PM2.5 reduction capacities and their relation to morphological and physiological traits in 13 landscaping tree species

Fine particulate matter (PM_2.5) is emerging as a serious environmental problem worldwide with the increase in anthropogenic emission sources, such as fossil fuels, transportation, and industries. In urban areas, where industrial complexes and human activities are concentrated, PM_2.5 poses a threat to human health. Recently, because of their ability to reduce PM_2.5, the introduction of landscaping trees as an environment-friendly solution has become popular; however, there remains a lack of research on the selection of species and their management. In this study, we quantified and compared the PM_2.5 reduction capacities of 13 major landscaping tree species and analyzed their relationship with the morphological and physiological characteristics of each species. The results showed that the amount of PM_2.5 reduction per leaf area differed among species and was the highest in Ginkgo biloba (28 165 ± 5353 # cm⁻² min⁻¹) and the lowest in Pinus strobus (1602 ± 186 # cm⁻² min⁻¹). Moreover, PM_2.5 reduction by the broadleaf species (18 802 ± 1638 # cm⁻² min⁻¹) was approximately 8.6-fold higher than that of the needleleaf species (2194 ± 307 # cm⁻² min⁻¹). Correlation analysis revealed that differences in PM_2.5 reduction were explained by differences in specific leaf area between species (P = 0.004) and by the length of margin per leaf area among individual trees (P < 0.05). Additionally, reduction in PM_2.5 correlated with photosynthetic properties such as maximum assimilation and carboxylation rates (P < 0.001), indicating that PM_2.5 is reduced not only by physical adsorption but also by physiological processes. These findings emphasize that for effective reduction in PM_2.5 using landscaping trees, comprehensive consideration of the morphological and physiological characteristics of the species is essential during species selection, and that continuous management is also necessary to maintain the active physiological conditions of the trees.     

Particle resuspension from leaf surfaces: Effect of species,leaf traits and wind speed

Particles deposited on leaf surfaces can be resuspended back into the atmosphere, thus generating pollution diffusion and hazarding to human health. The net amount of particles resuspended depends on leaf traits and weather conditions, such as speed wind and leaf roughness. However, little is known about the influence of leaf traits of different tree species on particle resuspension under certain conditions. In this study, we chose 6 typical greening tree species from Northeast China and focused on four-leaf traits: roughness, contact angle, stomatal density, and groove width. The wind tunnel was used to measure particle resuspension from leaf surfaces at different wind speeds (1, 2, 3 m/s) and test duration (10, 20, 30 min). Subsequently, we investigated the correlation between particle resuspension and leaf traits. The results indicated that Abies holophylla had the highest resuspension fraction (61.38%), followed by Salix babylonica (58.05%), Populus alba (54.21%), Juniperus chinensis (53.59%), and Pinus tabuliformis (50.51%), while Robinia pseudoacacia displayed the lowest particle resuspension fraction (32.02%). Particle resuspension rates of the tested species ranged from (8.24 ± 0.53) × 10⁻⁴/s to (2.65 ± 0.51) × 10⁻⁴/s, which was found to increase with wind speed enhancement and decrease with duration extension. With increasing the wind speed, the Pinus tabuliformis, and Juniperus chinensis were more efficient than Salix babylonica, and Populus alba in avoiding particle resuspension. Roughness and stomatal density were a significant negative correlation with particle resuspension rates, which demonstrates that the leaf surface traits can affect the particle resuspension process. Finally, our results suggest that the main factors influencing particle resuspension from leaf surfaces are wind speed, roughness, and stomatal density, which will provide a scientific foundation for pollution diffusion in future studies.     

