The findings show that pollution tends to build up on the leeward side of the street (the sheltered side) in relation to the wind’s direction at roof-top level. By simply changing their route, pedestrians and cyclists could decrease their intake of pollution. The team monitored traffic flow and carbon monoxide levels at the intersection between Marylebone Road and Gloucester Place in West London over a period of two months. They found that carbon monoxide levels were up to four times lower in parallel side streets compared to the main road. Similar patterns would be expected for other pollutants such as ultrafine particles and nitrogen dioxide.

“Most people would expect pollution levels to be slightly lower away from the many body of traffic, but our figures show a very significant difference,” said Professor Tomlin who led the research. “Pollution can be trapped within the street where it is emitted by recirculating winds. If it escapes to above roof-top level, it doesn’t tend to be mixed back into neighbouring streets very strongly.”

The research is published in Atmospheric Environment and is funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Natural Environmental Research Council (NERC).

By Leila Sattary