London

Plane truth: NASA's DC-8 forms part of a fact-finding fleet. Credit: NASA/DRYDEN

Scientists from North America and Europe took to the skies this week to track the movement of giant masses of polluted air.

During the six-week study, a tag team of five aircraft will follow parcels of air pollution as they travel from the east coast of the United States over the Atlantic towards Europe. An international team of some 100 scientists will pick apart the collected data.

Their mission: to understand the chemical interactions that take place as ozone-forming pollutants from factory smokestacks and car exhausts in the United States hitch a ride to Europe on prevailing winds — a journey that takes about four days.

The International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) is launching the project to discover how atmospheric pollutants such as aerosols, free radicals and ozone behave chemically as they are transported from one continent to the next — and how they affect climate change and health issues.

The pollution that the researchers are studying builds up over an area covering New York, Washington DC and Boston during periods of still weather throughout the year. When the weather changes, this mass of air moves from the lower part of the atmosphere to the upper atmosphere. Winds then push the air mass over to Europe. The lump tends to break up as it crosses the Atlantic, but scientists hope to track at least one parcel of pollution that holds together.

The aircraft will measure the size of aerosol particles and the chemical constituents of the invisible cloud, using weather forecasts, models and measurements to stay on track.

Similarly equipped planes have been used in the past to study small sections of the journey, but no sustained mission has successfully tracked the pollution right across the Atlantic.

Satellites have been used to monitor air transport over the Atlantic, but cannot be used to pick up on the details of the chemistry.

The multimillion-dollar study may one day help to shape global atmospheric policies, according to the team behind the project. Pollution isn't just a local problem, says its lead UK scientist, Alastair Lewis, an atmospheric chemist from the University of Leeds. Dust blows from Africa to North America, and Europe's smog may be caused in part by pollutants from the United States.

During the 2003 summer heatwave, there were about 2,000 more deaths than usual in Britain, some 21–38% of which were attributable to heightened atmospheric pollution (J. R. Stedman Atmos. Environ. 38, 1087–1090; 2004). “Disentangling where it came from is very tricky,” says Lewis.