Study On The Influence Of Dust Storms On Air Quality Based On The Data Of Lidars

During the 13th Five Year Plan period,the ambient air quality had been significantly improved,but heavy pollution caused by sand and dust weather occurred from time to time,especially in Northwest China.In order to effectively improve the ambient air quality in Gansu Province and properly deal with the heavily polluted events,firstly,the sand dust events in China from 2015 to 2020 were identified objectively and accurately,the temporal and spatial distribution characteristics,sand dust prone areas and strong dust occurrence area were studied.In addition,the aerosol lidar network detection results in Gansu Province was used to study a severe dust storm in Northwest China,combined with the ground observation data and the NCEP/NCAR reanalysis data made an in-depth study on the occurrence,development,and evolution process of dust weather,and fitted the particle concentration value in the vertical direction during dust,which made up for the single monitoring mode of dust events,realized the qualitative to quantitative research of aerosol lidar in dust events.Finally,the horizontal and vertical particle concentrations simulated by WRF-Chem were compared through ground observation and the lidar network,in order to provide reference for the improvement direction of WRF-Chem.The in-depth research on sand dust based on lidars had certain guiding significance for the prediction and early warning of dust events,improved the accuracy of sand dust prediction,and provided basic information and technical support for air pollution prevention and control.Based on the criteria of selecting dust weather proposed by China Environmental Monitoring Station recently,the hourly concentration of PM₁₀ and PM_2.5 of 336 cities in China from 2015 to 2020 were used to study the temporal and spatial characteristics of dust weather more accurately and objectively.The results showed that all the dust weather in China decreased obviously,but the strong dust weather did not decrease.There were 334 cities had dust weather except Shenzhen and Dongguan.The high frequency of dust weather was mainly distributed in Northern China,especially in Northwest China.The Hexi Corridor region was the area where sand dust made a greater contribution to particle concentration.The contribution of PM₁₀ was basically more than10%,and the contribution of PM_2.5 was about 5%-10%.The most likely month for dust was May.The starting time of dust was bimodal distribution,and the easiest starting time was 10:00-11:00,followed by 22:00-23:00.According to the PSCF results,the dust potential source contribution of different cities mainly came from the northwest,and was mainly affected by Mongolia in addition to the local dust in China.In addition,Beijing was obviously affected by dust return.The AQI and six pollutants of 14 cities in Gansu Province from 2015 to 2020 were used to count the daily AQI,primary pollutants,heavy pollution,daily average concentration of PM_2.5 and O₃?8h.It was found that the ambient air quality in Gansu Province was mainly good and the primary pollutant was PM₁₀,followed by O₃and PM_2.5.Heavy pollution was mainly caused by dust event.The dust event occurred on May 3,2020 was caused by the southeastward cold air under the upper-level trough and westerly jet.When the dust intensity reached strongest,the extinction coefficient is greater than 1 km^-1,using the lidar observations.The dust particles lifted upward during the transport,in which the particles concentrated in the height of 2 km.After about 200-300 km transported,the dust concentration decreases obviously,and the vertical height development increases by 1-2 km.Further,the depolarization ratio shown that dust in Tengger Desert were dominated by spherical particles.Moreover,the 532 nm extinction coefficient is linear with the concentration of PM_2.5 and PM₁₀,and the contribution of external transport to surface PM_2.5 was more significant than to PM₁₀.The dust event occurred on May 12,2019 was caused by the eastward movement of an East Asian Trough and affected most cities in northern China from northwest to Southeast.Consequently,the air quality was deteriorated seriously,especially over the Hexi Corridor.The hourly peak concentrations of PM₁₀ in Wuwei and Baiyin were close to 3000?g·m^-3.The observations from the lidar network show that the dust intensities were similar at different cities and their extinction coefficients were close.However,the depolarization ratio varied with the sources and the physical characteristics of dust particles.According to the simulation results of extinction coefficients and particle concentrations,due to the impact of dust transported at high-altitude,the concentration of particles in Dingxi did not decrease with the increase of altitude.The particles concentrations from ground-based monitoring were lower than that of Baiyin and Wuwei,while its particles concentrations above 0.3 km were higher than that of Baiyin and Wuwei.WRF-Chem was used to simulate the sand and dust process on May 3,2020.The horizontal characteristics of dust distribution from WRF-Chem compared with the observation data of national automatic air quality monitoring station,and the vertical characteristics of dust distribution from WRF-Chem compared with the results from the lidar network.The results shown that the WRF-Chem can accurately simulate the sand and dust process,but there was still a certain deviation between the simulated and the observations.