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

Effect of Racomitrium canescens on particulate matter reduction under flow and humidity condition

This study investigated the effectiveness of Racomitrium canescens in the removal of particulate matter (PM) under controlled flow and humidity conditions. PM pollution is a major environmental and public health concern and exposure to PM is linked to various adverse health effects. Conventional PM removal methods, such as filtration and electrostatic precipitation present challenges, including frequent filter replacement and ozone generation. To address these limitations, eco-friendly alternatives, such as plant-based air purification systems, have garnered increasing attention. In particular, mosses have shown promise in reducing PM concentrations through surface adsorption. In the present study, we evaluated the PM removal efficiency of R. canescens under controlled laboratory conditions. The results demonstrated that R. canescens reduced PM concentrations and its removal efficiency was enhanced under elevated humidity conditions. The ability of moss to capture PM probably is attributed to its unique surface morphology and moisture-retention properties. Rehydration increases the surface area, thereby enhancing the adsorption capacity. These findings suggest that R. canescens has the potential to be a sustainable and effective agent for mitigating air pollution.

Autumn and winter air phytofiltration - Are plants able to biofilter air during peak pollutant emissions?

Air pollution is highest in winter. The high concentration of particulate matter (PM) and trace elements (TE) after the growing season is influenced by increased pollutant emissions, unfavorable meteorological conditions, and the low efficiency of air phytofiltration. Plants that can remove pollutants from the air during the growing season are leafless in autumn/winter, and therefore unable to capture PM/TE effectively. This study investigated the ability of nine species of leafy evergreen plants to accumulate PM (surface and in-wax PM; PM2.5 and PM10) and TE in autumn and winter. Plant material was harvested in November and December from the park in Wuhan, China. The amount of accumulated pollutants depended on the species. The shrubs (Loropetalum chinense, Pittosporum tobira, Rhododendron simsii) and grass (Ophiopogon japonicus), were more effective at phytofiltration of PM and TE per leaf area unit than the trees. However, to better understand the potential of plants to accumulate PM in relation to a unit of land area, the leaf area index (LAI) has to be considered. Ligustrum lucidum and P. tobira characterized by low LAI, despite having PM deposition comparable to other trees and shrubs, exhibited a markedly reduced efficacy of pollutants accumulation in relation to square metre of land they occupy. In contrast to the TE concentration in winter, PM deposition on plants did not always increase after the autumn, probably due to the park's low density of vegetation, PM resuspension by wind, and a decrease in the plants' physiological activity. Seasonal variations in pollutants accumulation among species were recorded during the autumn/winter. This study reinforces the need for biodiversity and higher-density urban greening to optimize post-growth air phytofiltration. A holistic, year-round air pollution mitigation strategy should be provided by incorporating more diverse evergreen plant species with complementary phytofiltering properties.

A detailed simulation study on radionuclide dispersion under spent fuel road transportation conditions: Effects of vessel type and coniferous vegetation growth

Vegetation barriers are an important environmental characteristic of spent fuel road transportation accidents. Spent fuel vessels may be affected by force majeure factors during transportation, which leads to damage to spent fuel assemblies and containers and can cause radionuclides to gradually release from assemblies to vessels to the external environment. In this work, considering the growth periods of coniferous vegetation barriers and vessel type, a radionuclide dispersion model based on computational fluid dynamics (CFD) was established by adding a decay term and a pressure loss term. The simulations showed that, first, compared to the small (Type-II) vessel, the effects of fluid flow around the large vessel (Type-I) have a more significant impact on radionuclide dispersion. The backflow around the Type-I vessel causes leaked radionuclides to disperse towards the vessel, and the larger the vessel is, the more significant the rise of the leaked radionuclide plume tail will be due to the increased negative pressure gradient area. Moreover, the area contaminated exceeding the maximum allowable concentration by radioactivity for the Type-I vessel is reduced gradually with the growth of coniferous vegetation barriers due to the weakening of the backflow effect by growing vegetation. Second, compared to vegetation barriers of 15 years and 23 years, the horizontal distance exceeding the maximum allowable concentration of the leaked 131I dispersion from Type II vessels near vegetation barriers for 12 years is the longest. The older the vegetation barrier is, the shorter the horizontal dispersion range, and the shape of radionuclide dispersion gradually transforms from flat to semicircular with vegetation barrier growth, but this could cause a greater radioactive accumulation effect near the leakage point, and the maximum concentration of leaked 131I reached 0.54 kBq·m-3 for leaked radionuclides from the Type II vessel under vegetation barriers of 23 years. In addition, improvement suggestions based on the proposed method are presented, which will enable the Standards Institutes to apply the research methodologies described herein across various scenarios. ENVIRONMENTAL IMPLICATION: Compared to nonradioative pollutants, radioactive pollutants are intercepted by vegetation barriers and then migrate to the soil through leaves, stems, and roots, which can contaminate the surrounding environment. Considering the effects of vessel type and coniferous vegetation growth, a radionuclide dispersion model based on CFD was established. Suggestions for decontaminating radioactive pollution areas have been proposed based on the simulation results of hypothetical scenarios. The scenario applicability improvements based on the proposed model could assist relevant Standards Institutes to making improving measures.

