Atmospheric protection is a big challenge for the 21st century. In teaching scientists to design outputs that become the stuff of hard policy, the impact of EUROTRAC-2 is far-reaching. Nitrogen oxides, sulphur dioxide and aerosols, major contributors to atmospheric pollution, do not respect national borders. But thanks to EUREKA project E! 1489 EUROTRAC-2, the EUs largest ever study on atmospheric pollution, we know much more about where such pollutants were created, under what chemical disguises they travel and their human and environmental health consequences. EUROTRAC-2 marked the second phase of the original EUROTRAC research initiative, which started 15 years ago and was among the first projects sponsored by EUREKA. This second phase involved over 300 research groups in ,14 sub-projects, generating 900 scientific papers, more than 100 PhD theses and vastly expanding our collective knowledge bank. The 25 countries involved in EUROTRAC-2 overcame scientific and language boundaries to study the many types of air pollution - from the particles flying off car tyres to the movement of clouds of pollutants 18 kilometres above the earth. ,This hard evidence is helping to defeat scientific uncertainty, a huge barrier to political attempts to moderate global air pollution. With a clear remit to connect science to policy making, EUROTRAC-2 research is directly shaping negotiations to update the 1996 EU Air Quality Framework Directive and related legislation. Transboundary pollution is politically delicate, so the negotiators need a firm scientific platform, says Dr Pauline Midgley of the National Research Centre for Environment and Health (GSF), Germany, who co-ordinated the project. The major advance of EUROTRAC-2 was to promote truly interdisciplinary research, and I believe the results will heavily influence EU legislation. Air pollution is a continent-wide issue, and EUREKA helped scientists in Central and Eastern Europe to receive funds they may otherwise have had difficulty finding. Connecting science with policy,One of the sub-projects, SATURN, may help city dwellers breathe easier through its in-depth study on urban pollution in parking lots and between buildings. Researchers used wind tunnels to study how air flows over different shapes of buildings. Finding that air pollutants concentrate within the turbulence created by some designs, SATURN concluded that existing air sampling is inadequate. You can get different patterns of pollutants on different sides of a street, says Nicolas Moussiopoulos from the Aristotle University in Greece. In future, city planners may be obliged to consider pollution hot spots before building. Other examples of sub-projects are TROPOSAT, which was partially funded by the European Space Agency and used its satellite data to track regional pollutant drifts, and EXPORT-2, which monitored the global transport of pollution. EUROTRAC-2 is now complete, but this continent-wide network intends to continue with new funding under the EUs 6th Framework Programme.