Plant species differences in particulate matter accumulation on leaf surfaces

Do plant traits help to design green walls for urban air pollution control? A short review of scientific evidences and knowledge gaps

It is often claimed that green walls (GW) and living wall systems (LWS) have a positive effect on urban air pollution problems if their plants composition is optimal (design of the LWS). An in-depth review of the knowledge on plants traits maximizing GW effects on air pollution shows that these might be hasty conclusions: there are still some important knowledge gaps. Robust conclusions can only be drawn for particulate matter (PM): the other pollutants are not analyzed by a sufficient number of studies. It can be concluded that leaves with hairs/trichomes are the most effective to capture PM. The rougher and the smaller the leaf is, the more PM it catches. The analysis of the plant composition of six LWS in Belgium indicated that these LWS supported a plant community dominated by only a few species, which do not exhibit in majority the most effective traits to maximize their PM capture. Regarding climbing plants, only three out of seven commonly used creepers in Belgium present hairs/trichomes on their leaves. Studies conducted on other pollutants and other traits are required to optimize the GW plant composition and to maximize their effects on air quality.

Species-specific efficiency in PM2.5 removal by urban trees: From leaf measurements to improved modeling estimates

The growing population in cities is causing a deterioration of air quality due to the emission of pollutants, causing serious health impacts. Trees and urban forests can contribute through the interception and removal of air pollutants such as particulate matter (PM). The dry deposition of PM by vegetation depends on air pollutant concentration, meteorological conditions, and specific leaf traits. Several studies explored the ability of different plant species to accumulate PM on leaf structures leading to the development of models to quantify the PM removal. The i-Tree Eco is the most used model to evaluate ecosystem services provided by urban trees. However, fine particulate matter (PM_2.5) removal is still calculated with a poorly evaluated function of deposition velocity (which depends on wind speed and leaf area) without differentiating between tree species. Therefore, we present an improvement of the standard model calculation introducing a leaf trait index to distinguish the species effect on PM net removal. We also compared model results with measurements of deposited leaf PM by vacuum filtration. The index includes the effect of morphological and functional leaf characteristics of tree species using four parameters: leaf water storage, deposition velocity, resuspension rate and leaf washing capacity. Leaves of 11 common urban tree species were sampled in representative areas of the city of Ferrara (Italy) and at different times of the year from 2018 to 2021. This includes four deciduous broadleaf trees (Tilia cordata, Platanus acerifolia, Acer platanoides, Celtis australis), three evergreen broadleaf trees (Quercus ilex, Magnolia grandiflora, Nerium oleander), and four conifers (Thuja orientalis, Cedrus libani, Pinus pinaster, Picea abies). The results provide significant advancement in assessing PM removal using decision support tools such as models to properly select tree species for future urban tree planting programs aimed at improving air quality.

Evaluation of heavy metal phytoremediation potential of six tree species of Faisalabad city of Pakistan during summer and winter seasons

Environmental pollution induced by heavy metals has been identified as a leading threat in the modern era. Woody tree species may play a crucial role in the removal of heavy metals from soil and air, thus minimizing pollution potential. The present study was designed to evaluate the phytoremediation potential of six tree species; Azadirachta indica, Cassia fistula, Conocarpus erectus, Eucalyptus camaldulensis, Morus alba, and Populus deltoids, respectively, in the industrial and residential areas of Faisalabad based on the concentrations of lead (Pb), zinc (Zn), cadmium (Cd), and copper (Cu) in their leaves and barks in winter (2018) and summer (2019) seasons. The seasonal contents of heavy metals in both the leaves and barks of these trees decreased in the order of: Zn > Pb > Cu > Cd at both study sites. The highest heavy metal contents were recorded in the leaves and barks of trees grown in the industrial areas as compared to residential areas, with leaves and barks having higher contents of heavy metals in the summer than winter. The tree species exhibited significantly different capacity for heavy metal accumulation, with the accumulation of Cd decreased in the order of: E. camaldulensis > M. alba > C. erectus > A. indica > P. deltoids > C. fistula, and while the order varied for different heavy metals. Overall, M. alba, E. camaldulensis and A. indica performed well in accumulating the targeted heavy metals from the ambient environment. Among the six tree species grown commonly in Faisalabad city, M. alba, E. camaldulensis, and A. indica are recommended for the industrial and residential areas due to their phytoremediation capacity for heavy metals.

Capture of fire smoke particles by leaves of Cunninghamia lanceolata and Schima superba, and importance of leaf characteristics

Emission of particulate matter (PM) during forest fires is a major source of air pollution and hence purification of atmospheric pollution has gained increasing importance. Trees can absorb polluting gases and fine particles by their leaves from the atmosphere and act as a sustainable air purification filter. However, the capture efficiency varies among tree species; thus exploring the ability of forest trees to capture smoke PM released during forest fires provides a basis for assessing net emissions from forest fires and the impact of smoke on forest ecosystems. In this study, the main afforestation tree species, Cunninghamia lanceolata (Lamb.) Hook, and a fire-resistant tree species, Schima superba Gardn.et Champ, in southern China were exposed to different smoke concentrations by simulating forest fire. The amount of PM per unit leaf area, absorption of nutrient element, leaf surface characteristics and antioxidant enzyme activities were determined. The main findings were: (1) The total quantity of PM captured by unit leaf area (μg·cm^-2) of C. lanceolata was 28.25 ± 1.12, 30.52 ± 3.43 and 33.14 ± 3.00 in low, intermediate and high smoke concentrations, respectively. The corresponding values for S. superba was 5.96 ± 0.56, 10.09 ± 1.13 and 12.27 ± 0.39, respectively. (2) Both species had weak absorption capacity for inorganic ions in the PM. (3) The purification of smoke PM by leaves was mainly related to leaf surface roughness, where it was higher for C. lanceolata than S. superba leaves. (4) Smoke treatment positively affected the contents of chlorophyll and soluble protein as well as increased antioxidant enzyme activities. In conclusion, the findings highlight the importance of leaf structural characteristics in capturing smoke particles and C. lanceolata is better suited for purification of atmospheric smoke particles following forest fire than S. superba.

Phyto-cleaning of particulate matter from polluted air by woody plant species in the near-desert city of Jodhpur (India) and the role of heme oxygenase in their response to PM stress conditions

Particulate matter (PM) is one of the most dangerous pollutants in the air. Urban vegetation, especially trees and shrubs, accumulates PM and reduces its concentration in ambient air. The aim of this study was to examine 10 tree and shrub species common for the Indian city of Jodhpur (Rajasthan) located on the edge of the Thar Desert and determine (1) the accumulation of surface and in-wax PM (both in three different size fractions), (2) the amount of epicuticular waxes on foliage, (3) the concentrations of heavy metals (Cd and Cu) on/in the leaves of the examined species, and (4) the level of heme oxygenase enzyme in leaves that accumulate PM and heavy metals. Among the investigated species, Ficus religiosa L. and Cordia myxa L. accumulated the greatest amount of total PM. F. religiosa is a tall tree with a lush, large crown and leaves with wavy edge, convex veins, and long petioles, while C. myxa have hairy leaves with convex veins. The lowest PM accumulation was recorded for drought-resistant Salvadora persica L. and Azadirachta indica A. Juss., which is probably due to their adaptation to growing conditions. Heavy metals (Cu and Cd) were found in the leaves of almost every examined species. The accumulation of heavy metals (especially Cu) was positively correlated with the amount of PM deposited on the foliage. A new finding of this study indicated a potentially important role of HO in the plants' response to PM-induced stress. The correlation between HO and PM was stronger than that between HO and HMs. The results obtained in this study emphasise the role of plants in cleaning polluted air in conditions where there are very high concentrations of PM.

Macro-Morphological Traits of Leaves for Urban Tree Selection for Air Pollution Biomonitoring: A Review

Urban trees provide different ecosystem benefits, such as improving air quality due to the retention of atmospheric particulate matter (PM) on their leaves. The main objective of this paper was to study, through a systematic literature review, the leaf macro-morphological traits (LMTs) most used for the selection of urban trees as air pollution biomonitors. A citation frequency index was used in scientific databases, where the importance associated with each variable was organized by quartiles (Q). The results suggest that the most biomonitored air pollutants by the LMTs of urban trees were PM between 1-100 µm (Q1 = 0.760), followed by O₃ (Q2 = 0.586), PM_2.5 (Q2 = 0.504), and PM₁₀ (Q3 = 0.423). PM was probably the most effective air pollutant for studying and evaluating urban air quality in the context of tree LMTs. PM_2.5 was the fraction most used in these studies. The LMTs most used for PM monitoring were leaf area (Q1) and specific leaf area (Q4). These LMTs were frequently used for their easy measurement and quantification. In urban areas, it was suggested that leaf area was directly related to the amount of PM retained on tree leaves. The PM retained on tree leaves was also used to study other f associated urban air pollutants associated (e.g., heavy metals and hydrocarbons).

