Not Only Trees Matter—Traffic-Related PM Accumulation by Vegetation of Urban Forests

In terms of the process of air purification, a lot of attention has been devoted to trees and shrubs. Little attention has been paid to herbaceous vegetation from the lower forest layers. Urban forests are often located on the outskirts of cities and surround exit roads where there is heavy traffic, generating particulate matter (PM) pollution. The aim of this study was to investigate the spread of PM from the road traffic in the air and to investigate how individual layers of urban forests accumulate PM. We conducted comparative analyses of PM accumulation on plants in five zones away from the road, into the forest, in the air, and in four vegetation layers: mosses, herbaceous plants, shrubs and trees. The results show that all forest layers accumulate PM. We show that PM is very efficiently accumulated by herbaceous plants growing along roadsides, and that the PM that was not deposited on herbaceous plants was accumulated by trees and shrubs. With increasing distance from the road into the forest, the PM content on herbaceous plants decreased and the accumulation on trees and shrubs increased. We estimated that PM concentration in the air dropped significantly in the front line of the trees, but it was still detectable up to 50 m into the forest. The results presented herein show that meadow vegetation and urban forests play a very important role in air purification. Our results provide a better understanding of the complexity of urban forest interactions and provide the basis for better planning of urban greenery

How Much Does Weather Matter? Effects of Rain and Wind on PM Accumulation by Four Species of Australian Native Trees

As interest in improving urban air quality grows, phytoremediation-amelioration through plants-is an increasingly popular method of targeting particulate matter (PM), one of the most harmful pollutants. Decades of research has proven that plants effectively capture PM from air; however, more information is needed on the dynamics of PM accumulation. Our study evaluated the effects of meteorological conditions on the dynamics of PM deposition, wash off and resuspension using four Australian tree species growing under natural conditions near a busy highway. Accumulation of PM on foliage was analyzed over the short term (daily changes) and over a longer time period (weekly changes). The results obtained were correlated with ambient concentrations of PM2.5 and PM10, rain intensity and wind strength. The highest accumulation of PM was recorded for Eucalyptus ovata (100.2 µg cm−2), which also had the thickest wax layer while the lowest was for Brachychiton acerifolius (77.9 µg cm−2). PM accumulation was highly changeable, with up to 35% different PM loads on the foliage from one day to the next. Importantly these dynamics are hidden in weekly measurements. Changes in PM deposition on the leaves was mostly affected by rain and to a lesser extent by wind, but the extent of the effect was species specific. The large PM fraction (10-100 µm) was the first to be removed from leaves, while the smallest PM fraction (0.2-2.5 µm) was retained for longer. Precipitation affects also PM retained in waxes, which until now were believed to be not affected by rain. This work demonstrates important interactions between PM load and weather, as well as adding to the small inventory of Australian native tree PM accumulation data

Particulate matter accumulation – further differences between native Prunus padus and non-native P. serotina

Particulate matter (PM) is one of the most harmful inhaled pollutants. Where pollutants have been emitted into the atmosphere, the most effective method for cleaning the air is through phytoremediation, whereby plants act as biological filters. PM has a negative impact on plants, but knowledge of PM effects on the photosynthetic apparatus is limited. In European forests, species of the genus Prunus L. play a key role in the composition of the forest understory and urban as well as industrial plantings. Shrubs of the native P. padus L. and closely-related invasive alien P. serotina Ehrh. are particularly widespread. Thus, both are good model species in which to study the impact of PM pollution. The aim of this study was to assess the accumulation of PM in the context of leaf morphology and amount of epicuticular waxes on foliage, and the efficiency of the photosynthetic apparatus of P. padus and P. serotina. The study was conducted under controlled conditions using two variants of dust, cement and roadside PM. In addition, we analyzed the absorption of dust by leaves dividing it into three fractions by size (10−100 μm, 2.5−10 μm and 0.2−2.5 μm). Results showed that both P. padus and P. serotina accumulate PM mostly on the surface of their leaves (SPM), rather than in the wax layer (WPM). P. padus accumulated higher amounts of PM than did P. serotina. The higher presence of PM on leaves of P. padus resulted in a reduction of the efficiency of the photosynthetic apparatus, manifested by lower rates of photosynthesis and chlorophyll a fluorescence, coinciding with an increased stomatal resistance. A strong negative correlation was found between the amount of PM accumulation and the efficiency of the photosynthetic apparatus in P. padus, but not in P. serotina. We have concluded that alien P. serotina is more tolerant to the conditions of stress caused by PM pollution than is the native P. padus, which may partly explain its success in the invasion in Europe

