The Bureau of National Affairs, Washington D.C.: Air Pollution

Heat Wave Launches Intensive Phase Of Study on Ozone Formation in South

Wednesday, 7 July 1999, Barney Tumey

ATLANTA – While residents of Eastern states endured high temperatures over the July 4th weekend, a team of 170 scientists in Nashville were happy to see the weather finally heat up.

The scientists are participating in the Southern Oxidant Study, begun in 1990 and the nation's most comprehensive look at how and why ground-level ozone forms. This summer, researchers are trying to figure out the physical and chemical characteristics of fine particulate matter and ozone, which may be a factor in health-related problems as well as crop and forest damage.

But until the holiday weekend, the unseasonably cool and rainy weather for the last two weeks of June, along with problems with some of the airplanes they are using to take measurements, had restricted researchers to a handful of flights to collect air samples. But that does not mean they are disappointed so far.

"We don't just want to look at high pollution days. We want to be able to understand what happens on days that are clean and, in fact, why they're clean, as much as we want to understand on days that are polluted, why they are polluted," said James Meagher, chief scientist for the project, in a July 2 telephone interview. Meagher is a research chemist at the National Oceanic and Atmospheric Administration's Aeronomy Laboratory in Boulder, Colo.

Rainy days are a problem, however, Meagher said. It is harder to fly on rainy days and the conditions are more difficult to understand and interpret afterwards, he explained.

Airborne scientific teams are conducting the regional research from bases in Atlanta and Nashville.

High Pressure Ridge

But the forecast for the weekend was for hot weather, and the scientists were excited. "We're on the edge now of what looks like a big high pressure ridge that's moving into this area so things are going to get hot and heavy pretty quickly here," Meagher said.

The Southern Oxidant Study is a research effort involving numerous universities and state and federal environmental agencies, with the goal of learning more about air pollution in the South. Here, warm temperatures, high humidity, stagnant air, and natural emissions of hydrocarbons from the region's large rural and urban forests give the region unique air quality management problems.

So far, scientists have learned that instead of the large-scale mixing of the precursors of ozone--nitrogen oxides and volatile organic compounds--it is more like a plate of spaghetti, where plumes twist and turn around each other and mix much more slowly.

According to William Chameides, an atmospheric scientist at the Georgia Institute of Technology, researchers have learned that electric power plant plumes contribute to ozone formation, and "there is a very interesting interaction between power plants and urban plumes in producing ozone."

They have also found that, for reasons that are not entirely understood, the number of ozone molecules produced per molecule of NOx emitted is smaller than scientists originally thought. This means that more NOx reduction is needed, Chameides said in a July 2 telephone interview, to get the region "where we need to be."

Scientists have learned that NOx emitted by large power plants produces less ozone that the NOx emitted by smaller power plants. That might have implications "if you wanted to go to a bunch of small power generators," he said.

"It's very clear that these plumes keep their characteristics for a long, long time and are sort of mixing in a complicated way. We can track power plant plumes way downwind of where they are emitted, which is somewhat of a surprise," Chameides said.

Aircraft at Work

During this summer's part of the study, airplanes and helicopters will take a series of coordinated chemical and meteorological measurements during the day and the night. The samples will be collected over a wide range of the Southeastern and Midwestern United States to assess to what degree the problem is regional or local. Similar experiments are slated for Atlanta later this summer.

"We're expecting to develop a really good database from these experiments that will provide the sound science needed to find solutions to the special air pollution problems facing this region," Meagher said.

The study is in its ninth year, but the 1999 experiments are "bigger" and "more complex" than those conducted four years ago, Meagher said, and represent the most extensive sampling to date for the study. The team had more aircraft in 1995, but much more extensive ground monitoring in 1999.

The sampling instruments, both on the chemical measurement side and the particle measurement side, are greatly improved, Meagher said. They include "a really nice array of meteorological instrumentation" that allows them to look at the dynamics of the meteorology in greater detail, he said.

For example, they have learned that outflows from some of the gust fronts that are created when small thunderstorms go by produce low-level cold winds from high in the atmosphere virtually down into the city of Nashville. "It's really interesting to see some of those kinds of things," Meagher said.

The last flight for the Nashville portion is scheduled for July 17.

The scientists participating in the Southern Oxidant Study will publish papers on the results in scientific literature over the next two or three years, Meagher said. Concurrently, the team will put out "more user-friendly information" for the policymaking community, he added.