The ultrasonic cleaning method was applied to elute the particulate matter (PM) retained on leaf surfaces after PM was eluted by the conventional cleaning methods (water cleaning only or water cleaning plus brush cleaning). The methodology can help to improve the estimation accuracy for PM retention capacity of leaves.
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Method Article
Assessing the Particulate Matter Removal Abilities of Tree Leaves
* These authors contributed equally
In This Article
Summary
Abstract
Based on the conventional cleaning methods (water cleaning (WC) + brush cleaning (BC)), this study evaluated the influence of ultrasonic cleaning (UC) on collecting various sized particulate matter (PM) retained on leaf surfaces. We further characterized the retention efficiency of leaves to various sized PM, which will help to assess the abilities of urban trees to remove PM from ambient air quantitatively.
Taking three broadleaf tree species (Ginkgo biloba, Sophora japonica, and Salix babylonica) and two needleleaf tree species (Pinus tabuliformis and Sabina chinensis) as the research objects, leaf samples were collected 4 days (short PM retention period) and 14 days (long PM retention period) after the latest rainfall. PM retained on the leaf surfaces was collected by means of WC, BC, and UC in sequence. Then, retention efficiencies of leaves (AEleaf) to three types of the various sized PM, including easily removable PM (ERP), difficult-to-remove PM (DRP), and totally removable PM (TRP), were calculated. Only around 23%-45% of the total PM retained on leaves could be cleaned off and collected by WC. When the leaves were cleaned through WC+BC, the underestimation of the PM retention capacity of different tree species was in the range of 29%-46% for various sized PM. Almost all PM retained on leaves could be removed if UC was supplemented to WC+BC.
In conclusion, if the UC was complemented after the conventional cleaning methods, more PM on leaf surfaces could be eluted and collected. The procedure developed in this study can be used for assessing the PM removal abilities of different tree species.
Introduction
The abilities of different tree species to remove PM from ambient air can be assessed through quantifying the mass of PM retained on leaf surfaces. To achieve this objective, the subtraction method1,2, the membrane filter method3,4,5, and the elution-weighing method coupled with particle size analysis6 have been applied to quantitatively estimate the mass of PM2.5 (diameter ≤ 2.5 µm), PM10 (diameter ≤ 10 µm) or total suspended particulate (TSP) retain....
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Protocol
1. Leaf Collection, Elution and Mass Measurement of PM
- Select five healthy individual trees (i.e., five replicates) of each tree species with similar diameter at breast height. Collect four larger branches randomly from four directions of the outer canopy in the middle canopy layer and cut off all intact leaves.
NOTE: All plants for leaf sampling should be located closely in a greening strip with length and width of about 250 and 60 m, respectively, to ensure that the environment conditions (wind, light, and rain) of these trees are similar. The leaves used in the protocol were collected on October 15th (short dust retention (SDR) period) and....
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Results
The PM retained on leaf surfaces had two types under natural conditions. The PM falls off easily by rainfall and wind under natural conditions is defined as the easily removable particulate matter (ERP). This type of PM was represented by the PM eluted by WC in this study. The PM that tightly adheres to leaf surfaces and cannot be easily washed off by BC and UC is defined as the difficult-to-remove particulate matter (DRP). This kind of PM cannot be eluted by natural rainfall and wind.
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Discussion
Accurate and proper collection of the PM retained on leaf surfaces is the basis for assessing the PM removal abilities of different tree species. However, the conventional cleaning method (WC or plus BC) cannot completely remove the dust on leaf surfaces, which has been confirmed by scanning electron microscopy10. This was further demonstrated clearly by the present study (Figure 1, Figure 2, Fig.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by the Fundamental Research Funds for the Central Universities (2017ZY21) and the National Natural Science Foundation of China (21607038).
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| MSA2258-1CE-DU ten-thousandth scale | Sartorius Scientific Instruments (Beijing) Co., Ltd. | MSA2258-1CE-DU | precision: 0.01 mg |
| The IS13320 laser granularity instrument | Beckman Coulter, Brea, USA | IS13320 | working conditions: liquid/power samples; particle size range of measurement: 0.017-2000 μm |
| Epson Twain Pro high-quality scanner | Seiko Epson, Nagano, Japan | expression1680 | |
| Automatic image analysis software WinRHIZO | Regent Instruments Inc., Quebec, Canada | WinRHIZO Pro 2013a |
References
- Baidurela, A., Halik, U., Aishan, T., Nuermaimaiti, K. Maximum dust retention of main greening trees in arid land oasis cities, Northwest China. Scientia Silvae Sinicae. 51, 57-63 (2015).
- Fan, S. Y., et al. Dust capturing capacities of twenty-six deciduous broad-leaved trees in Beijing. Chinese Journal of Plant Ecology. 39, 736-745 (2015).
- Dzierzanowski, K., Gawroński, S. W.
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