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Article

Phytoremediation Potential of Urban Trees in Mitigating Air Pollution in Tehran

by
Marziyeh Rabiee
1,
Behzad Kaviani
1,*,
Dariusz Kulus
2,* and
Alireza Eslami
1
1
Department of Horticultural Science, Rasht Branch, Islamic Azad University, Rasht 4147654919, Iran
2
Laboratory of Horticulture, Faculty of Agriculture and Biotechnology, Bydgoszcz University of Science and Technology, Bernardyńska 6, 85-029 Bydgoszcz, Poland
*
Authors to whom correspondence should be addressed.
Forests 2024, 15(8), 1436; https://doi.org/10.3390/f15081436
Submission received: 18 July 2024 / Revised: 31 July 2024 / Accepted: 13 August 2024 / Published: 15 August 2024
(This article belongs to the Special Issue Trees and Their Benefits: Social, Ecological & Economic Considerations)
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Abstract

:
The rapid urbanization and growing number of factories, human population, and motor vehicles have led to a drastic increase in the concentration of air pollutants. This smog is one of the most important disturbances in city planning. Urban trees play a vital role in the improvement of air quality. The selection of high-potential trees to capture air pollutants provides an attractive route for the mitigation of urban smog. The current study explored the air purification potential of the four most abundant trees, i.e., white mulberry (Morus alba L.), plane tree (Platanus orientalis L.), European ash (Fraxinus excelsior L.), and Tehran pine (Pinus eldarica Ten.)], as phytoremediators grown in three parks located in regions with low, moderate, and high levels of air pollution in Tehran on the mitigation of four urban hazardous gases (O3, NO2, CO, and SO2) and in altering the content of respiratory gases (CO2 and O2). The measurement of gas levels was carried out in September–October, from 1.30 to 1.50 m above the ground. The concentration of gases was measured by an ambient gas assessment device (Aeroqual). Broad-leaf deciduous species had a greater ability to mitigate O3, NO2, CO, CO2, and SO2 concentrations than needle-leaf evergreen species. The lowest levels of O3 and CO were found around P. orientalis (0.035 and 0.044 ppm, respectively), whereas the content of O2 was the highest in the atmosphere of this tree (20.80 ppm). The lowest content of NO2 (0.081 ppm) and SO2 (0.076 ppm) was determined in the vicinity of M. alba and F. excelsior, respectively. Among the studied species, P. orientalis proved to be the best for air phytoremediation, effectively mitigating hazardous gases more than the other species. Conversely, P. eldarica is not recommended for air phytoremediation in urban green spaces. Future research should focus on exploring a wider range of tree species and their potential for air pollution mitigation in diverse urban settings across different seasons and climatic conditions.

