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.Skip to next paragraph
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"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.