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AVOID TRAFFIC POLLUTION BY CROSSING THE STREET Engineering and Physical Sciences Research Council I Case study 22
In built-up urban areas, pedestrians could reduce the amount of traffic pollution they breathe in simply by crossing the street, according to joint EPSRC/NERC-funded research. Fresher air can be found on the windward side of the street and in roads running parallel to a main road. The research has shown that urban air pollution levels change dramatically within small areas. Wind patterns, surrounding buildings and the location of traffic queues all influence how pollution accumulates.
≥4x lower carbon monoxide levels in side-streets parallel to main roads.
≥CO levels on the sheltered side of a street can be up to three times higher than those on the windward side.
IMPACT ON CYCLISTS AND PEDESTRIANS > Rethinking regular routes by travelling even just one road away from a main thoroughfare could massively reduce people’s exposure to pollution. > Pollution exposure would also fall if cycle routes were placed away from areas with heavy traffic. > New models that account for the influence of weather and street geometries on pollution would provide more accurate pictures of pollution dispersion. Monitoring hotspots The research team based at the University of Leeds and led by Professor Alison Tomlin, monitored traffic flow and carbon monoxide (CO) levels over eight weeks at the intersection between Marylebone Road and Gloucester Place in West London, one of the busiest junctions in the UK. They found that CO levels were highly variable over remarkably short distances. “As you’d expect, the junction itself showed high levels caused by queuing traffic,” reports Professor Tomlin, “but, with some wind patterns, these hotspots moved further down the street. However, the leeward [sheltered] side of the street had consistently higher concentrations of carbon monoxide than the windward side.” The same trends are likely to occur with other traffic-related pollutants, such as ultrafine particles and nitrogen dioxide.
The researchers also found that CO levels were up to four times lower in parallel side streets than in the main road. “Most people would expect pollution levels to be slightly lower away from the main body of traffic, but our figures show a very significant difference,” she says. “Pollution can be trapped within the street where it is emitted by recirculating winds. Even if it escapes above roof-tops, it doesn’t tend to be mixed back into neighbouring streets very strongly.” Currently, every city has a number of sites monitoring pollution levels to ensure compliance with EU standards. Monitoring stations tend to be sited in expected pollution hotspots, but this research has shown that hotspots move depending on meteorological conditions, particularly wind direction. Professor Tomlin: “We need to develop models which take these factors into account, so that the data from monitoring sites can be accurately analysed to provide a true reflection of air quality across the whole of an urban area.” For more information about EPSRC and the impact it is making visit www.epsrc.ac.uk
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Engineering and Physical Sciences Research Council
CARBON MONOXIDE LEVELS
FOUR TIMES LOWER IN SIDE STREETS
www.epsrc.ac.uk