Study On Dust Retention Capacity Of Different Green Plant Configurations And The Dry Deposition Velocity Of Ultrafine Particles

Urban forests and green spaces have a good effect on reducing and preventing air pollution.Plant leaves can absorb particulate matter in the atmosphere,reducing the impact particulate matter on the atmospheric environment,thereby improving air quality.The dry deposition process is the main mechanism for plants to purify the atmosphere,and the dry deposition velocity is an important parameter to measure the strength of dry deposition.In this study,we selected green spaces with different plant configurations to monitor the number concentration of particulate matter in urban road green belts and campus green spaces in Xi’an,the effect of different plant configuration modes on the reduction of particulate matter in green space and the influencing factors of the reduction of particulate matter were analyzed.Taking common greening plants in Xi’an as the research object,measured the dry deposition velocity of ultrafine particles on the leaves of different plants was measured,and the effects of different plants,different leaf area indexes,and different particle concentrations on the dry deposition velocity of ultrafine particles on plant leaves of plants were analyzed.The result shows:（1）The number of particles retained on the upper surface of plant leaves in the road green belt is greater than that on the lower surface,with a maximum of 14.1 times.The particles with particle size less than 1 μm and less than 2.5 μm retained on plant leaves accounted for 50.00～90.93% and 78.57～97.50% of the total,while the highest proportion of particles with particle size larger than 10 μm was 8.00%.The tree-shrub,tree-shrub-grass duplex configuration mode in the road green belt has a greater reduction effect on particulate matter than the single configuration mode.When the canopy closure is 0.6～0.7 and the porosity is 0.2～0.4,and the green belts in the duplex configuration are evenly arranged between the motor vehicle lane and the non-motor vehicle lane,and the non-motor vehicle lane and the sidewalk,the reduction of particulate matter is better.（2）Among the 9 plants selected from the campus green space,the retention of PM on Magnolia grandiflora,Fatsia japonica,Ligustrum lucidum and Trachycarpus fortunei are 4.55 g/m²,4.39 g/m²,4.30 g/m² and 4.25 g/m²,respectively.Among them,the leaf area,leaf length and leaf width of Magnolia grandiflora,Fatsia japonica and Ligustrum lucidum are too large,leaf area too small.Therefore,plants with larger leaf area have stronger dust retention capacity per unit leaf area;plants with larger leaf area have weaker dust retention capacity per unit leaf area.Tree-grass and tree-shurb duplex configuration mode has better dust retention capacity in green space,while the dust retention capacity of lawn is the worst.（3）When there is no plant hedge,at 0～5 min,5～15 min,15～30 min,30～60 min,the natural decay rates of ultrafine particles are 258.89 particles/（cm³·s）,73.33 particles/（cm³·s）,59.81 particles/（cm³·s）,22.77 particles/（cm³·s）,respectively.After placing the plant hedge,at 0～5 min,5～15 min,15～30 min,and 30～60 min,the decay rate of ultrafine particles are 241.67～386.67 particles/（cm³·s）,54.17～123.83 particles/（cm³·s）,22.00～78.00 particles/（cm³·s）,14.36～27.19 particles/（cm³·s）,respec tively.The plant hedge accelerated the deposition of ultrafine particles.（4）The dry deposition velocity of ultrafine particles on the leaves of 13 plants varied from 4.05×10^-4～6.47×10^-3 cm/s.Among them,the ultrafine particle dry deposition velocity of Ligustrum lucidum is the largest,which is 6.47×10-3 cm/s,followed by Sophora japonica,which is 6.08×10^-3 cm/s,and Swida walteri is the smallest,which is 4.05×10^-4 cm/s.The dry deposition velocity of the ultrafine particles of Ligustrum lucidum is 16 times that of Swida walteri.With the increase of leaf area index,the variation of ultrafine particle dry deposition velocity and unit leaf area dust retention is different.The initial concentration of particles increased,the decay rate of the number concentration of ultrafine particles increased,the dry deposition velocity of ultrafine particles and the dust retention per unit leaf area increased.