1. Introduction

Air pollution consists of a mixture of hazardous substances originating from both human activities and natural sources. Air pollutants are generally classified into two categories: primary and secondary pollutants. Primary pollutants are directly emitted into the atmosphere, whereas secondary pollutants are formed through the interaction of primary pollutants with other molecules present in the air [1]. Urban air pollution (smog) is a global concern driven by excess industrial activity, heavy transportation, and intensive population mobility [2]. Air pollution represents the most significant environmental risk to human health and is estimated to lead to the death of over 3 million people annually [3]. The world is experiencing a major shift towards urban living and projections indicate an increase to over 65% by 2050 [4]. Many studies revealed a direct correlation between increasing air pollution and human diseases, especially related to the respiratory (emphysema, asthma, and chronic obstructive pulmonary disease (COPD)) and cardiovascular (heart disease and stroke) systems [5,6,7,8,9]. Moreover, air pollution may negatively impact cognitive function and increase the risk of dementia [10] and severe cases of COVID-19 [11]. Even maternal exposure to ambient air pollution increases the risk of low birth weight and pre-term births, cerebral palsy, and early childhood cancers [12,13]. Nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and carbon monoxide (CO) are some of the most dangerous gaseous pollutants in the air.
Urban greenery generates significant ecosystem services and contributes to improving the environmental quality, quality of life, and sustainable urban development. Trees remove air pollution in gaseous form by uptake mainly via leaf stomata, but this role depends on the tree species, its physiological status, the environmental drivers of emission, and climate and air chemistry [5]. Urban vegetation improves air quality and microclimate, increases biodiversity, facilitates road traffic, enhances the aesthetic appeal of landscapes, regulates temperature, controls sound pollution, reduces stress, and thereby enhances the well-being of citizens [14,15,16,17]. Urban vegetation also plays a crucial role in enhancing slope stability by reinforcing soil cohesion and reducing the risk of landslides, particularly in clay slopes, through the mechanical support provided by plant root systems and water absorption processes [18]. Of course, urban vegetation also affects air quality negatively, including the allergenic effects of pollen and fungal spores, and by emitting volatile organic compounds, which can eventually form ozone [19]. Some studies revealed that plants can mitigate particulate matter (PM) concentration but have a negative effect on SO2, NO2, and O3 levels [2]. Moreover, while providing essential microclimate benefits by reducing mean radiant temperature and wind speed, urban evergreen vegetation can negatively impact building energy efficiency in cold region cities [20]. Selecting appropriate vegetation types and infrastructure during the design phase of urban green space is critical to mitigate these adverse effects [4].
The removal of air pollutants relates to the volume, type, and structure of the vegetation, leaf characteristics, and seasons [19,21]. Plant leaves, the primary receptors of air pollution, can function as biological filters to remove significant amounts of particles from the atmosphere of urban areas [22]. Crowns of urban tree species may greatly influence the ecosystem services that are generated. Tree canopies, most importantly the crowns of individual trees, i.e., their size and shape, play a prominent role in providing these services [23].
According to the lists of trees recommended for urban plantings, urban trees grow their crowns in shapes that widely differ from the cylindrical ones [23]. Huang et al. [24] discovered that variations in the height of branching points in roadside trees can significantly alter the distribution of air pollutant concentrations along urban roadways. A notable positive correlation exists between the size of the three-dimensional green volume of various plant communities and pollutants in open spaces [14]. Urban vegetation can mitigate the air pollutants concentration, with reduction rates of 16.5%–26.7% for PM, 13.9%–36.2% for NOx, and 20.5%–47.8% for SO2. However, they failed to significantly mitigate ground-level O3, corresponding to an increase of 5.1%–25.9% [2,25].
The growing number of people, factories, and motor vehicles in Tehran have led to a significant increase in toxic gas emissions, posing a severe threat to air quality. The city consistently experiences high levels of air pollutants, particularly particulate matter (PM2.5 and PM10), NO2, SO2, and O3. These elevated concentrations frequently exceed both national and international air quality standards. Besides anthropogenic factors, the primary sources of pollution include geographical factors such as Tehran’s location in a semi-arid basin surrounded by mountains, which trap pollutants [26]. Despite various mitigation efforts implemented by local authorities, including traffic restrictions and improvements in fuel quality, air pollution remains a critical issue affecting the city’s environmental health and quality of life. It is estimated that reducing ambient PM2.5 concentrations to WHO guideline levels could prevent approximately 3600 premature deaths annually in Tehran [27].
In recent years, air phytoremediation has been recognized as a sustainable and cost-effective approach to mitigating urban air pollution, as solid air pollutants can either deposit on canopy surface, be absorbed through stomata, or dissolve in the wax of the leaves of trees, shrubs, and herbaceous plants [2]. Research has been conducted on various tree species in different municipalities around the world [1,2,4,5]. Nonetheless, the effectiveness of air phytoremediation in cities still requires more synthesis to inform environmental management. There are no published reports comparing the air phytoremediation potential of common urban vegetation growing in differently polluted areas in Iran. Therefore, the purpose of the present study was to evaluate the efficiency of four tree species (Morus alba, Platanus orientalis, Fraxinus excelsior, and Pinus eldarica) as air phytoremediation grown in three parks (Lavizan, Mellat, and Laleh) in Tehran on the mitigation of urban hazardous and respiratory gases. We hypothesize that various tree species can differ in phytoremediation capability and that by optimally choosing the urban vegetation it would be possible to improve the air condition in Tehran.

