Research gives new meaning to ‘green’ cross code

The research, led by Professor of Environmental Modelling Alison Tomlin from Leeds' Faculty of Engineering, has shown that air pollution levels change dramatically within small geographical areas dependent on wind patterns, the location of traffic queues and the position and shapes of the surrounding buildings.

The findings showed that pollution hotspots tend to accumulate on the leeward side of the street, (the sheltered side) 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 the main road.

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," says
Professor Tomlin. "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."

"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. If it escapes to above roof-top level, it doesn't tend to be mixed back into neighbouring streets very strongly. It would be worth cyclists and pedestrians rethinking their regular routes, as they can massively reduce their pollution exposure by moving just one street away from the main traffic thoroughfares."

The research also 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 Professor Tomlin says these may need to be looked at 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," says 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."

The research is published in the latest issue of Atmospheric Environment and has been funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Natural Environment Research Council (NERC).

Professor Tomlin is available for interview.

Further information from:
Jo Kelly, Campuspr Ltd, tel 0113 258 9880, mob: 07980 267756, email jokelly@campuspr.co.uk
or
Simon Jenkins, University of Leeds press office, tel 0113 343 8299, email s.jenkins@leeds.ac.uk 

Notes to editors:

1. The study was carried out as part of the DAPPLE (Dispersion of Air Pollution & Penetration into the Local Environment) project, which looks to provide a better understanding of the physical processes affecting street and neighbourhood scale flows of air, traffic and people, and their corresponding interactions with the dispersion of pollutants. DAPPLE (www.dapple.org.uk) is funded by the Engineering and Physical Science Research Council. The project consortium includes the Universities of Bristol, Cambridge, Leeds, Reading, Surrey and Imperial College London.

2. The Faculty of Engineering at the University of Leeds is ranked 7th* in the UK for the quality of its research (2008 Research Assessment Exercise); an impressive 75% of the Faculty's research activity rated as internationally excellent or world leading. It includes the Schools of Computing, Mechanical Engineering, Civil Engineering, Electronic and Electrical Engineering and Process, Environmental and Materials Engineering. www.engineering.leeds.ac.uk/

3. The 2008 Research Assessment Exercise showed the University of Leeds to be the UK's eighth biggest research powerhouse. The University is one of the largest higher education institutions in the UK and a member of the Russell Group of research-intensive universities. The University's vision is to secure a place among the world's top 50 by 2015. ./

4. The Engineering and Physical Sciences Research Council (EPSRC) is the UK's main agency for funding research in engineering and the physical sciences. The EPSRC invests more than £800 million a year in research and postgraduate training to tackle the challenges of the 21st Century. www.epsrc.ac.uk

5. The Natural Environment Research Council (NERC) funds world-class science, in universities and its own research centres, that increases knowledge and understanding of the natural world. It is tackling major environmental issues such as climate change, biodiversity and natural hazards. NERC receives around £400 million a year from the government's science budget, which is used to provide independent research and training in the environmental sciences. www.nerc.ac.uk