Evaluation of atmospheric particulate matter pollution characteristics in Shanghai based on biomagnetic monitoring technology

Atmospheric particulate matter (PM) pollution is one of the world's most serious environmental challenges, and it poses a significant threat to environmental quality and human health. Biomagnetic monitoring of PM has great potential to improve spatial resolution and provide alternative indicators for large area measurements, with respect and complementary to standard air quality monitoring stations. In this study, 160 samples of evergreen plant leaves were collected from park green spaces within five different functional areas of Shanghai. Magnetic properties were investigated to understand the extent and nature of particulate pollution and the possible sources, and to assess the suitability of various plant leaves for urban particulate pollution monitoring. The results showed that magnetic particles of the plant leaf-adherent PM were predominantly composed of pseudo-single domain (PSD) and multi-domain (MD) ferrimagnetic particles. Magnolia grandiflora, as a large evergreen arbor with robust PM retention capabilities, proved to be a more suitable candidate for monitoring urban particulate pollution compared to Osmanthus fragrans, a small evergreen arbor, and Aucuba japonica Thunb. var. variegata and Photinia serratifolia, evergreen shrubs. Meanwhile, there were significant differences in the spatial distribution of the magnetic particle content and heavy metal enrichment of the samples, mainly showing regional variations of industrial area > traffic area > commercial area > residential area > clean area. Additionally, the combination with the results of scanning electron microscopy, shows that industrial production (metal smelting, coal burning), transport and other activities are the main sources of particulate pollution. Plant leaves can be used as an effective tool for urban particulate pollution monitoring and assessment of atmospheric particulate pollution characteristics, and the technique provided useful information on particle size, mineralogy and possible sources.

Particulate matter hinders the development and reproduction of predatory mites of Euseius finlandicus (Acariformes: Phytoseiidae)

The foliage of the small-leaved lime (Tilia cordata) is characterised by the nerve axils being grown by non-glandular trichomes, which trait contributes to the enhanced retention of the particulate matter (PM). This fact may disturb the ecological service of T. cordata related to the structure of its leaves, which is to provide acarodomatia (micro-shelters) for the predatory mites of the Phytoseiidae family. Phytoseiids are natural enemies of a variety of plant pests, widely applied in integrated pest management (IPM). Their occurrence is largely related to acarodomatia in which these mites hide, feed, reproduce, and develop. For the first time, the influence of PM deposition within spaces typically occupied by phytoseiids is investigated. Experimental populations of Euseius finlandicus were reared on T. cordata leaves in the progressive PM-pollution. The results showed that the values of life table parameters of the predator depended significantly on the level of PM deposition on leaves. Contrary to clean leaves from the control, the medium and high contamination intensities significantly reduced the daily (by 47% and 70%, respectively) and the total fecundity (by 62% and 77%, respectively) of females which, in turn, resulted in a decreased net reproductive rate (by 67% and 81%, respectively), intrinsic rate of increase (by 40% and 55%, respectively) and finite rate of increase (by 8% and 10%, respectively) of E. finlandicus. The pre-ovipositional period was prolonged, while the oviposition duration was shortened and the mites matured longer. In high pollution level the mortality of phytoseiids was boosted by 19% and some females were observed with pollutant lumps adhered to the idiosoma. Also, significant shares of juvenile forms (13%) and adult females (25%) made attempts to escape from highly contaminated experimental arenas. The implications of PM retention on the shelter vegetation are discussed in the context of IPM and ecological services.

