Resuspension Of Particulate Matter Research Articles

Characterizing leaf-deposited particles: Single-particle mass spectral analysis and comparison with naturally fallen particles

The size and composition of particulate matter (PM) are pivotal in determining its adverse health effects. It is important to understand PM's retention by plants to facilitate its atmospheric removal. However, the distinctions between the size and composition of naturally fallen PM (NFPM) and leaf-deposited PM (LDPM) are not well-documented. Here we utilize a single-particle aerosol mass spectrometer, coupled with a PM resuspension chamber, to analyze these differences. We find that LDPM particles are 6.8–97.3% larger than NFPM. Employing a neural network algorithm based on adaptive resonance theory, we have identified distinct compositional profiles: NFPM predominantly consists of organic carbon (OC; 31.2%) and potassium-rich components (19.1%), whereas LDPM are largely composed of crustal species (53.9–60.6%). Interestingly, coniferous species retain higher OC content (11.5–13.7%) compared to broad-leaved species (0.5–1.2%), while the levoglucosan content exhibit an opposite trend. Our study highlights the active role of tree leaves in modifying PM composition beyond mere passive capture, advocating for a strategic approach to species selection in urban greening initiatives to enhance PM mitigation. These insights provide guidance for urban planners and environmentalists in implementing nature-based solutions to improve urban air quality.

Assessing Worker and Pedestrian Exposure to Pollutant Emissions from Sidewalk Cleaning: A Comparative Analysis of Blowing and Jet Washing Techniques

Sidewalk cleaning operations are essential to maintaining a clean and safe urban environment. Despite their vital role, these activities, particularly the blowing of road dust, can lead to the resuspension of road dust and associated pollutants, which poses risks to human health and the environment. While the role of blowers on particulate matter resuspension has been investigated, there is limited information on emitted bioaerosols. This study aimed to compare the occupational exposure of operators and passersby during sidewalk cleaning using two manual methods—blowing and jet washing—in two distinct urban environments. The study focused on metal road traffic tracers (copper (Cu), zinc (Zn), manganese (Mn), cadmium (Cd), and lead (Pb)) and cultivable/non-cultivable microorganisms. We showed that blowing resuspends inhalable particles containing metals (Cu, Zn, and Mn, but not Cd or Pb) and bioaerosols (fungi and Gram-negative bacteria) throughout the year. This represents an important source of exposure for the blower operators and poses a potential long-term respiratory health risk for them. Operators working in cabs are shielded from such exposure, but passersby, especially vulnerable populations, may be at risk. While jet washing reduces operator exposure to Gram-negative bacteria in comparison to blowing, it does not mitigate fungal exposure, particularly in vegetated sites. These findings underscore the necessity for the implementation of effective protective measures and the development of alternative cleaning methods to mitigate exposure risks.

Dynamic characteristics of particulate matter resuspension due to human activities in indoor environments: A comprehensive review

Particulate matter (PM) resuspension from indoor surfaces is one of the leading causes of occupant exposure to PM. It has been recognized as a main source of indoor air pollution by many field studies. This review article explores the mechanisms and effects of single and multiple influential factors on PM resuspension, distribution characteristics, spatial and temporal PM distribution characteristics and interactions of human activities and mitigation measures. A roadmap is proposed to provide a strong basis for subsequent research into the dynamic characteristics of PM resuspension. The synthesis of existing literature suggests that the mechanism behind the opposite effect caused by multiple influential factors deserves further exploration. Microscopic simulations of motion over short periods and richer activity features based on various scenarios are needed to get more accurate results. More advanced strategies should be considered to change the control process and enhance the efficiency of the purification devices. Collaboration between multiple disciplines is required to get the complete picture of PM resuspension.

