We know trees are good at absorbing CO2 but our town planners should plant hedges near roads too, say scientists. Researchers from Surrey University's Global Centre for Clean Air Research (GCARE) looked at how three types of road-side planting – trees, hedges, and a combination of trees with hedges and shrubs – affected concentration levels of air pollution. The study used six roadside locations in Guildford as test sites, where the green infrastructure was between 1-2 metres away from the road.