Mancunian mornings see air quality plummet

While Manchester long ago shed its image as a polluted industrial city, early morning commuters are still having to deal with a less-than-healthy dose of pollution, according to a report published by the city's university this week.

As part of the wider CityFlux project, which measures and analyses air quality in cities throughout the EU, a team from the Centre of Academic Studies at the University of Manchester took samples along some of the city’s most congested streets.

They found that commuters inhale their biggest daily dose of harmful traffic fumes during the morning rush hour.

The analysis is currently at an early stage but should provide valuable data for other cities and also offer an insight into why pollutants should be at their peak early in the day, rather than during the evening rush hour.

The number crunching of 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.

Initial results, however, 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.

“Emissions like carbon dioxide affect the climate globally but other emissions are harmful to human health,” said the research team’s Dr Ian 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.

“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,” said Dr Longley.

“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.”

Sam Bond

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