Pollution Characteristics of Carbonaceous Components in PM10 and PM2.5 of Road Dust Fall and Soil Dust in Xi'an

To investigate the pollution characteristics of carbonaceous components in PM10 and PM2.5 of road dust fall and soil dust in Xi'an and enrich their source profiles, samples from five sites of road dust fall and 16 sites of soil dust were collected in Xi'an from April to May 2015. The ZDA-CY01 particulate matter resuspension sampler was used to obtain PM10 and PM2.5 samples, and the Model5L-NDIR OC and EC analyzer were used to determine the concentrations of organic carbon (OC) and elemental carbon (EC) in PM10 and PM2.5. The pollution and sources of carbonaceous aerosol in PM10 and PM2.5 were investigated by analyzing OC and EC characteristics, ratio, and the principal component analysis statistical model. The results showed that the proportions of OC in PM10 and PM2.5 at the various dust fall sites differed, ranging from 6.0% to 19.4% and 7.6% to 29.8%, respectively. The ratios of EC in PM10 and PM2.5at the different dust fall sites were relatively small, accounting for 0.6%-2.2% and 0.2%-3.6% in urban sites, respectively; however, EC was almost undetectable in most peripheral soil dust. The proportions of carbonaceous components in PM10 and PM2.5 followed the order of urban road dust fall>external control dust>river beach soil dust>soil dust and urban road dust fall>soil dust>external control dust>river beach soil dust, respectively. OC dominated the carbonaceous aerosols at the different sites, which was relatively low in urban road dust fall. The OC to total carbon (TC) ratios in PM10 and PM2.5 at urban road dust fall were 85.2%-95.3% and 87.9%-98.9%, respectively. The OC to TC ratios in PM10 and PM2.5 of soil dust were relatively high, exceeding 99%. Carbonaceous components were primarily concentrated in fine particles. The pollution distribution of carbonaceous components in the urban road dust fall sites was consistent, whereas that in the different soil dust sites were quite different. The carbonaceous components in urban road dust fall and soil dust were primarily affected by pollutant source emissions such as biomass burning, coal burning, gasoline, and diesel vehicle exhaust. There were differences in the source contribution rates of carbonaceous aerosols in PM10 and PM2.5.

Key factors for abating particulate matter in a highly industrialized area in N Spain: Fugitive emissions and secondary aerosol precursors

In highly industrialized areas, abating particulate matter (PM) is complex owing to the variety of emission sources with different chemical profiles that may mix in the atmosphere. Gijón—an industrial city in northern Spain—was selected as a case study to better understand the key emission sources and improve air quality in highly industrialized areas. Accordingly, the trends of various air quality indicators (PM10, PM2.5, SO2, NO2, and O3) during the past decade (2010–2019) were analyzed. Additionally, the inorganic and organic PM10 compositions were analyzed for source apportionment studies and to assess the impact of COVID-19 restrictions on PM10 levels.The results revealed that over the past decade, PM10 concentrations decreased, whereas PM2.5 concentrations dominated by secondary inorganic aerosols (SIA) remained relatively constant. Notably, during the COVID-19 lockdown, the PM10 concentration increased by 9.1%, primarily owing to an increase in regional SIA (>65%) due to specific meteorological conditions that favor the formation of secondary PM from gaseous precursors. Overall, eight key PM10 sources were identified: “industrial fugitive PM resuspension” (FPM, 28% of mean PM10 concentration), “aged sea spray” (SSp, 16%), “secondary nitrate” (SN, 15%), “local diffuse source” (LPM, 12%), “solid fuel combustion” (SFC, 7.8%), “biomass burning” (BB, 7.4%), “secondary sulphate” (SSu, 6.0%), and “sinter” (SIN, 4.5%). The PM10 concentration in Gijón is significantly influenced by the integrated steel industry (FPM, SFC, and SIN; 41% of PM10) and fugitive primary PM emissions were the main source (FPM and LPM; 40%). To reduce PM10 and PM2.5 concentrations, industrial fugitive emissions, which are currently poorly regulated, and SIA precursors must be abated.This study provides a methodological approach that combines trend analysis, chemical speciation, and source apportionment for assessing pollution abatement strategies in industrialized areas with a complex mix of emission sources.

