Planting roadside hedges, rather than just relying on trees, can most effectively reduce pollution exposure from cars in near-road environments, according to scientists including one of Indian origin. Researchers from University of Surrey in the UK looked at how three types of road-side green infrastructure -- trees, hedges, and a combination of trees with hedges and shrubs -- affected the concentration levels of air pollution. The study, published in the journal Atmospheric Environment, used six roadside locations in the UK, as test sites where the green infrastructure was between one to two metres away from the road.


The researchers found that roadsides that only had hedges were the most effective at reducing pollution exposure, cutting black carbon by up to 63 per cent. Ultrafine and sub-micron particles followed this reduction trend, with fine particles (less than 2.5 micrometres in diameter) showing the least reduction among all the measured pollutants.


The maximum reduction in concentrations was observed when the winds were parallel to the road due to a sweeping effect, followed by winds across the road. The elemental composition of particles indicated an appreciable reduction in harmful heavy metals originating from traffic behind the vegetation.


The hedges only -- and a combination of hedges and trees -- emerged as the most effective green infrastructure in improving air quality behind them under different wind directions. -- PTI