Bad air days

On board the Ronald H. Brown, NOAA's flagship research vessel, chief scientist Timothy Bates, takes a break from reviewing weather data to explain where New England fits into this larger picture. "This extension to the Northeast was a natural next step," he notes.

If the mix of chemicals and the meteorological conditions contributing to air pollution are a bit different from region to region, the Northeast is unique, he says. That's because the East Coast has two low-altitude air masses that show surprising variety in the way they interact. The warmer terrestrial boundary layer – the lowest part of the atmosphere – often will ride up over the top of its cooler, oceanic counterpart. Other times, the two masses mix.

In addition, the oceanic boundary layer tends to be shallower and more stable than its terrestrial counterpart, so any pollution it carries, or that is cooked within it, tends to be more concentrated, researchers say. "So the whole interaction between the cold ocean and the warm atmosphere makes this region a little different," Bates says.

In addition, over the past year, a regional network of sensors dubbed AIRMAP has turned convention wisdom about the sources of New England's pollution upside down.

Based on acid-rain studies over decades, regional officials identified emissions from power plants in the Ohio Valley as the main source of New England's air-quality troubles.

"When we looked at the AIRMAP data, it was just the opposite," Bates says.

The highest concentrations were measured on the Isle of Shoals, about 10 miles east of Portsmouth harbor.

"That's when people said, 'Wait a minute, we're missing something big here,' " he says.

The source of much of the region's air pollution, it turns out, is the rest of the East Coast. When weather patterns send southwest winds up the Eastern seaboard, they drive dirty air from the entire coastline into New England. Pollution from New York and Washington can be driven out to sea only to return to the New England shore.

This ocean-borne component of the region's pollution problem is the Ronald H. Brown's target. Four glistening mobile laboratories huddle on the second deck, forward of the bridge. One lab holds a lidar – the laser version of radar – tuned to measure ozone and small particles at different altitudes.

Already the project has yielded intriguing results.

The team is getting a better handle on the nature of ship emissions as a source of sea-based pollution. One surprise came as the NOAA vessel was cruising south of Nantucket Island, Bates says. Sensors tracked a half-hour-long spike in a range of pollutants, which formed a large plume. When they analyzed the composition, the scientists found the plume bore the signature of fishing boats.

In addition, a recent breakthrough in instrumentation is enabling researchers to measure chemical reactions that take place at night – what Fehsenfeld calls "the dark side of the force."

Typically, researchers focused on daytime reactions, because these sun-driven processes generated the smog. But Fehsenfeld adds that researchers now suspect that important processes take place at night as well. These either could remove the day's ozone from the atmosphere, or perhaps set the stage for another ozone "event" the next day.

The team is not ignoring natural background sources for ingredients that react to form ozone. Where isoprene dominated the Southeast's "background," in New England it's pinene, a hydrocarbon responsible for the piney smell of evergreens. In addition to any role they may play in ozone-forming chemical reactions, pinene molecules are thought to serve as nuclei for the formation of aerosols and small particles – of concern as new EPA standards include the concentration of small particles in the air.

This summer's work, which ends Aug. 10, is a run-up to a larger, East Coast-wide effort in 2004. But researchers are so enthusiastic about what they've learned with a ship as a research platform, that they may push to return to Houston in 2006 to get a better handle on how land-ocean interactions contribute to that city's air-quality problem.

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