Effective reduction of roadside air pollution with botanical biofiltration

Highlights: • Botanical biofiltration of NO₂, O₃ and PM_2.5 was achieved at roadside environments. • NO₂ was removed most efficiently, with a single pass removal efficiency of 71.5%. • Pollutant clean air delivery rates of 40–121 m³/h per 1 m² plenum were achieved. • All pollutant removal rates were positively correlated with ambient concentrations. Currently no sustainable, economical and scalable systems have been developed for the direct removal of roadside air pollutants at their source. Here we present a simple and effective air filtering technology: botanical biofiltration, and the first field assessment of three different botanical biofilter designs for the filtration of traffic associated air pollutants – NO₂, O₃ and PM_2.5 – from roadside ambient air in Sydney, Australia. Over two six month research campaigns, we show that all of the tested systems filtered NO₂, O₃ and PM_2.5 with average single pass removal efficiencies of up to 71.5%, 28.1% and 22.1% respectively. Clean air delivery rates of up to 121 m³/h, 50 m³/h and 40 m³/h per m² of active green wall biofilter were achieved for the three pollutants respectively, with pollutant removal efficiency positively correlated with their ambient concentrations. We propose that large scale field trials of this technology are warranted to promote sustainable urban development and improved public health outcomes.