London - Plant a hedge, tree/hedge combination or a "living wall". A study by the University of Surrey found this significantly reduced pollutants in busy, wide streets.
"Planting a hedge outside your home can filter out traffic fumes at the level of exhaust pipes," says Professor Prashant Kumar, chair in air quality and health at the University who led the research, published in the journal Atmospheric Environment earlier this year.
Professor Kumar said planting "hedges only" showed greater reductions in pollutants, including PM2.5, than either planting a hedge and trees in combination or trees alone.
But where there are tall buildings on either side, trees alone only seemed to increase PM2.5 underneath. "Trees may trap pollutants and restrict natural movements of the flow - so in those narrow 'street canyon' scenarios, it’s better to build green living walls [walls planted with vegetation] and hedges instead," says Professor Kumar.
A study published in the Journal of Living Architecture by researchers in Sydney last year found that such "bio" walls significantly reduced PM2.5 levels in an indoor environment.