Research on the horizontal reduction effect of urban roadside green belt on atmospheric particulate matter in a semi-arid area

In this study, the horizontal abatement effects of green belts on atmospheric particulate matter at different horizontal distances and plant community structures were investigated in urban roadside green belts in semi-arid areas.We collected mass concentrations of six types of atmospheric particulate matter (PM) per unit time of PM_0.3, PM_0.5, PM_1.0, PM_2.5, PM_5.0, and PM₁₀ and various meteorological indices, to compare the horizontal reduction efficiency of different distances and plant community structures on different particle sizes, and to establish a support vector machine model. The results showed that 1) the horizontal abatement efficiency of green belts was different for six particle sizes, while the horizontal abatement rate strengthened as the particle size increased. The abatement rate was significantly correlated with microclimatic factors such as temperature and humidity, but less correlated with wind speed. 2) The horizontal abatement rate of roadside green belts on atmospheric particulate matter varies with the increase of horizontal distance in a "single-peak" or "double-peak" pattern, with the best abatement effect of green belts on each particle size at a horizontal distance of 45m. Among the four types of plant community structures, the strongest abatement ability was in the arbor-shrub-herb structure. 3) The correctly tuned prediction model, based on Support Vector Machines, resulted in better horizontal abatement ability of green belts on atmospheric PM. The prediction results showed that the average horizontal abatement rate has the best abatement effect at 45–55 m, peaked at 50 m, and formed stagnant dust at 65 m. In the design of urban road green spaces in semi-arid areas, to achieve the best dust retention effect, the green belt width should be ≥40 m and it is desirable to choose arbor-shrub-herb structures. This study provides a design basis and theoretical support for urban road green space planning in semi-arid areas.     

Animal behavioral adaptation to changing landscapes: spring-staging geese habituate to wind farms

Wind farms are positioned in open landscapes and may cause loss of wildlife habitat due to disturbance, fragmentation, and infrastructure development. Especially flocking geese, swans, ducks and waders are regarded as vulnerable to wind farm development. We compared past and current displacement effects of two onshore wind farms and a line of land-based turbines on spring-staging pink-footed geese (Anser brachyrhynchus) to see if there was evidence of habituation. In one wind farm area, geese previously (1998) (Larsen and Madsen 2000) kept a distance of c. 200 m (the distance at which 50% of peak densities is reached) and they did not go between the turbines; today (2008) they keep a distance of c. 100 m, but do still not enter the wind farm area. In another wind farm, where foraging geese previously (2000) kept a distance of more than 100 m and did not enter the wind farm, they now (2008) forage between the wind turbines and keep a distance of c. 40 m to turbines. In 1998, geese kept a distance of 125 m to a line of turbines, compared to 50 m now. We conclude that geese have behaviorally adapted to changing landscapes created by wind farms. The difference in avoidance between the sites may be due to the sizes of the turbines which in this study were small in both rotor-swept area and in height compared to more recent “industry standard” of 2.5 and 3.0 MW turbines. The study points to the need for longer term studies to properly assess the impact of wind farms on wildlife, including consequent increased risks from inclement weather events of feeding, rafting, and migrating waterfowl.     

Evaluating the impact of individual leaf traits on atmospheric particulate matter accumulation using natural and synthetic leaves

The ability of vegetation to capture and retain atmospheric Particulate Matter (PM) is directly dependent on the interactions between PM and plant surfaces. However, the impact of individual leaf traits in this respect is still under debate due to variations in published findings. This study employed standardised experimental designs with natural and synthetic leaves in three experiments to explore the impact of individual leaf traits on traffic-generated PM accumulation whilst other influential variables were controlled. The impact of leaf size on PM deposition was explored using synthetic leaves of different sizes (small, medium and large) but with the same shape and surface characteristics (n = 20 for each category). The impact of leaf shape was examined using another set of synthetic leaves of different shape (elliptical, palmately-lobed and linear) but with the same surface area and the same surface characteristics (n = 20 for each category). PM accumulation (PM₁, PM_2.5 and PM₁₀) on these leaves was quantified using an Environmental Scanning Electron Microscope (ESEM) and ImageJ software. Any differences in PM capture levels due to leaf size and leaf shape were identified using one-way Anova and Tukey’s pairwise comparison. In a subsequent experiment, equal-sized, square-shaped leaf sections obtained from four plant species (n = 20 for each species) with different micromorphology were exposed to traffic-generated pollution and any PM capture differences due to leaf micromorphology identified employing the same SEM/ImageJ and statistical approach. The results of all three experiments showed significant differences in PM accumulation between different leaf sizes (p < 0.001), between different leaf shapes (p < 0.001) and between different leaf micromorphology (p < 0.001) suggesting that all these characters are influential in the capture and retention of PM on leaves. Smaller leaves and complex leaf shapes (lobed leaves) showed a greater potential to capture and retain PM. Leaf surfaces with hair/trichomes, epicuticular wax, and surface-ridges accumulated more PM compared to smooth surfaces; of these characters, leaf hairiness/presence of trichomes was found to be the most important. Species sharing most of these important leaf traits are recommended as effective PM filters.     