Influence of particulate matter on air quality due to “Nortes” events in the Gulf of Mexico

The Gulf of Mexico is a region of great international importance, as well as the movement of ships that occur in it, with the port of Veracruz being the most important and currently being expanded. The objective of the study was to evaluate the impact of the particulate matter resulting from this expansion, considering the “Nortes” effect that occurs annually from September to May in the Gulf of Mexico. Four periods of “Nortes” were evaluated from 2017 to 2020 were evaluated, identifying 52 events to examine their influence on air quality. Using in situ meteorological parameters and the HYSPLIT model's cluster reanalysis database, 15 “Nortes” events were linked to measurements from the air quality monitoring station located at the port. The results reveal that “Nortes” events influence poor air quality due to particulate matter within a 30 by 30 km grid, as simulated by the CALPUFF dispersion model. This was attributed to particulate matter resuspension caused by wind speeds exceeding 11 m/s within an 8 km downwind from the expansion area. A concentration range of particulate matter of 60–70 μg/m3 was associated with the effect “Nortes” at the air quality monitoring station and the CALPUFF model. However, maximum concentrations ranged from 1,030 to 2,800 μg/m3 at different receptors, as indicated by the CALPUFF model. These findings underscore the importance of accounting for the impact of meteorological phenomena on air quality during the expansion and operation of ports around the world.

Characterization and Health Risk of Heavy Metals in PM2.5 from Road Fugitive Dust in Five Cities of Yunnan Province

In order to study the contents, sources, and health risk of PM2.5 in road fugitive dust in Yunnan, road fugitive dust samples were collected from five typical cities including Kunming, Baoshan, Wenshan, Zhaotong, and Yuxi. Particulate matter resuspension technology was used to levitate the dust samples and collect PM2.5. Eight heavy metals including chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), selenium (As), cadmium (Cd), and lead (Pb) in PM2.5 were detected using ICP-MS. The results showed that the contents of Cr, Ni, Cu, Zn, and Pb in road fugitive dust seriously exceeded the background values of Yunnan soil. The enrichment factors showed that most of the heavy metals in PM2.5 of road fugitive dust in the five cities of Yunnan were moderately enriched and strongly enriched, which were greatly influenced by human activities. The results of correlation analysis and principal component analysis showed that the heavy metals in PM2.5 of road fugitive dust in Yunnan were all affected by soil and traffic sources. The other sources varied greatly in different cities:Kunming was affected by iron and steel melting sources, Baoshan and Yuxi were affected by non-ferrous metal smelting sources, and Zhaotong was affected by coal sources. Health risk analysis showed that Cr, Pb, and As in road fugitive dust PM2.5 had non-carcinogenic risk in children in Kunming, Yuxi, and Zhaotong, respectively, and Cr in Kunming also had a lifetime carcinogenic risk.

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

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. 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. 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. 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.

Impact of Carpets on Indoor Air Quality

Interest in having a healthy and well-being environment has increased the awareness to improve indoor air quality (IAQ). Building materials influence the contribution of indoor air pollution, so understanding their behaviour on IAQ is essential. Among building materials, carpets cover surfaces of indoor environments and significantly impact IAQ due to their large surface area and multi-layers of materials components. This review aimed to consolidate what is known about how carpet impacts indoor volatile organic compounds (VOCs) concentrations and particulate matter (PM) distributions. The results showed that carpets are not only a source of primary emission but also can ad/absorb VOCs and emit VOCs through secondary emission, sink effects, and transformation reactions. The material composition of each carpet layer, environmental parameters (e.g., humidity, temperature, air velocity), and chamber size influence a carpets’ behaviour. Previous studies on the resuspension of PM from carpets mainly focused on the effects of human activities and humidity. Further studies are needed to enhance knowledge related to carpet behaviours in the indoor environment and on how the common materials of carpets should be designed and sustained to reduce exposure to harmful pollutants indoors while maintaining its benefits.

