A multinational team of climatologists embarked yesterday on what it says will be the most extensive study of air quality ever conducted, providing valuable data about the origins and content of pollution as it moves across North America and the Atlantic Ocean.

Scientists leading the project, slated to last until late August, said it will improve their ability to forecast poor air quality as easily as they predict the weather, and to better understand how pollution produced in one region affects air quality in other places.

Much of the research will be focused on New England, sometimes referred to as "America's tailpipe" because of the heavily polluted air passing over it and out to sea.

"This number of people and organizations, aircraft and ships involved will lead to a truly unprecedented data set," said Robert Talbot, director of the Climate Change Research Center at the University of New Hampshire's Institute for the Study of Earth, Oceans and Space, located in Durham, a few miles from a former Air Force base that will serve as headquarters of the study.

The massive collaboration, dubbed the International Consortium for Atmospheric Research on Transport and Transformation, brings together a host of air quality experiments already underway. Each agency will conduct its own experiments and pool the results.

Led by NASA, the National Oceanic and Atmospheric Administration and hundreds of academic and government scientists from the United States, Canada, France, Germany and the United Kingdom, the collaboration will include 12 airplanes, one 274-foot research ship at sea, dozens of balloons equipped with sensors, satellite imaging and a network of ground-based stations for measuring air quality.

Such an assembly of equipment will allow scientists to track 40,000-foot-high columns of air for thousands of miles, and determine when and where they acquire pollutants -- such as carbon dioxide, carbon monoxide, gas-phase mercury, hydrocarbons and methane -- and distribute them to remote locations.

Sensitive equipment at fixed ground stations throughout the Northeast and on board the research craft will measure the chemical composition of the air. Planes will circle separate geographic areas on flights lasting as many as nine hours. Balloons launched daily will gather samples from points higher up in the atmosphere.

"When people develop strategies in dealing with adverse air qualities, we want to be able to provide accurate information about how pollution on a regional scale impacts global air quality," said Jim Meagher, air quality program manager for NOAA. "There are important public health implications and climate implications, and we'd like to improve our ability to give people advance warning when bad air is headed their way."

The findings, which will not be known until later this year, will be of particular concern to policy-makers in states such as Vermont, New Hampshire and Maine, which occasionally experience extremely poor air quality. Acadia National Park, for example, on a remote island off the coast of Maine, periodically experiences severe air pollution.

Sen. Judd Gregg (R-N.H.) played a major role in securing $5.75 million for the New England portion of the project and $9 million for efforts to improve air quality forecasting. "This is a big issue for us, because we consider a pure and pristine environment an important element of our quality of life," he said.

Scientists have long hypothesized that pollutants emitted in the midwestern Rust Belt and large East Coast cities converge on northern New England, are carried by prevailing winds and are then distributed across the Atlantic Ocean, harming both the marine environment and air quality in western Europe.

But that explanation has never been fully proved and quantified by research, Talbot said, adding that scientists want to determine how different pollutants enter the air and where they go.

"We are after hard numbers that show what's happening up there," said Talbot, who oversees several ground-based monitoring stations, including one atop Mount Washington, New England's highest peak, and another in a Durham field a few miles from the UNH campus. "We'll know how species X got here, where it's from and where it goes. We have also never really measured intercontinental transfer of pollutants."

Environmental advocacy groups applauded the initiative but said it would likely confirm what they believe is already evident: Pollutants produced in one region have a significant impact on those downwind.

"We may not have tracked every molecule, but there's no doubt that pollution crosses state and national lines," said Frank O'Donnell, executive director of Clean Air Trust, a Bethesda-based watchdog. The study "may give us a broader understanding and help pinpoint things, and I think that's for the best."

Related experiments will measure the public health effects of days in which pollution levels are high. One will monitor about 550 people scattered throughout the Northeast, who will breathe daily into small devices that look like inhalers and measure the effect of the air on their respiratory system.

A smaller study of pollution in the northeastern United States was conducted two years ago, involving UNH's monitoring stations, a ship provided by NOAA and one or two aircraft. Organizers said they hoped to conduct another round of collaborative research in 2006.