Effects of plant leaf surface and different pollution levels on PM2.5 adsorption capacity

We selected 6 species of landscape plants growing under different pollution levels and performed quantitative determination of PM_2.5 adsorption. We compared the measured adsorption to the leaf morphology and the water-soluble ion content. The results indicated that the pollution level and plant leaf surface PM_2.5 adsorption capacity were positively correlated. There was variation in the leaf area PM_2.5 adsorption capacity for plants in different locations, allowing us to determine species-specific effects and effects of different pollution levels. The results of the study have important significance to design strategies to reduce urban air particulate matter pollution and improve air quality.     

Particulate matter pollution capture by leaves of seventeen living wall species with special reference to rail-traffic at a metropolitan station

Atmospheric Particulate Matter (PM) constitutes a considerable fraction of urban air pollution, and urban greening is a potential method of mitigating this pollution. The value of living wall systems has received scant attention in this respect. This study examined the inter-species variation of particulate capture by leaves of seventeen plant species present in a living wall at New Street railway station, Birmingham, UK. The densities of different size fractions of particulate pollutants (PM₁, PM_2.5 and PM₁₀) on 20 leaves per species were quantified using an Environmental Scanning Electron Microscope (ESEM) and ImageJ image-analysis software. The overall ability of plant leaves to remove PM from air was quantified using PM density and LAI (Leaf Area Index); any inter-species variations were identified using one-way Anova followed by Tukey’s pairwise comparison. This study demonstrates a considerable potential for living wall plants to remove particulate pollutants from the atmosphere. PM capture levels on leaves of different plant species were significantly different for all particle size fractions (P < 0.001). Smaller-leaved Buxus sempervirens L., Hebe albicans Cockayne, Thymus vulgaris L. and Hebe x youngii Metcalf showed significantly higher capture levels for all PM size fractions. PM densities on adaxial surfaces of the leaves were significantly higher compared to abaxial surfaces in the majority of the species studied (t-test, P < 0.05). According to EDX (Energy Dispersive X-ray) analysis, a wide spectrum of elements were captured by the leaves of the living wall plants, which were mainly typical railway exhaust particles and soil dust. Smaller leaves, and hairy and waxy leaf surfaces, appear to be leaf traits facilitating removal of PM from the air, and hence a collection of species which share these characters would probably optimize the benefit of living wall systems as atmospheric PM filters.     

Effects of different vertical façade greenery systems on pedestrian thermal comfort in deep street canyons

Vertical greenery systems (VGSs) have been adopted in city planning operations to mitigate excess heat in hot and humid subtropical cities. This study focused on the influence of different arrangements of vertical greening on pedestrian thermal comfort and particulate matter with a diameter of 10 µm (PM₁₀) in street canyons. In this paper, the ENVI-met computational fluid dynamics (CFD) method was used to investigate the effects of different façade greenery arrangements with the same amount of greenery in the Nan Hai Yi Ku (NHYK) industrial district. On-site measurements were used to validate the simulation results in a transition season. The results showed that greening façades could improve pedestrians' thermal comfort with physiological equivalent temperature (PET) value reductions varying from 0.17 °C to 1.4 °C. Under a certain amount of greenery, the critical factor determining pedestrians' thermal comfort was the coverage rate of the greening façade near the pedestrian level. Specifically, increasing the greening façade coverage near the lower parts of street canyons could enhance the pedestrian-level cooling effect. In addition, the VGSs positively affected the pedestrian-level air quality in the street canyons. Nevertheless, the changes in pedestrian-level PM₁₀ concentration induced by the presence of VGSs were not very obvious under the building-parallel wind direction.     

