Abstract: The objective of this study was to explore the vertical and horizontal variations of leaf particulate matter retention amount of park greening trees. Three broad-leaved tree species, Quercus robur,Rhus typhina and Fraxinus rhynchophylla, widely distributed in Urumqi People’s Park and with different canopy structures, were selected. Leaves were collected at 12 positions of different canopy heights (2, 4, 6 m) and directions (east, south, west, north) at leaf maturity stage in July. The difference of retention capacity per unit leaf area of different tree species to atmospheric particulate matter (PM_0.2-3, PM_3-10, PM_>10 and PM_total) at different positions of canopy was analyzed. The results showed that: (1) There was a significant difference in retention amount of different sized particulate matters on leaves among different tree species (P<0.05). The retention capacity of PM_3-10 per unit leaf area of different tree species across different positions was ranked as: Q. robur>R. typhina>F. rhynchophylla, while the retention capacity for PM_0.2-3, PM_>10 and PM_total was ordered as: Q. robur>F. rhynchophylla>R. typhina. Q. robur had the highest and stable retention capacity for particulates of different sizes, R. typhina had better retention capacity for medium-sized particulates, and F. rhynchophylla had better retention capacity for particulates except PM_3-10. (2) There was a certain difference in retention capacity of various particulates at different canopy heights of the three species (P<0.05), and such difference of different sized particulates followed a same pattern, i.e.: 2 m > 4 m > 6 m. Canopy height had a significant effect on leaf retention amount of PM_3-10, PM_>10 and PM_total (P<0.05), with an extremely significant effect on PM_3-10 (P<0.01). There was no significant difference in leaf retention capacity to different sized particulates at different directions of canopy (P>0.05). There was no significant interaction of canopy height and direction (P>0.05). (3) PM_>10 was the main particulate on leaf surface of examined tree species, PM_3-10 was the second, and PM_0.2-3 was the least. PM_0.2-3 was mainly concentrated at 4 m height in the northwest direction, while PM_3-10 was concentrated in the northwest direction, without obvious pattern in canopy height. PM_>10 was more distributed at 2 m height in the bottom of canopy, but there was no obvious pattern in the direction. Our results can provide a scientific basis for reasonable selection of greening tree species for the urban park greening management department.

Key words: urban park, greening tree, particulate matter, retention amount, canopy structure.