Research led by Prof Alison Tomlin from Leeds University’s faculty of engineering has shown that air pollution levels change dramatically within small geographical areas.
More specifically, the changes are dependent on wind patterns, the location of traffic queues and the position and shapes of the surrounding buildings.
The findings also showed that pollution hotspots tend to accumulate on the leeward, or sheltered side of streets, in relation to the wind’s direction at roof-top level. They also revealed that that carbon monoxide levels were up to four times lower in parallel side streets, compared to main roads.
The team monitored traffic flow and carbon monoxide (CO) levels over an eight-week period at one of the busiest junctions in the UK – the intersection between Marylebone Road and Gloucester Place in west London.
‘CO levels were highly variable over remarkably short distances. As you’d expect, the junction itself showed high levels caused by queuing traffic, but with some wind patterns these hotspots moved further down the street.
‘However, the leeward side of the street had consistently higher concentrations of carbon monoxide than the windward side. The same trends would be expected for other traffic-related pollutants, such as ultrafine particles and nitrogen dioxide,’ said Tomlin.
The research has significance for local authorities and other bodies monitoring air-quality levels in urban areas. Currently, every city has a number of sites monitoring pollution levels to ensure compliance with EU standards, but Tomlin says these may need to be examined in relation to the other factors identified by the research to ensure an accurate spatial picture.
‘Monitoring stations tend to be sited in what are expected to be pollution hotspots, but our research has shown that hotspots move depending on meteorological conditions, particularly wind direction,’ said Prof 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.’