The City and the Sky
Matthias Beekmann of the CNRS, France’s largest scientific research group, believes that traffic exhaust fumes are the greatest man-made influence polluting the air within Paris.
With a population of more than 10 million, Paris belongs to a group of 20 so-called “megacities”. The city is now at the centre of a European research project that is investigating the effect street pollution is having on the climate and atmosphere. However, the aim is not just to trace the pollution and its impacts on the urban scale, but rather to see how one city can have an impact on a continental or even global scale.
Frank Drewnick, from the Max Planck Institute for Chemistry, and his team can use their mobile lab to take measurements for air composition, particles and gases while driving about. By an isolated field on Paris�s north eastern edge the team can take untainted readings of background air pollution arriving from other regions of Europe. They can identify the Benelux countries as being a close-by source of emissions, while a large part of the pollution appears to be sulphur dioxide from the coal-fired power plants of eastern Europe.
Matthias Beekmann and the project coordinator Alexander Baklanov collect pollution data during the winter. This will be compared with similar data collected in the last summer. Their instruments, situated on a roof in central Paris, run around the clock gathering data concerning organic aerosols that can pose a health risk - organic aerosols being very fine particles, or dust, composed of elements like carbon, oxygen and hydrogen.
An Irish team from the University College Cork is also involved in the field work, using a spectrometer to detect particles from cars, wood fires and heating systems. With a strong westerly wind they also find particles of sea salt from the Atlantic Ocean. This time the scale of the measurements is more local. The air quality is at its best between 3-4am, while the pollution will jump dramatically at 7am and 5pm or 6pm, reflecting the traffic rush.
Having been emitted by a car or factory, a particle or gas might remain in the air for several days, or perhaps hundreds of years. Matthias Beekmann remarks that a particle could be carried up into the atmosphere, from where it can travel hundreds or even thousands of kilometres.
Research by Bill Collins, a climate expert from UK's Met Office in south-west England, is dealing with air quality and climate on a global scale. Plots of the pollutant called ozone from the cities New York, Boston and Washington shows how the strong westerly winds over the north Atlantic carries the pollutant across into the UK and western Europe.
Another point of interest for Bill Collins is the effect that sulphur dioxide can have on climate. This compound reacts quickly in the atmosphere to create sulphate aerosols, which reflects sunlight back into space and ultimately has a cooling effect on the atmosphere. Bill Collins wants to find out to what extend this short term effect counter-acts the long lived greenhouse effect caused by carbon dioxide.
Urban pollution has been studied before in the past. Now this research project is broadening the scale from the street to the megacity, the regional scale and on to the global scale.