Particulate Matter Phytoremediation Effectiveness of Japanese Prunus × Yedoensis Tree Through Spring and Summer Season

. Using green biofilters can help eliminate air pollutants and improve urban air quality. In the current study, Prunus × Yedoensis capacity of phytoremediation was investigated as a bio filter of Particulate matter (PM) in spring and summer seasons in Japan. Two samples were analysed to extract three fractions of PM (coarse, fine and ultra-fine). Results showed lower deposition of PM in spring season with total of 20.2 μg.cm -2 and high proportion for fine fraction (2.5-10μm), comparing with summer season which showed a higher deposition of PM with total of 31.9 μg.cm -2 . Ultra-fine fraction (0.2 –2.5μm) recorded the highest values with a percentage of 23.9% of the total PM deposition. Leaf micromorphological characteristics such as, rough surface and serrated margin can enhance the Prunus × Yedoensis ability of particulate matter accretion. This study confirms that vegetation has an efficient role in improving the quality of urban air. Further structural analysis should be included to deepen the understanding of phytoremediation phenomena in plants.


Introduction
Particulate matter (PM) which is a mixture of organic and inorganic compounds and elements suspend and transport for long time and distances in ambient air, is directly responsible to aggravate many incurable childhood diseases including post-neonatal infant mortality and sudden infant death syndrome (SIDS) [1][2][3].In Japan, PM polluted air has been observed to be associated with severe health problems for healthy school children and pregnant women during spring and summer in the west of Japan (Kyushu Island) [4][5][6].Therefore, applying various techniques and methods can decline high concentrations of PM, as stated in 2018 annual report of Japanese Ministry of Environment, which declared that achievement rate of Japan Environmental Standards for fine particulate matter (PM2.5) has recently increased from 30-40% from 2010-2014 to over 80% in 2017, even though, PM concentration still increasing steadily and using such techniques can be costly and complicated.
Simply, naturally and cost effectively, plants can adsorb air pollutants through phytoremediation approach, which has been approved in many empirical studies such as [7] and [8].In particular, Japanese plants have been investigated in many studies concerning pollution removal and remediation, such as Acer palmatum, Euonymus japonicus Thunb, Spiraea japonica L., and Aesculus turbinata Blume [9,10].Present study aims to investigate and address phytoremediation ability of PM in another Japanese tree which has not been studied in the previous studies as its growing period though the year is very short.Yoshino * duha.hammad.436@s.kyushu-u.ac.jp cherry (Prunus × yedoensis) is a Japanese tree that just blooms in Spring and its summer leaves fall totally in Autumn, while considering substantial connections between PM deposition and leaf size, leaf compositional morphology, leaf structure, and plant type.

Plant types and experimental sites
Four samples (n = 20 leaves/ sample) have been collected randomly from Yoshino cherry tree (Prunus × yedoensis) at end of two different season, spring season represented by month of May and summer season by month of August, with a time gap between every two samples of every month is 14 days when there was no previous rainfall for more than 3-5 days.(More details show in table I).This tree is planted in urban areas, along roads, streets in Kyushu university campus (Fukuoka, Japan) with a distance between the road and the tree ranges from 2 to 3 m.
Sampling height was 3-5 m above ground level in four directions (north, south, east and west).All leaf samples were individually placed and sealed into prelabelled sample paper bags to minimize PM loss and stored at ambient temperature (4⁰C) in laboratory refrigerator until analysis.Weather conditions were standard to spring and summer season conditions in Fukuoka prefecture (shown in

Quantitative gravimetric analysis of PM
Both adaxial and abaxial surfaces of the leaves were washed (water, SDS), analysed, according to [7], method which was applied through four filtration tools (i-106 μm sieve, ii-10 μm membrane filter, iii-2.5 μm glass microfiber filter, iv-0.2 μm PTFE membrane filter).Total leaf area was measured using ImageJ software.Allowing the amount of PM to be expressed as μg.cm −2 , further analysis was conducted using LEXT OLS4000 3D Laser Measuring Microscope (Olympus, Japan) to analyse correlations among leaf traits in the tested species and PM accumulation.

Equations
The particulate matter amount has been measured according to [7].

W(F+PM):
Weight the filter with the particulate matter after filtration WF: Weight of the filter before filtration, A: Total Surface area of leaf in cm 2 .

