Effects Of Different Rainfall Intensity And Wind Speed On Plant Retained Particulate Matter

Plants play an important role in the removal of atmospheric particulate matter,but they are affected by many factors such as leaf surface characteristics,atmospheric particle characteristics,meteorological conditions ect,indicating a complex dynamic process.This article uses six common evergreen plants in Xi'an:Osmanthus fragrans,Photinia serrulata,Magnolia grandiflora,Pinus bungeana,Ligustrum lucidum and Pittosporum tobira as the research objects,the amount of particulate matter retained by different leaf types and the particle size distribution of leaf surface particles under different typical weather and different exposure time were determined by water filtration using different pore size filters and filtrate drying method.In addition,rainfall and wind can wash off or blow off the dust on the surface of the plant and bring it into the soil to restore the surface of the plant.In order to clarify the dynamic mechanism of rainfall and wind speed on the retained particles of the plant,the simulation experiments using artificial simulated precipitation and wind tunnel were carried out.The results show:(1)There were significant differences in the retention of different particle size particles(PM,PM>10,PM2.5-10,PM2.5)on the leaf surface of the 6 plant species,among them,the epidermis of Pinus bungeana has the highest total retention of particulate matter and particulate matter with different particle sizes.As followed Magnolia grandiflora>Photinia serrulata>Pittosporum tobira>Osmanthus fragrans?Ligustrum lucidum.(2)The mass of particulate matter retained on the leaf surface is dominated by PM>10,and its contribution can reach 53.57%?97.25%,followed by PM2.5,which is 1.66%?30.67%,while the contribution of PM2.5-10 is the smallest,0.45%?20.47%.The effects of precipitation on the retention of different particle sizes on the leaf surface varies from species to species.After two days of precipitation(8.5 and 13.1 mm),PM>10 decreased significantly,and the changes of PM2.5-10 and PM2.5 were more complicated.Among them,Pinus bungeana,Osmanthus fragrans,and Magnolia grandiflora decreased,while Pittosporum tobira increased.The PM2.5-10 was increased in the leaves of the Photinia serrulata and Ligustrum lucidum,but the PM2.5 was decreased.This may be due to the fact that the water-soluble substance dissolves under precipitation,and the large particles are broken into small particles by splashing of the raindrops.(3)The results of laser particle size analyzer showed that the volume fraction of particles with particle size less than 100 ?m accounted for 56.63%?100%of the total retained particles,while the volume fraction of particles larger than 100 ?m varied from 0%to 43.07%.Except for Pittosporum tobira,the particle size distribution of the remaining five plant leaf retaining particles showed an increase in the volume fraction of the small particle size as the exposure time increased.(4)Precipitation intensity has a significant effect on the elution rate of PM>10,and the effect on PM2.5-10 and PM2.5 is not so obvious.The threshold of 6 plant retention PM and PM>10 is from large to small is:Pinus bungeana>Ligustrum lucidum>Magnolia grandiflora>Photinia serrulata>Pittosporum tobira>Osmanthus fragrans.At the beginning of rainfall,the elution rate of particulate matter on the leaf surface increased sharply with the rainfall duration,and then stabilized.When the rainfall intensity increased,the time effect on the eluted particles was not obvious.The rainfall has a good fitting relationship with the elution rate of particulate matter.With the increase of rainfall,the elution rate of particulate matter increases logarithmically,and the elution rate of particulate matter rises faster in the first 30 minutes of rainfall,and then rises slowly.The trend tends to be flat.(5)With the increase of the simulation experiments,the resuspension rate of particulate matter increased rapidly first,and the growth rate decreased after 20 minutes,and the increasing trend gradually became flat.With the increase of wind speed,the resuspension rate of particulate matter increased first and then decreased except for Osmanthus fragrans.According to the actual weather conditions,the amount of retained particulate matter in 6 plants was estimated.It was found that Pinus bungeana,a coniferous species,had the greatest effect of wind speed on particulate matter,especially PM2.5.The Magnolia grandiflora,a broad-leaved tree species,the retention effect was also obviously better than the other four.These findings provide a scientific basis for quantifying vegetation retention of different particle sizes and better selection of dust-retaining species.