Conditions Affecting Wind-Induced PM10 Resuspension as a Persistent Source of Pollution for the Future City Environment

Air pollution by particulate matter (PM) in cities is an ongoing problem with increasing severity. The biggest PM contributors are traffic and domestic fire burning. With the shift towards electromobility and the use of low-emission fuels, attention should be shifted to less mentioned sources of pollution. Such sources of pollution include wind-induced resuspension. This study focuses on determining the threshold wind speed causing the resuspension of particulate matter (TWSR) with aerodynamic diameter smaller than 10 µm. A methodology is introduced that examines how data could be treated to identify its characteristics (for locations where only PM10 data are available). The most significant monitored parameters are air humidity, wind direction, time of the day, and surface type. The characteristic wind speeds causing resuspension are identified in four locations for different times of day. It was proven that at times of intense human activity, particles are lifted by wind more easily. The mean threshold wind speed causing resuspension in the studied urban environment was identified as 1.58 m/s at a height of 2 m above the surface. The wind speeds were also compared with experimental studies of resuspension. The results proved correspondence between the identified wind speeds and the experimental results.

Numerical study of particle spatial distribution under column attachment ventilation

Column attachment ventilation mode (CAV) is a new form of air distribution based on pillars widely distributed in buildings and uses the column-based Coanda effect to efficiently transport the supply air from the top of the room to the lower occupied zone. Since CAV is essentially a down-supply ventilation mode, it may lead to the resuspension of particulate matter (PM). In this study, considering the pollutant particle size, air supply velocity (u0), and air supply temperature difference (ΔT) (including cooling and heating conditions), a numerical simulation method was used to study the PM movement and diffusion characteristics. The results indicated that the particles (<20 μm) could be suspended and carried by the airflow and have good airflow followability. The particles of 50–100 μm were mainly deposited in the airflow intersection zone. 21% of the particles can be blown up by the airflow and finally discharged through the air exhaust outlets. The concentration decay of PM 2.5 in the vertical direction decreased linearly with u0. The air supply temperature difference (ΔT) did not affect the indoor PM distribution in cooling conditions but significantly affected the heating conditions. In this study, the indoor PM concentration exceeded the Chinese standard threshold of 35 μg/m3, when the air supply temperature difference was 10 K. In the CAV mode, the airflow intersection zone between the two columns showed a larger PM mass concentration. The results of this study proved that the CAV mode can provide suitable IAQ under reasonable design parameters.

Precipitation plays a key role in the processes of accumulation, retention and re-suspension of particulate matter (PM) on Betula pendula, Tilia cordata and Quercus robur foliage

Precipitation plays a key role in the processes of accumulation, retention and re-suspension of particulate matter (PM) on Betula pendula, Tilia cordata and Quercus robur foliage

High resolution vehicular exhaust and non-exhaust emission analysis of urban-rural district of India

Air quality deterioration due to vehicular emissions in smaller Indian cities and rural areas remains unacknowledged, even though the situation is alarmingly similar to megacities. The resulting lack of knowledge on travel behavior and vehicle characteristics impacts accuracy of emission studies in these regions. This study uses a novel approach and appropriate primary and secondary data sets to allocate vehicular activities (vehicle population and vehicle kilometer travelled) and associated emissions at a high spatial resolution for estimation and dispersion analysis of vehicular exhaust and non-exhaust PM2.5 emission in an Indian urban-rural landscape. The study indicates that using approaches that do not allocate vehicles kilometers travelled to areas of their expected travel results in underestimating the percent share of PM2.5 emissions from rural roads and motorways while overestimating overall PM2.5 emissions. Particulate matter resuspension is the dominant form of PM2.5 emissions from the vehicular sector on all road types, constituting an even higher fraction on rural roads. Two-wheelers contribute a high fraction of PM2.5 emissions (exhaust and non-exhaust combined), followed by heavy commercial vehicles and four-wheelers on urban roads. Light commercial vehicles, especially agricultural tractors dominate these emissions on rural roads. PM2.5 hotspots are prevalent in urban areas, but several rural areas also experience heavy particulate matter concentrations. Thus, vehicle movement incorporation results in more accurate emission estimation, especially in an urban-rural landscape.

