Characteristics, Source, Long-range Transport Of Dust Aerosol Over The Central Asia And Its Potential Effect On Global Change

Atmospheric aerosol would have tremendous impact on the global environmental andclimate change through influencing radiation,atmospheric chemistry,andcloud/precipitation processes and shifting the balance of the radiation energy andwater cycle.The long-range transport of aerosol has been regarded as the importantpath of the global biogeochemical cycle.The study on the atmospheric aerosol is thestudy on the balance of the global biogeochemical cycling among atmosphere,hydrosphere,biosphere,and human-sphere,which has been of the vital significance tohuman being,and it has been the important domain of the study on the globalenvironmental and climate change.Atmospheric aerosol can travel across over Pacific and Atlantic,and it would exertgreat influence on both the regional environment and the global climate change.Theair pollution has been global issue.Those deserts located in the center of Asia andLoess Plateau is the major sources of those aerosols over Pacific.To investigatedeeply into the temporal and spatial distribution,the physicochemical characteristics,and sources of Asian dust would understand the mechanism of the mixing and theinteraction of mineral with pollution aerosols,which has been the urgent need indeveloping economy and improving the life quality of human being.The major results of this study are as below:1.The physic-chemical characteristics,sources,and the formation mechanism of thedust aerosol from those typical areas of Central Asian Dust as well as theirpossible impact on the regional environment of the downstream urban cities aswell as the global climate change were revealed.The aerosols from Taklimakandesert,one of the two major sources of Asian dust storm,which also is the secondgreat desert over the world,are characterized of high mass concentration,highcontent of sulfur and calcium.It was found that 90% of the sulfur in the aerosolsover Taklimakan desert and in the soil collected from the desert is in the form ofsulfate.Additionally,the sulfate in the aerosols shows a high positive relation withthose ions of sodium,chlorine,and potassium,which indicated evidently thatthose components in the aerosols were from the paleo-marine source.Theseresults were the evidence to support the hypotheses that Taklimakan desert wasused to be the ocean～5.3 millions year ago. 2.It was found that the ratio of Ca/Al in the aerosols over Taklimakan is over 1.5,whereas it is only～0.5 in Gobi located in Mongolia and Inner Mongolia.Thisdistinct difference makes the ratio of Ca/A1 be used as excellent tracer todistinguish the two major source areas of Asian dust and to distinguish the out-citysources of those local urban areas.3.The annual transport of dust from Taklimakan desert is 1.69*10⁷ ton,whichincludes 2.1*10⁵ ton of sulfate and 6.2*10⁴ ton of black carbon.As most ofsulfur in the dust aerosol and soil of Taklimakan was found to be in the form ofsulfate,the amount transported out from this second largest desert would be muchmore than previously estimated.Those sulfate emitted and transported fromTaklimakan desert would have great impact on the regional atmosphericenvironment and the global climate change.4.Urumqi is one of the heavy polluted cities in the world,as the days of hazespanned over one third of the year and accounted for 60-80% of the heating periodfor the past six years.High aerosol concentration of fine aerosols,frequentoccurrence of haze,and rapid formation of heavy haze were the three maincharacteristics.With comparison of the pollution elements,As,Cd,and S,and theratio of Ca/Al in aerosols and soils in those sites located on the south of JunggerBasin as tracers,it was found that As,Cd,and S highly enriched in the aerosolsover urban Urumqi were not only derived from the re-suspended road dust butalso from the soil transported from south of the Jungger Basin.Different from themost cities in China,the high concentration of sulfate in Urumqi was partiallyfrom the primary soil dust transported from the surrounding areas.The mixing ofthe local anthropogenic aerosols with the soil transported from outside the citywas the main source of the high sulfate concentration.Equivalent ammoniumconcentration were higher than the summed equivalents of SO₄^2-,NO₃^-,and Cl^- inUrumqi and much higher than that in other Chinese cities.The total water solubleions and the total ammonium salts were as high as 57.8% and 51.0% in PM_2.5.Thehigh concentration of soluble salts with high hygroscopicity,especiallyammonium and sulfate salts,were the main factors contributing to the heavy hazeover Urumqi.5.It was found that there is a certain degree pollution of As,Pb,Cd even in such adesolate area,Taklimakan desert.The enrichment factor of As in the aerosolsover Tianshan mountain was as high as 5000,while those of Pb and Cd were over 20.In the soil of Tianshan and its surrounding areas the content of As,Zn,Cd was1.4-15.7 times higher than the average in crust content of the world.Theseresults strongly indicated that the air-pollutant in aerosol originally from the heavycoal burning have spread everywhere over China due to the long-range transport.The air-pollution in many urban cities was not only from local pollution sources,but also from the long-range transport out of the cities.The long-range transportof aerosols,i.e.the biogeochemical cycle has been one of the major sources andone of the main characteristics of air-pollution in China.