Forest filter effect : role of leaves in capturing/releasing air particulate matter and its associated PAHs

Terzaghi, Elisa and Wild, Edward and Zacchello, Gabriele and Cerabolini, Bruno E.L. and Jones, Kevin C. and Di Guardo, Antonio (2013) Forest filter effect : role of leaves in capturing/releasing air particulate matter and its associated PAHs. Atmospheric Environment, 74. pp. 378-384. ISSN 1352-2310

Abstract

Plants play a key role in removing particulate matter and their associated Semi-volatile Organic Compounds (SVOCs) from the atmosphere. Understanding the processes involved in particle capture by vegetation is essential to understand the interactions between SVOCs, particles and plants. In the present study Two Photon Excitation Microscopy (TPEM) was used to visualise particle matter uptake and encapsulation, together with its distribution on leaf/needle surface of different broadleaf (cornel and maple) and conifer species (stone pine). Phenanthrene accumulation, the number of particles associated with this compound and its migration from particles into the leaf cuticle was also identified and quantified. Species-specific deposition velocities were estimated to model temporal PM10 leaf/needle accumulation and to investigate the role of Planet Boundary Layer (PBL) height variation in influencing PM10 flux to plants. Particles at the leaf/needle surface were visualised to range in size from 0.2 to 70.4 μm, but cuticular encapsulation was negligible for particles larger than 10.6 μm, which were removed by a washing procedure. Phenanthrene concentration varied between ≈5 and ≈10 ng g−1 dw according to plant species and between ≈10 and ≈200 ng g−1 dw depending on needle age; this compound was visualized to migrate from particles into the adjacent leaf cuticle. Species-specific deposition velocity range between 0.57 and 1.28 m h−1 and preliminary simulations showed that the diel variability of PBL structure influenced the temporal PM10 flux and leaf/needle concentration, e.g. during daytime hours characterized by high PBL height, PM10 accumulated on cornel leaves was about 65% lower than the amount accumulated during night time. The capability of vegetation to capture particles from the atmosphere, retain, encapsulate them into the cuticle and release them to soil and/or lower biomass, highlighted the value of vegetation in removing pollutants from the atmosphere and influencing their environmental fate.