 17.2%during W₂019,respectively.Although the adverse effects of meteorological conditions increased the NOx input by 503 g/s,the significant regional NOx reduction still resulted in a net reduction of 699 g/s in Beijing.This result showed that with the regional joint prevention and control of air pollution,the emissions of surrounding cities in Beijing were significantly reduced,and the contribution rate of foreign input to NOx in Beijing was on the decline,while the impact of local emissions of NOx in Beijing will be more prominent.