Analysis of the influencing factors of atmospheric particulate matter accumulation on coniferous species: measurement methods, pollution level, and leaf traits

Urban trees, especially their leaves, have the potential to capture atmospheric particulate matter (PM) and improve air quality. However, the amount of PM deposited on leaf surfaces detected by different methods varies greatly, and quantitative understanding of the relationship between PM retention capacity and various microstructures of leaf surfaces is still limited. In this study, three measurement methods, including the leaf washing (LW) method, aerosol regeneration (AR) method, and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX) method, were used to determine the PM retention capacity of leaf surfaces of three coniferous species. Additionally, we analyzed the leaf traits and elemental composition of PM on leaves collected from different sites. The results showed that Pinus tabulaeformis and Abies holophylla were more efficient species in capturing PM than Juniperus chinensis, but different measurement methods could affect the detected results of PM accumulation on leaf surfaces. The concentrations of trace elements accumulated on leaf surfaces differed considerably between different sites. The greatest accumulation of elements that occurred on the leaf surface was at the Shenfu Highway site exposed to high PM pollution levels and the smallest accumulation at the Dongling park site. The stomatal density and contact angle were highly correlated with the PM retention capacity of leaf surfaces of the tested species (Pearson coefficient: r = 0.87, p < 0.01 and r =  - 0.70, p < 0.05), while the roughness and groove width were not significantly correlated (Pearson coefficient: r = 0.16 and r =  - 0.03). This study suggests that a methodological standardization for measuring PM is urgently required and this could contribute to selecting greening tree species with high air purification capacity.

Air pollutant removal by four sidewalk tree species in the largest city in Taiwan

Air pollutants pose risks to human health, especially in densely populated cities. We compared the interception of suspended particles and metal elements by four sidewalk tree species with different leaf surface wettability (based on contact angle), leaf area, and phenology in Taipei, Taiwan. Suspended particles were enriched 2.0-2.5 times in throughfall relative to rainfall due to wash-off of suspended particles deposited on leaf surfaces during rainless periods. The enrichment in throughfall was greater in tree species with larger leaf areas. Despite greater concentrations of suspended particles in rainfall during the low-leaf-area period, enrichment was greater in the high-leaf-area period, indicating that leaf area was a key factor affecting canopy interception of pollutants. Throughfall enrichment of suspended particles positively correlated with water quantity, indicating that air pollutants intercepted by tree canopies were not fully washed off by rainfall. Annually, ∼830 g of suspended particles were intercepted and washed off from one tree canopy, with a crown area of 42 m² . Scaling up, a rough estimate of 72.7 Mg of suspended particles were intercepted annually by the 90,000 sidewalk trees in Taipei City. Copper, chromium, and aluminum were enriched in throughfall compared with rainfall. However, lead was depleted in throughfall, indicating greater interception than wash-off. Based on our results, leaf area and length of foliated period are key characteristics affecting canopy interception of particulate matter and associated metal elements, whereas leaf surface wettability is of secondary importance.

Protecting playgrounds: local-scale reduction of airborne particulate matter concentrations through particulate deposition on roadside ‘tredges’ (green infrastructure)

Exposure to traffic-related particulate air pollution has been linked with excess risks for a range of cardiovascular, respiratory and neurological health outcomes; risks likely to be exacerbated in young children attending schools adjacent to highly-trafficked roads. One immediate way of reducing airborne PM concentrations at the local (i.e., near-road community) scale is installation of roadside vegetation as a means of passive pollution abatement. Roadside vegetation can decrease airborne PM concentrations, through PM deposition on leaves, but can also increase them, by impeding airflow and PM dispersion. Critical to optimizing PM removal is selection of species with high particle deposition velocity (Vd) values, currently under-parameterised in most modelling studies. Here, the measured amounts of leaf-deposited magnetic PM after roadside greening (‘tredge’) installation, and measured reductions in playground PM, particle number and black carbon concentrations demonstrate that air quality improvements by deposition can be achieved at the local, near-road, community/playground scale. PM deposition on the western red cedar tredge removed ~ 49% of BC, and ~ 46% and 26% of the traffic-sourced PM_2.5 and PM₁, respectively. These findings demonstrate that roadside vegetation can be designed, installed and maintained to achieve rapid, significant, cost-effective improvement of air quality by optimising PM deposition on plant leaves.

Particulate matter and polycyclic aromatic hydrocarbon uptake in relation to leaf surface functional traits in Mediterranean evergreens: Potentials for air phytoremediation

We explored relationships between particulate matter (PM) and polycyclic aromatic hydrocarbon (PAHs) leaf concentrations, uptake rates and leaf surface functional traits in four Mediterranean evergreen trees (Chamaerops humilis, Citrus × aurantium, Magnolia grandiflora, and Quercus ilex) during a dry month. Pollutant leaf concentration at different dates and uptake rate were correlated. We quantified PM by gravimetric analysis, PAHs were extracted from intact and dewaxed leaves and analyzed by GC-MS, and cuticle thickness, number and surface of stomata (N_s and S_S) and trichomes (N_t and S_t) were determined by optical microscopy. Infrared spectroscopy was used to investigate the leaves surfaces composition and assess esterification index (E). Studied species were characterized by unique combinations of functional traits and pollutant uptake capacities. PM₁₀ uptake scaled positively with S_S, S_t and upper cuticle thickness (T_c,u) across species. PM_2.5 uptake scaled positively with T_c,u, and thicker cuticles were also associated with greater shares of uptake of hydrophobic PM fractions. Uptakes of different fractions of PAH were generally weakly related to different leaf functional traits, except for some correlations with E and S_S. We conclude that both plant surface morphological and chemical leaf traits influence PM and PAH retention, unveiling their potential role in air phytoremediation.

Materials on Plant Leaf Surfaces Are Deliquescent in a Variety of Environments

Materials on plant leaf surfaces that attract water impact penetration of foliar-applied agrochemicals, foliar water uptake, gas exchange, and stomatal density. Few studies are available on the nature of these substances, and we quantify the hygroscopicity of these materials. Water vapor sorption experiments on twelve leaf washes of sample leaves were conducted and analyzed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray diffraction. All leaf surface materials studied were hygroscopic. Oils were found on the surface of the Eucalyptus studied. For mangroves that excrete salt to the leaf surfaces, significant sorption occurred at high humidity of a total of 316 mg (~0.3 ml) over 6-10 leaves and fitted a Guggenheim, Anderson, and de Böer sorption isotherm. Materials on the plant leaf surface can deliquesce and form an aqueous solution in a variety of environments where plants grow, including glasshouses and by the ocean, which is an important factor when considering plant-atmosphere relations.

Factors influencing the cleaning of plant samples with ultrasonic technology

Effective cleaning of biological samples is a critical step in environmental studies. However, the literature lacks standardized cleaning procedures and protocols and there is little information about how even the most basic conditions may affect cleaning efficiency. Here, leaves of different species were first exposed to the soil naturally containing mercury particles and then washed in an ultrasound water bath under the following conditions: newly cleaned/reused beakers, water temperature, sample immersion/free-floating, sample quantity, and the number of washing cycles. Additionally, the effects of sample pubescence on cleaning efficacy were also assessed. Results indicated that the best cleaning efficacy was recorded when samples were placed in cold water under forced immersion and beakers were cleaned between washing cycles. At least two of these three conditions were needed for adequate washing. The results also indicated that, for the glabrous leaves, a cumulative leaf surface area of ≤10,000 mm² was efficiently cleaned after 3-5 washing cycles, while as pubescence increased, 9-11 cycles were needed and often the sample quantity had to be reduced (<5,000 mm²). Our experiments reveal that cleaning can be optimized by applying easy procedures and according to individual sample typology, resulting in faster and more effective cleaning. Novelty statementThe cleaning of samples is a frequent stage in the analytical processes of phytoremediation studies. This work provides new and valuable information to optimize the cleaning of plant samples by simply applying ultrasonic technology and distilled water. In fact, we have tested the influence of some factors never taken into account previously.

