Study focuses on airborne particles

Urban air quality is being investigated by environmental health researchers at Birmingham University, who aim to gain a better knowledge of the sources and concentrations of airborne particles.

The team hopes its three-year research programme will lead to further collaborative work that will better quantify the effects of airborne particles on human health.

Roy Harrison, leader of the research programme, said his team will use air samples taken from roadside and non-roadside sites mostly in Birmingham and London.

The group will determine the size and chemical composition of the particles in the samples — allowing them to infer their source and learn about their behaviour in the atmosphere.

He said: ‘We measure personal exposure by attaching air samplers to people and measuring what is collected.

‘Most sampling work involves sucking air through filters that retain the particles. We do, however, have other sampling devices, such as cascade impactors, which separate particles on the basis of their size and hence inertial properties.’

Harrison added that the Birmingham laboratory is also equipped with an instrument called an aerosol time-of-flight mass spectrometer, which sucks in air and creates a stream of particles from the inlet air.

He said: ‘It then determines the size of each individual particle and then blasts it with a laser. This process forms ions from the particles, which are then characterised in positive and negative ion mass spectrometers. 

‘From this information we can reconstruct the chemistry of the original particle, which tells us a lot about its source.’

Harrison described fine particles found in the air as either primary — meaning it is directly emitted to the atmosphere — or secondary — meaning it is formed within the atmosphere.

He said: ‘The main source of primary particles in the air of London is road traffic, although there are also particles from many other sources, including vegetation.

‘The main components of secondary particles are sulphates from oxidation of sulphur dioxide, nitrates from oxidation of NOx and secondary organic compounds from oxidation of volatile organic compounds.’

Harrison said the main contributors of more coarse particles are sea spray, which penetrates many hundreds of miles inland, and non-exhaust particles from road traffic. 

He added: ‘Such non-exhaust particles come from tyre and brake wear and suspension from the road surface in the turbulent wake of a vehicle.’

Harrison said airborne particles can impact human health differently depending on their size.

Very large particles tend to deposit in the nose and mouth, while fine particles reach the deep lung. Intermediate-size particles mostly deposit in the conducting airways between the throat and the deep lung.

He added that current research indicates that particles of all sizes have adverse health effects, but that the capacity of the fine particles to deposit in the deep lung is likely to give them greater overall toxicity.

Harrison said a better understanding of the sources of airborne particles could eventually lead to the development of more effective and cost-effective abatement measures in polluted areas, which in the long term could lead to improved air quality.