Study On The Spatial And Temporal Distribution,source And Interaction Of Air Pollutants In Typical Cities Of Yangtze River Delta Based On MAX-DOAS

As the most important economic,cultural and trade center in the east of China,the Yangtze River Delta(YRD)has always been one of the focuses of attention to its air quality change.At present,the in-depth analysis of the causes of air pollution in this region is limited by the lack of spatial information,unknown spatial-temporal characteristics,diverse pollution sources and complex interactions of atmospheric pollutants(such as aerosols,NO2,SO2,HCHO and HONO).In addition,higher requirements on the spatial distribution,detection technology and source control of air pollutants also have been proposed according to the air pollution prevention and control regulations issued by the government,while the traditional in situ measurement technology cannot provide comprehensive and reliable monitoring data for monitoring the spatial migration of pollutants.As an optical telemetry method,Multi-Axis Differential Optical Absorption Spectroscopy(MAX-DOAS)can obtain the spatial and temporal distribution information of air pollutants more conveniently,quickly and effectively,which provides a new idea for studying the spatial distribution and transport law of air pollutants.Based on the existing MAX-DOAS observation network in the Yangtze River Delta,this study studied the spatial and temporal distribution,sources and interactions of typical urban air pollutants in combination with the analysis method of pollutant potential sources and the interaction relationship of precursors.The spatial distribution characteristics of potential sources of key gaseous pollutants were also analyzed,and the inter-regional/intra-regional transport contributions were quantified.The causes of pollution during the period of high concentration ozone and straw burning were revealed from the perspective of spatial and temporal distribution and transport of pollutants.To meet the needs of long-term detection of spatial-temporal distribution of key pollutants and analysis of pollution sources in the YRD region,MAX-DOAS observation network was used to obtain the vertical column densities and profile of key atmospheric pollutants in the YRD region from 2016 to 2021.The spatial-temporal distribution characteristics of potential sources of gaseous pollutants(NO2,SO2 and HCHO)were obtained by combining MAX-DOAS three-dimensional observation data with the potential source model.The results show that the interaction between cities within the YRD region is an important factor causing air pollution in this region.The distribution of potential source for Nanjing is the most widely,and the interregional interaction is most significant.Based on the analysis of pollution sources in Nanjing,it was found that the main source of pollution gases for Nanjing is from southwest in spring and summer,but it is from north in autumn and winter.In winter,the transport from northern Jiangsu and Northern Anhui to Nanjing is more prominent(0.5<WPSCF<0.8,especially at altitudes of 1 km)due to the dominant wind direction from the northwest.In addition,important potential sources of NO2(h<0.2 km)and SO2(h=0.5 km-1.0 km)are from the local area of Nanjing,the border area of southeast Anhui province and Jiangsu Province,and the central and southern parts of Jiangsu province.HCHO sources are mainly concentrated in the central and southern parts of the YRD(mainly in southern Anhui and Southern Jiangsu,especially in summer).Transport estimates for different regions indicate that NO2 transport accounts for an average of about 13%(<0.2 km),while the average proportion of SO2 transportation can be as high as 45%(h=1.0 km).The contribution of polluted gas transport is more significant in the northwest and west.Aiming at the research needs of the spatial interaction and transformation of pollutants during photochemistry in the YRD,the spatial interaction of O3 and its precursors during a typical O3 pollution process in Hefei(2020.9.3-9.11)was analyzed by combining three-dimensional detection techniques such as 2D-MAX-DOAS and lidar.The results show that the main control factors affecting ozone concentration show a significant spatial distribution,as,VOCs(surface)-NOx(0.4km)-Transition(1.0km)VOCs(1.6km).In the period of 6:00-8:00,high concentration HONO can promote the transformation of O3-sensitive region to VOCs-limited.When the ozone concentration increased sharply,the proportion of VOCs control area expanded and the sensitive area in the direction of Hefei urban area has a strong change(from NOx-limited to VOCslimited transformation).The interaction relationship between O3 and its precursors shows that when the ratio of HCHO/NO2 in the atmosphere is in the range of 3.55-7.46(the optimal is 5.50),O3 concentration shows a downward trend and pollution is alleviated.To study the three-dimensional distribution and causes of key pollutants in the process of straw burning,typical cities in the YRD region(Hefei,Nanjing and Shanghai)were selected as research objects to sort out the process of atmospheric particulate matter pollution in the Yangtze River Delta region.Based on the existing MAX-DOAS observation,model simulation and meteorological data,the straw burning period in the YRD region from May to June 2021 was selected for in-depth analysis.The study finds that the transport sources from outside the YRD region are southwest Shandong(17.6%),eastern Henan(12.4%)and northern Jiangxi(6.6%)are,with contribution about 36.6%.Within the region,the open combustion in central Jiangsu is the main internal cause of this pollution(WCWTAOD=1.2-3.0),indicating that the influence of fine particles generated by the open combustion in the YRD region is higher than the influence of external transport,which is consistent with the simulation of WRF-chem.In this paper,the spatial and temporal distribution,sources and interactions of air pollutants in typical cities in the YRD region were studied.The results provide a new method for understanding the spatial characteristics of pollution sources and revealing the interaction of pollutants.It promotes the improvement of the means of atmospheric monitoring and analysis,and has certain guiding significance in clarifying the source of pollutants and studying the formation mechanism of pollution.