Abstract: [Objective] Rapid and complete collection of the atmospheric particles retained on leaves is the premise of precisely evaluating the retention of tree leaves to atmospheric particles. In this study Ginkgo biloba as an example and based on the routine leaf cleaning methods, the role of ultrasonic cleaning in quantitative evaluation of the retention of tree leaves to atmospheric particles was investigated. In addition, the optimal ultrasonic cleaning parameters were also determined for Ginkgo biloba leaves.[Method] Routine cleaning methods (soak & stirring and scrubbing) and ultrasonic cleaning procedure were sequentially conducted to leaf samples to collect particles retained on leaves. And then the mass proportion of particles cleaned off through each cleaning step, eluent color changed, amount of chlorophyll a exuded from leaves in all scenarios, and the residue of particles on leaves after all cleaning processes were estimated or observed.[Result] Results showed that:1) under ultrasonic powers of 200, 300, 400 and 500 W, the best ultrasonic cleaning time was 5, 5, 5 and 3 min, respectively; 2) under different ultrasonic powers, soak & stirring or plus scrubbing contributed 33%-50% and 34%-43% to all the particles cleaned off from leaves, respectively; 3) after routine cleaning procedures, further cleaning with ultrasonic under power of 500 W could make the leaves more clean, and washed off at the maximum about 27% of the particles retained on leaves; 4) the observation with a scanning electronic microscope, showed that ultrasonic was able to help to clean off particles within small diameter classes retained in leaf surface gaps efficiently.[Conclusion] Consequently, it is essential to introduce ultrasonic into the leaf cleaning procedure so as to improve the evaluation precision of atmopheric particles retained on leaves. The optimal cleaning procedure was demonstrated to be "soak & stirring-scrubing-ultrasonic power of 500 W for 3 min" for Ginkgo biloba leaves in our laboratory, but its stability and general applicability to different plant species should be further investigated.

Key words: atmospheric particulate matter, ultrasonic cleaning, Ginkgo biloba