CIRES researchers sail through New England air quality study

Ocean-going researchers track regional air pollution

By Susan Bacon
winter, 2002

July 19, 2002: Scientists Fred Fehsenfeld, Roger Jakoubek, both of NOAA's Aeronomy Lab, and Douglas Worsnop, Aerodyne Research Inc. wave as they leave the Ronald H. Brown on a rigid hull inflatable boat. Two crew members, Chief Boatswain Bruce Cowden and Deck Utilityman David Owen, ferried the scientists to Star Island, among the Isles of Shoals. The Ronald H. Brown was anchored a few miles off the coast of New Hampshire nearby the Isles of Shoals. From Star Island, scientists took another ferry to Portsmouth.

Following pockets of polluted air in a ship might not make for a relaxing cruise. But as 34 scientists found out this summer, it can produce useful data. For one month in late July and early August, the scientists-about a third of whom were from CIRES-sailed along the coast of New England on NOAA's largest research vessel, Ronald H. Brown, in order to track how polluted air moves into and around the region.

Levels of unhealthy ozone and particulates in the area exceed EPA standards. Some researchers suggest that the dirty air is floating in, not just from nearby cities and industries but also from the Midwest and the Eastern Seaboard, making the pollution a regional problem.

"New Englanders believe that much of the problem is not homegrown and speculate that pollution is being produced elsewhere and transported in. So they want to understand the problem," said Jim Meagher, a research chemist and program coordinator with the Aeronomy Laboratory at NOAA [ About this Lab ] who has helped organize a research project on air pollution in New England. "That's how we got involved-to help them understand the problem."

Meagher is one of several hundred researchers from more than 20 institutions working on the New England Air Quality Study, which is part of a series of intensive field campaigns that have been supported by NOAA's Health of the Atmosphere research program. Previous studies were conducted in Nashville, Atlanta, and Houston.

"We were particularly interested in the New England area as it provided a nice contrast from previous studies, which focused on large cities as the source of much of the local pollution," Meagher said.

"Using the Ronald H. Brown for the first field study last summer was an ideal way to get a better picture of New England's air pollution problem," said Eric Williams, a CIRES researcher and atmospheric chemist at NOAA's Aeronomy Lab, who is also the lead scientist for the gas phase chemistry research on the ship.

"We could go where the pollution was," Williams said. "This is really important because what we're interested in is seeing the continual changes in the chemistry of the air."

July 25, 2002: Joanne George, a CIRES computer specialist working with NOAA's Environmental Technology Laboratory releases a radio sonde on the fantail of the Ronald H. Brown. Several radio sondes per day were released during NEAQS 2002 to measure vertical profiles of temperature and humidity.

Researchers brought extensive instrumentation aboard to analyze the air composition and detect how pollutants like ozone are formed as the air masses moved to and from land.

Williams' group measured concentrations of ozone as well as nitrogen oxides and volatile organic compounds that form ozone. Although ozone high in the atmosphere is beneficial because it protects people from the sun's ultraviolet radiation, ozone close to the ground is harmful.

Both ozone and aerosols, which are tiny particles suspended in air, cause lung irritation and are unhealthy for young children, for the elderly, and for people who have respiratory problems.

Figuring out where the pollution comes from is the first step to reducing it. The sources of ozone and fine particles in New England's air could be as far away as power plants in the Ohio Valley, as close as local forests, or from an intermediate source such as cars driving along the urban corridor between Washington D.C. and Boston, Williams said.

Williams' preliminary analyses of this summer's data show a clear pulse of nitrogen oxides, which help form ozone, associated with rush-hour traffic on highways between Boston and Washington, D.C. Other significant sources of pollution included power plants and large ships sailing along the coast.

New England's coastal position might make it more susceptible to high levels of ozone, because ozone builds up more quickly over the ocean than it does over land.

"If the air shifts and blows on shore, people get hammered with high levels of ozone," Williams said.

Ozone accumulates over the ocean for two reasons. First, ozone is not destroyed efficiently when it hits the ocean surface, and second, the air above the ocean does not mix as well as it does above land. When land heats up during the day, air close to the ground also warms and rises and so mixes the air. Over the cooler ocean, however, vertical mixing is less common, and the air tends to form layers, which can contain high levels of ozone and particulates.

Documenting the vertical structure of the air masses above the ocean was important during the cruise because researchers needed to know when measurements taken at ship level represented the air composition above the ship.

To show how the air masses were layered, scientists used a lidar system. The instrument sent a laser beam into the atmosphere 10 times per second and then detected with a telescope the tiny fraction of laser light backscattered by aerosols and air molecules. The information contained in these return signals allowed scientists to infer the concentrations of aerosols and ozone in different layers of air up to 3,000 meters above the ship. Lidar systems were also set up at two spots on shore.

Christoph Senff, a CIRES researcher and physicist with NOAA's Environmental Technology Lab, worked as principal investigator for the lidar study aboard the ship.

Although it's too early for conclusions, Senff said the lidar research suggested that emissions from the Boston to Washington D.C. urban corridor caused the highest ozone levels.

"That stuck out like a sore thumb," he said. One key use for the data collected on the ship is to compare and improve models that forecast air quality and so help residents prepare for pollution levels, said Stu McKeen, a CIRES researcher who works on air quality modeling.

"There's not a lot of data to compare these models against," McKeen said. "Where this experiment has really been helpful is to hammer down which model parameterizations really need to be looked at."

Some of the most ground-breaking research on the ship took place at night when Steve Brown, a CIRES researcher with the NOAA Aeronomy Laboratory's atmospheric chemical kinetics group, collected data with his Cavity Ring-Down Spectrometer.

Brown built the instrument to detect two types of nitrogen oxides that, until now, have been either impossible or cumbersome to measure. These highly reactive chemicals are destroyed by sunlight but are important to forming ozone because they can build up at night and affect the chemical concentration of the atmosphere.

Both chemicals play a role in determining how much ozone is created during the day.

"In order to understand what happens to ozone during the day, it's important to understand what happened the night before," Brown said.

This research cruise was the first time the cavity ring-down spectrometer was used outside Boulder, Brown said. In Boulder, nitrogen oxides stay stable overnight and turn into a large reservoir of ozone-forming molecules once the sun rises.

July 27, 2002: friends and family of scientists and crew participating in the New England Air Quality Study get a tour of the NOAA Ship Ronald H. Brown while docked in Portsmouth Harbor, New Hampshire.

But over the ocean along New England, nitrogen oxides react with other chemicals at night, removing a source of ozone-precursors.

Brown's research offers another piece of information that will help put together a more complete picture of New England's air pollution. He said he was pleased that his part of the research worked well and that the cruise as a whole was successful.

"We had a lot of comraderie with people on the ship," Brown said. "There was a lot of good science going on."

Meagher agreed with Brown that this summer's cruise was a success.

"It was as good as it gets, actually," Meagher said. "We've certainly learned a lot from this summer's measurements. We're now more anxious to go back."

The researchers will return to New England in 2004, next time with more extensive sampling methods that include another research cruise as well as the use of a fleet of air craft to measure pollution levels aloft. In the 2004 study, air pollution will be examined on local, regional, continental and intercontinental scales.

"It will be the first time we're going to try to do all scales-local to regional to intercontinental- during the same period," Senff said. "The intercontinental segment underscores the fact that air pollution transport is not only a regional problem but can be a global problem."

See www.al.noaa.gov/neaqs for more information on the New England Air Quality Study.