基于超声清洗的植物叶片吸滞大气颗粒物定量评估——以银杏为例

Analysis of the Role of Ultrasonic Cleaning in Quantitative Evaluation of the Retention of Tree Leaves to Atmospheric Particles:A Case Study with Ginkgo biloba

【目的】以银杏为例,在常规叶片清洗方法的基础上,定量评估增加超声波清洗步骤在植物叶片表面大气颗粒物完整收集中的效果和必要性,为本研究条件下的银杏叶片确定最佳超声波清洗技术参数组合。【方法】首先,采用常规清洗（浸泡＋搅拌—刷洗）＋超声波清洗;6个超声时长（1、2、3、5、10、20 min）和4个超声功率[200（40%）、300（60%）、400（80%）、500 W（100%）]组合成24种处理方法对叶片（雨后4天采样）进行清洗;然后,测定或观察每个洗脱步骤的叶表面颗粒物洗脱比例、洗脱液颜色变化、叶绿素析出量和叶表面颗粒物残留情况,来判断加入超声清洗的必要性。【结果】1）在40%、60%、80%和100%功率下,当超声波清洗时长分别为5、5、5和3min时不会破坏叶片结构致使叶绿素析出叶片;2）不同超声功率下,浸泡＋搅拌和进一步刷洗分别能洗脱掉叶表面33%~50%和34%~43%的颗粒物;3）在叶片经历常规清洗后,采用＂100%功率＋超声清洗3 min＂的参数组合进行超声波清洗,可使叶表面洁净程度明显提高,且最高还可洗脱约四分之一（27%）的叶表面颗粒物;4）超声波清洗可将大量吸滞于叶表面细小、连续、条带状缝隙中的小粒径颗粒物洗脱掉。【结论】在定量评估植物叶片大气颗粒物吸滞能力时,加入超声波叶片清洗程序极为必要,其可帮助大幅提高叶片颗粒物吸滞量的评估精度。本研究条件下,银杏叶片的最佳清洗方法流程为＂浸泡＋搅拌—刷洗—100%功率下超声波清洗3 min＂,但该方法的稳定性和普适性尚需进一步研究。

【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 [24 treatments which were a factorial combinations of six ultrasonic cleaning time（ 1,2,3,5,10,20min） and four ultrasonic power（ 200（ 40%）,300（ 60%）,400（ 80%）,500 W（ 100%）） ] were sequentially conducted to leaf samples to collect particles retained on leaves. And then the mass proportion of particles cleaned offthrough 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.