Analysis of urban residential greening in tropical climates using quantitative methods

Urban green spaces play a crucial role in mitigating urban heat islands, providing shade, cooling, absorbing carbon dioxide, and releasing oxygen to enhance air quality. Understanding the user perceptions of residential greeneries is essential for effective planning and implementation of greening systems. This quantitative research explored user perceptions and preferences regarding residential greeneries through a structured questionnaire survey from 578 respondents. The responses from the densely populated Chennai city and the rest of Tamil Nadu, India, were analyzed. About 90% of residents are interested in having a garden, irrespective of location and residential characteristics. The most available space in Chennai's urban region is a balcony at 45%, followed by front and back gardens at 30% and vice versa for Chennai's suburban areas. The most preferred type is potted plants (30%) and climbers (20%) on balconies and near windows in Chennai. The most perceived challenges are installation and maintenance costs. The most influencing factors over the preference for greeneries and green walls are the house typology, house ownership, and site location. This study provides more insights to building designers and architects on planning and implementation of residential greeneries as per end users' preferences and perceptions.

Dynamic fluctuations in plant leaf interception of airborne microplastics

Plant leaves have been demonstrated to be a crucial sink of airborne microplastics (MPs). However, because of the particular shape of MPs and their relatively weak forces with leaves, the traditional accumulation model used for the adsorption of particulate matter and persistent organic pollutants may not be appropriate for describing the interception of MPs by leaves. Here, we performed a 7-day exploration of the interception of MPs by leaves in downtown Nanning. The abundances and characteristics of leaf-intercepted MPs showed dramatic diurnal fluctuations and interspecies differences (conifers > arbors > shrubs). The fluctuation (Coefficient of Variation (CV) = 0.459; abundances 0.003 ± 0.002 to 0.047 ± 0.005 n·cm-2) was even more drastic than that measured across species (CV = 0.353; 0.06 ± 0.01 to 0.40 ± 0.04 n·cm-2). Further analysis using partial least-squares path modeling demonstrated that stomatal variation and divergence largely dominated diurnal fluctuations and interspecies differences in microplastic interception by leaves, respectively. Our results highlight that the leaf-intercepted MPs is characterized by dynamic fluctuations rather than static equilibrium and reveal the important regulatory roles played by leaf micromorphological structures in intercepting MPs, thus enhancing our understanding of the interactions between terrestrial plants and airborne pollution.

Differences in particulate matter retention and leaf microstructures of 10 plants in different urban environments in Lanzhou City

Particulate matter (PM) is a major primary environmental air pollutant and poses a threat to human health. Differences in the environment and leaf microstructures of plants will result in varying abilities to retain PM, but the effects of changes in these factors on PM retention are not yet well understood. This study selected 10 plant species in four urban areas (sports field, park, residential green space, and greenway) as the study objects. The amount of retained PM by the different species was measured, and the leaf microstructures were observed. It was found that the environment significantly affected both PM retention and leaf microstructure. The ranking of PM retention in the 10 species in four areas was greenway > residential green space > park > sports field. The ranking of average stomatal width and length was park > sports field > residential green space > greenway, while that of average stomatal density was greenway > residential green space > park > sports field. Different environments affected the length and density of trichomes in the leaves. These changes represented the adaptation of plant species to the growth environment. The stomata and grooves of the leaf surface significantly affected the ability of plants to retain PM. The amount of PM retained by different species varied. In all four urban areas, Prunus × cistena N. E. Hansen ex Koehne (purple leaf sand cherry), Prunus cerasifera Ehrhart f. atropurpurea (Jacq.) Rehd. (cherry plum), Buxus sinica var. parvifolia M. Cheng (common boxwood), and Ligustrum × vicaryi Rehder (golden privet) showed strong PM retention. The results of this study will provide information for planners and urban managers for the selection of plant species.

Accelerated settling velocity of airborne particulate matter on hairy plant leaves

Phytoremediation has emerged as an ecofriendly technique to reduce hazardous particulate matter (PM) in the air. Although previous studies have conducted statistical analyses to reveal PM removal capabilities of various plant species according to their leaf characteristics, the underlying physical mechanism of PM adsorption of plants remains unclear. Conventional methodologies for measuring PM accumulation usually require long-term field tests and provide limited understanding on PM removal effects of individual leaf traits of various plants. In this study, we propose a novel methodology which can compare the electrostatic interactions between PMs and plant leaves according to their trichome structures by using digital in-line holographic microscopy (DIHM). Surface characteristics of Perilla frutescens and Capsicum annuum leaves are measured to examine electrostatic effects according to the morphological features of trichomes. 3D settling motions of PMs near the microstructures of trichomes of the two plant species are compared in detail. To validate the PM removal effect of the hairy microstructures, a polydimethylsiloxane (PDMS) replica model of a P. frutescens leaf is fabricated to demonstrate accelerated settling velocities of PMs near trichome-like microstructures. The size and electric charge distributions of PMs with irregular shapes are analyzed using DIHM. Numerical simulation of the PM deposition near a trichome-like structure is conducted to verify the empirical results. As a result, the settling velocities of PMs on P. frutescens leaves and a PDMS replica sample are 12.11 ± 1.88% and 34.06 ± 4.19% faster than those on C. annuum leaves and a flat PDMS sample, respectively. These findings indicate that the curved microstructures of hairy trichomes of plant leaves increase the ability to capture PMs by enhancing the electric field intensity just near trichomes. Compared with conventional methods, the proposed methodology can quantitatively evaluate the settling velocity of PMs on various plant leaves according to the morphological structure and density of trichomes within a short period of time. The present research findings would be widely utilized in the selection of suitable air-purifying plants for sustainable removal of harmful air pollutants in urban and indoor environments.

