| Dust weather is a kind of special disastrous weather in arid areas,which makes the fragile ecological environment of Northwest China worsen further,and has a serious impact on air quality,human health and social economy.The Northwest District is located in the inland of Northwest China,with complex climate characteristics and diverse land types.It is an area with high frequency of dust weather in China,and an important contribution source of dust storm area in Central Asia.Dust weather occurs mostly in spring and appeared in winter in 2017.Therefore,it is of practical significance to study the characteristics of dust weather in different seasons,transport of particles and potential source areas in this area.In this paper,firstly,WRF-Chem model,NCEP data,coupled with MOZART-MOSAIC chemical aerosol scheme,AFWA sand scheme were used to simulate the two dust processes in spring and winter in the northwest of China in 2017.The meteorological station observations verified the simulation effect of the model on sand and dust weather,meanwhile this paper showed the changing process of sand and dust weather and sand and dust concentration.Secondly,by using HYSPLIT model,potential source contribution factor analysis?PSCF?and weight concentration method?CWT?,the movement track of two dust weather air masses was traced,and the influence degree of potential source area on the concentration of PM10 in Northwest typical cities was quantitatively calculated.Finally,by using hourly monitoring data,the characteristics of PM10 and PM2.5 concentration changed and the pollution characteristics in the early,middle and later stages of dust occurrence were analyzed,and then the relationship between atmospheric particles and wind speed and temperature was further analyzed.The main results are as follows:?1?The WRF-Chem model can well reproduce the process of dust weather change.The main influencing factors of dust process in spring were cyclones and cold front on the ground,and in winterwere cold front on the ground.The main source areas of sand dust in spring are Tarim Basin and its surrounding areas in South Xinjiang,northwest Inner Mongolia and North Shaanxi,and Turpan Basin and Kumtag Desert in winter.At the same time,the movement of dust air mass in Tarim Basin and Northern Gansu Province was also well captured.The simulation effect of the model was better than that of the wind speed,and the correlation coefficient was0.89.The simulation results of different seasons were also different.The simulation results of spring temperature and wind speed were better,but the simulation results of winter extreme weather conditions were not ideal.?2?WRF Chem simulation results showed that the intensity of dust was different in spring and winter.In spring,the dust weather intensity was relatively high,the highest dust concentration on the ground was over 400 mg/m3,and the highest dust emission flux was 128?g/?m2·s?;in winter,the dust weather intensity was relatively small,the highest dust concentration on the ground is 162 mg/m3,and the highest dust emission flux was 86?g/?m2·s?.?3?Using HYSPLIT model to study the backward trajectory of the air mass during the dust period,the transport path of the dust was different in different seasons.Sand dust was a northerly path in spring and a northwestern path in winter,and all had air masses from outside the country.The results of CWT and PSCF were different.On the whole,CWT results showed that the potential source area was more comprehensive and detailed,and the contribution to the target city was well reflected.The potential sources of dust were different in different seasons.The potential source areas of sand dust in spring were Tarim Basin,Turpan Basin,Hexi Corridor,Qaidam Basin and Gobi Desert in the west of Inner Mongolia,and in winter are Tarim Basin,Turpan Basin and Hexi corridor.?4?Dust weather had a serious impact on urban air quality.AQI increased significantly during the occurrence of sand dust,and maintained a high value during the period of sand dust.In some cities,AQI continued to be 500.The effect of dust weather on PM10 was greater than that of PM2.5.In the middle period of sand dust,the average concentrations of PM10 in Lanzhou,Xi'an,Xining,Urumqi and Yinchuan were 797.42?g/m3,991.20?g/m3,193.55?g/m3,231.07?g/m3,951.36?g/m3,respectively,and the average concentrations of PM2.5 were 174.91?g/m3,305.80?g/m3,42.37?g/m3,41?g/m3,239.28?g/m3,respectively.?5?No matter in spring or winter,the time of PM2.5/PM10 value sudden drop was earlier than that of PM10 or PM2.5 concentration sudden increase.The correlation between particles and wind speed and temperature were stronger in spring than in winter,and the correlation between particles and wind speed and temperature were stronger in the early stage of dust than in the middle and late stage.To sum up,the temporal and spatial distribution of dust aerosols,dust flux and concentration were different in different seasons in Northwest China.The dust path was northward in spring and northwest in winter,and the potential source area of dust in spring was larger than that in winter.Dust weather had a strong negative impact on air quality,and had a greater impact on PM10.PM2.5/PM10 can be used as early warning index of sand dust weather,which should be paid attention to. |
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