Characteristics Of Tropospheric NO₂ Vertical Column Densities In Korla City,Xinjiang

Korla City as the focus of the development of Xinjiang "north Urumqi south Korla" strategy in the development of the city,gathered an important political,economic and cultural center.It is the throat of the ancient Silk Road and enjoys the reputation of the first "national civilized city" in the northwest region.However,in recent years the development of industry and the rapid growth of the motor vehicle ownership caused its regional air pollution becomes more and more heavy.Ranked the air quality ranking in 19 cities in Xinjiang.Based on the MAX-DOAS instrument,monitoring the different functional areas of Korla in 2014-2016 and monitoring along the ring road inversion of NO₂ column concentration in 2015-2016.The temporal variation characteristics and spatial distribution characteristics of NO₂ column concentration in the atmosphere of Korla city are studied.The influencing factors of NO₂ concentration are analyzed from terrain,meteorology and human activities.The conclusions are as follows:（1）The seasonal diurnal variation of tropospheric NO₂ column concentration at the monitoring sites in the Korla City is basically a bimodal-peak curve,the peak appears at 9:00 and 20:00,the minimum time appears inconsistent;compared with spring,summer and autumn,the diurnal variation of winter has large range.The monthly mean shows “U”distribution,the minimum appears in June（1.376）,the maximum appears in January（7.061）.The seasonal variation patterns are found for tropospheric of NO₂ VCD,which are high in winter and low in summer.The concentration level of tropospheric NO₂ in different functional areas throughout the year was city center> Industrial Park> Suburban farmland,the values of the order4.774、4.452、2.493（unit:1015mloec·cm-2）.（2）In the Korla city-wide mobile observation,it is found that the NO₂ column concentration of mobile monitoring in 2015-2016 are winter（4.690）,autumn（2.097）,spring（1.978）and summer（1.230）.From the spatial distribution point of view,the high concentration of NO₂ column concentration in the traffic flow is relatively large or poor motor vehicle operating conditions,according to the Hysplit model analysis,it is found that the source of the four seasons of Korla City is different.In addition to the influence of the local source,the Korla City is affected by the external source.（3）Factors influencing the temporal variation characteristics and spatial distribution characteristics of tropospheric NO₂ column concentration in Korla City.Winter heating period of coal,unreasonable industrial layout and year-on-year growth of motor vehicles are the main source of NO₂ in the atmosphere,also affectedthe internal causes of NO₂ pollution.（4）The local terrain features and meteorological conditions are the auxiliary conditions that affect the accumulation and diffusion of NO₂,the results show that the influence of each meteorological element on the concentration of NO₂ is as follows: temperature> visibility> relative humidity> vapor pressure> pressure> wind speed> total cloud cover,there is a positive correlation between air pressure,relative pressure and relative humidity,but when the relative humidity of 80% after a negative correlation;the temperature,vapor pressure,total cloud cover,visibility and wind speed are negatively correlated with NO₂ column concentration.Further analysis of wind speed greater than 1.5 conducive to NO₂ diffusion,wind direction and NO₂ column concentration shows that the concentration of NO₂ column in the troposphere is increased in the northeast,northwest and southwest of Korla.