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

Abstract

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.

Breathing Fresh Air in the City: Implementing Avenue Trees as a Sustainable Solution to Reduce Particulate Pollution in Urban Agglomerations

“…Urban meadows are also a key component of cities’ nature-based strategies for trapping PM released from the street (or transport) because of species biodiversity (plants with various growth and development patterns, stem and leaf morphology) and the height of canopies, particularly in areas where shrubs and trees are impossible and undesirable [ 153 ]. In order to maximize the effectiveness of PM immobilization effects, vegetation should be located as close to the emission source as feasible [ 153 , 154 , 155 ]. The effectiveness of PM accumulation through plants is reduced if the vegetation is far from the sources.…”

Identifying Common Trees and Herbaceous Plants to Mitigate Particulate Matter Pollution in a Semi-Arid Mining Region of South Africa

“…round, tree canopies act as a sink of PM, complex resulting in greater dust deposition on foliage and taining PM [14,15,[27][28][29]. Herbaceous plants immo along roads because traffic is a major source of PM resuspension from the soil, are feasible for inclusi are recognized as ruderal species to re-establi [11,13,16,18,19].…”

“…Evergreen trees collect dust all year round, tree canopies act as a sink of PM, complex tree structures resist wind movement resulting in greater dust deposition on foliage and tree bark could absorb toxic metal containing PM [14,15,[27][28][29]. Herbaceous plants immobilize dust at ground level, especially along roads because traffic is a major source of PM at surface level, limit hazardous dust resuspension from the soil, are feasible for inclusion in most outdoor urban spaces, and are recognized as ruderal species to re-establish vegetation in disturbed habitats [11,13,16,18,19].…”

“…However, transportation of tailings pollutes the air with fine particles [3,4]. Hence, planting the woody species M. oleifera and the three forbs (C. roseus, G. fruticosus and I. batatas) that have shown efficiency in accumulating larger and fine PM fractions, could be the best choice to immobilize dust along haul roads in the study region [13,18,19,39].…”

“…While some plants can be sensitive to air pollution and thus be used as bioindicators, others can adapt, survive and even thrive due to traits including the ones that enable them to accumulate large quantities of dust particles on leaf surfaces that serve as natural air filters [10,11,[13][14][15][16]. Of late, much interest and effort have been dedicated to investigating dust accumulation capacity, tolerance and adaptability of trees and herbaceous plants to abate air pollution in a cost-effective, sustainable and safe way [10,11,[16][17][18][19]. Urban greenery extends these beneficial effects by restoring degraded soils, restricting soil erosion and improving ecosystem services by re-establishing vegetation cover [11,12].…”