Study on Characteristics of Particulate Matter Resuspension in School Classroom through Experiments Using a Simulation Chamber: Influence of Humidity

Resuspension of particulate matter (PM) in classrooms, which increases the risk of negative impact on student health from exposure to PM, is influenced by humidity level in the indoor environment. The goal of this study is to investigate the properties of PM resuspension in accordance with relative humidity through classroom test chamber experiments. In actual classrooms, it is challenging to control factors influencing resuspension. Therefore, the classroom chamber that reflects the environment of elementary school classroom (e.g., structure, floor material) is used in this study. The humidity of the classroom chamber is adjusted to 35%, 55%, 75%, and 85% by placing it inside a real-size environmental chamber, which allows artificial control of climatic conditions. At the respective humidity conditions, PM resuspension concentration and resuspension factor caused by occupant walking across the classroom chamber are analyzed. The results show that both of the resuspension concentration and resuspension factor reveal a linear negative correlation to humidity increase. Furthermore, coefficient of determination (R2) indicating goodness-of-fit of the linear regression model between the resuspension concentration and humidity is 0.88 for PM10 and 0.93 for PM2.5. It implies that accuracy of the regression model for estimating PM10 and PM2.5 resuspension concentrations is 88% and 93%, respectively.

The impact of airflow and air purification on the resuspension and removal of deposited particulate matter

Air purifiers are a popular tool to manage indoor particulate matter; however, their effectiveness with respect to resuspending and removing particles that have been deposited on surfaces is limited. This study proposed and evaluated a method of removing both suspended and deposited particulate matter using an air purifier in conjunction with an airflow source. First, the effectiveness of the air purifier with respect to removing deposited particulate matter was determined in a static environment and under forced airflow. Then, the removal efficiency of the purification system was evaluated under varying airflow orientations and velocities. Results showed that the air purifier contributed to particulate matter resuspension and removal, and the efficiency was significantly improved under forced resuspension due to airflow generation. The orientation of the airflow was found to have an impact on the resuspension and removal efficiency of particulates, and four-way airflow was more effective compared to one-way airflow. This was attributed to four-way flow increasing the airflow diffusion radius compared to one-way flow. A flow velocity of 5 m/s or greater was necessary to resuspend deposited particulate matter. These findings illustrate that forced resuspension is an effective means of reducing deposited particulate matter in indoor environments, and four-way airflow with a wide diffusion radius and a velocity of 5 m/s or higher are the optimum conditions for this purpose.

Experiments and simulations of human walking-induced particulate matter resuspension in indoor environments

A clean indoor environment, which is essential for human health, can be achieved by reducing PM2.5 pollution from indoor ground fugitive dust. This study quantifies different indoor PM2.5 dust loads and the human walking-induced indoor PM2.5 resuspension for different cumulative times, and investigates the indoor PM2.5 pollution caused by indoor floor dust using experiments and simulations. The concentration of human walking-induced indoor PM2.5 resuspension reached a maximum value of approximately 1 min for different dust loads. The quantitative analysis of PM2.5 resuspension using the particle transport model showed that the magnitude of dust loads was unrelated to the resuspension fraction of PM2.5, and the resuspension fraction of PM2.5 was 2.2 × 10−8. When the indoor PM2.5 dust loads were 0.11, 0.18, and 0.30 g/m2, the diffusion rates of the human walking-induced indoor PM2.5 resuspension were 7.62 × 10−11, 1.25 × 10−10, and 2.08 × 10−10 kg/s, respectively. The movement of PM2.5 concentration and deposition was influenced by airflow from the air conditioner and particles collision with the wall. The source strengths (dust loads) were related to the cumulative time of dust. The indoor PM2.5 concentration increased with the increasing number of people walking indoors. Human walking-induced indoor PM2.5 resuspension leads to an increase in indoor particulate matter; therefore, regularly cleaning indoor dust can reduce secondary pollution caused by indoor activities.

