‘Only a third’ of traffic pollution caused by exhaust

Study suggests majority of particulate matter PM10 emissions comes from sources such as brake and road surface wear

Vehicle exhausts are responsible for only a third of traffic pollution, according to research led by the University of Hertfordshire.

The sampling equipment used to measure PM10 emissions in the Hatfield Tunnel, Hertfordshire (photo: Samantha Lawrence)

The study, published in the journal Atmospheric Environment, says nearly half of the air pollution from road traffic is down to non-exhaust sources such as brake-wear, road surface-wear, and particles launched into the air from the road by passing vehicles.

As a result, Professor Ranjeet Sokhi of the University of Hertfordshire, who led the study, is calling for greater control of non-exhaust pollution.

He said: “In terms of mass, non-exhaust sources can be more important than exhaust fumes, but legislative control has focussed on exhaust emissions.

“As exhaust regulations become stricter, non-exhaust sources become proportionately more important. Continuing to control exhaust emissions alone may not be enough to achieve legal air-quality standards.”

Research

The research team took air samples from the Hatfield Tunnel on the A1 (M) in Hertfordshire, focussing on particulate matter PM10, which is linked with long-term health problems such as heart disease.

“Other studies have looked at non-exhaust components of PM10, but those have mostly been done in open-air locations,” said Professor Sokhi. “We wanted to look at them in a more controlled environment, where the influence of the weather could be significantly reduced.”

“The Hatfield tunnel provided an ideal laboratory; you are protected from the elements and it confines the airborne particles, making it easier to collect sufficient material for analysis.”

Back in the laboratory, samples were separated out into their chemical components. By analysing these, scientists were able to calculate where up to 82% of the pollution in the samples had come from.

Petrol and diesel exhausts are responsible for only 33% of the particles. 27% are thrown into the air from the road by vehicles, while brake and road surface wear account for 11% each.

Road traffic is thought to be the most important source of air pollution in the UK. As well as the health effects, poor air quality is estimated to cost the UK economy up to £16 billion every year.

London

In 2010, Transport for London began spraying a calcite glue solution onto roads in an attempt to tackle emissions by sticking pollution to the road surface.

Launching the programme, Mayor Boris Johnson said it was “a wonderful contraption that tackles air quality head on.” But a recent study by scientists at King’s College London has questioned the effectiveness of the scheme.

Commenting on this, Professor Sokhi said: “It is important to recognise that controlling non-exhaust emissions is more difficult; a number of different approaches might be needed.

“Where possible, new technologies and other pollution reduction options should be investigated. These might include, for example, new materials for tyres and brakes and different methods for constructing road surfaces.”

The study ‘Source apportionment of traffic emissions of particulate matter using tunnel measurements’, was part of a PhD project undertaken by Samantha Lawrence.

Funded by the Natural Environment Research Council (NERC) and the British Oxygen Company (BOC), the study was published in the journal Atmospheric Environment and is available online.