Temporal And Spatial Distribution Characteristics And Pollution Sources Of NO₂ Pollution In Yangtze River Delta

Nitrogen dioxide（NO₂）is one of the main pollutants in the atmosphere.It plays an extremely important role in the tropospheric chemical reactions.It not only participates in the catalytic formation of tropospheric ozone,but also contributes to the formation of aerosols and leads to climate disasters such as acid rain,endangering human health.Accurate monitoring data and analysis of NO₂pollution sources are of great significance for effective pollution control and sustainable development.Based on the MAX-DOAS observation network built in the Yangtze River Delta region,long-term observation of NO₂was conducted in this paper.Through the MAX-DOAS observations and TORPOMI satellite observation data contrast,found that the variation trend of the two over time had a good consistency,and the correlation coefficient R was 0.87.By analyzing the MAX-DOAS data of Shanghai in the summer,autumn and winter of 2019,it is found that NO₂VCDs are greatly affected by traffic emissions.By analyzing the variation trend of NO₂in February,it is found that NO₂is low in summer and high in autumn and winter.It is deduced that the atmospheric NO₂is easier to be dissolved and diffuse because of the intense illumination and abundant rainfall in summer.In autumn and winter,the light radiation is less,the temperature is lower,the NO₂life is longer,the boundary layer height drops,and the local emission is easy to form accumulation and produce high concentration pollution.The HYSPLIT backward trajectory model was used to analyze the backward trajectory of air mass transport at an altitude of 500m during a pollution event in Shanghai in summer,and it was found that the NO₂pollution in Shanghai was greatly affected by the transport of polluted air mass from coastal areas.In addition to emissions from industrial parks,ships and ports along the Yangtze River estuary and castlines,the combined pollution processes in the Yangtze River Delta region,intra-city traffic and industrial emissions will have a significant impact on air quality in Shanghai.Due to the severe winter pollution of cities in the Yangtze River Delta region,based on backward trajectory clustering analysis,PSCF,CWT and other methods,this paper carried out a study on the sources of NO₂pollution in winter in the Yangtze River Delta region.Firstly,the vertical distribution of NO₂pollution in Ningbo,Nanjing and Shanghai was compared.It was found that the high concentration of NO₂VCDS was concentrated near the ground,and there was no influence of upper air transmission.In addition,NO₂VCDS in the three cities had obvious stratification in height,and the upper layer of NO₂VCDS accounted for about 20%of the lower layer.This indicates that NO₂pollution in winter in the three cities is mainly affected by local emissions.The contribution analysis of potential sources of NO2 pollution shows that industrial parks in the Yangtze River Delta,coastal ports in Jiangsu and Zhejiang,and the southeast coastal waterway are all potential sources of NO2 pollution.The results show that the NO₂pollution in winter in the Yangtze River Delta region is affected by the local emission and the inter-city pollution transport in the Yangtze River Delta region.The results show that the ground-based MAX-DOAS system,as a real-time,rapid and continuous atmospheric monitoring method,can be widely used in urban area pollution monitoring applications.The observation and study of tropospheric NO₂in the Yangtze River Delta provides some data support for the prevention and control of urban air pollution in the Yangtze River Delta.