Objective  Effects of atmospheric dust particle size and landscape tree type on urban air quality improvement through dust retention of the plants were investigated.

  Methods  Dust retention of 8 varieties of landscape trees in Chengyang District of Qingdao City was studied according to the particle sizes determined by eluting the retained dust on leaves with water followed by microporous filtration membrane filtration. The leaf surface morphology was examined under a JEOL7500F electron microscope. The average total leaf area and dust retention rates on varied particle sizes per plant of each variety were obtained for analysis.

  Results  Among the tested species, Sophora japonica and Prunus cerasifera collected the highest, while Populus tomentosa and Platanus orientalis the lowest, amounts of PM₁₀ particles. The overall dust retention rates of the 8 varieties ranked as:S. japonica > P. cerasifera > Ligustrum lucidum > Fraxinus pennsylvanica > Koelreuteria paniculata > Salix matsudana > P. tomentosa > P. orientalis. PM₅ adhered more to the leaves of P. cerasifera but less to those of K. paniculata. The dust retention per unit leaf area of P. cerasifera was approximately 2.4 times higher than that of K. paniculata. The greatest retention on PM_2.5 was found with S. japonica followed by K. paniculata, and lowest with S. matsudana. On dust retention of all particle sizes, P. orientalis was the highest, whereas, K. paniculata and P. cerasifera the lowest. It appeared that the rougher the surface, the denser the villi, the larger the stomatal openings, and the more apparent the gully of the leaves were, the greater ability of the plants to retain dust fallen from the atmosphere.

  Conclusion  S. japonica and P. cerasifera demonstrated a superior capacity to adsorb PM₁₀ on their leaves, but not P. tomentosa or P. orientalis; P. cerasifera to PM₅, but not K. paniculata; and, S. japonica to PM_2.5 followed by K. paniculata, but not S. matsudana. Including all varied particle sizes, the overall dust retention amount per plant of P. orientalis was the highest, while K. paniculata and P. cerasifera the lowest of the 8 tree varieties tested. And, trees of leaves with rough surface, dense villi, large stomatal openings, and obvious gully tended to collect more atmospheric dust that benefits air quality improvement for the vicinity. The information would aid the tree selection in urban landscape planning.