The Evolution Of The Dust Aerosol Chemical Characteristics From North To South Long-distance Transmission And Pollution Aerosol Mixing Mechanism

With the accelerated modern industrialization,deterioration of ecology,the majority of northern/northwestern China and central Asia saw the wide-spread movement of surface dust due to the powerful air mass activities in the desert/Gobi areas in the spring season.The transport of dust particles to the downwind locations brought dust event of different intensity and resulted in different influences on atmospheric environment quality,ecological health of the site on the pathway,and even the global climate change,which has been the focus of atmospheric environmental research in recent years inland and overseas.This study showed the chemical characteristics,sources and mixing mechanisms of dust particles during the medium/long range transport,with the analysis of dust aerosol samples collected at the four sites distributed from north to south China:Duolun in Inner Mongolia in north China,Beijing the capital city,Mount Tai in Shandong province,Shanghai in Yangtze River Delta in Southeast China,in spring of 2007,and evaluated the environmental and climatic implication of particulate pollution and the relevant measurements and policies over the atmospheric environmental protection ought to be taken along the path of the dust transport.The main results of this research are as follows:A dust aerosol sampling network consisting of four ground sites were operated to monitor the China dust events and the median/long range dust transport from north to south China,in spring of 2007.The loading of dust particles peaked at all sites during dust days(DS),with the concentration of TSP and PM2.5 increased 1.86-12.13 and 0.97-13.03 times over non-dust days.Combined with the backward/forward air mass trajectories analysis, the main low-Ca dust source from the northern China/Mongolia and the transport pathway from the Northern/Northeastem low Ca dust source regions to Shanghai,a downstream site in the Yangtze River Basin,were identified with the Ca/A1 elemental tracer analysis.The chemical characterization of dust transport was conducted with examining the variations of mass concentrations,elemental/ionic compositions of dust from site to site.The elemental enrichment factor analysis indicated the dust from near the dust source site DL was slightly polluted and had considerable significant mineral source for the "pollution" elements Pb and Zn relative to the downstream sites.It was still found that the mixing of pollution and mineral already existed and was less in the dust source regions.An increase of 5-35 times and 1-19 times respectively in DS was observed for the concentrations of Al,Ca,Fe,Sr,Mg,Mn,V etc.and As,Cd,Cu,Pb,Zn,S etc.,indicating that the dust not only brought in abundant minerals but also pollutants.The ionic characterization analysis showed that while the dust not only brought in a lot of soluble primary ions as Ca²⁺,Mg²⁺ etc., more of which tend to be enriched in fine mode particles,but also more significant insoluble materials during the transport.The mixing mechanisms of dust with pollution aerosol during the dust transport was examined and elucidated.The mixing existed and was less in the northern China/Mongolia dust source regions due to less anthropogenic sources,while it was enhanced and complicated and aggravated the acidification of particles through the heterogeneous reaction.As an example,the dust that reached Shanghai had a pH value as low as 2.81.Even so,influenced by the northern/northeastern China low-Ca dust source,its mixing mechanism involved the interaction between transported/local floating dust,local pollutants and sea salts. Different dust source and pathways might associate with different mixing processes of dust,and would necessarily lead to different environmental impact via radiative forcing.The severe degradation of air quality in many cities of Eastern China due to the long-range transport of dust in this study should be urgently concerned.The mixing or atmospheric modification processes through so-called internally coatings on dust particles during the transport from northern China/Mongolia Low-Ca dust source regions to Yangtze Rive Delta and the fact that not only coarse particles but also fine mode dust will exert influence on the air environment quality during the dust transport episodes in this study would be sure to provide high value for the regulations, policies,and relevant modeling on the interaction of Asian dust and regional/global air quality and environmental change.