2. Materials and Methods

2.1. Sampling Site

This study was conducted in three parks (Lavizan Forest Park, Mellat Park, and Laleh Park, with a relatively similar tree structure and composition) located in three areas of Tehran (Figure 1) in 2023. Lavizan Forest Park (35°45′49.36″ N 51°30′3.5″ E), with an area of 1100 hectares, located in the northeast of Tehran, is an area with low air pollution. This park was put into operation in 1963. The purpose of its establishment was to prevent the expansion of the urban fabric and to reduce pollution. Mellat Park (35°46′41.78″ N 51°34′37.73″ E) with an area of 34 hectares, located in the north of Tehran, is an area with medium pollution; it reaches the highway from the south and a large street from the east. This park was originally a barren land, and due to its special location, its construction started in 1966 in two phases. The first phase included the part located along Valiasr Street called “Roadside Boulevard”. The construction work of the second phase continued in the western hills, based on an English park construction, and was inspired by the gardens of that country. It was put into operation in 1974. Laleh Park (35°42′37.13″ N 51°23′32.68″ E), with an area of 35 hectares, located in the center of Tehran, is an area with high pollution. This park is limited to the street from the north, west, and east, and from the south to the boulevard. Laleh Park was founded in 1966. Before that, it was a military area used for riding and parades (known as Jalalieh or Khosro Golesorkhi Garden). The four selected trees are present in all three parks and their abundance distribution is moderate to high [28]. Traffic at the peripheral streets of Lavizan, Mellat, and Laleh parks is low, moderate, and heavy, respectively.
The climate in Tehran is characterized as semi-arid (Köppen: BSh/BSk) with elements of a Mediterranean climate (Köppen: Csa) in its northern areas. It is marked by hot, dry summers and cool, rainy winters, with significant temperature and precipitation variations influenced by its topography and geographic location between the Alborz mountains to the north and the central desert to the south.

2.2. Selected Trees

Four abundantly growing plant species in the studied areas [white mulberry (Morus alba L.), plane tree (Platanus orientalis L.), European ash (Fraxinus excelsior L.), and Tehran pine (Pinus eldarica Ten.)] were selected for the phytoremediation experiments. Some vegetative characteristics and the crown shapes of these tree species are presented in Table 1 and Figure 2.
Table 1. Evaluated tree species and some of their vegetative characteristics.
Table 1. Evaluated tree species and some of their vegetative characteristics.
Trees SpeciesVegetative Characteristics
Morus albaIndigenous to Iran, fast-growing, deciduous, medium-sized, 4–10 m height, dense spreading with spherical crown, generally wider than the height, leaves light green, simple or compound, 5–15 cm long, dentate, palmate-veined, coriaceous and caduceus, Tehran is one of its distribution areas, and alternate phyllotaxis
Platanus orientalisIndigenous to Iran, 20–30 m height, open spherical crown with wide shade, leaves simple, deeply lobed, and palmate or maple-like, 14–16 cm long, petiole swollen at the base, deciduous, and Tehran is one of its distribution areas
Fraxinus excelsiorIndigenous to Iran, deciduous tree, 5–7 m height, trunk up to 2 m diameter, leaves opposite, 20–35 cm long, pinnately compound leaf containing 7–13 leaflets with coarsely serrated margins, elliptic to narrowly elliptic, 3–12 cm long and 0.8–3 cm wide and sessile on the leaf rachis, containing a round crown of erect-spreading branches, Tehran is one of its distribution areas, and seldom shrubs
Pinus eldaricaNon-indigenous, medium-sized tree, reaching 20–35 m tall with a trunk diameter of up to 1 m. The evergreen leaves are needle-like, slender, 10–16 cm long, dark green to yellow–green, long bunch leaves and 2–5 of them in a pod, monopodial growth, with long and short broad branches with different crowns, mostly cylindrical, and Tehran is one of its distribution areas.
Adopted from Ghahraman [29].
Forests 15 01436 g002
Figure 2. Crown and leaf shape illustrations of evaluated tree species. From Wikipedia® [30].
Figure 2. Crown and leaf shape illustrations of evaluated tree species. From Wikipedia® [30].
Forests 15 01436 g002

2.3. Measurement of Ambient Air Pollutant Gases

The levels of four hazardous gases (O3, NO2, CO, and SO2) and altering respiratory gases (CO2 and O2) were measured in September–October 2023 with an environmental gas-measuring device (Aeroqual, Auckland, New Zealand). The Real-Time Air Quality Monitoring System s300 is a portable device with electrochemical sensors approved by Iran’s Environmental Protection Organization. This device can measure gases in the air in the temperature range of 0 to 40 °C and the humidity range of 0 to 95%. To measure environmental gases around the trees, this device was installed under tree canopies, at a distance of 1.30 and 1.50 m from the ground. The sampling occurred exclusively on working days, within the time window from 8:30 a.m. to 8:30 p.m. At each location, a total of six samples were collected hourly, with three samples obtained during the morning period between 8:30 and 11:30 a.m. and another three samples collected during the evening period between 5:30 and 8:30 p.m. This highly-sensitive technique may facilitate the detection of gas molecules (using over 30 inter-changeable sensor heads) at the ppm and ppb levels. A technical specification of the monitor system is given in Table S1 (Supplementary Materials).

