Analysis On The Change Rules Of The PM_2.5 Concentration In Different Plant Community Types On The Campus Of Zhejiang A&F University

In order to study the effects of plant communities on PM2.5 concentration in different seasons and change rules of PM2.5 concentration in different plant communities under the effects of different meteorological factors,this paper applied fixed-point observation method in Donghu Campus of Zhejiang Agriculture and Forestry University in Lin'an District,Hangzhou.Three plant communities were selected as research objects to conduct structural investigation and analysis,and the paving plaza near the sample plot community played as a control point.The data of PM2.5 concentration were collected at the center point of each sample plot by means of a microcomputer dust meter.The daytime meteorological factors were monitored simultaneously using a hand-held anemometer at the control point.The main findings are as follows:(1)Among the lateral plant communities,the average height of the arbor is inversely related to the concentration of PM2.5 in the community.In winter and summer and before November in autumn,the PM2.5 concentration in each plant community is ranked as:stratified mixed stand>arbor-lawn>sparse woodland lawn,which is directly proportional to the canopy closure,planting density and the number of evergreen plants.After October,the order of PM2.5 concentration in each plant community and its relationship with the characteristic index of community structure are opposite to that before.(2)The ranking of the ability of plant communities to regulate PM2.5 is:stratified mixed stand>arbor-law>sparse woodland lawn,When the concentration of PM2.5 was 150-250?g/m3,the ability of plant community to regulate PM2.5 particles was the strongest,while when the concentration of PM2.5 was 35-75?g/m3,the regulation ability was weakened.(3)The PM2.5 concentration in each plant communities in the four seasons generally maintains the "L" shape curve.When the weather changes suddenly,the correlation between the meteorological factors and the PM2.5 concentration in each community will be disturbed,especially during the rainy season.When the PM2.5 concentration in the air is high,the meteorological factors have a significant effect on the change of PM2.5 concentration in the plant community,while as the PM2.5 concentration in the air decreases to a certain critical value(about 30 ?g/m3),the influence of meteorological factors will be weakened or even disappear.(4)The PM2.5 concentration in each community is significantly negatively correlated with temperature and wind speed,but this correlation can only be reflected together with the combined action of relative humidity.The PM2.5 concentration has a significant positive correlation with relative humidity and this correlation is thestrongest,serving as the leading factor in four seasons,and there is no obvious correlation between PM2.5 concentration and light intensity.Under breezy weather conditions,the influence of meteorological factors are ranked as:relative humidity>temperature>wind speed>light intensity.When the season is different,the correlation between the same meteorological factor and PM2.5 concentration in plant communities is also different.The correlation of temperature in the four seasons is:autumn>spring>summer>winter.And that of the relative humidity is:spring>autumn>winter>summer.