The Study On The Level Of Heavy Metals In Urban Surface Dust Before And After Rain

In order to explore the impact of rainfall on the distribution of heavy metals in urban surface dust,Taking the central City of Guiyang as the research area,Collect surface dust samples before and after the two rainfall processes at the crossroads of 20 main roads in the urban area.A total of 12 samples in three typical sample areas distributed in different orientations were passed through 425,250 and 105 ?m nylon sieves and the rest of the samples were all directly over the 105 ?m sieves to study the changes of the level of heavy metals and the effect of grain size on surface dust before and after rainfall.The results show:1)The change of dust particle size before and after the two rainfall processes is consistent.The specific manifestation is that the proportion of coarse particles increases obviously after rain.The average change in the average mass percentage before and after the two rainfalls increased from 8.3% to 17.7%.After two rainfalls,the mass percentage of fine particles decreased significantly.Before and after the two rainfalls,the average mass percentage decreased from 56.8% to 44.1%.The mass percentage of medium granules did not change significantly before and after two rainfalls.(2)Before and after the two rainfall processes,there were differences in the mean changes in the contents of different heavy metals.The average content of As,Cd,Cu,Ni,Pb,and Zn in dust less than 105 ?m before the rainfall was 9.41,0.637,141,24.7,67.7,and 276 mg/kg.The average content of As,Cd,Cu,Ni,Pb,and Zn in the dust after rainfall was 9.21,0.675,129,25.4,69.2,and 346 mg/kg.Before and after the two rainfall processes,only the performance of Cu and Zn was consistent.Cu was higher than the rain before the rain and Zn was higher than the rain after the rain,The elemental difference analysis showed that the content of Zn was significantly higher than that before rain during the second rainfall,and there was no significant difference in the content of other elements in the dust before and after the two rainfall processes.In general,the content of heavy metals in dust after rain is slightly higher than that before rain.(3)Before and after the two rainfall processes,the particle loading and grain-level effects of surface dust and heavy metals are as follows: After rainfall,the content of Zn in the surface dust increased and slightly tended to be concentrated in the coarse particles,Cu was more concentrated in the middle particles and fine particles,and the particle size effect of the remaining elements varied before and after rainfall,and there was no obvious regularity.With the exception of Ni,the contribution of particulate matter to heavy metals after a rain before rain was fine,medium,and coarse.Heavy metal loads in coarse particles after rain.(4)The influence of rainfall on the level of heavy metal in surface dust is related to many factors.The grain level effect of surface ash heavy metal,rainfall intensity,time,external pollution,changes in environmental pH,and the form of dust heavy metal are all factors that may affect the impact.The grain-level effect of heavy metals is not an established law of necessity,and its grain-level enrichment is affected by many factors.(5)The increase in the load of heavy metals in surface dust after rainfall in Guiyang City may be related to the difference in the concentration of heavy metals in dusts of different grain sizes and the influence of rainfall on elements in dusts of different particle sizes.Different rainfall processes have different effects on the distribution of heavy metals on surface dust.