Big data-based urban greenness in Chinese megalopolises and possible contribution to air quality control

Urban greenness is essential for people's daily lives, while its contribution to air quality control is unclear. In this study, Streetview big data of urban greenness and air quality data (Air Quality Index, PM_2.5, PM₁₀, SO₂, NO₂, O₃, CO) from 206 monitoring stations from 27 provincial capital cities in China were analyzed. The national averages for the sky, ground and middle-level (shrub and short trees) view greenness were 5.4%, 5.5%, and 15.4%, respectively, and the sky:ground:middle ratio was 2:2:6. Street-view/bird-view greenness ratio averaged at 1.1. Large inter-city variations were observed in all the greenness parameters, and the weak associations between all street-view parameters and bird-eye greenspace percentage (21%-73%) indicate their representatives of different aspects of green infrastructures. All air quality parameters were higher in winter than in summer, except O₃. Over 90% of air quality variation could be explained by socioeconomics and geoclimates, suggesting that air quality control in China should first reduce efflux from social economics, while geoclimatic-oriented ventilation facilitation design is also critical. For different air quality components, greenness had most significant associations with NO₂, O₃ and CO, and street-view/bird-view ratio was the most powerful indicator of all greenness parameters. Pooled-data analysis at national level showed that street-view greenness was responsible for 2.3% of the air quality variations in the summer and 3.6% in the winter; however, when separated into different regions (North-South China; East-West China), the explaining power increased up to 16.2%. Increased NO₂ was accompanied with decreased O₃, indicating NO titration effect. The higher O₃ aligned with the higher street-view greenness, showing the greenness-related precursor risk for O₃ pollution. Our study manifested that big internet data could identify the association of greenness and air pollution from street view scale, which can favor urban greenness management and evaluation in other regions where street-view data are available.

Leaf surface traits related to differential particle adsorption - A case study of two tropical legumes

We aimed to test a set of epidermal traits in two legume species with contrasting chemical, physical, and micromorphological leaf-surface features to assess which ones would determine higher PM retention. For that, we performed a biomonitoring study in southeastern Brazil at the Steel Valley Metropolitan Region, where there is predominance of steel industry and one of the largest vehicle fleets in the country. A reference station was installed at a neighboring park. We evaluated leaf-surface roughness at two hierarchical levels, leaf wettability, epidermal-cell anticlinal-wall undulation, epidermal-cell perimeter, and the micromorphology and chemical composition of epicuticular waxes. Particle retention was significantly higher in Paubrasilia echinata than in Libidibia ferrea var. leiostachya, the former of which has lower roughness given by both the epidermal tissue (macro-roughness; 0.6 vs 2.6 μm) and epicuticular waxes (micro-roughness; 68 vs 220 nm), higher leaf wettability (82° vs 143°), lower epidermal-cell undulation index (1.2 vs 1.8), lower epidermal-cell perimeter (93 vs 146 μm), wax deposition in the form of a smooth layer (as opposed to densely aggregated rosettes of vertical platelets), and more polar wax chemical constitution (68% vs 47% of polar compounds). While all of the assessed traits contributed to particle retention, canonical loadings revealed that macro-roughness was the trait that contributed the most to the retention of PM_2.5 (ca = 1.47; r = -0.56), PM₁₀ (ca = 1.08; r = -0.61), PM₁₀₀ (ca = -4.95; r = -0.39) and TSP (ca = 0.98; r = -0.62), although this trait was shown by factor analysis to be secondary in distinguishing between species (0.92 contribution to the second axis). Our findings shed new light on the criteria that should be considered when selecting species for green infrastructure aiming to reduce urban air pollution, as well as on novel possibilities for PM biomonitoring in the tropics.

Seasonal variations in the amount of black carbon particles deposited on the leaf surfaces of nine Japanese urban greening tree species and their related factors

As black carbon (BC) particles can be deposited on the leaf surfaces, urban greening is considered to be effective in purifying urban air. However, little information on the seasonal variations in the amount of BC particles deposited on the leaf surfaces (BC amount on the leaves) is available in Japanese urban greening tree species. Therefore, we investigated seasonal variations in the BC amount on the leaves of evergreen (Quercus glauca, Quercus myrsinaefolia, Osmanthus fragrans and Ilex rotunda) and deciduous (Zelkova serrata, Styrax japonica, Magnolia kobus, Cornus kousa and Cornus florida) broad-leaved tree species. The BC amount on the leaves tended to increase from April for different periods, and then reached a saturated state in the tree species, excluding M. kobus. In the 4 evergreen broad-leaved trees, the seasonal variation was positively correlated with the atmospheric concentration of BC particle. In the 5 deciduous broad-leaved trees, the seasonal variation was negatively and positively correlated with the water-repellence (water droplet contact angle) and the amount of epicuticular wax on the leaf surface, respectively. Therefore, the BC amounts on the leaves of evergreen and deciduous broad-leaved urban tree species are considered to be mainly regulated by environmental factors and leaf surface characteristics, respectively.

Pollution monitoring using the leaf-deposited particulates and magnetism of the leaves of 23 plant species in a semi-arid city, Northwest China

We conducted a study of the leaf-deposited particles and magnetism of plant leaves in different functional areas (traffic areas, parks, and residential areas) in Lanzhou, China. The saturation isothermal remanent magnetization (SIRM) of the washed and unwashed leaves of 23 plant species (including evergreen shrubs, deciduous shrubs, deciduous liana species, and deciduous trees) at three sampling heights (0.5 m, 1.5 m, and 2.5 m) was measured. In addition, the mass of the leaf-deposited particles was measured using the elution-filtration method and the leaf morphological characteristics were determined by scanning electronic microscope (SEM) analysis. The results revealed significant differences in particle retention capacity among the 23 plant species, with evergreen shrub species at the heights of 0.5 m and 1.5 m having higher particle concentrations. Buxus sinica, Buxus megistophylla, Prunus cerasifera, and Ligustrum×vicaryi were the most effective plant species for accumulating particles. The SEM results showed that leaves with a relatively complex adaxial surface (such as deep grooves and protrusions) were more effective at accumulating particles. The SIRM of washed leaves, unwashed leaves, and leaf-deposited particles were significantly higher in traffic areas than in parks and residential areas. In addition, significant correlations were found between SIRM of unwashed leaves and leaf-deposited particles and the mass of leaf-deposited particles, and therefore the leaf magnetic properties effectively reflect levels of PM pollution under different environmental conditions. Overall, our results provide a valuable reference for the selection of plant species with high particle retention capacity that is suitable for urban greening and pollution mitigation.

Planning, Designing, and Managing Green Roofs and Green Walls for Public Health – An Ecosystem Services Approach

Installing green roofs and green walls in urban areas is suggested to supply multiple ecosystem services of benefit to human health and well-being. In a three-step literature review, we examined current knowledge on the link between public health and green roofs and green walls. A systematic search identified 69 scientific articles on green roofs/walls with a public health discourse. These articles were categorized according to type of health path covered (reduction of temperature, air pollution, noise or environmental appraisal) and coverage of issues of relevance for strategies on planning, design/construction, and maintenance of green roofs and green walls. Articles identified through the structured search were complemented with reviews (with no explicit public health rationale) covering reduction of noise, temperature, or air pollution and environmental appraisal. Other relevant studies were identified through snowballing. Several of the articles provided guidelines for optimizing the effect of green roofs/walls in supporting ecosystem services and maximizing well-being benefits to support health pathways identified. These included specifications about planning issues, with recommended spatial allocation (locations where people live, sun-exposed for maximum ambient temperature reduction) and with physical access needed for environmental appraisal. Recommendations regarding design parameters covered substrate depth (deeper generally being better), plant choices (more diverse roofs providing more services), and maintenance issues (moist substrate positively correlated with heat reduction).

Analyzing Air Pollutant Reduction Possibilities in the City of Zagreb

This paper aims to present possible areas to plant different vegetation types near traffic jams to reduce air pollution in the capital of Croatia, the city of Zagreb. Based on main traffic road and random forest machine learning using WorldView-2 European cities data, potential areas are established. It is seen that, based on a 10 m buffer, there is a possible planting area of more than 220,000 square meters, and based on 15 m buffer, there is a possible planting area of more than 410,000 square meters. The proposed plants are Viburnum lucidum, Photinia x fraseri, Euonymus japonicus, Tilia cordata, Aesculus hippocastanum, Pinus sp., Taxus baccata, Populus alba, Quercus robur, Betula pendula, which are characteristic for urban areas in Croatia. The planting of proposed trees may result in an increase of 3–5% in the total trees in the city of Zagreb. Although similar research has been published, this paper presents novelty findings from combined machine learning methods for defining green urban areas. Additionally, this paper presents original results for this region.

Defining a Pedagogical Framework for Integrating Buildings and Landscapes in Conjunction with Social Sustainability Discourse in the Architecture Graduate Design Studio

The primary objective of this research is to define a pedagogy framework for architecture Graduate Design Studio. The proposed pedagogy framework pursues the following three principal objectives: The first objective focuses on buildings and landscapes and the interconnection between them. Such connectivity facilitates a ground for walkability. The second goal is to incorporate green elements within buildings and landscapes with regard to increasing the percentage of available green spaces within contemporary and future cities, which may encourage human respect for nature. The third objective promotes the notion that contemporary and future built environments should be envisioned as environments wherein fresh local food can be cultivated, processed and distributed. It incorporates urban agriculture within buildings and landscapes. The Graduate Studio pedagogy focuses on the concept of social sustainability. The three mentioned objectives of the framework are in line with the core concept of social sustainability, which includes improving the well-being and quality of life of contemporary and future urban dwellers. Overall, the Graduate Studio envisions buildings and landscapes as pedestrian environments, as grounds where green elements are incorporated and local fresh food is cultivated. The mentioned framework has been implemented within the Graduate Studio. Four design project samples are presented as successful precedents.

