A new study has found that diesel exhaust fumes have a considerable effect on people suffering from asthma.
The study looked at the effects that diesel exhaust fumes had on 60 people with mild and moderate asthma, who walked along the western end of busy Oxford Street in London, where only diesel- powered taxis and buses are permitted.
The researchers, from Imperial College London, the New Jersey School of Public Health, and other international institutions, found that both during and after a two hour walk along Oxford Street, the test volunteers experienced increased asthmatic symptoms, reduced lung capacity, and inflammation in the lungs.
It took a few hours for these to return to their normal levels.
The same volunteers were then made to walk for two-hour in the traffic-free, western part of London's Hyde Park. The researchers confirmed their results when they found that the volunteers experienced some of the same problems but to a far lesser degree.
This is the first time that an investigation in a real-life setting, has been set up outside of a laboratory, to study whether traffic fumes increases the symptoms of asthma.
Two thirds of people with asthma believe this to be the case, according to Asthma UK.
The researchers believe that diesel exhausts cause problems for people with asthma because of the particulates - minute particles of dust, dirt, soot and smoke - which they release into the air.
Particulates come in different sizes but those of less than 2.5 microns, and the tiniest "ultra fine" ones, can interfere with the respiratory system, because they are so tiny that they can be inhaled deeply into the lungs. Ultra fine particles can also be absorbed in the blood, which may have damaging effects.
The researchers found a correlation between the level of diesel exhaust particulates at street level during the two walks and reductions in lung capacity and increases in lung inflammation in the volunteers.
Diesel engines emit lower concentrations of carbon monoxide and carbon dioxide than petrol engines, but they can generate over 100 times more particles per distance travelled than similar sized petrol engines, and are major contributors to particulate pollution in the atmosphere. Previous studies have shown that in urban environments, almost 90 per cent of traffic-generated particulate matter is from diesel exhausts.
"Our study illustrates the need to reduce pollution in order to protect people's health," said professor Fan Chung, from the National Heart and Lung Institute at Imperial College London and one of the authors of the study.
"For the first time we are able to measure exactly what's happening inside the lungs of people with asthma when they spend only a couple of hours strolling in a real-life polluted area. By observing the effect of pollutant diesel particles on the lung surfaces, we can confirm that such an exposure causes inflammation in the lungs of asthmatic people," he said.
The researchers measured lung function; symptoms; exhaled nitric oxide and condensate from the breath; bronchial reactivity; sputum and blood. They took measurements before, during and after the volunteers' walks.
The study has been published on 6 December in the New England Journal of Medicine.