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Keeping a close watch on urban pollution


For nearly fifteen years now, a European directive has governed the way urban air pollution is controlled. The research conducted by the JRC has facilitated the development of innovative air quality control technologies which are both simple and inexpensive.

There isn't a city in the world which has managed to escape the threat of air pollution - mainly due to the growth in road traffic. In an effort to bring this pollution under control, since the early 1980s various European directives have required Member States to report to the European Commission, firstly, on the levels of various pollutants present in the urban environment - including nitrogen dioxide (NO2) - and secondly, on the measures taken to reduce these levels. Every EU country has thus been instructed to establish a network of air control stations in its cities.

The main problem with this is that establishing such networks is complicated and expensive, particularly as, until recently, there was no way of knowing where best to site these control points. This problem has now been solved, however, thanks to an ingenious technology developed by the European Reference Laboratory for Air Pollution (ERLAP*), based at the European Commission's Joint Research Centre in Ispra, Italy.

Testing the atmosphere

Small diffusion tubes (7 cm long, 1 cm in diameter), are positioned at various strategic urban locations, on objects situated in the open air - e.g. lamp posts. Their function is to absorb the NO2 for a given period of time (about two weeks), before being despatched to the control stations where the amount of nitrogen dioxide stored is measured. The information gathered is used, among other things, to determine the optimum location of the monitoring stations which can then be established permanently.

This method of testing is flexible, reliable and inexpensive. It has been used by ERLAP for conducting three measuring campaigns, each with its own specific objectives, in the French, Spanish and Belgian capitals.

Measuring campaigns in Paris...

Paris city council wanted to restructure its monitoring network. It thus installed 146 diffusion tubes between July 1989 and January 1990. None of the sites tested exceeded the limits stipulated by the Directive, even though eight of them were classed as "high risk" in the case of exceptional weather or heavy traffic conditions. Conducted in collaboration with AIRPARIF, the survey enabled the Parisian network to be rearranged, with the setting-up of 26 control points - compared with 9 previously.

... Madrid...

In Madrid, the level of urban pollution frequently exceeded the limits stipulated in the Directive. At the request of the local authorities, ERLAP conducted a critical study of the monitoring network, between June 1990 and February 1991. It emerged that the measuring stations were all situated in areas of maximum traffic - and hence of maximum pollution. In order to obtain a more balanced picture of the atmosphere, it was thus necessary to install additional stations, in less sensitive spots.

In the course of this assignment, ERLAP also analysed the city's sulphur dioxide levels (SO2) and found that Madrid was divided in two, with high levels of SO2 in certain old districts, where many homes still used coal-fired heating systems, and significantly lower levels in the new districts, where the boilers were oil- or gas-fired.

... and Brussels

In Brussels, ERLAP monitored NO2 levels at 200 sites over a period of nearly a year (June 1993-March 1994), in collaboration with the Brussels regional authorities, the Institut Bruxellois pour la Gestion de l'Environnement, Inter-Environnement Bruxelles and the World Wide Fund for Nature. Measurements were also carried out, in a rather spectacular fashion, using a laboratory truck, and also with the aid of a beam of light which travelled through the air over a distance of 800 metres, 30 metres above one of the city's busiest streets.

During the same assignment, BTX tubes (benzene, toluene, xylene) were also used - for the first time ever - to measure the volatile organic compounds which are the precursors of ozone. This campaign helped draw attention to the fact that, in areas of heavy traffic, the benzene levels exceeded the limit proposed for a new European directive on benzene (10 microgrammes per cubic metre of air). This alarming finding is true for other European cities as well.

A standardised measuring method

Since then, with the backing of ERLAP, similar measuring campaigns have been conducted in France (Rouen, Le Havre, Toulouse, Mulhouse, Lyons) and in Sicily (Palermo, Catania, Messina), while others are planned in Bologna, Athens and Barcelona.

"The diffusion tube measuring technique can be extended to a large number of air pollutants," claims Maurice Payrissat. "The EDSI project (European Diffusive Sampling Initiative) supported by the Community LIFE programme (DG XI) aims to demonstrate and also to disseminate this approach in order to systematise measurements of other substances (sulphur dioxide, ammonia, formaldehyde). This simple, inexpensive technique will shortly become the norm, because the European Committee for Standardization and the International Organization for Standardization are due to make it a standardised measuring method."

* This name replaces the old one by which it was known at the time: Central Laboratoty for Air Pollution measurements (CLAP).