Influence of tree crown characteristics on the local PM10 distribution inside an urban street canyon in Antwerp (Belgium): A model and experimental approach

Apart from influencing the amount of leaf-deposited particles, tree crown morphology will influence the local distribution of atmospheric particles. Nevertheless, tree crowns are often represented very rudimentary in three-dimensional air quality models. Therefore, the influence of tree crown representation on the local ambient PM₁₀ concentration and resulting leaf-deposited PM₁₀ mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met^® and ground-based LiDAR imaging. The modelled leaf-deposited PM₁₀ mass was compared to gravimetric results within three different particle size fractions (0.2–3, 3–10 and >10 μm), obtained at 20 locations within the tree crown. Modelling of the LiDAR-derived tree crown resulted in altered atmospheric PM₁₀ concentrations in the vicinity of the tree crown. Although this model study was limited to a single tree and model configuration, our results demonstrate that improving tree crown characteristics (shape, dimensions and LAD) affects the resulting local PM₁₀ distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution.     

Particulate phase polycyclic aromatic hydrocarbons in the ambient atmosphere of a protected and ecologically sensitive area in a tropical megacity

This study reports, for the first time, the profiles and source analysis of 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) associated with PM₁₀ (particulate matter with aerodynamic diameter ≤10 μm) at a protected and ecologically sensitive area – the Yamuna Biodiversity Park – located in the megacity Delhi, India. Weekly PM₁₀ sampling was carried out at this location for 1 year (2009–2010) and the annual mean PM₁₀ level was found to be ～9 times the World Health Organization limit. Seasonal variation of PAHs (range 37.2–74.0 ng m^?3) was significant with winter values being 72% and 68% higher than summer and monsoon respectively. Principal component analysis coupled with multiple linear regression identified diesel, natural gas and lubricating oil combustion (49.5%), wood combustion (25.4%), gasoline (15.5%) and coal combustion (9.6%) sources for the observed PAHs. Heavy traffic on the national highway and arterial roads and domestic emissions from suburban households in the vicinity of the park appeared to have significantly affected its air quality. A substantial portion (～55%) of the aerosol PAH load was comprised of carcinogenic species, which yielded a considerably high lifetime inhalation cancer risk estimate (8.7E?04). If considered as a conservative lower-bound estimate, this risk translates into ～211 excess cancer cases for lifetime inhalation exposure to the observed PAH concentrations in Delhi.     

Multiparametric model of urban park cooling island

This paper presents a study of mitigation of the heat island effect in the built environment with urban (city) parks. The park cooling island (PCI) effect, considering park grass cover and trees’ density and age, is determined for selected extreme summer days at various wind speeds under the optimum soil water conditions in the root zone based on an all-day quasi-stationary thermal response. PCI was determined numerically by coupling a CFD model of an urban park and quasi-steady state, two-zone thermal response boundary condition models of each park element. The boundary models are evaluated in form of multi-parameter approximation polynomials taking into account the sensible and latent heat transfer and the geometrical, optical and thermal properties of park elements. Three-dimensional CFD modelling was used for the determination of temperature, humidity and air velocity fields in an urban park with a size of 140 m × 140 m. Based on the comparison of the measured and numerically determined air temperatures in the tree crowns, we proved that the method of linking the models is adequate for temperature and flow condition modelling in the city park environment.The results are presented in the form of local PCI as the difference between local air temperature in the pedestrian zone and the reference air temperature preceding the park. The study proved that it is possible to normalise the cooling effect using the specific dimensionless coefficient of leaf area (LAI_sp), which includes an approximation of the density of trees planted in the park and their size or age. It was found out that the cooling effect of the park is up to ?4.8 °C at LAI_sp, equal to 3.16, which corresponds to a planting density of 45 trees per hectare, with an age of 50 years. It was also found that with the length of the park cooling effect change decreases. The optimal length of the park with a LAI_sp 3 is 130 m.     

