Particulate matter (PM) is an air contaminant in urban and industrial areas that often exceeds limit values, creating serious problems due to its harmful effects on health. Planting trees and shrubs as air filters is a way to improve air quality in these areas. However,further knowledge on species effectiveness in air purification is essential This study compared four species of tree (Acer campestre L, Fraxinus excelsior L, Platanus x hispanica Mill. ex Muenchh. 'Acerifolia', Tilia cordata Mill.), three species of shrub (Forsythia x intermedia Zabel, Physocarpus opulifolius (L.) Maxim., Spiraea japonica L.), and one climber species (Hedera helix L) that are commonly cultivated along streets in Poland to capture fine, coarse and larger particles from air. Separate gravimetric analyses were performed to quantify PM deposited on surfaces and trapped in waxes. Significant differences were found between the plant species tested. The distribution of different particle size fractions differed between and within species and also between leaf surfaces and in waxes.

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Particulate matter (PM) as an air pollutant can be harmful for human health through allergic, mutagenic and carcinogenic effects. Although the main focus is on decreasing air pollution, after PM has been emitted to the atmosphere, one ofthe realistic options to decrease it's concentrations in urbanized area will be phytoremediation. This study compared the capacity to capture PM from air of seven tree species commonly cultivated in Poland (Catalpa bignonioides Walter, Corylus colurna L., Fraxinus pennsylvanica Marsh., Ginkgo biloba L., Platanus x hispanica Mill. ex Muenchh., Quercus rubra L., Tilia tomentosa Moench 'Brabant') and six shrub species (Acer tataricum subsp, ginnala (Maxim.) Wesm., Sambucus nigra L., Sorbaria sorbifolia (L) A.Br., Spiraea japonica L.f., Syringe meyeri C.K. Schneid. 'Palibin', Viburnum lantana L.). Significant differences were found between species in mass of total PM accumulation for two PM categories and three size fractions determined and in amount of waxes. A positive correlation was found between in-wax PM of diameter 2.5-10 microm and amount of waxes, but not between amount of waxes and amount of total PM or of any size fraction.

Since air pollution has been linked to a plethora of human health problems, strategies to improve air quality are indispensable. Despite the complexity in composition of air pollution, phytoremediation was shown to be effective in cleaning air. Plants are known to scavenge significant amounts of air pollutants on their aboveground plant parts. Leaf fall and runoff lead to transfer of (part of) the adsorbed pollutants to the soil and rhizosphere below. After uptake in the roots and leaves, plants can metabolize, sequestrate and/or excrete air pollutants. In addition, plant-associated microorganisms play an important role by degrading, detoxifying or sequestrating the pollutants and by promoting plant growth. In this review, an overview of the available knowledge about the role and potential of plant–microbe interactions to improve indoor and outdoor air quality is provided. Most importantly, common air pollutants (particulate matter, volatile organic compounds and inorganic air pollutants) and their toxicity are described. For each of these pollutant types, a concise overview of the specific contributions of the plant and its microbiome is presented. To conclude, the state of the art and its related future challenges are presented.

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