Research On Physical Properties Of Atmospheric Aerosols In Xinjiang Based On Multi-source Data

Based on data from surface observations and satellite remote sensing,this study investigates physical properties of atmospheric aerosols over Xinjiang,China,including characteristics of mass concentrations of surface aerosols,characteristics of aerosol column mass densities,absorption optical depths and absorption Angstrom exponents,and variations of aerosol properties before,during and after a severe dust-snow events over typical areas of Xinjiang.Main conclusions follow:(1)Surface aerosol mass concentrations in Xinjiang show distinct regional distributions,and evident interannual,monthly,seasonal and diurnal patterns can be seen.Aerosol mass concentrations in Xinjiang show decreasing from 2015 to 2018.Among selected cities,the highest aerosol mean mass concentrations are observed in Hotan,followed by Urumqi,and Altay shows the lowest values.The average mass concentrations of PM_2.5(PM₁₀)in Hotan,Urumqi and Altay are 116?g/m³(429?g/m³),58?g/m³(119?g/m³)and 9?g/m³(19?g/m³),respectively,in 2018.About 46.3%(76%)and 24.5%(23.2%)of daily PM_2.5(PM₁₀)mass concentrations in Hotan and Urumqi,respectively,exceed the National Ambient Air Quality Standard(NAAQS)average level II standard in 2018.The PM_2.5(PM₁₀)mass concentrations in Hotan are the highest in spring with mean seasonal values of 224?g/m³(835?g/m³),and reach peak monthly values of 307?g/m³(1021?g/m³)in April.The PM_2.5(PM₁₀)mass concentrations in Hotan show diurnal variations with high values in 11:00-12:00 and low values generally during 16:00-20:00.The PM_2.5(PM₁₀)mass concentrations in Urumqi and Altay are the highest in winter with seasonal mean values of 132?g/m³(189?g/m³)and 15?g/m³(23?g/m³),respectively.(2)Aerosol column mass density and absorption optical depth(AAOD)over Xinjiang also have regional distributions,and interannual,monthly and seasonal patterns.High values of aerosol column mass density and AAOD in the Tarim Basin are seen.Aerosol column mass densities in the Tarim Basin show annual average value of 0.33 g/m²,having largest seasonal mean values of 0.47 g/m² in spring and lowest values of 0.13 g/m² in winter.Aerosol monthly average column mass densities over the Tarim Basin show maximum value in May(0.57 g/m²)and minimum in January(0.1 g/m²).The AAODs at 388 nm and 500 nm have lowest annual mean values of 0.073 and 0.034,respectively,in 2008 and highest values of 0.140 and 0.065,respectively,in 2018.The AAOD exhibits maximum in spring with values of 0.105 and 0.049at 388 nm and 500 nm,respectively,and minimum in summer with values of 0.073 and 0.032,respectively.The highest monthly mean AAOD_388nm(AAOD_500nm)are seen in April with values of 0.123 and 0.058,respectively.The absorption Angstrom exponent(AAE)between 388 nm and 500 nm shows minimum value of 2.937 in 2005 and maximum in 2015 with an annual mean value of 3.116.The seasonal mean AAE is highest in summer(3.232)and lowest in winter(2.825).The AAE shows maximum in June with a value of 3.254.(3)A severe dust-snow event occurred over Xinjiang in 2018,and coarse particles are found to be dominated in aerosol particles.The PM_2.5(PM₁₀)mass concentrations during dust-snow in Urumqi can reach 510?g/m³(4443?g/m³),which are 6 times(24 times)higher than the average concentrations in the day before dust-snow period.The mean PM_2.5(PM₁₀)mass concentrations decrease to 36?g/m³(79?g/m³)in the day after the period of dust-snow.In Hotan,the average concentrations of PM_2.5(PM₁₀)are 60?g/m³(229?g/m³)during the dust-snow period.The vertical structures based on the CALIPSO data show that the dust and snow are mixed mainly above 3 km and dust is dominated in Urumqi.After dust-snow event,the height of dust layer generally decreases,while the snow disappears between 2 and 5 km above ground and a few dust aerosols still exist in the heights between 1 and 3 km in Altay.