Particulate matter resuspension from simulated urban green floors using a wind tunnel-mounted closed chamber

Background

Green areas are thought to reduce particulate matter (PM) concentrations in urban environments. Plants are the key to PM reduction via various mechanisms, although most mechanisms do not lead to the complete removal of PM. Ultimately, PM falls into the soil via wind and rainfall. However, the fallen PM can re-entrain the atmosphere, which can affect plants capacity to reduce PM. In this study, we simulated an urban green floor and measured the resuspension of PM from the surface using a new experimental system, a wind tunnel-mounted closed chamber.

Methods

The developed system is capable of quantifying the resuspension rate at the millimeter scale, which is measured by using the 1 mm node chain. This is adequate for simulating in situ green floors, including fallen branches and leaves. This addressed limitations from previous studies which focused on micrometer-scale surfaces. In this study, the surfaces consisted of three types: bare sand soil, broadleaves, and coniferous leaves. The resuspended PM was measured using a light-scattering dust detector.

Results

The resuspension rate was highest of 14.45×10^-4 s^-1 on broad-leaved surfaces and lowest on coniferous surfaces of 5.35×10^-4 s^-1 (p < 0.05) and was not proportional to the millimeter-scale surface roughness measured by the roller chain method. This might be due to the lower roughness density of the broad-leaved surface, which can cause more turbulence for PM resuspension. Moreover, the size distribution of the resuspended PM indicated that the particles tended to agglomerate at 2.5 µm after resuspension.

Conclusion

Our findings suggest that the management of fallen leaves on the urban green floor is important in controlling PM concentrations and that the coniferous floor is more effective than the broadleaved floor in reducing PM resuspension. Future studies using the new system can be expanded to derive PM management strategies by diversifying the PM types, surfaces, and atmospheric conditions.

A systematic review of urban green space research over the last 30 years: A bibliometric analysis

Worldwide, due to rapid urbanization, the provision of urban green spaces (UGSs) has become a primary goal of urban planning. As such, research on the benefits, effects, and challenges of UGSs has gained widespread attention among scholars. This paper comprehensively analyzes three decades of UGS research and its evolution; it conducts a bibliometric analysis of approximately 4000 articles and reviews from the Web of Science platform to discover the patterns and trends characterizing UGS research over time. We found that the pioneers of initial UGS research were the United States and Canada, whereas recently the European Union and China have become the global engines of research in the field. UGS research initially focused on studying urban forests, gradually shifting toward green spaces located in inner urban areas. Early on, researchers investigated UGSs (i.e., urban forests) from an ecological perspective. However, the most current research phase focuses on the social aspects of UGSs, characterized by such keywords as environmental justice and accessibility. Furthermore, the introduction of geographic information systems (GIS) has given new impetus to the evolution of UGS research and has remained the most used technological advancement besides remote sensing techniques. As the social aspects of UGS research have gained importance, new research methods have been employed, such as machine learning, big data and social media data analysis, and artificial intelligence, most recently.

Imaging particulate matter exposed pine trees by vehicle exhaust experiment and hyperspectral analysis

This study analyzed spectral variations of the particulate matter (PM hereafter)-exposed pine trees using a spectrometer and a hyperspectral imager to derive the most effective spectral indices to detect the pine needle exposure to PM emission. We found that the spectral variation in the near-infrared (NIR hereafter) bands systemically coincided with the variations in PM concentration, showing larger variations for the diesel group whereas larger dust particles showed spectral variations in both visible and NIR bands. It is because the PM adsorption on needles is the main source of NIR band variation, and the combination of visible and NIR spectra can detect PM absorption. Fourteen bands were selected to classify PM-exposed pine trees with an accuracy of 82% and a kappa coefficient of 0.61. Given that this index employed both visible and NIR bands, it would be able to detect PM adsorption. The findings can be transferred to real-world applications for monitoring air pollution in an urban area.