2.4. Data Analysis

The experiment was conducted as factorial with two factors and three replications. The first factor was the type of park and the second one was tree species. The data were subjected to the analysis of variance (ANOVA) and means were compared by Duncan’s test at p < 0.05 using the SAS ver. 9.1 software [31].

3. Results

The potential of air phytoremediation by four urban dominant trees in three parks of the capital city of Tehran was estimated. The vegetation had a significant effect on the concentration of air pollutants and respiratory gases (by increasing or reducing their concentration). We identified different species-specific trends, but not location-specific trends for the mitigation of urban pollution (Table 2, Table 3, Table 4 and Table 5). The reduction effect on O3, NO2, CO, CO2, and SO2 levels was significant by tree species and the reciprocal effect of trees and parks (Table 2).
All five pollutants showed an upward trend in concentrations within P. eldarica—an evergreen needle-leaf tree. On the other hand, all four pollutants showed a downward trend in concentrations within P. orientalis and M. alba deciduous broad-leaf species (Table 3). The difference between the parks (independently) was not significant, except for CO2 and CO (Table 4), which suggests that these gases are the easiest ones to eliminate.
As for the interaction of the two studied factors (parks and tree species), shown in Table 5, complex plant configurations containing broad leaves exhibited more substantial pollutant reduction capabilities in the medium and high pollution regions. Mean O3, CO, CO2, and NO2 concentrations were significantly lower in the P. orientalis-covered area located in Mellat Park compared to the others. The concentration of O2 was notably but insignificantly higher in the M. alba of Mellat Park and P. orientalis of Laleh than in the other trees and parks. The lowest O3 (0.033 ppm), CO (0.041 ppm), and CO2 (0.000 ppm) concentrations were identified at the P. orientalis of Mellat (Table 5). Also, the air content of NO2 was low in P. orientalis of Mellat. Conversely, the effectiveness of P. eldarica in removing air pollutants was relatively low. The peak of O3 (0.042–0.052 ppm), NO2 (0.125–0.219 ppm), CO (0.06–0.062 ppm), SO2 (0.089–0.106 ppm), and CO2 (0.126–0.24 ppm) level was recorded at this species grown in all three parks (Table 5).

