Early findings from a new urban pollution study suggest that commuters in Manchester inhale their biggest daily dose of harmful traffic fumes during the morning rush hour.
A team from the Centre for Atmospheric Studies at the University of Manchester took measurements in 2005 and 2006 along some of the city's busiest routes.
The work forms part of the wider CityFlux project, which has involved sophisticated air sampling in major cities in England and Europe over the last two years.
Analysis of all the data collected during the study is continuing, and the full results are not expected to be published until at least the end of 2007.
But initial results appear to show that harmful particles produced by vehicles stay trapped near to ground level during the morning rush hour.
Researchers have observed that in the middle of the day, warm bubbles of air rise up from the city streets. This warm air lifts particles from vehicle exhausts away from the built environment. But earlier in the morning the air is too cold to rise and the particles remain trapped at street level.
The research team hopes the mass of data they have collected during their study will give them a better picture of the type and level of harmful particles city dwellers are being exposed to.
They also hope to discover how and when particles are exported away from Manchester, what factors affect their distribution, and if chemical and physical reactions in the atmosphere affect the toxicity of the particles.
Lead researcher Dr Ian Longley from the School of Earth, Atmospheric and Environmental Sciences will present some initial findings during a lecture to the North West branch of the Royal Meteorological Society tonight (Tuesday 28 November 2006).
"Emissions like carbon dioxide affect the climate globally but other emissions are harmful to human health," said Dr Longley. "They include gases like nitrogen dioxide but also microscopic particles."
"These particles can be things like fine oily mists from vehicle exhausts and flecks of dust from tyres and brakes. Studies have shown that they have the greatest effect on our health.
"Analysis of the data is at an early stage and it's going to be at least another year before we can present comprehensive findings. What we hope to end up with is a picture of the type and level of vehicle-related emissions Manchester is contributing to the atmosphere.
"The effect of particles on our climate, both locally and globally, is poorly understood compared to the effect of greenhouse gases."
Weather conditions such as temperature and wind are known to have an effect on pollution levels, and so in addition to taking air samples at street level, the Manchester team set up equipment on rooftops to sample air as it rose and dispersed out of the city centre.
During his talk, Dr Longley will respond to recent local reports that pollution levels in the Manchester have dropped.
"While it's true that pollution levels are decreasing in the city, much of this can be attributed to the fact people continue to buy new vehicles, which are being made more environmentally friendly by the manufacturers.
"We must also be careful when looking at figures taken in 2003 because that was a very unusual year. The wind was much lighter than you would normally expect and it came largely from central Europe rather than the Atlantic. This led to unusually high levels of air pollution being recorded for that year but it could happen again any year in the future.
"Recent reports have also suggested that the level of sulphur dioxide has dropped in Manchester during this decade. That is true but the amount in the atmosphere of UK cities was negligible to start with, so you have to view it in context.
"What we really need to be looking at is the concentration of particles in the air, which has been dropping by about one per cent per year. That's an improvement but not a plummet by any stretch of the imagination -- and the improvement may now have stopped."
The CityFlux project has been run in conjunction with the Centre for Ecology and Hydrology (CEH) in Edinburgh.
During the two studies in Manchester, measuring devices were positioned on buildings at both ends of Deansgate, near the BBC on Oxford Road and on top of the landmark Portland Tower. Measurements took place between June and July 2005 and during May 2006.
Researchers from the Centre for Atmospheric Science have plans to link up with medical researchers to study the effects particles from vehicles are having on the health of Manchester's people.
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