Study on different particulate matter retention capacities of the leaf surfaces of eight common garden plants in Hangzhou, China.

The severity of inhalable particulate matter (PM) pollution in the atmosphere is increasing; however, plants can effectively reduce the concentration of atmospheric PM by retaining it on their leaves. In this paper, eight common garden plants in Hangzhou, China, were selected as the study objects to observe the morphological features of the leaf surfaces and the retained particles and to analyze the elemental composition of the particles. Confocal laser scanning microscopy (CLSM) was performed to detect the morphological features of the leaf surfaces, and the relationship between the roughness of the leaf surface and the number of the retained particulates was quantitatively analyzed. In addition, the elements in the soil were measured via inductively coupled plasma-optical emission spectrometry (ICP-OES) to locate the possible particulate sources. The results revealed that leaves are able to retain particulates via the synergy of multiple microstructures on the leaf surface, such as grooves, folds, small chambers, flocculus projections, long villi, pubescent hairs and waxes. Moreover, the leaf surface roughness is closely related to the number of retained particulates, with rougher surfaces corresponding to more rugged folds and grooves and a stronger retention ability. The retained particulates are primarily composed of C, O, Si, Al, Ca, K, Mg, Nb, Fe, Na and Ti, and a comparison with the elements in the soil samples indicated that these elements originated from soil dust. Among the different particle sizes, PM with a diameter <2.5 μm (PM) presented the greatest retention on the surfaces of the different plant leaves, while a much smaller amount of PM with a diameter larger than 10 μm was retained. The research results provide an important theoretical scientific basis for the mechanism underlying PM adsorption by plants and strategies for the reasonable selection of garden dust-retaining tree species.