4. Discussion

The results of our study proved the effectiveness of urban vegetation, particularly broad-leaf trees, as phytoremediators for the mitigation of air pollutants. Air pollutants are commonly emitted from various sources such as vehicle exhaust, wildfire smoke, and activities related to oil and gas extraction [8]. Currently, ozone (O3) is gradually becoming the main air pollutant (next to SO2, CO, particulates, hydrocarbons, nitrogen oxides, and lead) in megacities, such as Tehran [32].
Urban vegetation improves air quality and thereby enhances the well-being of citizens. We studied the ability of urban park/forest vegetation to remove air pollutants (O3, NO2, CO, and SO2) in three parks in Tehran. Air pollutant concentrations were measured at a height of 1.5 m above ground level, a significant level that corresponds to the breathing zone for both children and adults [9]. Exploring the utilization of landscape plants for air pollutant mitigation and assessing the influence of various plant concentrations on reducing air pollution holds great significance in urban ecological environment protection and urban development [14]. Open green spaces with ventilated structures and high tree planting density (deciduous trees are preferred) exhibit optimal purification effects [14], which was also observed in the present study. Trees actively remove pollutants from the urban atmosphere via enhanced rates of deposition due to their relatively large surface area and, depending on the species, surface properties [33]. Nonetheless, the results of our study suggest that the role of urban trees in reducing air pollutant concentrations is not straightforward.
The results of the analysis of variances showed that the coefficient of variation in the measured parameters except for NO2 and CO2 was below 30%. Park and tree interaction was significant on CO2, SO2, CO, NO2, and O3 concentrations, but neither the main effects nor the interaction effect of park and tree on O2 concentration was significant. The comparison of tree species performed here revealed that deciduous species had a greater ability to mitigate O3, NO2, CO, CO2, and SO2 concentrations than evergreen species. It is especially important to underline the high efficiency of P. orientalis in lowering the O3 concentration, as some other species, such as Populus trees and Sophora trees, under stress conditions release biogenic volatile organic compounds (BVOC) contributing to the photochemical production of O3 in conjunction with NOx, leading to elevated O3 concentrations within the greenspaces [2]. Our findings are in contrast with Gong et al. [2], who demonstrated that evergreen species had a greater ability to mitigate air pollutant concentrations, including PM, SO2, and NOx, compared to deciduous species. However, they also reported that evergreen species, unlike deciduous ones, have a significant effect on increasing O3 concentrations. Coniferous species have narrow leaves but a larger surface area per unit area. As a result, the area for absorption and deposition into the leaves is larger, resulting in a higher mitigation capacity. Furthermore, evergreen species have more absorption and deposition time due to leaves presenting in the canopy throughout all seasons compared to deciduous species [2]. According to a rating system for 100 regularly utilized tree species based on their ability to filter out PM, many conifers perform optimally due to their year-round foliage; thick, fine-textured canopies; and high leaf area index [34]. It is important though to note that phytoremediation potential can vary based on factors like local climate [35], which could explain the varied results of the other authors. Nonetheless, we do not recommend P. eldarica for air pollutant mitigation in cities with similar climate conditions to Tehran.
Our results highlight the plant species-specific ability to capture atmospheric pollutants based on their morphological leaf and crown traits. The crown shapes of common urban tree species are modified by the age of a tree and its local environment. A tree’s crown shape influences its volume and thus the ecosystem service provision of a tree [23]. Our findings revealed that the trees with wider canopy width and spherical shape were more suitable for the mitigation of air pollutants compared to the narrower and long, oval ones. On the other hand, vegetation structure showed no consistent pattern in adsorbing air particles, NO2, and volatile organic compound (VOC) pollutants in the northern climates [19]. As for Tehran, the trees with large, broad leaves with lobed structures, such as Morus alba and Platanus orientalis, are more suitable for capturing pollutants. A dense arrangement of trichomes additionally enhances the ability of M. alba to capture particulate matter and absorb gaseous pollutants [36]. As for the physiological mechanisms underlying the high phytoremediation potential of the studied species, one can mention the increased activities of antioxidant enzymes (such as catalase and peroxidase), as well as the high levels of phenolic compounds and flavonoids, which help in detoxifying reactive oxygen species generated by pollutants [37]. Moreover, the high photosynthetic efficiency and stomatal conductance of P. orientalis help in the uptake of CO2 and gaseous pollutants and release of O2, improving local air quality [38]. Nonetheless, cuticle thickness, its chemical composition, stomata density, trichomes density, and other species-related traits, affected also by the climate, affect the adsorption capacities of pollutants [39]. This could explain the differences observed here between the studied tree species.
To achieve air pollution mitigation, spatial configuration and the aerodynamic effect of green spaces (e.g., canopy structure, planting density, planting distance, and shape of street canyon) should be considered in urban planning [2]. Street morphology plays a crucial role in influencing the volume of air in which pollutants emitted by road traffic are dispersed. The dispersion of pollutants in urban environments is affected by the interplay of buildings with diverse shapes and heights along with the layout of roads. If the surrounding buildings are low, then there is a higher potential for air dispersion and dilution [9]. In the present study, three parks were included from different parts of Tehran with low, medium, and high air pollution. In the end, there was no difference between the efficiency of air phytoremediation in these three parks, except for CO2 and CO concentrations. This could be explained by the fact that since the parks had similar plant species, their overall phytoremediation capacity might be comparable, regardless of pollution levels. Moreover, plants may have a maximum capacity for pollutant uptake. In highly polluted areas, this capacity could be reached quickly, limiting further remediation [40].
In future studies with deciduous trees, it is important to consider the effect of season on their phytoremediation efficiency, as recommended by Neves de Lima et al. [41]. Also, soil conditions and other ambient factors that have not been studied in Tehran yet, but could directly affect the air phytoremediation capacity of trees which should be considered.