Seasonal Variability in Near-bed Environmental Conditions in the Vazella pourtalesii Glass Sponge Grounds of the Scotian Shelf

The Scotian Shelf harbors unique aggregations of the glass sponge Vazella pourtalesii that provides an important habitat for benthic and pelagic fauna. Recent studies have shown that these sponge grounds have persisted in the face of strong inter-annual and multi-decadal variability in temperature and salinity. However, little is known of these environmental characteristics on hourly-seasonal time scales. This study presents the first hydrodynamic observations and associated (food) particle supply mechanisms for the Vazella sponge grounds, highlighting the influence of natural variability in environmental conditions on sponge growth and resilience. Near-bottom environmental conditions were characterized by high temporal resolution data collected with a benthic lander, deployed during a period of 10 months in the Sambro Bank Sponge Conservation Area. The lander was equipped with temperature and oxygen sensors, a current meter, a sediment trap and a video camera. In addition, water column profiles of temperature and salinity were collected in an array across the sponge grounds from high to lower sponge presence probability. Over the course of the lander deployment, temperature fluctuated between 8.8–12°C with an average of 10.6 ± 0.4°C. Dissolved oxygen concentration was on average 6.3 mg l–1, and near-bottom current speed was on average 0.12 m s–1, with peaks up to 0.47 m s–1. Semi-diurnal tidal currents promoted constant resuspension of particulate matter in the benthic boundary layer. Surface storm events episodically caused extremely turbid conditions on the seafloor that persisted for several days, with particles being resuspended to more than 13 m above the seabed. The carbon flux in the near-bottom sediment trap peaked during storm events and also after a spring bloom in April, when fresh phytodetritus was observed in the bottom boundary layer. While resuspension events can represent a major stressor for sponges, limiting their filtration capability and remobilizing them, episodes of strong currents and lateral particle transport likely play an important role in food supply and the replenishment of nutrients and oxygen. Our results contextualize human-induced threats such as bottom fishing and climate change by providing more knowledge of the natural environmental conditions under which sponge grounds persist.

Immobilized atmospheric particulate matter on leaves of 96 urban plant species.