Integrating Tree Species Identity and Diversity in Particulate Matter Adsorption

The amount of PM bound by tree canopies depends on leaf traits, but also the leaf area available, both of which are dependent on tree identity. We investigated four species (Acer platanoides L., Tilia cordata Mill., Quercus robur L., Carpinus betulus L.) grown in monocultures and in two and four species polycultures. The amount of PM on the leaves of these species was determined by washing and fractionation of the PM into PM2.5, PM10 and PM100 size classes using a filtering method. The leaf area index was estimated by litter collection. The amount of PM2.5 per m2 leaf area was significantly higher in T. cordata compared to Q. robur and A. platanoides, and in C. betulus compared to A. platanoides. The leaf area index in monocultures was similar for all species except T. cordata which was considerably lower. Overyielding of LAI was shown in the two species polyculture of T. cordata and A. platanoides, and also in the four species polyculture. In polyculture, higher amounts of PM were determined in the two species polyculture of Q. robur and C. betulus and also in the four species polyculture. The result show that both tree identity and mixture influence the amount of PM in the canopy, and this is related to tree leaf traits, and also to overyielding of LAI in the polyculture.

Surface charge affects foliar uptake, transport and physiological effects of functionalized graphene quantum dots in plants

The present study focused on evaluating the effects of surface charge on foliar uptake, translocation and physiological response of graphene quantum dots (GQDs) in maize (Zea mays L.) plants. Here, maize seedlings were foliar exposed to 10 mg/L GQDs modified with positively charged amino functional groups (NH₂-GQDs) and negatively charged hydroxyl functional groups (OH-GQDs) for 8 days, respectively. Positively charged NH₂-GQDs adhered on the cuticle layer were approximately 2.1 times more than the negatively charged OH-GQDs due to the electrostatic attraction to plant cell wall with negative charge. Within the initial 5 days, most of the GQDs internalized into the leaves via stomatal opening were efficiently translocated to the vasculature and moved down to the roots. Thereafter, the enlargement of aggregation made the particle sizes approach and even exceed the pipe diameter of vascular bundle, thus limiting the leaf-to-root translocation of GQDs, especially for NH₂-GQDs. Compared with positively charged NH₂-GQDs, negatively charged OH-GQDs induced stronger inhibitory effect on photosynthesis, higher accumulation of malondialdehyde and stimulation to enzyme activities of superoxide dismutase, catalase, and peroxidase. Overall, our findings provide direct evidence for the influence of surface charge on foliar uptake, translocation, and physiological effects of GQDs in crop plants, and imply that foliar exposure of GQDs negatively impact plant photosynthesis and growth health.

Mapping of Urban Vegetation with High-Resolution Remote Sensing: A Review

Green space is increasingly recognized as an important component of the urban environment. Adequate management and planning of urban green space is crucial to maximize its benefits for urban inhabitants and for the urban ecosystem in general. Inventorying urban vegetation is a costly and time-consuming process. The development of new remote sensing techniques to map and monitor vegetation has therefore become an important topic of interest to many scholars. Based on a comprehensive survey of the literature, this review article provides an overview of the main approaches proposed to map urban vegetation from high-resolution remotely sensed data. Studies are reviewed from three perspectives: (a) the vegetation typology, (b) the remote sensing data used and (c) the mapping approach applied. With regard to vegetation typology, a distinction is made between studies focusing on the mapping of functional vegetation types and studies performing mapping of lower-level taxonomic ranks, with the latter mainly focusing on urban trees. A wide variety of high-resolution imagery has been used by researchers for both types of mapping. The fusion of various types of remote sensing data, as well as the inclusion of phenological information through the use of multi-temporal imagery, prove to be the most promising avenues to improve mapping accuracy. With regard to mapping approaches, the use of deep learning is becoming more established, mostly for the mapping of tree species. Through this survey, several research gaps could be identified. Interest in the mapping of non-tree species in urban environments is still limited. The same holds for the mapping of understory species. Most studies focus on the mapping of public green spaces, while interest in the mapping of private green space is less common. The use of imagery with a high spatial and temporal resolution, enabling the retrieval of phenological information for mapping and monitoring vegetation at the species level, still proves to be limited in urban contexts. Hence, mapping approaches specifically tailored towards time-series analysis and the use of new data sources seem to hold great promise for advancing the field. Finally, unsupervised learning techniques and active learning, so far rarely applied in urban vegetation mapping, are also areas where significant progress can be expected.

Microplastics retained in stormwater control measures: Where do they come from and where do they go?

Stormwater control measures (SCM) can remove and accumulate microplastics and may serve as a long-term source of microplastics for groundwater pollution because of their potential for downward mobility in subsurface. Furthermore, the number of microplastics accumulated in SCM may have been underestimated as the calculation typically only accounts for microplastics accumulated via episodic stormwater loading and ignores microplastic accumuation via continuous atmospheric deposition. To evaluate the source pathways of accumulated microplastics and their potential for downward mobility to groundwater, we analyzed spatial distributions of microplastics above ground on the canopy around SCM and below ground in the subsurface in and outside the boundaries of fourteen SCM in Los Angeles. Using an exponential model, we link subsurface retardation of microplastics to the median particle size of soil (D₅₀) and land use. Despite receiving significantly more stormwater, microplastic concentrations in SCM at surface depth or subsurface depth were not significantly different from the concentration at the same depth outside the SCM. Similar concentration in and outside of SCM indicates that stormwater is not the sole source of microplastics accumulated in SCM. The high concentration of microplastics on leaves of vegetation in SCM confirms that the contribution of atmospheric deposition is significant. Within and outside the SCM boundary, microplastics are removed within the top 5 cm of the subsurface, and their concentration decreases exponentially with depth, indicating limited potential for groundwater pollution from the microplastics accumulated in SCM. Outside the SCM boundary, the subsurface retardation coefficient decreases with increases in D₅₀, indicating straining of microplastics as the dominant removal mechanism. Inside the boundary of SCM, however, the retardation coefficient was independent of D₅₀, implying that microplastics could have either moved deeper into the filter layer in SCM or that compost, mulch, or organic amendments used in the filter media were pre-contaminated with microplastics. Overall, these results provide insights on microplastics source, accumulation, and downward mobility in SCM.

The Nature and Size Fractions of Particulate Matter Deposited on Leaves of Four Tree Species in Beijing, China

Particulate matter (PM) in different size fractions (PM0.1–2.5, PM2.5–10 and PM>10) accumulation on four tree species (Populus tomentosa, Platanus acerifolia, Fraxinus chinensis, and Ginkgo biloba) at two sites with different pollution levels was examined in Beijing, China. Among the tested tree species, P. acerifolia was the most efficient species in capturing PM, followed by F. chinensis, G. biloba, and P. tomentosa. The heavily polluted site had higher PM accumulation on foliage and a higher percentage of PM0.1–2.5 and PM2.5–10. Encapsulation of PM within cuticles was observed on leaves of F. chinensis and G. biloba, which was further dominated by PM2.5. Leaf surface structure explains the considerable differences in PM accumulation among tree species. The amounts of accumulated PM (PM0.1–2.5, PM2.5–10, and PM>10) increased with the increase of stomatal aperture, stomatal width, leaf length, leaf width, and stomatal density, but decreases with contact angle. Considering PM accumulation ability, leaf area index, and tolerance to pollutants in urban areas, we suggest P. acerifolia should be used more frequently in urban areas, especially in “hotspots” in city centers (e.g., roads/streets with heavy traffic loads). However, G. biloba and P. tomentosa should be installed in less polluted areas.

