Research On The Temporal And Spatial Dynamic Changes Of Atmospheric NO₂ In The Urban-rural Fringe Of Urumqi And Changji Area

Urumqi-Changji area（referred to as Wuchang area）is one of the key construction areas during the"Thirteenth Five-Year Plan"period.With the rapid economic development and the continuous migration of industries to the suburbs,most companies and factories in the urban area have moved out to the urban-rural fringe.As the scale of the urban-rural fringe continues to expand,the heavily polluting factories in Urumqi-Changji area account for 79.19%,and air pollutants are transferred from the city to the urban-rural fringe.This paper uses Multi-axis differential optical absorption spectroscopy（MAX-DOAS）technology to carry out fixed monitoring and vehicle-mounted mobile monitoring of atmospheric tropospheric NO₂ concentration in different seasons in Urumqi-Changji area from 2020 to 2021,combined with the dominant wind direction and building height,analyze the temporal and spatial changes of NO₂ concentration in the urban and rural area of Urumqi-Changji area.This paper uses Global Data Assimilation System（GDAS）meteorological data and ground monitoring data to analyze the sources of air masses and potential sources of pollutants in the urban-rural fringe of Urumqi-Changji area.From the perspective of nature and man-made,the influencing factors of NO₂ pollution in the urban-rural fringe of Wuchang area are analyzed.The main conclusions are as follows:（1）From 2020 to 2021,the diurnal variation characteristics of NO₂ column concentrations in the urban-rural fringes and urban areas of Urumqi-Changji area show a"U"shaped change trend of"high in the morning,high in the evening,and low at noon",and the seasonal changes are all in the order of winter>autumn>Spring>summer characteristics.（2）The concentration of atmospheric NO₂ pollutants in the troposphere in the urban-rural junction of Urumqi gradually decreased from southeast to northwest.There are two obvious high-value centers,which are distributed near the industrial park in the northeast and southeast of the urban-rural fringe of Urumqi,and the concentration in the southeast is the largest.The concentration of atmospheric NO₂ pollutants in the troposphere at the urban-rural junction of Changji is generally high in the southeast and low in the northwest.The concentration of NO₂in the north gradually decreases from the northeast to the northwest.The highest value is located in the residential area in the southeast.（3）The main source of air mass in the urban-rural junction of Urumqi-Changji area is the northwest.The effect of air mass on pollutants is different in different seasons.The diffusivity of air mass in each season is summer>spring>autumn>winter.The seasonal atmospheric NO₂concentration in the urban-rural fringe is greatly affected by the pollution of the local and surrounding areas.（4）Westerly,northwesterly and southwesterly winds prevail in each season in the urban-rural fringe of Urumqi-Changji area.In this area,atmospheric NO₂pollutants in the upwind direction are gathered in the downwind direction.Due to the influence of the suburban thermal circulation,the urban-rural fringe of Urumqi-Changji area is affected by the urban circulation effect in spring and summer,which intensifies the pollution,while the pollutants in the urban-rural fringe of Urumqi-Changji area in autumn and winter are affected by the circulation effect.It is transmitted to the urban area,thereby aggravating the NO₂ pollution in the urban area.（5）The emission of pollutants in different functional areas leads to an increase in the concentration of NO₂.The companies and factories in the urban-rural fringe of Urumqi are mainly petrochemical enterprises with heavy pollution,the companies and enterprises in the urban-rural fringe of Changji are mainly agricultural products processing.The urban-rural fringe of Urumqi and the urban service-intensive areas are characterized by high south and low in the north,while the urban-rural fringe and urban area of Changji are characterized by high north and low south,which is consistent with the distribution of pollutants.