Résumé
Because air quality is nowadays a major societal issue, assessing the effectiveness of urban greens for mitigating the fine particulate matter (Fp) air pollution in urban and peri-urban areas is a very dynamic research topic in the scientific literature that is increasingly making headlines in public policies. To this end, we are questioning here if urban plants do really represent a sufficiently effective sink for Fp. So far no consensus was made in the efficiency of plants to trap Fp. Regarding the numerous studies based on CFD modeling, some of them show an effectiveness extraction by the foliage with dry deposition processes, whereas other emphasize the negative role of hedges for atmospheric dispersion of pollutants and therefore increase pollution at the level of emission sources such as traffic. Unfortunately, these models do not necessarily take into account input parameters very close to the real situations such as: Fp concentration and size, prevailing wind, surface structures, epicuticular wax, to mention just a few examples. A first step toward the understanding of the impact of urban greens on air quality is the precise determination of the deposition velocity (Vd) parameter. This latter is specific for each specie and it is most of the time out-of-calibration in modeling-based studies by taking standard values. In that perspective, we built a wind tunnel to perform analogical experiments on different Mediterranean species. All parameters are controlled: the wind speed, the nature and the injection time of pollutants (Diesel exhausts, dust). We can provide the Fp concentrations upwind and downwind of natural reconstituted hedges with six optical particle counters. Beforehand, the hedge resistance (%) or the leaf area index (LAI) have been estimated for each studied specie to allow comparability between plant removal potentials. The interest would ultimately check whether it would be possible to precisely determine for real cases the dust removal rate by urban greens.