Abstract: Since the current washing-membrance-filtering method is not good enough to determine dust-retaining capacity of plant leaves, it is essential to quantitatively define some new potential methods to make up or amend shortages of the current method and to determine intuitively and accurately dust-retaining capacity of plant leaves.  Two sampling sites, the Beijing Botanical Garden and Guomao Bridge, in Beijing were selected. The former is relatively clean and the latter severely polluted. Leaves were collected from Euonymus japonicas, Sophora japonica, Populustomentosa, Ginkgo biloba and Prunus cerasifera in the two sites in Beijing for determination of quantity and particle-size composition of particulate matter (PM) detained on the upper and lower surfaces of the leaves with a scanning electron microscope and then quantity of detained PM per unit leaf area was calculated for comparison with that obtained by the washing-membrance-filtering method. It was found that the PM on leaf surfaces was dominated by the PM_<10 (PM with diameter less than 10 μm), which accounted for over 90% of the total quantity of particles. The leaf surfaces of the investigated trees growing at the heavily polluted site (Guomao Bridge) had more PM_<2.5 detained than those at the less polluted site (Beijing Botanical Garden) did. A significant linear relationship was observed between the counting method and the washing method in PM mass obtained. However, the difference between the two was very sharp. The PM mass obtained with the washing method was only about 9% as high as that with the counting method. It is, therefore, essential to design and conduct more strictly controlled experiments to determine causes and affecting factors of this big difference, and also to develop techniques for calibrating the current washing methods, or multi-approach combined application techniques.

Key words: quantify ofparticulate matter, dust-retaining capacity, washing-membrane filtering method