Analysis Of Spatial And Temporal Distribution And Influencing Factors Of Nitrogen Dioxide Column Concentration In Four East Asian Countries

In this paper,the satellite OMI（Ozone Monitoring Instrument）sensor inversion product is used to analyze the nitrogen dioxide data of Mongolia,North Korea,South Korea and Japan from 2013 to 2021,aiming to grasp the transport and diffusion of NO₂in the atmosphere and analyze the influence of different factors on NO₂ under different conditions.It has guiding significance for assessing the status of air pollution,as well as atmospheric environmental research and air quality control among countries.The results show that:1.Mongolia’s NO₂ column concentration is much lower than that of North Korea,South Korea and Japan.In the overall spatial distribution,the concentration of NO₂ column gradually increased from northwest to southeast in Mongolia,high in the south and low in the north of Korea,the highest in the northwest coastal area,and decreased from north to south in South Korea.In terms of time,the NO₂ column concentration of North Korea,South Korea and Japan showed a downward trend in the past 9 years,with the fastest decline in 2017～2020 and a recovery in 2021.Mongolia has an overall upward trend,with a decline in 2020 and a rapid and substantial increase in 2021.In the monthly average change,the monthly mean NO₂column concentration in Mongolia in 9 years showed an inverted’V’type distribution,the lowest in winter and the highest in summer.In space,the high concentration area expanded from southeast to northwest from January to July,and contracted from northwest to southeast from July to December.The monthly variation of NO₂ column concentration in North Korea,South Korea and Japan showed a’V’type,with the lowest in summer and the highest in winter.The low concentration area expanded from North Korea and northern Japan,as well as South Korea and southern Japan,to the middle from January to July,and contracted from the middle to the south from July to December.2.Using python to analyze the rank correlation between NO₂ column concentration and various factors,correlation analysis showed that temperature,O₃,AOD and HCHO were positively correlated in most parts of Mongolia,and negative in North Korea,South Korea and Japan;air pressure,specific humidity,uplift index and SO₂ are negatively correlated in most parts of Mongolia,and are positive in North Korea,South Korea and Japan.Relative humidity was negatively correlated throughout the study area.The correlation between AOD and NO₂ column concentration was negative in southern Mongolia,and did not pass the P test in northern Mongolia,as well as in North Korea,South Korea and Japan.In Mongolia,the NO₂ column concentration is too low,and the correlation between air pressure and NO₂ column concentration cannot pass the P value test.In Japan,the higher the NO₂ column concentration,the stronger the correlation between air pressure,uplift index,SO₂ and NO₂ column concentration;the factors and NO₂ column concentration in the whole study area are mainly moderately correlated,but the temperature is highly correlated in most areas,and the uplift index and specific humidity are highly correlated in some areas.In Ulaanbaatar,as well as a small part of North Korea and Japan,the correlation between various factors and NO₂ column concentration may not pass the P test,or the correlation is quite different from the surrounding area.3.The XGBoost model and SHAP model were used to analyze the influence of various factors on the monthly NO₂ column concentration.It was found that the NO₂column concentration in the four East Asian countries was greatly affected by natural factors such as temperature,pressure and relative humidity,and was less affected by AOD,SO₂ and HCHO,and AOD>SO₂>HCHO,and the influence of O₃ was slightly less than that of natural factors.The sum of NO₂ column concentration affected by various factors was’V’type distribution in DPRK,South Korea and Japan,with the minimum in July and the maximum in January and December,while Mongolia showed a slow upward trend.The temperature of DPRK,South Korea and Japan has the greatest influence on the concentration of NO₂ column,followed by relative humidity.Mongolia is greatly affected by air pressure,followed by temperature.However,from June to August,O₃ has the greatest influence on the concentration of NO₂ column.In February and March,SO₂ has a great influence on the concentration of NO₂ column,especially in March.The influence of other factors in the two study areas is relatively small.The influence of each factor is different in different months and different regions.The change trend of the same factor and its influence value is not necessarily the same in different study areas.4.The XGBoost model was used to predict the NO₂ column concentration in the DPRK,South Korea and Japan during the cross-border transmission period.Compared with the actual value,it was found that in May 2016,January 11-15,2019,and February20-25,2019,due to cross-border transmission,the NO₂ column concentration increased in a few areas such as Hokkaido and Kanto Plain in North Korea,South Korea,and Japan,while cross-border transmission reduced the NO₂ column concentration in most areas of Japan.From February 26 to March 3 to March 4-8,2019,the NO₂ column concentration growth area caused by cross-border transmission moved from southern Korea to northern Korea,and Kyushu Island in southern Japan and Hokkaido in northern Japan moved to northern Honshu Island.