Predicting the removal of atmospheric particles by vegetation with a dynamic multimedia model

It is well known that vegetation is capable of capturing contaminants from air. In particular, plant leaves can act as a biological filter and as a sink for airborne particles and their associated Semi Volatile Organic Compounds (SVOCs) such as Polycyclic Aromatic Hydrocarbons (PAHs), influencing their environmental fate. In order to assess the filtration performance of plants with respect to atmospheric particulate matter (PM) and their associated SVOCs, deposition on vegetation has recently been investigated by a number of different methods (field, laboratory studies as well as modelling approaches). Some authors studied the particulate matter uptake and retention capacity of different plant species, showing that some plant type are much more efficient than other at collecting particulate matter and PAHs contained upon them. Other researches were focused on measuring particle deposition velocities not only for specific tree species but also at different wind speeds. Furthermore different predictive approaches were developed to evaluate PM uptake by trees in urban areas and to estimate dry particle matter deposition on leaf surfaces using species-specific deposition velocity. Nevertheless, the existing multimedia fate models do not generally account for PM mass balance in predicting PM deposition to vegetation and the corresponding chemical flux. In the present study we used a dynamic multimedia fate model (SoilPlusVeg), which incorporates a vegetation compartment, to calculate leaf particle-bound PAHs uptake from air. In this model, formulated in terms of fugacity, the vegetation compartment can be composed by a mono- or multi- specific forest canopy, which interacts with dynamic air and the soil compartments. The model, which incorporates some forest structural parameters such as specific leaf area (SLA) and leaf area index (LAI), was modified to account for some of recent findings concerning the particulate matter uptake by vegetation. Simulations were performed for some high molecular weight PAHs, as they exist predominantly in the particulate phase, for a multi-specific semi-urban wood located in Como. The results were compared to data measured in air, deposition and vegetation in the same location.