Characteristics of airborne particles retained on conifer needles across China in winter and preliminary evaluation of the capacity of trees in haze mitigation

To fully understand the characteristics of particulate matter (PM) retained on plant leaves (PMR) and the effect of vegetation on haze on a large spatial scale, we investigated needle samples collected from 78 parks and campuses in 31 cities (30 provincial cities) of China and developed a comprehensive method to characterise PMR. Both the PMR load (including water-insoluble particulate matter (WIPM), water-soluble inorganic ions (WSIS) and water-soluble organic matter (WSOM)), with a mean value of 554 ± 345 mg m^-2 leaf area, and component profiles of PMR showed obvious spatial variation across the cities. Though haze pollution levels vary greatly among the 31 cities, the PM retention capacity of needles does not depend on haze level because PMR generally reaches saturation before precipitation in winter. The water-soluble component (WSC, the sum of WSIS and WSOM) accounted for 52.3% of PMR on average, among which WSIS and WSOM contributed 21.4% and 30.9% to PMR, respectively. The dominant ions of WSIS in PMR in the cities were Ca²⁺, K⁺ and NO₃^-, indicating that raised dust, biomass combustion and traffic exhaust are significant sources of PM in China. Compared with previous reports, the particle size distributions of PMR and PM across China were consistent, with fine PM (PM_2.5) constituting a substantial proportion (43.8 ± 17.0%) of PMR. These results prove that trees can effectively remove fine particles from the air, thereby reducing human exposure to inhalable PM. We proposed a method to estimate the annual amount of PMR on Cedrus deodara, with an average value of 11.9 ± 9.6 t km^-2 canopy yr^-1 in China. Compared with the load of dust fall (atmospheric particles naturally falling on the ground, average of 138 ± 164 t km^-2 land area yr^-1 in China), we conclude that trees play a significant role in mitigating haze pollution.

Season impacts on estimating plant's particulate retention: Field experiments and meta-analysis

Plants can effectively remove atmospheric particles, which contribute to air pollution. However, few studies have focused on seasonal variability of plant dust retention, an essential factor to estimate annual dust removal from the atmosphere. This study conducted a field experiment to explore the seasonal variability of particulate retention on evergreen leaved urban greening shrub plants. We performed a meta-analysis to synthesize the available literature on the subject to discuss our findings further. Results showed that particulate matter deposited on leaf surfaces (sPM) in autumn and winter was significantly higher than in spring and summer. In comparison, the particulate matter trapped in epicuticular waxes (wPM) in summer was significantly higher than in the other three seasons. The seasonal differences also existed in both sPM and wPM among particle sizes. The total dust retention of Rhododendron × pulchrum Sweet, Osmanthus fragrans Lour, and Photinia × fraseri Dress were estimated as 360.89 t, 586.66 t, and 448.84 t per year, respectively. They were significantly different from model estimates if only one season was chosen as an estimator. Furthermore, the meta-analysis revealed significant differences among seasons, particle sizes, and different leaf habits (evergreen or deciduous). In contrast, no significant differences were observed between life forms or between growth forms. Our findings both from field experiment and met-analysis highlights that seasonal variation can significantly affect the dust retention capacity of plants, which should be taken into account into particle matter retention capacity evaluations.

Particulate Pollution Capture by Seventeen Woody Species Growing in Parks or along Roads in Two European Cities

This research aims to extend the existing knowledge on air quality improvement by the arboreal–shrub heritage. The PM accumulation (PM10–100, PM2.5–10, and PM0.2–2.5 (µg·cm−2)) was measured with consolidated gravimetric techniques during spring, summer, and fall for 2160 leaf samples belonging to the basal, median, and apical part of the crown of 17 species located in the streets and parks of 2 European cities (Rimini and Krakow). On the same samples, the deposition (PM10 and PM2.5 (µg·cm−2·day−1)) was evaluated according to a model based on the wash-off rain effect. Quercus ilex accumulated more PMx than the other species in Rimini, while in Krakow, the highest accumulators were Pinus nigra for PM10–100, Tilia cordata for PM2.5–10, and Populus nigra for PM0.2–2.5. Only in Krakow was the capture capacity of some species affected by the street or park growing condition. The basal leaves showed greater PM10–100 accumulation than the median and apical ones. In Rimini, the total PM accumulation tended to increase throughout the year, while in Krakow, the opposite occurred. However, as the accumulation increased, the deposition decreased. The PM accumulation was reduced by rainfall and enhanced by the air PM concentration, while the wind speed effect was opposite, depending on the city. These findings are useful for directing decision makers in the design of greener, healthier, and sustainable cities.

Relationship between leaf dust retention capacity and leaf microstructure of six common tree species for campus greening

Green plants can effectively retain atmospheric particle pollution and purify the air. As an important part of the campus ecosystem, they have a significant effect on absorbing atmospheric pollutants and improving the quality of the campus air environment. Six common greening plants were selected as the object in Xiangnan University. The dust retention capacity of plant leaves, leaf micro-structure, and leaf contact angle were measured. The results show that the highest amounts of dust removed by Osmanthus fragrans Lour was 3.451 g/m², and the least amounts of dust removed by Magnolia denudata Desr. was 1.005 g/m², and the maximum is 4.148 times of the minimum. The micro-structure of the plant leaf surface affects the amount of dust retention. The plant dust retention capacity with gully of the leaf surface and fluff, stomata, and sawtooth structure is relatively strong; The plant dust retention capacity with smooth, wax layer, leathery, and gully is relatively weak. The leaf contact area of a plant is related to its dust retention ability, that is, when the measured leaf contact angle is <90°, the leaf dust retention ability of the plant is strong. When the blade contact angle is >90°, the dust retention capacity is weak.

Accumulation pattern of polycyclic aromatic hydrocarbons using Plantago lanceolata L. as passive biomonitor

Biomonitors are considered a cheap alternative of active air samplers, especially where spatial pattern of air quality is to be monitored, requiring numerous parallel measurements. Of higher plants, Plantago lanceolata L. has been proven a good monitor species with proper accumulation capacity. While biomonitoring studies are difficult to compare due to inherent errors such as the diverse plant material used in different studies, the No. 227 OECD GUIDELINE FOR THE TESTING OF CHEMICALS: Terrestrial Plant Test: Vegetative Vigour Test provides a tool to test extract of aerosol samples under controlled laboratory conditions. In our study, this guideline was followed to experimentally treat Plantago with the aqueous extract of a diesel exhaust sample. Accumulation pattern of polyaromatic hydrocarbons (PAHs) was assessed and compared to samples collected in the field. Unlike most studies reported in the literature, both in the experimentally treated and field Plantago samples, high ratio of high molecular weight PAHs was experienced. Distribution pattern of accumulated PAHs showed strong correlation between the experimentally treated sample and most of the field plantain samples, underlying the usefulness of laboratory treatments for bioaccumulation studies.

Contribution of the flag leaf to lead absorption in wheat grain at the grain-filling stage

Wheat flag leaf (FL) is one of the primary sources of carbohydrates in grains; however, its role in grain lead (Pb) absorption remains unclear. A field experiment was conducted to assess the relative contribution of the FL to Pb accumulation in wheat grain by two contrasting treatments: without (CK) and with FL removal (FLR) at the grain-filling stage. The Pb concentration in leaves was closely related to leaf strata and decreased from FL to the third leaf. FLR treatment significantly reduced the yield and grain Pb concentration by 2.79% and 11.47%, respectively. The contribution of FL to grain Pb accumulation decreased gradually with the filling process, from 35.08% (at early stage) to 13.94% (at maturity stage). After FLR, the contribution proportion of atmospheric fallout to grain Pb decreased from 69.01% (CK) to 62.43% (FLR). Combined isotope analysis with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) revealed that the main contribution of FLs to grain Pb originated from Pb fallout in fine atmospheric particles. Therefore, taking measures to reduce the influence of fine atmospheric particles on wheat may be an effective way to control wheat grain Pb contamination.

Evaluating and comparing the green wall retrofit suitability across major Australian cities

Urban densification continues to present a unique set of economic and environmental challenges. A growing shortage of green space and infrastructure is intrinsically linked with urban growth and development. With this comes the loss of ecosystem services such as urban heat island effects, reduction of air quality and biodiversity loss. Vertical greenery systems (VGS) offer an adaptive solution to space-constrained areas that are characteristic of dense urban areas, and can potentially improve the sustainability of cities. However, in order to promote VGS uptake, methods are required to enable systematic appraisal of whether existing walls can be retrofitted with VGS. Further, feasibility studies that quantify the potential for retrofit suitability of VGS across entire urban areas are lacking. This study established an evaluation tool for green wall constructability in urban areas and validated the assessment tool by determining the quantity of walls in five major Australian cities that could potentially have VGS incorporated into the existing infrastructure. Each wall was analysed using an exclusionary set of criteria that evaluated and ranked a wall based on its suitability to VGS implementation. Sydney and Brisbane recorded the greatest proportional length of walls suitable for VGS, with 33.74% and 34.12% respectively. Conversely, Perth's urban centre was the least feasible site in which to incorporate VGS, with over 97% of surveyed walls excluded, mainly due to the prevalence of <1 m high fence lines and glazed shopfronts. This study aimed to evaluate feasibility assessments of green wall retrofitability in highly urbanised areas with the intention of creating an analytical method that is accessible to all. This method, coupled with the promising number of feasible walls found in this study, emphasises the need for more government policy and incentives encouraging green wall uptake and could play a pivotal role in the expansion of green infrastructure and urban forestry.