Unmanned aerial systems for modelling air pollution removal by urban greenery

Urban greenery plays an important role in reducing air pollution, being one of the often-used, nature-based measures in sustainable and climate-resilient urban development. However, when modelling its effect on air pollution removal by dry deposition, coarse and time-limited data on vegetation properties are often included, disregarding the high spatial and temporal heterogeneity in urban forest canopies. Here, we present a detailed, physics-based approach for modelling particulate matter (PM₁₀) and tropospheric ozone (O₃) removal by urban greenery on a small scale that eliminates these constraints. Our procedure combines a dense network of low-cost optical and electrochemical air pollution sensors, and a remote sensing method for greenery structure monitoring derived from Unmanned aerial systems (UAS) imagery processed by the Structure from Motion (SfM) algorithm. This approach enabled the quantification of species- and individual-specific air pollution removal rates by woody plants throughout the growing season, exploring the high spatial and temporal variability of modelled removal rates within an urban forest. The total PM₁₀ and O₃ removal rates ranged from 7.6 g m^-2 (PM₁₀) and 12.6 g m^-2 (O₃) for mature trees of Acer pseudoplatanus to 0.1 g m^-2 and 0.1 g m^-2 for newly planted tree saplings of Salix daphnoides. The present study demonstrates that UAS-SfM can detect differences in structures among and within canopies and by involving these characteristics, they can shift the modelling of air pollution removal towards a level of individual woody plants and beyond, enabling more realistic and accurate quantification of air pollution removal. Moreover, this approach can be similarly applied when modelling other ecosystem services provided by urban greenery.     

Spatial attenuation of ambient particulate matter air pollution within an urbanised native forest patch

Of interest to researchers and urban planners is the effect of urban forests on concentrations of ambient air pollution. Although estimates of the attenuation effect of urban vegetation on levels of air pollution have been put forward, there have been few monitored data on small-scale changes within forests, especially in urban forest patches. This study explores the spatial attenuation of particulate matter air pollution less than 10 μ in diameter (PM₁₀) within the confines of an evergreen broadleaved urban forest patch in Christchurch, New Zealand, a city with high levels of PM₁₀ winter air pollution. The monitoring network consisted of eight monitoring sites at various distances from the edge of the canopy and was operated on 13 winter nights when conditions were conducive for high pollution events. A negative gradient of particulate concentration was found, moving from higher mean PM10 concentrations outside the forest (mean=31.5 μg m^?3) to lower concentrations deep within the forest (mean=22.4 μg m^?3). A mixed-effects model applied to monitor meteorological, spatial and pollution data indicated temperature and an interaction between wind speed and temperature were also significant (P?0.05) predictors of particulate concentration. These results provide evidence of the potential role that urban forest patches may play in mitigating particulate matter air pollution and should be considered in plans for improving urban air quality.     

A spatially-explicit method to assess the dry deposition of air pollution by urban forests in the city of Florence,Italy

Urban forests (UF) provide a range of important ecosystem services (ES) for human well-being. Relevant ES delivered by UF include urban temperature regulation, runoff mitigation, noise reduction, recreation, and air purification. In this study the potential of air pollution removal by UF in the city of Florence (Italy) was investigated. Two main air pollutants were considered – particulate matter (PM₁₀) and tropospheric ozone (O₃) – with the aim of providing a methodological framework for mapping air pollutant removal by UF and assessing the percent removal of air pollutant.The distribution of UF was mapped by high spatial resolution remote sensing data and classified into seven forest categories. The Leaf Area Index (LAI) was estimated spatially using a regression model between in-field LAI survey and Airborne Laser Scanning data and it was found to be in good linear agreement with estimates from ground-based measurements (R² = 0.88 and RMSE% = 11%). We applied pollution deposition equations by using pollution concentrations measured at urban monitoring stations and then estimated the pollutant removal potential of the UF: annual O₃ and PM₁₀ removal accounted for 77.9 t and 171.3 t, respectively. O₃ and PM₁₀ removal rates by evergreen broadleaves (16.1 and 27.3 g/m²), conifers (10.9 and 28.5 g/m²), and mixed evergreen species (15.8 and 31.7 g/m²) were higher than by deciduous broadleaf stands (4.1 and 10 g/m²). However, deciduous forests exhibited the largest total removal due to the high percentage of tree cover within the city. The present study confirms that UF play an important role in air purification in Mediterranean cities as they can remove monthly up to 5% of O₃ and 13% of PM₁₀.     

