Temporal And Spatial Variation Monitoring Of SO₂ And NO₂ Concentrations In Northeast Asia Using Remote Sensing

With the rapid development of economy,Northeast Asia has become one of the three most developed regions in the world.At the same time,Northeast Asia is also one of the regions with the worst air pollution in the world.At present,regional and complex air pollution problems including aerosol and photochemical smog issues had appeared in China.The increase of SO₂ and NO₂ concentrations in the atmosphere will cause harm to animals and plants and even the human body.At the same time,SO₂and NO₂,as trace gases,can undergo a series of chemical reactions in the atmosphere to generate secondary aerosols,further causing the quality of the atmospheric environment to decline.Therefore,it is important to pay attention to the distribution characteristics,causes and control measures of SO₂ and NO₂ in Northeast Asia to improve regional air quality.This paper uses OMI sensor data from Aura satellites to analyze the spatial and temporal distribution characteristics of SO₂ and NO₂ in Northeast Asia from 2009 to 2018,and further analyzes the effectiveness of air pollution control measures in Japan,South Korea,and some cities of the“Three Regions and Ten Groups”"of China.The results are as follows:?1?From 2009 to 2018,the mean SO₂ vertical column density?VCD?in the boundary layer of Northeast Asia was 0.68DU,and the NO₂ VCD in the troposphere was 4.08×10¹⁵molec/cm².the high-value SO₂ and NO₂ VCD regions in Northeast Asia were similar,with obvious regionality.The high-value regions are regions with rapid economic development and high energy demand.For example,areas with high SO₂VCD in the boundary layer:Beijing-Tianjin-Hebei region?1DU?,Shandong?1.05DU?,Shanxi,and Henan provinces.The regions with high NO₂ VCD in the troposphere are mainly distributed in Beijing-Tianjin-Hebei(11.84×10¹⁵molec/cm²),Shandong province(13.33×10¹⁵molec/cm²),the Pearl River Delta(6.45×10¹⁵molec/cm²)and the Yangtze River Delta regions(9.23×10¹⁵molec/cm²),Seoul of South Korea,and Tokyo of Japan.The overall spatial distribution of SO₂ VCD had shown a downward trend over the past 10 years.The area of high-value were decreased,and the area of low-value were increased,the change amplitude of the spatial distribution of NO₂ VCD were not been as significant as that of SO₂.The seasonal spatial distribution of SO₂ and NO₂ VCD were similar.It showed the highest rules in winter,followed by spring and autumn,and the lowest in summer,the seasonal variation of NO₂ was more obvious than that of SO₂.After China implemented the“Air Pollution Prevention and Control Action Plan”in 2013,the high-value areas of SO₂ and NO₂ VCD in Northeast Asia have been reduced,and the low-value region were remained stable,the average SO₂ VCD in2014-2018 decreased by 0.1DU(2.69×10¹⁵molec/cm²)compared with 2009-2013,and the NO₂ VCD decreased by 0.97×10¹⁵molec/cm².?2?From 2009 to 2018,both SO₂ and NO₂ annual average VCD in Northeast Asia showed a downward trend,in which the distribution of SO₂ VCD was divided into three stages:“sharp fluctuation”-“stable decline”–“maintaining stability”.In the first stage?2009-2012?,the distribution of SO₂ VCD in Northeast Asia showed a sharp fluctuation,showing a“descending-rising–decreasing”trend.In 2011,the SO₂ VCD increased by 0.07DU compared to 2009,and it decreased 0.06DU in 2012 compared to2011,which was closely related to the change of SO₂ distribution in China.In the second stage?2012-2016?,the VCD distribution of boundary layer SO₂ column in Northeast Asia showed a stable downward trend with an annual growth rate of-44.7%.The third stage was from 2016 to 2018.The distribution of SO₂ VCD in Northeast Asia remained stable,with an average SO₂ VCD of 0.61 DU.The NO₂ VCD showed two stages:“rise-decline”,and reached its peak in 2011,which was 4.99×10¹⁵molec/cm².In Northeast Asia,the monthly changes of SO₂ and NO₂ VCD showed a wave pattern with a period of 12 months,the maximum value of SO₂ in 10 years appeared in January2012,which was 0.93DU,and the minimum value appeared in July 2016,which was0.48DU.The monthly changes of SO₂ VCD were not obvious,while the periodicity of NO₂ was strong,the NO₂ VCD was high in November,December,and January of the following year,and was low in June,July,and August.During the 10 years,the maximum monthly average value of NO₂ VCD appeared in January 2013 as 13.09×10¹⁵molec/cm²,the minimum value appeared in August 2018 as 1.88×10¹⁵molec/cm²;the seasonal distribution of SO₂ and NO₂ VCD showed the law of summer<spring<autumn<winter,winter maximum and summer minimum.The seasonally highest value of SO₂ VCD in Northeast Asia appeared in the winter of 2011,which was 0.89DU,and the lowest value appeared in the summer of 2016,which was 0.50DU;the highest value of NO₂ VCD appeared in the winter of 2011,which was 9.89×10¹⁵molec/cm²,the minimum appeared in the summer of 2018,which was 1.93×10¹⁵molec/cm².?3?From 2009 to 2018,the variation trend of SO₂ VCD in Japan and South Korea were similar,both showed the first rise and then decline,the VCD was the lowest in2009?0.62DU in Japan and 0.61DU in South Korea?,after which the two regions showed the highest value in 2011 at the same time,the maximum value in Japan was0.69DU,and South Korea was 0.68DU.The average annual growth rate of SO₂ VCD in Japan?0.17%?over the past 10 years was much lower than that in South Korea?1.09%?.The distribution trends of NO₂ VCD was opposite to the SO₂,the NO₂ VCD in Korea(7.0×10¹⁵molec/cm²)is much higher than that in Japan(2.69×10¹⁵molec/cm²).?4?Changes in SO₂ and NO₂ VCD in China's severely polluted areas were directly affected by the promulgated policies,especially after the implementation of the“Air Pollution Prevention and Control Action Plan”policy in 2013,the concentrations of SO₂ and NO₂ in Beijing-Tianjin-Hebei,Shandong Province,the Yangtze River Delta and the Pearl River Delta had rapidly decreased,the emission reduction tasks proposed by the“Air Pollution Prevention and Control Action Plan”have been successfully completed,and air quality of China have been improved.During the study period,the SO₂/NO₂ ratio in the Beijing-Tianjin-Hebei region and Shandong Province showed a downward trend,the Yangtze River Delta and the Pearl River Delta region remained stable.After 2014,SO₂/NO₂ of Beijing-Tianjin-Hebei region and Shandong Province decline rapidly,until 2018,SO₂/NO₂ of the Beijing-Tianjin-Hebei region?1.97?and Shandong Province?1.74?were both lower than 2,which were close to the levels of the Yangtze River Delta?1.97?and the Pearl River Delta?1.92?.Reflected the effectiveness of desulfurization measures of the two places.