Magnetism and Grain-Size Distribution of Particles Deposited on the Surface of Urban Trees in Lanzhou City, Northwestern China

Studies on the variation in the particulate matter (PM) content, Saturation Isothermal Remanent Magnetization (SIRM), and particle grain-size distribution at a high spatial resolution are helpful in evaluating the important role of urban forests in PM removal. In this study, the trees located in dense urban forests (T0) retained more PM than trees located in open spaces (T1–T4); the SIRM and PM weight of T0 were 1.54–2.53 and 1.04–1.47 times more than those of T1–T4, respectively. In addition, the SIRM and PM weight decreased with increasing distance to the road, suggesting that distance from pollution sources plays a key role in reducing the air concentration of PM. The different grain-size components were determined from frequency curve plots using a laser particle-size analyzer. A unimodal spectrum with a major peak of approximately 20 μm and a minor peak between 0.1 and 1 μm was observed, indicating that a large proportion of fine air PM was retained by the needles of the study trees. Additionally, more <2.5 μm size fraction particles were observed at the sampling site near the traffic source but, compared to a tree in a row of trees, the percentage of the >10 μm size fraction for the tree in the dense urban forest was higher, indicating that the particles deposited on the needle surface originating from traffic sources were finer than those from natural atmospheric dust. The exploration of the variation in the PM weight, SIRM, and grain size of the particles deposited on the needle surface facilitates monitoring the removal of PM by urban forests under different environmental conditions (e.g., in closed dense urban forests and in open roadside spaces), different distances to roads, and different sampling heights above the ground.

'Green barriers' for air pollutant capture: Leaf micromorphology as a mechanism to explain plants capacity to capture particulate matter

Finding ways to mitigate atmospheric particulate matter (PM) is one of the key steps towards fighting air pollution and protecting people's health. The use of green infrastructure is one option that could help improving urban air quality and promoting more sustainable cities. Detailed knowledge of how plants capture particulate matter can support plant selection for this purpose. Previous studies have primarily focused on 2D techniques to assess the micromorphology of plant leaves. Here, 3D optical profilometry and SEM imaging (2D) are used to quantify leaf roughness and other micromorphological leaf traits of three contrasting plant species (Hedera helix 'Woerner', Thuja occidentalis 'Smaragd', and Phyllostachys nigra) located within a mixed-species green barrier. These techniques have allowed us to identify the relative distribution of adhered atmospheric PM with respect to the surface topography of leaves, with high spatial resolution. Leaf surface roughness did not show a direct relationship with PM deposition; however, the descriptors width, depth and frequency of the grooves are important to explain PM capture by the leaves. Additionally, the presence of wax on leaves was relevant for PM adherence. All species captured PM, with their overall PM capture efficiency ranked from highest to lowest as follows: Thuja occidentalis > Hedera helix > Phyllostachys nigra. All green barrier species contributed to air quality improvement, through PM capture, regardless of their location within the barrier. Having multiple species in a green barrier is beneficial due to the diverse range of leaf micromorphologies present, thus offering different mechanisms for particulate matter capture.

Particle Retention Capacity, Efficiency, and Mechanism of Selected Plant Species: Implications for Urban Planting for Improving Urban Air Quality

Atmospheric particulate matter (PM) has been of concern owing to its negative effects on human health and its role in environmental degradation. For mitigation purposes, it is important to select the most efficient plant species in urban greening. Here, a fast, cost-saving methodology was first added to the conventional method to investigate the size-resolved PM retention capacity and efficiency of twenty plant species. Surface PM (SPM), which can be removed by water and brushing, accounted for 44.9–66.9% of total PM, in which the water-soluble PM (DPM) accounted for 12.9–22.1% of total PM. A large mass proportion of in-wax PM (14.1–31.7%) was also observed. Platycladus orientalis, Eriobotrya japonica, Viburnum odoratissimum, Magnolia grandiflora had the highest AE_leaf (retention efficiency on per unit leaf area) to retain SPM within different diameter classes (DPM, PM_0.1–2.5, PM_2.5–10, PM_>10). AE_plant (retention efficiency of individual tree) varied greatly among different plant species, mainly due to the dependence on the total area of a tree. AE_land (retention efficiency on per unit green area) is a suitable index for PM retention ability and efficiency. In general, P. orientalis, V. odoratissimum, Pittosporum tobira, Photinia serrulate, M. grandiflora, E. japonica were the efficient species in retaining PM at different scales (i.e., leaf, individual tree, green area). The species like Trifolium repens, Phyllostachys viridis, were the least efficient plant species. The investigated species are all evergreen species, which will remove PM throughout the whole year, even in winter. So, we recommended that the plant species with the highest PM retention efficiency can be used in urban greening. Meanwhile, horticulture practices should also be considered to improve the leaf area index to improve their PM retention and air purification abilities.

The legacy effects of PM2.5 depositon on Nerium Oleander L

Green plants have the capability to retain atmospheric particulate matter (PM) on their leaves, which can effectively reduce PM pollution, especially in the urban settings. Some studies reported that the periodic PM pollution could change plant retaining PM capacity, which, indeed, was the reason of physiological responses. In advancing the previous studies, we selected Nerium oleander L. to measure PM retention on leaf surface in a controlled environment by the following periods: initial pollution period (S1), recovery period (R), and secondary pollution period (S2) for a total of 12 weeks. The experimental design was one elevated pollution treatment (166 μg m^-3) and one ambient control (28 μg m^-3) with three replications. Results showed that during S2, the total retention decreased by 8.87 μg cm^-2, which was about 10.4% significant lower than in S1. During the third week, the ascorbic acid content (ASA) in S1 was 6.71 mg g^-1 significantly lower than that in S2 in the treatment. The total chlorophyll (Chl T) of the treatment decreased continuously and significantly by 33.8% in S1, but showed no similar trend in S2. The net photosynthetic rate of the treatment was significantly lower than that of the control, and the plants in the treatment showed a consistently high dark respiration rate than that in the control. The correlations between PM retention and ASA, Chl T and RWC were weaker in S1 than that in S2. In addition, air pollution tolerance index (APTI) showed a significant decline in plant pollution tolerance in the treatment during the third week.

Effectiveness of plants and green infrastructure utilization in ambient particulate matter removal

Air pollution is regarded as an increasingly threatening, major environmental risk for human health. Seven million deaths are attributed to air pollution each year, 91% of which is due to particulate matter. Vegetation is a xenobiotic means of removing particulate matter. This review presents the mechanisms of PM capture by plants and factors that influence PM reduction in the atmosphere. Vegetation is ubiquitously approved as a PM removal solution in cities, taking various forms of green infrastructure. This review also refers to the effectiveness of plant exploitation in GI: trees, grasslands, green roofs, living walls, water reservoirs, and urban farming. Finally, methods of increasing the PM removal by plants, such as species selection, biodiversity increase, PAH-degrading phyllospheric endophytes, transgenic plants and microorganisms, are presented.

Screening of Particulate Matter Reduction Ability of 21 Indigenous Korean Evergreen Species for Indoor Use

The formation and pollution of particulate matter (PM), a side effect of rapid industrialization and urbanization, is considered a global issue. However, various plant species are able to effectively capture and reduce atmospheric PM concentrations. We investigated the indoor growth and morphology of 21 indigenous Korean evergreen species at low light intensities to ascertain their ability to reduce PM of aerosol particles in a closed acrylic chamber. The decrease in PM mass concentration differed significantly across species, with a significant correlation (8 h; p < 0.001). The reduction in the mass concentration of PM differed with particle size and across species. The highest reduction of PM_2.5 occurred after 8 h with Dryopteris lacera (86.8%), Ilex × wandoensis (84.9%), Machilus thunbergii (84.3%), and Rhododendron brachycarpum (84.0%). Reduction of PM₁₀ after 8 h was highest with Cephalotaxus harringtonii (98.3%), I. × wandoensis (98.5%), M. thunbergii (98.5%), and R. brachycarpum (98.3%). Plant morphological characteristics (category, plant height, leaf shape, leaf area) and relative humidity were closely related to the decrease in PM mass concentration. In conclusion, our findings can be used to identify Korean plant species that can reduce PM concentration and are suitable for indoor use.