5. Conclusions

Urban trees significantly reduced the level of hazardous gases in the air (O3, NO2, CO, and SO2) in Tehran and can be used in air remediation. In contrast to some findings, the present investigation revealed that broad-leaf deciduous species had a greater ability to mitigate O3, NO2, CO, CO2, and SO2 concentrations than needle-leaf evergreen species. The cylindrical shape, often used in urban tree growth models, was the least observed within this urban sample. Instead, the ovoid and spherical shapes were the prevalent shapes independent of tree species. We recommend P. orientalis and do not recommend P. eldarica as phytoremediators for urban parks with climate conditions similar to those in Tehran.
The implications of these findings are substantial for urban planning and environmental policy. By prioritizing specific tree species and acknowledging the importance of tree morphology, city planners can enhance urban green spaces’ effectiveness in combating air pollution. This research underscores the necessity for tailored urban greening strategies that align with local climatic conditions, ultimately contributing to healthier urban environments and improved public health outcomes.
Future research should be conducted towards the evaluation of pollution in the source, and optimization of tree and shrub species selection based on their function, morphology, and canopy, as well as their ability related to air pollutant mitigation in urban planning and greening to achieve better air quality. The cooperation of urban planners, policymakers, environmental managers, and researchers (architects, designers, and botanists) for the establishment of new parks can be a benefit.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/f15081436/s1, Table S1: Technical specifications of the monitor system.

