Characteristics Of Air Pollution In Yungang Grottoes And Its Role In Sandstone Weathering

Yungang Grottoes as a world cultural heritage,has the very high historical value and artistic value.The characteristics of atmospheric pollutants in Yungang Grottoes and their roles in the weathering process of sandstone were studied in this paper.The following work was carried out:?1?The atmospheric fine particle samples were collected at the Yungang Grottoes in spring?April 14-18,2014?,summer?July 2-7,2014?,autumn?November 30-December 3,2014?and winter?December 16-20,2014?in front of the sculpture?Cave #20?through a modified MAY seven-stage cascade impactor,conducted the different seasons single-particle analysis by using a quantitative energy-dispersive electron probe X-ray microanalysis?ED-EPMA?,and than the characteristics of atmospheric pollutants in this area were summarized.?2?Fresh and weathered sandstone samples were collected outside cave #10 and #3 of Yungang Grottoes and their compositions were identified by XRD and SEM-EDX.On this basis,the experiments of SO₂ fumigation and acid solution erosion were carried out.The micro-structure of rock surface during fumigation was studied and the erosion mechanism of acid contaminants on sandstone is proposed by measuring the changes of compressive strength,effective porosity and elastic wave velocity during acid leaching.The results show that:?1?Among the four seasons samples,the unreacted mineral dust particles whose content was most and it contained more aluminosilicate,silicon dioxide and alkaline minerals containing Ca or Mg;the sulfate in reacted mineral dust particles was more than nitrate in four seasons,and the nitrate increased slightly in summer;carbonaceous particles are mainly contained coal dust and soot,which is the main component of EC particles,while OC content is less;Fe-rich particles,K-rich particles,secondary particles,Na-containing particles and fly ash is low.?2?After soaking in the acid liquor,P-wave velocity decreased significantly,compressive strength decreased and effective porosity increased,with increasing acidity;while in the water-treated sandstone samples,the P-wave velocity decreased first and then gradually recovered to the original values,implying that the acid solutions damaged the microstructure of the sandstone.?3?Calcium sulfate crystals can be observed on the surface of rocks due to SO₂ erosion.The SO₂–fumigation can increase the weight of rocks in dry states,and reduce the weight of rocks in dry-wet cycle,indicating that SO₂ reacts with alkaline mineral components in rocks to form sulfate which dissolves in water and destroys the surface structure of rocks.The above experimental results showed that mineral dust particles and carbonaceous particles is the main composition of airborne fine particulate in Yungang Grottoes scenic area,which are greatly affected by coal burning and sand dust.Sandstone is threatened by erosion by acid gas and acid solution.It is suggested to control the emission of air pollutants in the surrounding area according to the characteristics of air pollutants and reduce the risk of weathering of sculpture in Yungang scenic area...