Air pollution removal through deposition on urban vegetation: The importance of vegetation characteristics

Urban vegetation has the potential to improve air quality as it promotes pollutant deposition and retention. Urban air quality models often include the effect vegetation have on pollution dispersion, however, processes involved in pollution removal by vegetation are often excluded or simplified and does not consider different vegetation characteristics. In this systematic review, we analyze the influence of the large interspecies variation in vegetation characteristics to identify the key factors affecting the removal of the major urban pollutants, particulate matter (PM) and nitrogen dioxide (NO₂) from the air through vegetation deposition. The aim is to identify key processes needed to represent vegetation characteristics in urban air quality modelling assessments.We show that PM is mainly deposited to the leaf surface, and thus representation of characteristics affecting the aerodynamics from canopy down to leaf surface are important, such as branch/shoot complexity and leaf size, leaf surface roughness and hairiness. In addition, characteristics affecting PM retention capacity, resuspension and wash-off, include leaf surface roughness, hairiness and wax content. NO₂ is mainly deposited through stomatal uptake, and thus stomatal conductance and its responses to environmental conditions are key factors. These include response to solar radiation, vapour pressure deficit and soil moisture.Representation of these vegetation characteristics in urban air quality models could greatly improve our ability to optimize the type and species of urban vegetation from an air quality perspective.     

Seasonal changes in CO2 assimilation in leaves of five major Greek olive cultivars

Leaf CO₂ assimilation rate, stomatal conductance (g_s), internal CO₂ concentration (C_i), chlorophyll (a + b) content, specific leaf weight (SLW) and stomatal density were measured during the season, under field conditions, for five major Greek olive cultivars, ‘Koroneiki’, ‘Megaritiki’, ‘Konservolia’, ‘Lianolia Kerkiras’, and ‘Kalamon’, with different morphological and agronomic characteristics and diverse genetic background. Measurements were taken from current-season and 1-year-old leaves, and from fruiting and vegetative shoots, throughout the season, from March to November in years 2001 and 2002. CO₂ assimilation rates showed a substantial seasonal variation, similar in all cultivars, with higher values during spring and autumn and lower values during summer and late autumn. Stomatal conductance (g_s) followed similar trends to leaf CO₂ assimilation rates, increasing from March to July, following by a decrease during August and increasing again in autumn. ‘Koroneiki’ had the highest leaf CO₂ assimilation rate and g_s values (21 μmol m⁻² s⁻¹ and 0.45 mol m⁻² s⁻¹, respectively) while ‘Lianolia Kerkiras’ and ‘Kalamon’ showed the lowest leaf CO₂ assimilation rate and g_s values (13–14 μmol m⁻² s⁻¹ and 0.22 mol m⁻² s⁻¹, respectively). One-year-old leaves had significantly higher leaf CO₂ assimilation rate than current-season leaves from April to June, for all cultivars. From August and then, leaf CO₂ assimilation rate in current-season leaves was higher than in 1-year-old leaves. There were no significant differences in leaf CO₂ assimilation rate between fruiting and vegetative shoots. Total chlorophyll (a + b) content increased with leaf age in current-season leaves. In 1-year-old leaves chlorophyll content increased in spring, then started to decrease and increased slightly again late in the season. Chlorophyll content was higher in 1-year-old leaves than in current-season leaves throughout the season. Total specific leaf weight (SLW) increased throughout the season for all cultivars. Stomatal density in lower leaf surface was lowest for ‘Koroneiki’ (399 mm⁻²) and highest for ‘Megaritiki’ (550 mm⁻²). Our results showed differences in leaf CO₂ assimilation rate among the five different olive cultivars, with a diverse genetic background, ranging from 12 to 21 μmol m⁻² s⁻¹. From the five cultivars examined, ‘Koroneiki’, a drought resistant cultivar, performed better and was able to maintain higher leaf CO₂ assimilation rate, even under high air vapor pressure deficit. All cultivars had a pronounced seasonal variation in leaf CO₂ assimilation rate, affected by date of the year, depending on ambient conditions. The high temperatures and high air vapor pressure deficit occurring during summer caused a reduction in leaf CO₂ assimilation rate in all cultivars. Leaf CO₂ assimilation rate was also affected by leaf age for all cultivars, with old leaves having significantly higher leaf CO₂ assimilation rate than young leaves early in the season.     