Dynamics of particle retention and physiology in Euonymus japonicus Thunb. var. aurea-marginatus Hort. with severe exhaust exposure under continuous drought

Frequent drought events and particulate matter pollution from vehicular exhaust seriously affect urban plant growth and provisioning of ecological services. Yet, how plants respond physiologically and morphologically to these two combined stressors remains unknown. Here, we assessed particle retention dynamics and plant morphology and physiology of Euonymus japonicus Thunb. var. aurea-marginatus Hort. under continuous drought with severe exhaust exposure. Our results showed that continuous drought insignificantly lowered particle retention in each of three size fractions by 1.02 μg·cm^-2 on average in the first 28 days, but significantly lowered total particle retention by 35.75 μg·cm^-2 on the 35th day. We observed evident changes in morphology, leaf mass per area (LMA), pigments, gas exchange in all stressed plants. Compared with single stress, combined drought and pollution caused earlier yellowing and shedding of old leaves, significantly lowered LMA by 1.21 mg·cm^-2, caused a greater decline in pigments and net photosynthetic rate (P_n). Large particles may mainly explain pigment reduction, lower weekly LMA increases, and stomatal restriction, while coarse particles may be the main drivers of the decline in P_n. Continuous drought mediated the influence of all three particle sizes on some parameters, such as weakening the impact of total particles on LMA, strengthening the impact of fine particles on photosynthesis. Our findings suggest that drought accelerates the physiological responses of plants to exhaust pollution. Under controlled severe exhaust pollution conditions, the optimal time to maintain high particle retention during continuous drought without decline in physiological conditions for E. japonicus var. aurea-marginatus was 14 days. Some additional interventions after 14 days (it could be postponed appropriately under field conditions) may help ensure healthy growth of plants and retention of particulate matter.

Where trees cannot grow - Particulate matter accumulation by urban meadows

It has already been proven that trees and shrubs, can efficiently remove particulate matter (PM) from air. However, almost nothing is known about PM accumulation by herbaceous plants (grasses and forbs) found in urban meadows. Meadows, unlike trees and shrubs, can be located close to roads, one of the main sources of PM in cites. The aim of this study was to investigate the tolerance to urban condition and PM accumulation in the immediate roads vicinity of selected plants species in urban meadows. PM accumulation of annual and perennial meadows was compared with that of lawns. Results were interpreted in the context of species composition, biomass production, soil conditions and ambient PM concentrations. Of the species grown in annual meadows, the highest PM accumulation was found in Achillea millefolium L., Chenopodium album L. and Echium vulgare L., while Centaurea scabiosa L., Echium vulgare L. and Convolvulus arvensis L. accumulated the largest amounts of PM in perennial meadows. PM deposition on plants was positively correlated with a feathery leaf shape. For species in the annual meadows, a positive correlation was also found between PM accumulation and the wax content on plants. The presence of hairs on leaves, leaf size and plant growth pattern had no effect on PM deposition on plants. PM accumulation in one square metre of urban meadow was on average greater than that of lawn, regardless of meadow species' composition, age and location. The greatest accumulation of PM was found in a perennial meadow with low biodiversity but the greatest biomass. It would appear that the biomass produced by meadows and canopy structure has a crucial impact on the amount of PM accumulated by meadow plants. The results obtained indicate that meadows could be an important element of nature-based solutions for mitigating air pollution in urbanised areas.

Assessment of Air Pollution Tolerance and Particulate Matter Accumulation of 11 Woody Plant Species

High concentration of particulate matter (PM) threatens public health and the environment. Increasing traffic in the city is one of the main factors for increased PM in the air. Urban green spaces play an important role in reducing PM. In this study, the leaf surface and in-wax PM (sPM and wPM) accumulation were compared for 11 plant species widely used for landscaping in South Korea. In addition, biochemical characteristics of leaves (ascorbic acid chlorophyll content, leaf pH, and relative water content) were analyzed to determine air pollution tolerance. Plant species suitable for air quality improvement were selected based on their air pollution tolerance index (APTI) and anticipated performance index (API). Results showed a significant difference according to the accumulation of sPM and wPM and the plant species. PM accumulation and APTI showed a positive correlation. Pinus strobus showed the highest PM accumulation and APTI values, while Cercis chinensis showed the lowest. In 11 plants, API was divided into five groups. Pinus densiflora was classified as the best group, while Cornus officinalis and Ligustrum obtusifolium were classified as not recommended.

Smart Cities Landscape and Urban Planning for Sustainability in Brno City

This study aimed to explore the case study of Brno city regarding smart city models. We analyzed Brno considering smart and sustainable city elements, i.e., smart mobility/public transport, smart technology, smart people, smart governance, smart economy, smart living, and smart environment based on transport, energy, and environment referred herein as the smart city and sustainability model. Therefore, we investigated a case study of Brno city in the Czech Republic. We used qualitative techniques such as case study, exploration, observation, and description. We analyzed and comprehended the trends in the various features of smart city and sustainable development of the city of Brno. The findings showed that Brno city is doing its best to maintain smart city models through its governance organs and structures. The city is also working hard to improve some of the aspects that are still lagging. The ongoing developments and the future ones are based on strategic planning for both the short term and long term such as Brno2023, Brno2030, and Brno2050. It was found that Brno has a very well-planned transport system and is integrated with other aspects such as technology, energy, such as the electricity that moves the trolleybuses and trams, and environment. We strongly conclude that even though Brno city still struggles to achieve total sustainability, it is still a model and reflection of a smart and sustainable city. Finally, we noted that Brno city has very good plans and vision the “DNA” of a smart city. However, the implementation still suffers political willingness.

Assessing the uptake and accumulation of heavy metals and particulate matter from ambient air by some tree species in Isfahan Metropolis, Iran

The main scope of this study is to evaluate the uptake and accumulation potential of heavy metals in unwashed and washed leaves and particulate matter (PM) in leaf surfaces plus waxes of different tree species in Isfahan city. The highest mean concentrations of Cd, Cr, and Ni in unwashed and washed leaves were detected in M. nigra, Zn and Cu in P. fraxinifolia, and Pb was related to P. orientalis. The highest and lowest mean total depositions of total particulate matter (sum of PM₁₀, PM_2.5, and PM_0.2) were found in the leaf of M. nigra (190.23 ± 23.5) and S. alba (11.9 ± 4.42 μg/cm²), respectively. The maximum bio-concentration factor (BCF) of Cd, Pb, and Ni was observed in Morus nigra; Cu and Zn in Pterocarya fraxinifolia, with the BCF of Cr found in Acer negundo. Comprehensive bio-concentration index (CBCI) and metal accumulation index (MAI) were applied for comparing different tree species in HMs accumulation from soil and ambient air. The highest CBCI was measured for M. nigra (0.86), so this tree has the potential to remediate metals from the polluted soil. Higher MAI values in washed and unwashed leaves were found in S. alba (6.77 and 6.98) and M. nigra (5.93 and 5.62), demonstrating the high capability of these trees for controlling air born-metal pollution. Based on the AOM factor, M. nigra, P. fraxinifolia, U. umbraculifera, P. fraxinifolia, A. altissima, and M. alba trees had the highest ability to capture Cd, Zn, Cu, Ni, Pb, and Cr from air. So, planting these trees would be beneficial in sensitive and critical zones such as industrial and urban areas with such atmospheric pollutants.

Impact of urban morphology on the spatial and temporal distribution of PM2.5 concentration: A numerical simulation with WRF/CMAQ model in Wuhan, China

The urban morphology can significantly change the urban microclimate, which in turn affects the diffusion of air pollutants. Urban planning is the most important means of shaping urban morphology. Therefore, this study takes Wuhan as an example and uses the method of WRF/CMAQ coupled UCM model to analyze the spatial and temporal distribution characteristics of PM_2.5 in the Wuhan metropolitan area in winter 2015. The six most important urban morphological indicators in urban planning: the floor area ratio and building height, building density and building width, vegetation coverage ratio, and urban fraction, are selected and classified into three groups. Studying their impact on the spatial and temporal distribution of PM_2.5 concentration provides support for urban planners to improve air quality. The results show that the maximum value of PM_2.5 concentration in Wuhan urban area occurs in the morning rush hour, and PM_2.5 is distributed concentrically in the downtown of the city (within the second ring highway) according to the highways around the city. The PM_2.5 concentration in the downtown area with the most extensive urban morphological index is the highest, and it decreases with increasing distance from the downtown. Among the six indicators, building density and urban fraction have the most significant impact on PM_2.5 concentration because they have the greatest impact on the wind speed at 10 m. The height of the planetary boundary layer is the key factors affect the vertical and horizontal diffusion of air pollutants. Except for the vegetation coverage ratio, the increase of other urban morphological indicators will lead to a decrease of PM_2.5 concentration in Wuhan urban area at night. During the daytime, increasing the floor area ratio and building height will cause an increasing of PM_2.5 concentration, but other indicators have the opposite effects.

Roughness measurement of leaf surface based on shape from focus

BACKGROUND

Surface roughness has a significant effect on leaf wettability. Consequently, it influences the efficiency and effectiveness of pesticide application. Therefore, roughness measurement of leaf surface offers support to the relevant research efforts. To characterize surface roughness, the prevailing methods have drawn support from large equipment that often come with high costs and poor portability, which is not suitable for field measurement. Additionally, such equipment may even suffer from inherent drawbacks like the absence of relationship between pixel intensity and corresponding height for scanning electron microscope (SEM).

