Beyond leaf traits: context dependent particulate matter accumulation across outdoor, indoor and active green walls

Source abstract

Improving air quality in cities is a social challenge related to human health. Nature-based Solutions (NbS) have been shown to effectively remove air pollutants such as particulate matter (PM) from the atmosphere, with the PM removal capacity appearing to be largely dependent on the species morphological traits. However, other factors, such as chemical interactions and atmospheric and microclimatic parameters, can also affect the PM removal efficiency. To test this hypothesis, we compared the PM accumulation in five plant species with different morphological traits (Chlorophytum comosum, Hedera helix, Monstera deliciosa, Nephrolepis exaltata, Tradescantia zebrina) upon their installation in three different green walls (GWs) located outdoor (OGW), indoor (IGW), and in a closed chamber with a forced ventilation (active green wall - AGW). Leaf surfaces were analysed through Scanning Electron Microscopy (SEM) to characterise their micromorphological features associated with PM accumulation. The deposited PM load was estimated by combining gravimetric and conductimetric approaches, and the PM chemical composition was assessed by Microwave Plasma Atomic Emission Spectroscopy (MP-AES). Statistical differences between species in PM capture were observed. Species exhibited distinct PM accumulation patterns across the green walls, with notable species-specific affinities for certain potentially toxic elements, demonstrating that PM retention is not driven by leaf morphology alone. Among species, Chlorophytum comosum best performed in OGW and IGW while Tradescantia zebrina in AGW. In AGW, the presence of the plants reduced PM concentration by approximately 50% and high humidity enhanced wet deposition and increased fine-particle capture, confirming the relevance of microclimatic factors for air-purification.