Reduction Of Airborne Particulate Matter Concentration By Spontaneous Ground Covers And Artificial Lawns In Guanzhong Region At Different Heights

With the accelerating rate of urbanisation,urban air particulate pollution is significantly exceeding the standard.Green spaces are an effective measure to mitigate urban particulate pollution,but the ecological value of ground cover in cleaning the air is often overlooked in planning and design.Ground cover,as one of the most important and commonly used types of urban green infrastructure,should be properly designed and maintained as a valuable complement to other green elements to mitigate air pollution.In addition,autochthonous ground cover and artificial turf are two typical urban ground cover types,but there is a lack of data to confirm the difference between the two types of ground cover in reducing airborne particulate concentrations.Therefore,this study aimed to explore the reduction effect of urban ground cover on air particulate concentrations by selecting six types of typical spontaneous ground cover and seven types of artificial lawn in the Guanzhong area and observing air particulate concentrations in ground cover and bare ground control at 150cm,50cm and 20cm for a period of one year from August 2021 to July 2022 under the same urban environment.Analysis using Spss 26.0 and the results were interpreted in the dimensions of ground cover type,meteorological conditions,temporal variation and species composition.As follows:1.In the same background environment,both ground cover type and ground cover subclasses had a highly significant effect on particulate matter concentrations at different heights.150 cm,spontaneous ground cover had a better reduction capacity than artificial ground cover,while 50 cm and 20 cm had the opposite effect.Among the ground cover subclasses,In the ground cover sub-category,Coronilla varia-Veronica persica-Cynodon dactylon-Trigonotis peduncularis（CVCT）has the best reduction effect at 150cm and Dianthus deltoides x hybrida（Dh）at 50cm and 20cm.It is recommended to use spontaneous ground cover in spaces where there is a lot of activity such as standing and running,and artificial ground cover in spaces where there is a lot of activity near the ground such as sitting,standing and lying down.It is not recommended to use a combination of Gramineae as the main dominant species for spontaneous ground cover and Cynodon dactylon×C.transvaalensis（Cc）for artificial ground cover,as it has a poor reduction capacity.2.Meteorological factors were highly significantly correlated with airborne particulate concentrations at all three heights,but with different trends.Temperature was negatively correlated with all four particle sizes,relative humidity was positively correlated with particle concentrations at 150cm,negatively correlated with con centrations of TSP and PM₁₀ at 50cm and 20cm,and positively correlated with concentrations of PM_2.5 and PM₁;air pressure was positively correlated with particle concentrations at 150cm and 50cm,negatively correlated with concentrations of TSP and PM₁₀ concentrations were negatively correlated with PM_2.5concentrations and positively correlated with PM_2.5 concentrations.Wind speed was only positively correlated with TSP and PM₁₀ concentrations at 20cm.3.Both month and daily observation time variations had a highly significant effect on particulate matter concentrations.The trends were relatively consistent across the three heights.With the exception of March when exceptional weather caused higher airborne particulate concentrations,both TSP and PM₁₀ concentrations were highest in November at the beginning of the heating season,PM_2.5 and PM₁ concentrations were highest in February due to low temperatures,and air was worse throughout the year in winter,followed by spring and autumn,and lower in summer with the best air quality in July.Particulate matter concentrations at all three heights follow the same trend with the time of day observed,with higher concentrations in the morning,followed by midday and lowest in the afternoon.It is recommended that activity be reduced in November and February and increased in July.4.Both plant species diversity and functional groups have a highly significant effect on particulate matter concentrations.The Shannon-Wiener diversity index and Simpson diversity index were negatively correlated with particulate matter concentrations at 150 cm and positively correlated at 50 cm and 20 cm.The reduction capacity of multi-constituent functional groups was significantly higher than that of single-constituent functional groups at150 cm,while the opposite was true at 50 cm and 20 cm.The effectiveness of ground cover in reducing particulate matter may be influenced by a combination of plant species diversity and functional groups.At 50cm and 20cm near ground level,the L and F functional groups were more effective than the G functional group.It is recommended that more plants from families other than grasses be expanded as ground cover material in the future.This study is the first to quantify,by means of controlled experiments,the factors influencing the concentration of airborne particulate matter in ground cover in the same urban background environment at multiple heights,revealing them in several dimensions,with a view to providing a theoretical basis for future planning and design,material selection for the construction of air-purifying oriented ground cover,and better guiding residents in the rational use of urban ground cover.