Roadside Moss Turfs in South East Australia Capture More Particulate Matter Along an Urban Gradient than a Common Native Tree Species

Urbanisation largely consists of removing native vegetation. Plants that remain interact with air quality in complex ways. Pollutants can be detrimental to plant growth; plants sometimes reduce air quality, yet some species also improve it through phytoremediation. A common pollutant of concern to human health in urban areas is particulate matter (PM), small particles of solid or liquid. Our study compared roadside moss turfs with leaves of a common Australian tree species, Pittosporum undulatum, in their ability to capture PM along an urban gradient. We sampled nine sites, three in each of three levels of urbanisation: low, medium, and high according to road type (freeway, suburban road, quiet peri-urban road). In addition, we deployed a PM monitor over a two-week period in one site of each urban level to provide concentrations of PM2.5. We used chlorophyll fluorescence (Fv/Fm; maximum quantum yield of photosystem II) as a measure of plant stress. We extracted PM in three size fractions using a filtration and washing technique with water and chloroform. Site averages for moss turfs were between 5.60 and 33.00 mg per g dry weight for total PM compared to between 2.15 and 10.24 mg per g dry weight for the tree leaves. We found that moss was more sensitive to increasing urbanisation, both in terms of trapping proportionately more PM than the leaves, and also in terms of photosynthetic stress, with moss Fv/Fm declining by a site average of 40% from low to high urban class (0.76 to 0.45). Our study highlights the stressors potentially limiting moss persistence in cities. It also demonstrates its ability to trap PM, a trait that could be useful in urban applications relating to urban greening or air quality

Of turf, trees and air quality: does roadside moss trap more particulate matter than leaves?

Plants in urban areas interact with air quality in numerous ways. Firstly, pollutants from industry, vehicular and residential sources can be detrimental to plant growth. Secondly, plants sometimes contribute to poor air quality, for instance by emitting allergens such as pollen, or by trapping pollutants in street canyons and thirdly, with appropriate placement some species improve air quality through phytoremediation. A common urban pollutant is particulate matter (PM - small particles of solid or liquid). While this is of concern to human health, less well known is its effect on vegetation and while moss is commonly studied as a biomonitor, there is little research on how it is affected by urbanisation. Our objective was to measure PM entrapment by roadside moss turfs and compare it to leaves of a common Australian tree species, Pittosporum undulatum on an urban gradient.,

The Role of Spontaneous Flora in the Mitigation of Particulate Matter from Traffic Roads in an Urbanised Area

Particulate matter (PM) is a serious air pollutant that poses significant health risks. One solution to reduce PM concentrations in these areas is through phytoremediation, a process that involves using plants to remove contaminants from the environment. In this study, we investigated the capacity of spontaneous flora—herbaceous plants, shrubs, and trees growing in five zones from the road—to absorb PM on their foliage. The study found significant differences in the accumulation of PM, with the highest PM accumulation recorded in Zone V, which boasted a blend of the three mentioned vegetation types together. In contrast, Zones I and II, which were located close to the road and comprised solely herbaceous plants, exhibited 14.3% and 43.4% less PM accumulation, respectively. Similarly, Zone IV, with a mix of herbaceous plants and shrubs, showed 64.5% less PM accumulation, while Zone III, with only herbaceous plants, had a staggering PM accumulation reduction of 76.8%. The sum of Si+Al+Ca displayed a similar pattern. Furthermore, the findings highlighted the valuable role of plants in decreasing PM concentrations in the air, resulting in reductions of 76%, 39%, and 47% for PM10, PM2.5, and PM1.0, respectively. The results indicate that various spontaneous flora can work in unison to reduce PM, providing a multifaceted approach to combating air pollution