Modelling air pollution abatement in deep street canyons by means of air scrubbers

Deep street canyons are characterized by weak ventilation and recirculation of air. In such environment, the exposure to particulate matter and other air pollutants is enhanced, with a consequent worsening of both safety and health. The main solution adopted by the international community is aimed at the reduction of the emissions. In this theoretical study, we test a new solution: the removal of air pollutants close to their sources by a network of Air Pollution Abatement (APA) devices. The APA technology depletes gaseous and particulate air pollutants by a portable and low-consuming scrubbing system, that mimics the processes of wet and dry deposition. We estimate the potential pollutant abatement efficacy of a single absorber by Computational Fluid Dynamics (CFD) method. The presence of the scrubber effectively creates an additional sink at the bottom of the canyon, accelerating its cleaning process by up to 70%, when an almost perfect scrubber (90% efficiency) is simulated. The efficacy of absorber is not proportional to its internal abatement efficiency, but it increases rapidly at low efficiencies, then tends to saturate. In the particular configuration of the canyon we choose (aspect ratio of 3) the upwind corner is the most favourable for the absorber application. In the downwind corner the maximum pollutant abatement is -24%, while in the upwind corner the maximum abatement is twice as much at -51%. The efficacy of the absorber increases much faster at low efficiencies: at 25% efficiency, the abatement is already about half that obtained with the 90% efficiency. These first results, suggest strategies for the real-world application of a network of absorbers, and motivates further theoretical study to better characterize the details of the air flow inside and around the absorber.