Plants provide many ecosystem services in urban environments, including improving ambient air quality. Leaves of plants permit the deposition of particulate matter (PM) and, depending on their leaf traits, PM may be immobilized within the epicuticular wax (EW) layer, on trichomes, on hyphae of fungi, or inside stomatal cavities. In this study, leaves of 96 perennial urban plant species consisting of 45 deciduous broadleaf/needle-like trees, 32 deciduous broadleaf shrubs, 12 evergreen needle/scale-like trees, 5 evergreen broadleaf trees, and 2 climber species were investigated in June and September 2016 to determine the effectiveness of distinct leaf surfaces in PM immobilization after leaf washing treatment. The leaf surfaces were washed vigorously using a vortex shaker. The magnetizable component of accumulated and immobilized PM on the leaf surfaces was estimated using saturation isothermal remanent magnetization (SIRM) of the unwashed and washed leaves, respectively. In June, the washed leaf SIRM of deciduous (broadleaf/needle-like) tree and shrub species (n = 77) ranged between 0.1 and 13.9 μA. In September, the washed leaf SIRM of all investigated plant species (n = 96) ranged between 1.2 and 35.0 μA. Outcomes of this study indicate that leaves of Buddleja davidii, Viburnum lantana, and Sorbus intermedia showed the highest washed leaf SIRM and thus were the most effective in immobilizing PM on their leaf surfaces while leaves of Populus alba, Robinia pseudoacacia, and Abies fraseri with lowest washed leaf SIRM were the least effective. On average, more than half (i.e., 60%) of the magnetic signal still remained after vigorous washing but a large variation exists between species (9-96%). The leaf SIRM of washed leaves of deciduous broadleaf tree and shrub species was significantly higher compared to leaves of evergreen needle/scale-like species. Evidently, the magnetic signal of unwashed leaves was higher than washed ones and higher in September than in June. Leaf traits significantly influenced the magnetic signal of both washed and unwashed leaves: leaves with a high trichome density or high leaf wettability showed a higher unwashed and washed leaf SIRM compared to leaves with no trichomes or low leaf wettability. The effect of epicuticular wax structure types on leaf SIRM was indicated to be only marginally significant. Moreover, also the immobilized fraction of PM was significantly affected by trichome density and leaf wettability, thus substantiating that plant species with high trichome density and/or leaf wettability not only accumulate more PM but are also less prone to PM re-suspension than other species. In general, the results also indicate that leaf SIRM of unwashed leaves can be a good indicator to determine the effectiveness of a plant species in PM immobilization. Plant species effective in immobilizing PM on their leaf surfaces may likely improve ambient air quality when planted in urban environments. However, it is vital that leaves of these plant species (i.e., with high PM immobilization abilities) are carefully recycled as they may be polluted.

Particulate matter exchange between atmosphere and roads surfaces in urban areas

The deposition and the re-suspension of particulate matter (PM) in urban areas are the key processes that contribute not only to stormwater pollution, but also to air pollution. However, investigation of the deposition and the re-suspension of PM is challenging because of the difficulties in distinguishing between the resuspended and the deposited PM. This study created two Bayesian Networks (BN) models to explore the deposition and the re-suspension of PM as well as the important influential factors. The outcomes of BN modelling revealed that deposition and re-suspension of PM10 occurred under both, high-traffic and low-traffic conditions, and the re-suspension of PM2.5 occurred under low-traffic conditions. The deposition of PM10 under low-volume traffic condition is 1.6 times higher than under high-volume traffic condition, which is attributed to the decrease in PM10 caused by relatively higher turbulence under high-volume traffic conditions. PM10 is more easily resuspended from road surfaces compared to PM2.5 as the particles which larger than the thickness of the laminar airflow over the road surface are more easily removed from road surfaces. The increase in wind speed contributes to the increase in PM build-up by transporting particulates from roadside areas to the road surfaces and the airborne PM2.5 and PM10 increases with the increase in relative humidity. The study outcomes provide a step improvement in the understanding of the transfer processes of PM2.5 and PM10 between atmosphere and urban road surfaces, which in turn will contribute to the effective design of mitigation measures for urban stormwater and air pollution.

Effects of Foliar Trichomes on the Accumulation of Atmospheric Particulates in Tillandsia Brachycaulos.

Foliar trichomes are specialized structures that have first contact with atmospheric particulate matter (PM), while their effects on PM accumulation are rarely investigated. In this study, epiphytic Tillandsia brachycaulos with foliar trichomes was investigated. Trichomes were removed artificially to investigate PM adsorption and resuspension. The results showed that the maximum PM (13.94±0.20 g•m-2) and natural PM content (10.65±1.10 g•m-2) on T. brachycaulos samples with foliar trichomes was significantly higher than those without foliar trichomes. After PM deposition on the leaf surface, more than 85% of PM was dispersed by wind in plants without trichomes, significantly higher than those with trichomes (30.2%). Therefore, the effects of foliar trichomes on PM were reflected not only on PM adsorption, but on PM resuspension. Foliar trichomes can decrease PM resuspension falling on the leaf surface and promote the accumulation of these particles.