RESULTS

An imaging system with variable object distance was created to capture images of plant leaves, and a method based on shape from focus (SFF) was proposed. The given space-variantly blurred images were processed with the proposed algorithm to obtain the surface roughness of plant leaves. The algorithm improves the current SFF method through image alignment, focus distortion correction, and the introduction of NaN values that allows it to be applied for precise 3d-reconstruction and small-scale surface roughness measurement.

CONCLUSION

Compared with methods that rely on optical three-dimensional interference microscope, the method proposed in this paper preserves the overall topography of leaf surface, and achieves superior cost performance at the same time. It is clear from experiments on standard gauge blocks that the RMSE of step was approximately 4.44 µm. Furthermore, according to the Friedman/Nemenyi test, the focus measure operator SML was expected to demonstrate the best performance.

Selective retention of particulate matter by nine plant species in central Shanxi Province, China

Plant leaves can accumulate particulate matter (PM) from the air, thus mitigating air pollution. Nine plant species from the central part of Shanxi Province, China, were investigated to characterize differences in their PM retention capacity and the grain sizes of the collected PM. Styphnolobium japonicum, Syringa oblata, and Cerasus serrulata demonstrated strong retention capacity for PM particles of diverse size fractions. Philadelphus incanus, Viburnum opulus, and Yulania biondii had relatively weak retention capacity for overall and fine PM. Generally, species with smaller leaves and roughness surfaces, waxy leaves, or leaves with hair had strong PM retention capacity. Leaves with suitable groove widths better retained fine PM. Foliar dust observed on leaves presented multimodal distribution curves, including bimodal, trimodal, and four-peak distributions, which differed from the trimodal distribution of natural dustfall. The different PM retention capacities of the nine investigated species and the differing grain sizes between foliar dust and atmospheric dustfall indicated that plant leaves could selectively retain PM. The results of this study provide a scientific basis for the use of the plant to mitigate particulate air pollution.

Analysis of Particulate Matter Concentration Intercepted by Trees of a Latin-American Megacity

Urban areas with trees provide several ecosystem services to citizens. There is a growing interest in ecosystem services for the removal of air pollutants such as particulate matter. The objective of this paper is to show a study on the variation of intercepted particulate matter concentration (IPMC) by tree leaves in the megacity of Bogotá (Colombia). The relationship between IPMC and PM2.5 concentrations observed in air quality stations in two urban zones with different air pollutions was studied. Influences of climate and leaf morphology variables on IPMC were also analyzed. The species under study were Ligustrum-lucidum, Eucalyptus-ficifolia, Tecoma-stans, Callistemon-citrinus, Lafoensia-acuminata, and Quercus-humboldtii. The results showed that leaf IPMC decreased as the PM2.5 concentration increased. Species that best described this trend were Ligustrum-lucidum and Lafoensia-acuminata. These two species also showed the largest IPMC in their leaves. Indeed, species that showed the largest leaf area were those with the highest IPMC. On average, it was observed that for each 5.0 µg/m3 increase in PM2.5 concentration the IPMCs of the species Ligustrum-lucidum and Lafoensia-acuminata decreased by 33.6% and 23.1%, respectively. When wind speed increased, there was also an increase in PM2.5 concentrations and a reduction in the leaf IPMCs.

The relationship between particulate matter retention capacity and leaf surface micromorphology of ten tree species in Hangzhou, China

Atmospheric particulate matter (PM) is one of the main environmental air pollutants, but it can be retained and adsorbed by plants. To systematically and comprehensively conduct qualitative and quantitative research on the relationship between the leaf PM retention ability and the microstructure of leaf surfaces, this study evaluated the PM retention abilities of ten common tree species (1860 leaf pieces in total) in the greenbelts around the Lin'an toll station of the Hang-Rui Expressway in Hangzhou, China, in October 2019. The leaf surface roughness and contact angle were measured with confocal laser scanning microscopy and a contact angle measuring instrument. Scanning electron microscopy was applied to collect data on the stomata and groove morphology. The PM retention ability of the leaves was assessed by quantifying the PM mass and number density on the leaves. The results revealed that Platanus acerifolia and Sapindus mukorossi had a strong ability to retain particulates of different sizes. The mass of the retained PM_2.5 on their leaves accounted for the lowest proportion (mean: 8.12%) among the total retained particulate mass, but the number density of the retained PM_2.5 accounted for the highest proportion (mean: 97.49%) among the total number density. A significant negative correlation between the PM_2.5 mass and the groove width on the adaxial surface (R² = 0.746, P < 0.05) and a significant positive correlation between the roughness and the PM number density on the adaxial surface (R² = 0.702, P < 0.01) were observed. No obvious correlations were found among the groove width, roughness and number density of the retained PM on the abaxial surface. Leaf surfaces with dense and narrow grooves, strip-like projections, high roughness and high wettability had strong retention abilities. This study can provide a theoretical reference for selecting plants with strong PM retention ability for green urban garden design.

Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest

Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM_2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM_2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model parametrization and the estimate of particulate matter removed by urban trees.

Using a land use regression model with machine learning to estimate ground level PM2.5

Ambient fine particulate matter (PM_2.5) has been ranked as the sixth leading risk factor globally for death and disability. Modelling methods based on having access to a limited number of monitor stations are required for capturing PM_2.5 spatial and temporal continuous variations with a sufficient resolution. This study utilized a land use regression (LUR) model with machine learning to assess the spatial-temporal variability of PM_2.5. Daily average PM_2.5 data was collected from 73 fixed air quality monitoring stations that belonged to the Taiwan EPA on the main island of Taiwan. Nearly 280,000 observations from 2006 to 2016 were used for the analysis. Several datasets were collected to determine spatial predictor variables, including the EPA environmental resources dataset, a meteorological dataset, a land-use inventory, a landmark dataset, a digital road network map, a digital terrain model, MODIS Normalized Difference Vegetation Index (NDVI) database, and a power plant distribution dataset. First, conventional LUR and Hybrid Kriging-LUR were utilized to identify the important predictor variables. Then, deep neural network, random forest, and XGBoost algorithms were used to fit the prediction model based on the variables selected by the LUR models. Data splitting, 10-fold cross validation, external data verification, and seasonal-based and county-based validation methods were used to verify the robustness of the developed models. The results demonstrated that the proposed conventional LUR and Hybrid Kriging-LUR models captured 58% and 89% of PM_2.5 variations, respectively. When XGBoost algorithm was incorporated, the explanatory power of the models increased to 73% and 94%, respectively. The Hybrid Kriging-LUR with XGBoost algorithm outperformed the other integrated methods. This study demonstrates the value of combining Hybrid Kriging-LUR model and an XGBoost algorithm for estimating the spatial-temporal variability of PM_2.5 exposures.

Foliar dust and heavy metal deposit on leaves of urban trees in Budapest (Hungary)

This work considers dust deposition and the heavy metal (HM) content on leaves of urban trees (Acer platanoides L. 'Globosum,' Fraxinus excelsior L. 'Westhof's Glorie' and Tilia tomentosa Moench.) in order to estimate the trees' capacity to remove dust and HM from the air. Leaves were collected from the Buda Arboretum and from different streets of heavy traffic in Budapest, Hungary, during 2015 and 2016. At each site, five trees were sampled by collecting 6 leaves from each tree from the height of 2-3 m. Dust deposits on the leaves were removed by soaking the fresh foliage in distilled water for 20 h and then washed with ultrasound shaking. Afterward, the leaves were dried to constant weight and then they were digested in nitric acid-hydrogen peroxide treatment, and their Pb, Fe, Ni, Zn and Cu contents were measured using an inductively coupled plasma (ICP AS) spectrometer. The removed dust deposit was dried, and after a similar digestion treatment the Pb, Fe, Ni, Zn and Cu contents were measured using an AURORA AI 1200 AAS appliance. The HM deposit was calculated in mg m^-2 leaf surface area. In 2015, the amount of foliar dust deposit from spring to autumn increased from 86.3 to 270.2 mg m^-2. The most efficient tree species in trapping dust on their leaves was the silver linden (98.5-123.5 mg m^-2), followed by the Norway maple (74.2-84.8 mg m^-2) and the common ash (62.8-74.6 mg m^-2). The deposit of HM elements showed seasonal differences: the quantity of Fe and Pb deposit on autumnal leaves increased five- to tenfold, while other heavy metals did not show accumulation. Silver linden with its pubescent (hairy) leaf surface proved to be most efficient in entrapping and retaining dust and heavy metals. The 60-100% higher Pb and Fe content of autumnal leaves indicate that over the season leaves may absorb Fe and Pb from the foliar dust. Our results confirmed that the foliar dust is a potential indicator for monitoring the HM content in the air. We also show that foliar dust deposits should be considered when estimating the capacity of urban trees to clean the air.