The effect of eye-level street greenness exposure on walking satisfaction: The mediating role of noise and PM2.5

While there are plenty of studies on the effects of neighborhood and park greenness on personal overall satisfaction and walking behavior, the relationship between street greenness exposure and walking satisfaction has received limited attention. Also, the possible pathways by which street greenness exposure affects walking satisfaction need to be further examined. To fill these research gaps, we measured eye-level street greenness using street view images, machine learning techniques and global position systems. A structural equation model was used to examine the mediating effects of objective noise and PM_2.5 exposure and related subjective annoyance, on the relationship between street greenness exposure and people’s walking satisfaction. The results showed that street greenness exposure not only had a significant direct effect on walking satisfaction, but also has a significant indirect effect on walking satisfaction through subjective environmental annoyances (including noise and PM_2.5 annoyances) rather than through objective noise and PM_2.5 exposures. Besides physical activity and social interaction, the indirect effect of street greenness exposure on walking satisfaction through subjective environmental pollution annoyance accounted for about 17.39% of the total effect and cannot be ignored. These results suggest that the urban greenness layout policy should not only consider residential greenness but should improve people’s environmental perception and walking satisfaction by allocating more greenness on streets with high noise and PM_2.5 levels.     

Direct somatic embryogenesis and plant regeneration from leaf cultures of ornamental species of Dianthus

Protocol for direct somatic embryogenesis from leaf explants of economically important species of Dianthus, viz. D. caryophyllus, D. barbatus and D. chinensis has been developed. Murashige and Skoog’s (MS) liquid medium supplemented with 2,4-D (1 mg/l) was used for direct induction of somatic embryogenesis without an intervening callus phase. Initially globular structures were observed after 21 days of culture of leaf explants in liquid medium. Development of embryos to heart and torpedo stages was achieved in the liquid medium incorporated with polyethylene glycol (PEG 6000) at a concentration of 2.5%. Embryo maturation was further promoted by addition of casein hydrolysate (CH) (200 mg/l) in MS liquid medium. Embryos germinated to form plantlets on solid MS medium supplemented with GA₃ (1 mg/l). Regenerated plants with well-developed root and shoot systems were successfully transferred to field conditions.     

Dependence of urban park visits on thermal environment and air quality

Activities in urban parks contribute to greater socialization and a more active lifestyle, yet such health benefits could be mingled with health concerns – e.g., extreme thermal events or hazardous air quality, which received much less attention than the benefits. Particularly, there is a lack of empirical studies on behavioral changes under different thermal and air-quality conditions. To address the research gap, this study quantitatively measured the impact of thermal environmental parameters (air temperature, humidity, wind scale) and air quality parameters (PM_2.5, PM₁₀, NO₂, SO₂, O₃, integrated air quality index (AQI)) on the daily attendance at Haidian Park – a neighborhood park – and Chaoyang Park – an urban recreational park – in Beijing covering consecutive days from April 1, 2020 to March 31, 2021. The analysis revealed the degrees to which urban park visits were influenced by temperature and air quality. Temperature had the greatest impact on the attendance, while the impact was asymmetric: The effect of low temperature showed more elasticity than that of high temperature. The influence of air quality was not as significant as that of the air temperature. The analysis also showed that such impacts of thermal and air-quality conditions on park visits were mediated by type of activities (the everyday-recreational continuum), days (weekday/weekend), and seasons. The findings provide useful implications for tackling the wicked problem of promoting outdoor activities in parks while controlling adverse effects of thermal and air-quality conditions.