Bad air days

A different kind of detective is closing in on the complex causes of and some possible solutions for those smoggy summer skies.

It's the kind of sultry, late July day that drives tourists and locals to the beach for a cool ocean dip. But for atmospheric scientists aboard the research vessel Ronald H. Brown, the day is just what they've been looking for: ideal for cooking up smog.

"These are the kind of conditions we love," says Fred Fehsenfeld, as the 274-foot ship rides the tide down the Piscataqua River.

The atmospheric chemist and a small army of colleagues hope to analyze those conditions that lead to smog to help solve the riddle of air pollution in New England. Over the next five years, the National Oceanic and Atmospheric Administration (NOAA) has budgeted $9.4 million for the New England Air Quality Study, which is designed to determine how smog forms in the Northeast and what its patterns of movement are. It already has raised significant questions about prevailing notions that Northeast air pollution comes primarily from industry and power plants in the Ohio Valley. And its lessons could have implications in other parts of the country as well.

The study's results, combined with earlier studies in Nashville, Atlanta, and along the Pacific Coast, could help build reliable forecasting tools to warn the public up to three days in advance of a bad-air day.

Scientists hope to do this by building better pollution-forecast models based on their new research. The first step has been to gain a better sense of the sources of air pollution and the way it spreads.

Scientists know that ozone forms through a series of chemical reactions that combine oxides of nitrogen – a byproduct of burning fossil fuels – and natural as well as manmade hydrocarbons. Sunlight provides the energy for these reactions.

That said, the patterns of smog are not all the same. As a result, scientists are learning, as Dr. Fehsenfeld of NOAA's Aeronomy Laboratory in Boulder, Colo, puts it, that air pollution regulations should not be designed like men's socks. "One size," he says, "does not fit all."

For one thing, the mix of natural and manmade air pollution ingredients varies among regions, notes James Meagher, a lead NOAA investigator of the New England study.

"Understanding emissions should be first and foremost," he says. "We really don't know these as well as we could or should."

Without that understanding, he adds, forecasting models inevitably fall short.

In cities such as Atlanta and Nashville, for example, researchers found that on some hot days, smog levels exceeded those attributable to urban sources alone. The culprits turned out to be coal-fired power plants in the region around the cities and a hydrocarbon, isoprene, emitted from broad-leaved trees as a byproduct of photosynthesis. When winds blew power-plant emissions over the woods toward Nashville or Atlanta, each city could be enveloped in a haze of pollution.

If Southeastern cities demonstrated the critical role played by natural sources of ozone-forming ingredients in urban air pollution, Houston highlighted the need to "get it right" for human sources as well.

During the summer of 2000, a NOAA research team endured sweltering heat and long, turbulent runs in an aircraft in hopes of discovering why Houston's smog levels consistently exceeded model forecasts.

Scientists found the region's petrochemical plants were emitting vastly larger amounts of hydrocarbons, as measured by NOAA's airborne sensors, than they were reporting to air-quality officials using US EPA-approved estimation techniques.

"There's a lot of leeway in how the petrochemical industries can report their emissions," NOAA modeler Stuart McKeen says. Plants didn't really know "how much they were releasing in 'fugitive' emissions," he adds.

New, faster, and more sensitive sampling instruments hold out the promise of identifying the source of an emissions plume more precisely than in the past, Dr. McKeen says.

Not surprisingly, the discovery that emissions were higher than previously believed "changed the landscape in terms of how Houston approaches air quality," Dr. Meagher adds.

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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