Quantification of PM
Considering finding of Nakata [13], who noticed higher PM concentrations during spring and summer as a result of dust events in spring and photochemical reactions in summer.A notably high amount of PM was captured on foliage of Yoshino cherry (Prunus × yedoensis) tree throughout experiment period with a higher quantity for summer season samples (total of 31.9 μg.cm -2 , 61.2 %) than spring season samples (total of 20.2 μg.cm -2 , 38.7%) (shown in Fig. 1).Lower values were also measured in spring season in different previous studies (for example, Silli et al. [14]).
Smaller size particles recorded higher deposition than large size particles in both seasons.In total, fine and ultra-fine particles recorded 21.9 μg.cm -2 (42.1%) and 15.6 μg.cm -2 (29.9%) respectively.Reflecting the findings of Weerakkody et al [15], that smaller diameter of particles, the higher deposition captured (according to Buxus sempervirens with (34.6 mm −2 and 12.8 mm −2 respectively for PM1 and PM2.5).On contrary, Dzierzanowski et al [7] found comparatively higher deposition of large size particles on plant foliage leaves compared to small size particles.In spring season (early May), Yoshino cherry (Prunus × yedoensis) leaves, were young unmatured leaves, as a result it recorded low deposition of PM.This demonstrated by Weerakkody et al [15], who noted that unmatured leaved species showed comparatively low PM deposition, suggesting that this was due to low capacity to withstand PM contaminated air flow, thus lowering turbulence surrounding the leaf boundary.In second sample (at the end of spring season), PM deposition was higher than first sample (at the start of experiment).The reason may be correlated to accumulative increase in surface area of tree leaves, as it shows in Fig. 2. Fine particles (2.5-10) μm which mainly originate from vehicle emissions, combustion, and industrial processes, recorded highest proportion of total PM deposition in spring season with 10.04 μg.cm - 2 (19.2%), followed with coarse fraction (10-100) μm with 7.04 μg.cm -2 (13.5%), while ultra-fine fraction (0.2-2.5) μm was the lowest with 3.14 μg.cm -2 (6%) [16].
Similarly, in the summer season, PM quantity on the leaf's foliage was higher in second sample, that's can be explained, that leaves became more mature leaves and had significantly larger surface area than it was in the spring season, (it shows in Fig. 3) Additionally, anthropogenic and transportation activities, in summer season are more prevalent than other seasons.On contrary of the spring season, ultra-fine fraction (0.2-2.5) μm recorded the highest portion with 12.5 μg.cm -2 (23.9%), followed with fine fraction (2.5-10) μm with 11.9 μg.cm -2 (22.9%), while coarse fraction (10-100) μm was the lowest with 7.5 μg.cm -2 (14.4%), as main    Leaves with complex micromorphological traits, especially, surface roughness owing to threedimensional leaf structures such as hairs, scales, and veins, has been demonstrated to surge particulate retention in different studies [8, 17 -20].

Effects of leaf morphological structural traits on PM deposition
Similarly, present study proved that rough surface, veins, and leaf surface hair density (Fig. 4) were significant predictors of accumulation of ambient PM inside foliage of Prunus × yedoensis tree.Rough surface and hairs can create dissimilar species with convex veins and wavy edges such as F. religiosa contact angles (θ) between rain droplets and leaf surface, thus increase boundary resistance of the leaf and adhesion period of PM on the leaf surface through weather changes such as air turbulence and precipitation.Additionally, presence of leaf hairs can also change deposited PM chemical composition as some leaf hairs are hydrophobic which can attract charged particles attached to different compounds and elements such as heavy metals [21].Hairy leaves with a complex micromorphology have been considered as being sufficient in capturing more particulates than smooth leaved species in Saebø et al [8] and Leonard et al [18].Moreover, Weerakkody et al [15] found higher densities of PM1(ultra-fine particles) on Geranium macrorrhizum due to dense surface hair of their leaves, confirming results of Prunus × yedoensis tree in the present work.On other hand, Perini et al [22] found negative correlation among presence of leaf hairs and PM accumulating.
Furthermore, Leaf margin may enhance particulate matter accumulation process in vegetation, for instance, Prunus × yedoensis serrated margin with sharp toothed edges may act as border in front of weather conditions and decrease repeated deposited washing off or resuspension.It was noted that relatively higher deposition of PM on leaf margins of species with convex veins and wavy edges such as F. religiosa [20,23,24].
This study found that trees are effective species in PM capturing, while it is strongly related to characteristics of plant species [8,25].Trees with large surface area (LA) and crowns resulting from the complex form of foliage leaves can increase turbulent air movement, hence, can enhance capturing more particles than other types of plant species [26,27].
It worth mentioning that leaf traits were differed among selected seasons, especially leaf surface area which can explain significant difference in PM deposition among spring and summer season, in spring season, leaf surface area was smaller (15.3 cm 2 ) than summer season (38.2 cm 2 ).

Conclusions
Particulate matter accretion is different through year seasons, summer season proved to has higher effect on PM accumulation, because of anthropogenic activities and photochemical reactions.At the same time, spring season had lower effect on PM accumulation.Leaf morphological traits such as rough surface and leaf hairs can enhance PM capturing inside leaves foliage of vegetation.The PM accumulation on leaves foliage may influenced to repeated wind and rain events which can interrupt PM accumulation process and increase PM deposition loss.

Fig. 1 .
Fig. 1.Accumulation of particulate matter (means± SD) on leaves within three different size fractions for Prunus × yedoensis in spring and summer season.

Fig. 2 .
Fig. 2. Accumulation of particulate matter (means± SD) on leaves within three different size fractions in the spring season for Prunus × yedoensis.

Fig. 3 .
Fig. 3. Accumulation of particulate matter (means± SD) on leaves within three different size fractions in the summer season for Prunus × yedoensis.

Table 1 .
Analyzed plant characteristics according to north carolina university plant box.

Table 2 .
Weather characteristics through spring and summer season in sampling location.