Author Contributions

Conceptualization, M.R.; methodology, M.R. and B.K.; software, B.K. and M.R.; validation, M.R., B.K. and D.K.; formal analysis, M.R., B.K. and D.K.; investigation, M.R. and A.E.; resources, M.R. and B.K.; data curation, M.R.; writing—original draft preparation, B.K., D.K. and A.E.; writing—review and editing, D.K.; data curation, A.E.; visualization, M.R.; supervision, M.R. and D.K.; project administration, M.R.; funding acquisition: D.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data are available by email at reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 15 01436 g001
Figure 1. Location of the three study sites in Tehran (GPSMap 64S, GARMIN Taiwan).
Figure 1. Location of the three study sites in Tehran (GPSMap 64S, GARMIN Taiwan).
Forests 15 01436 g001
Table 2. Analysis of variance of the source of variations (parks, trees, and interaction effect of them) on the content of the measured air pollutants and respiratory gases.
Table 2. Analysis of variance of the source of variations (parks, trees, and interaction effect of them) on the content of the measured air pollutants and respiratory gases.
Source of Variations Mean of Squares
dfCO2O2SO2CONO2O3
Replication20.001 ns9.138 ns0.0001 ns0.000007 ns0.007 ns0.00001 ns
Park20.031 **9.013 ns0.0004 ns0.00005 **0.002 ns0.00001 ns
Tree30.035 **9.142 ns0.0008 **0.00045 **0.015 **0.00028 **
Park × Tree60.0004 *8.929 ns0.0003 **0.00003 **0.001 **0.00006 **
Error220.00079.3820.00010.000010.0020.00001
CV (%)-32.415.115.16.145.97.3
*, **: significant at the 0.05 and 0.01 probability levels, respectively; ns: not significant; CV: coefficient of variation; df: degrees of freedom.
Table 3. Mean comparison of the source of variations (tree species) on the content (ppm) of the measured air pollutants and respiratory gases (means and standard deviation).
Table 3. Mean comparison of the source of variations (tree species) on the content (ppm) of the measured air pollutants and respiratory gases (means and standard deviation).
TreeO3NO2COSO2O2CO2
Morus alba0.039 b ± 0.00690.081 b ± 0.0130.049 b ± 0.00400.079 b ± 0.009220.79 a ± 5.760.041 b ± 0.001
Platanus orientalis0.035 c ± 0.0010.083 b ± 0.00110.044 c ± 0.00520.078 b ± 0.001820.80 a ± 4.530.044 b ± 0.0043
Fraxinus excelsior0.040 b ± 0.0020.087 b ± 0.00010.048 b ± 0.00770.076 b ± 0.004918.72 a ± 4.20.063 b ± 0.0039
Pinus eldarica0.048 a ± 0.0080.167 a ± 0.00010.061 a ± 0.00340.097 a ± 0.016020.56 a ± 3.180.174 a ± 0.0066
Mean values with different letters are significantly different at p < 0.05 (Duncan’s test).
Table 4. Mean comparison of the source of variations (parks) on the content (ppm) of the measured air pollutants and respiratory gases (means and standard deviation).
Table 4. Mean comparison of the source of variations (parks) on the content (ppm) of the measured air pollutants and respiratory gases (means and standard deviation).
ParkO3NO2COSO2O2CO2
Laleh0.041 a ± 0.0050.121 a ± 0.0180.052 a ± 0.000 0.081 a ± 0.01019.22 a ± 2.340.063 b ± 0.0011
Lavizan0.042 a ± 0.0040.103 a ± 0.0070.051 a ± 0.0060.077 a ± 0.00420.70 a ± 1.450.138 a ± 0.0016
Mellat0.039 a ± 0.0060.093 a ± 0.0080.048 b ± 0.0030.089 a ± 0.00520.74 a ± 3.690.040 c ± 0.0024
Mean values with different letters are significantly different at p < 0.05 (Duncan’s test).
Table 5. Mean comparison of the source of variations (interaction effect of parks and trees) on the content (ppm) of measured air pollutants and respiratory gases (means and standard deviation).
Table 5. Mean comparison of the source of variations (interaction effect of parks and trees) on the content (ppm) of measured air pollutants and respiratory gases (means and standard deviation).
ParkTreeO3NO2COSO2O2CO2
LalehMorus alba0.036 ce ± 0.00920.09 b ± 0.0060.05 b ± 0.00410.08 b ± 0.011320.75 a ± 3.780.02 de ± 0.008
Platanus orientalis0.034 e ± 0.00150.082 b ± 0.008110.045 de ± 0.00330.075 b ± 0.005620.81 a ± 2.640.023 de ± 0.008
Fraxinus excelsior0.040 cd ± 0.00510.091 b ± 0.010870.054 b ± 0.00630.083 b ± 0.082014.72 a ± 2.800.053 d ± 0.008
Pinus eldarica0.052 a ± 0.00620.219 a ± 0.0150.06 a ± 0.00550.089 ab ± 0.007220.63 a ± 5.880.156 b ± 0.006
LavizanMorus alba0.046 b ± 0.00450.071 b ± 0.0190.052 bc ± 0.00680.082 b ± 0.002620.76 a ± 3.060.103 c ± 0.006
Platanus orientalis0.038 ce ± 0.00970.087 b ± 0.02630.047 cd ± 0.00940.077 b ± 0.010220.8 a ± 2.250.11 bc ± 0.014
Fraxinus excelsior0.042 bc ± 0.00430.086 b ± 0.01180.046 de ± 0.00710.092 ab ± 0.009620.74 a ± 3.630.10 c ± 0.019
Pinus eldarica0.042 bc ± 0.01100.156 ab ± 0.00930.06 a ± 0.00510.097 ab ± 0.012020.41 a ± 2.880.24 a ± 0.021
MellatMorus alba0.036 de ± 0.01040.083 b ± 0.0130.045 de ± 0.00640.077 b ± 0.013020.85 a ± 4.070.000 e ± 0.000
Platanus orientalis0.033 e ± 0.00110.079 b ± 0.00210.041 e ± 0.00910.081 b ± 0.014920.79 a ± 1.510.000 e ± 0.000
Fraxinus excelsior0.037 ce ± 0.00640.085 b ± 0.0140.044 de ± 0.0160.053 c ± 0.004320.71 a ± 3.870.036 de ± 0.001
Pinus eldarica0.052 a ± 0.00760.125 b ± 0.007030.062 a ± 0.00180.106 a ± 0.018320.60 a ± 4.460.126 bc ± 0.011
Mean values with different letters are significantly different at p < 0.05 (Duncan’s test).
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Rabiee, M.; Kaviani, B.; Kulus, D.; Eslami, A. Phytoremediation Potential of Urban Trees in Mitigating Air Pollution in Tehran. Forests 2024, 15, 1436. https://doi.org/10.3390/f15081436

AMA Style

Rabiee M, Kaviani B, Kulus D, Eslami A. Phytoremediation Potential of Urban Trees in Mitigating Air Pollution in Tehran. Forests. 2024; 15(8):1436. https://doi.org/10.3390/f15081436

Chicago/Turabian Style

Rabiee, Marziyeh, Behzad Kaviani, Dariusz Kulus, and Alireza Eslami. 2024. "Phytoremediation Potential of Urban Trees in Mitigating Air Pollution in Tehran" Forests 15, no. 8: 1436. https://doi.org/10.3390/f15081436

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