Hedge planting can halve traffic pollution reaching children

A new University of Surrey study has found that simply planting a hedge in front of a park can halve the amount of traffic pollution that reaches children as they play.

Experts from Surrey’s Global Centre for Clean Air Research (GCARE) conducted a five-month continuous experiment, measuring traffic pollutants with the use of emerging pollution sensing technology behind and in front of a hedge that shielded a children’s park in Guildford. The aim of the study was to measure any discernible difference in pollution reduction during the vegetation cycle of a Beech hedge – from dormancy to green-up to maturity.  

The results showed that a drop in pollution concentration levels behind the hedge was dominated by three factors – the weather, public holidays, and the stage of the hedge’s life cycle. The researchers reported reductions of more than 50 per cent of the particulate matter after the hedge’s green-up stage in late April. Experts believe that this could be because the density of the hedge or the stickiness of the leaves had a sizable impact on particle pollutants passing through it. However, the results also revealed smaller reductions for gaseous pollutants including carbon monoxide and nitrogen dioxide, and that wind direction had little impact on the concentration levels.

Professor Prashant Kumar, founding Director of GCARE at the University of Surrey, said: “We believe our study is the first to look at how a hedge affects the pollution from traffic – assessing the influence of the vegetation lifecycle, wind direction and other variables. The reduction in pollution after the green-up stage gives valuable information regarding where to install green infrastructure across our communities.

“This study has not only produced unique evidence and support for our advocacy to install hedges and other forms of green infrastructure (where appropriate) along busy roadsides to protect schools, playgrounds and pedestrians/cyclists from air pollution exposure; it has also provided a clear indication that evergreen species should be favoured for barriers against air pollution to exploit their year-round performance.”