Analysis On Spatial And Temporal Variation Of NO₂ Column Density In Beijing-tianjin-hebei Air Pollution Transmission Path Cities Using Remote Sensing

In recent years,due to the rapid development of urban transportation and industry,air pollution has become prominent,and air quality has decreased severely,which has greatly harmed human health.As an important trace gas in troposphere and stratosphere,the change of NO₂ column density is an important indicator of air quality.Beijing-Tianjin-Hebei and its surrounding areas are China’s economically developed regions with a large population and also cause some damage to the atmospheric environment.Therefore,the temporal and spatial changes of polluting gas in this area has certain significance for future pollution control and prevention work.In this paper,SCIAMACHY,GOME-2,and OMI satellite remote sensing data were used.Arc GIS software was used to process the tropospheric NO₂ column density in Beijing-Tianjin-Hebei air pollution transmission channel cities from 2003 to 2017.Temporal change and spatial distribution characteristics were analyzed.From the two major aspects of meteorological factors（precipitation,air humidity）and human factors（key monitored enterprise distribution,coal consumption and GDP）,the reasons affecting NO₂ column density change were analyzed.Also the reliability was verified using remote sensing data and wind direction data,and NO₂values from SCIAMACHY and GOME-2,GOME-2 and OMI were compared respectively at the same time;TROPOMI data and OMI data were used to conduct a preliminary comparative study.The results were as follows:（1）Three types of satellite remote sensing data and measured ground NO₂ density in typical cities were selected,and through fitting analysis,it was found that except the low correlation coefficient in Taiyuan,there was a clear correlation between them in other cities.The Hysplit model was used to simulate the backward trajectory of certain date of each season in one year.Compared with the typical wind direction frequencies in wind direction rose chart,there existed good consistency,further illustrating that the NO₂ data was feasible.The GOME-2 NO₂data was consistent with SCIAMACHY and OMI NO₂data,but the overall trend was higher than OMI NO₂data.Comparing the spatial distribution of NO₂column density of TROPOMI and OMI at the same time,it was clear that the spatial distribution of NO₂ column density of these two types were similar.（2）The spatial distribution of tropospheric NO₂ column density of Beijing-Tianjin-Hebei air pollution transmission channel cities during 2003-2017 was analyzed.During the 15 years,the spatial distribution of NO₂column density showed a downward trend from the northwest to the southeast.The area NO₂of high-value areas expanded first and then decreased,but the areas with relatively high NO₂ column density were still concentrated in Shijiazhuang-Xingtai-Handan,Beijing-Tianjin-Tangshan areas,and Jinan City and Zibo City in Shandong Province.The NO₂low-value areas were mainly in the northwest mountainous area of the study area and the northern Yanshan mountainous area.The spatial distribution of the four seasons was quite different.The range of NO₂ high value area was the largest in winter,followed by spring and autumn,and the overall NO₂ column density decreased in summer.（3）The interannual,seasonal and monthly variation characteristics of tropospheric NO₂column density of Beijing-Tianjin-Hebei air pollution transmission channel cities from 2003to 2017 were analyzed.From the perspective of interannual changes,the NO₂density overall trend was increasing from 2003 to 2011.The NO₂density reached a maximum of31.6×10¹⁵molec/cm² in 2011,and gradually decreased in 2012,Then,in 2017 the NO₂density reached the lowest,which was 11.12×10¹⁵molec/cm².In terms of seasonal changes,the NO₂column density in winter was the highest in a year,which was 27.81×10¹⁵molec/cm²,and the NO₂density in summer was the lowest,which was 10.7×10¹⁵molec/cm².From the perspective of monthly changes,the NO₂density showed the characteristics of cyclical fluctuations.With peak and low values in a year.（4）The changes of NO₂ column densities in Beijing-Tianjin-Hebei air pollution transmission channel cities varied greatly in three different periods.From 2013 to 2017,the NO₂annual growth rate of all cities was negative,That is,it showed downward trend,which showed that the"Ten Atmospheric Laws"introduced in 2013 achieved initial results.（5）The factors affecting NO₂ column density were mainly meteorological factors and human factors.The relationships between precipitation and air humidity and NO₂ column density were significant,and the correlation coefficients r were-0.72 and-0.92 respectively.In winter,the prevailing wind direction is the northwest wind,which is blocked by the Taihang Mountains in northwest,which makes the central plain area poor in air mobility,and it is difficult to disperse and sharply increase pollutants.In summer,south wind can bring enough water vapor and rich precipitation,and can dilute the concentration of pollutants,making NO₂ column density reach the lowest value in a year.The human factors included the location distribution of key pollution enterprises,coal consumption and GDP growth rate,which can cause changes of NO₂ column density in a region.