Characteristics And Environmental Significance Of Chemical Composition Of Topsoil Source Dust Aerosols In Hunshandake Sand Land

Studying the physical and chemical characteristics of sand and dust aerosols and exploring the sources of sand and dust aerosols are helpful for a deeper understanding of the series of changes and effects of sand and dust aerosols from emission to transport and settlement,and it is also helpful for a better understanding of dust aerosols with its impact on the environment and important role in the prevention and control of dust weather.The Hunshandake Sand Land is one of the main sources of dust storms in China,and the dust storms on the north road will inevitably pass through here when entering Beijing.To a certain extent,the dust generating device in the laboratory can replace or simulate the natural dust emission process,which directly affects the practical significance of the laboratory dust emission research.This study explored the previous dust generation devices at home and abroad.The PI-SWERL dust generation system was used to resuspend 40 dune topsoil samples collected in the source area and collect the dust aerosol PM₁₀ samples(PM₁₀ for short).The water-soluble ions and chemical elements were detected.The results are as follows:Among the 10 water-soluble ions of SO₄^2-,NO₃^-,NO₂^-,Cl^-,F^-,NH₄⁺,Ca²⁺,Na⁺,K⁺and Mg²⁺,NO₂^-and F^-are below the detection limit.The average mass ratio of water-soluble components in PM₁₀ is only 1.32%,which is lower than that in the western Taklimakan Desert?about 11%?and Tengger Desert?4%⁵%?.The ions with the highest proportion are SO₄^2-,K⁺,Na⁺,Ca²⁺,which together account for 80.8%of the mass of the water-soluble components.K⁺accounted for 0.26%of the total mass of PM₁₀,which was higher than that of other source areas.In addition to the source of the crust,there may be a certain relationship with the higher vegetation coverage in the source area.K⁺is homologous to Mg²⁺and Ca²⁺,indicating that the crust is one source of K⁺.The correlation coefficient between NH₄⁺and K⁺is 0.571,and NH₄⁺may have the same source as K⁺.NH₄⁺and SO₄^2-these two ions may exist in the form of the compound ammonium sulfate.The results of sieving the bulk sample and extracting water-soluble components showed that the average content of water-soluble components in the topsoil sample was 23.23?g/g,the median value was 21.28?g/g,and the percentage was about0.002%.The four ions with the highest content are Ca²⁺,K⁺,NO₃^-and SO₄^2-,which together account for 85.29%of the total ion mass.Comparing and analyzing the water-soluble components of PM₁₀,it is known that the water-soluble components in the particles have obvious geo-gas differentiation,so the chemical characteristics of dust aerosol particles emitted from topsoil cannot be replaced by the chemical characteristics of topsoil bulk sample.Twenty-six chemical elements?Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,V,Cr,Fe,Co,Cu,Zn,Ga,Br,Sr,Ba,Mn,Ni,Se,Pb,Sc,As?were detected.The elements with the highest proportion are Si,Fe,K,Al and Ca,accounting for 93.11%of the total mass of all elements.According to the EF value,the analyzed elements can be divided into5 categories:?1?The elements with EF value close to 1 or less than 1 are Mg,Na,Si,P,which represents that the main source of these elements is the crust.?2?The EF values of elements Cl,Ca,and Cu are slightly greater than 1,indicating that the main source of these three elements is still the crust,but the enrichment degree is relatively higher than that of the first type.However,in individual samples,the EF value of these elements exceeds 5,which indicates that some sampling points in the source area have human interference.?3?The EF values of Fe,Ni,Cr,V,Sr,Co,and Ba elements are in the range of2-4,indicating that their source may be mainly crust,which is more enriched than the previous elements.?4?The EF value of Ti,Mn,Ga,and Pb elements is greater than or slightly equal to 5,indicating that these four elements are highly enriched,and their sources include both crust and pollution sources caused by human activities.?5?The elements with EF value greater than 10 are Zn,Br,Sc and As,indicating that these elements are mainly caused by man-made pollution.In addition,the EF values of Sc and As elements are much higher than other elements,indicating that the elements Sc and As are extremely enriched in the topsoil of the source area.The median value Ca/Al of 37 dust aerosol samples PM₁₀0 emitted from topsoil in Hunshandake Sand Land is 0.57,very close to Duolun area.This proves the conclusion in the previous study that there is a difference between the sand and dust sources in the northeast and the west.The abundance of most elements in the total mass of particles is smaller than that in the crust and soil.The main elements in PM₁₀samples are close to the main elements?Si,Fe,K,Al and Ca?in PM_2.5.5 and PM_2.5-10collected by Sanggen Dalai in the source area.The PI-SWERL dust generation system used in this study can well simulate the sampling results of the source region's atmosphere,and it also shows that after the dust aerosols emitted from topsoil,they are not affected by other pollution sources in the source region's atmosphere.