Global pollution will be detected by new satellite

By Jim Downing
Seattle Times staff reporter

NASA PHOTO / Aura is shown after completing acoustic testing, one of several tests performed before the launch tomorrow from California.

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"At least we hope it will," Mount says.

Since 1997, Mount and his team in Pullman have worked to design an instrument capable of taking high-resolution "pictures" from space of common ground-level air pollutants such as ozone, nitrogen dioxide and sulfur dioxide.

Tomorrow's launch kicks off a new generation of satellites able to detect air pollution on a local and global scale.

Mount's device, called the Ozone Monitoring Instrument, or OMI, will be able to observe air quality at a resolution 150 times greater than is now possible, and in such places as the open ocean where daily air sampling cannot be done.

OMI is one of four instruments aboard NASA's $750 million "Aura" satellite, which will collect data on the ozone layer, surface-level air quality and gases in the upper atmosphere. It will travel 438 miles above Earth in an orbit perpendicular to the equator.

	NORTHROP GRUMMAN / This is an artist's conception of the Aura spacecraft built for NASA to study the environment and climate.

Aura completes a trio of satellites that make up NASA's Earth Observation System: "Terra," launched in 1999, looks at cloud cover, surface temperature and greenhouse gases; "Aqua" joined Terra in 2002 and monitors various aspects of the planet's water cycle.

Damage to ozone

Satellites have been used to monitor atmospheric ozone since 1978. Growing concern over damage to the ozone layer and worsening ground-level air quality have driven dramatic improvements in satellite technology.

The "pixel" size of the atmospheric pictures produced now by orbiting instruments is very large — a rectangle about 50 miles by 200 miles — useful only for looking at global-scale issues, like the depletion of the ozone layer.

OMI brings the pixel size down to eight-mile squares — sharp enough to be useful in local air-pollution management.

Tracking ozone What is ozone? Ozone is a gas made up of three oxygen atoms, as opposed to the two oxygen atoms in common atmospheric oxygen, which humans and animals alike need for respiration. Ozone plays different roles in the atmosphere depending on its altitude. The "ozone layer" is an area of very high concentration of ozone in the stratosphere, from 10 to 30 miles above the Earth's surface. There, ozone reacts with harmful ultraviolet radiation and converts it into harmless heat. At ground level, ozone contributes to smog and damages lung tissue and plants. The EPA says ozone pollution is responsible for 10 to 20 percent of all summertime respiratory-related hospital admissions in the United States and Canada. The near-surface ozone is formed by a complex series of chemical reactions involving pollutants — like vehicle exhaust or forest fire smoke — along with atmospheric oxygen, sunlight and heat. The cool and cloudy weather in Western Washington tends to keep ozone levels low in comparison with places like Los Angeles and Denver. Unhealthy ozone levels also may occur in rural areas hundreds or even thousands of miles downwind from an urban pollution source. Source: earthobservatory.nasa.gov

"What the satellite will do is give you complete coverage over an entire area, not just where we're able to put monitoring stations," Mount says. "So the predictive power of local air-quality models becomes better."

Air-quality models now use data collected at ground-based stations. The models generate a 24-hour forecast of air conditions. People sensitive to low air quality, including asthmatics, can use these forecasts to see what hazards the next day's air might hold.

But data from ground-based stations is irregular and incomplete, says Brian Lamb, a civil-engineering professor in the Lab for Atmospheric Research at WSU. "OMI has the potential to fill in a lot of the gaps," he says, such as what air-quality conditions are like out in the ocean.

For the Pacific Northwest, an improved understanding of air pollution over the Pacific is especially important, since a serious future threat to this region's air quality will come from pollutants generated by industry in Asia and blown across the ocean.

"Most of the pollution in downtown Seattle today is our own, don't forget that," says Dan Jaffe, a Professor of Environmental Science at the University of Washington's Bothell campus. "But what the pollution from Asia does is add to the background levels, and a few days a year, these pollution levels can be high enough to push us up over the EPA's ozone limit."

In other words, Mount says, "You'll be able to watch ozone events begin in Asia and move across the Pacific. We'll be able to watch the timing and the specifics of the chemistry."

Three other instruments will be aboard the rocket, which is scheduled to lift off from California's Vandenberg Air Force Base. Each uses a different approach in detecting atmospheric gases. While OMI's sensors use ultraviolet and visible light, the others use microwaves, radio waves and infrared waves.

While OMI is designed to look at air quality near the surface, the High Resolution Dynamics Limb Sounder, for instance, specializes in sensing the subtleties of ozone in the upper atmosphere.

OMI's "eye" is a device called a spectrograph, which detects patterns in different wavelengths of light reflected off Earth and through the atmosphere.

The spectrograph on OMI is so sensitive that it should be able to detect common atmospheric pollutants to an accuracy of about one-half of one part per billion.

Mount says OMI was funded and built by the Dutch government, which wanted to develop a satellite that would help figure out complicated trans-national air quality problems surrounding the densely populated Netherlands. The project came to Pullman because Mount is one of a group of NASA scientists regarded as world experts in ozone detection technology.

Work on successor

Mount and his team in Pullman have already started work on the successor to OMI and expect to have a prototype, called GeoSpec, ready for testing by 2006. GeoSpec's resolution would offer "pixels" of a half-mile square, far superior to OMI.

GeoSpec would be parked in a geostationary orbit 22,000 miles above the Earth's surface and would give minute-by-minute, high-resolution information about air pollution over a 60,000-square-mile area.

"You'll be able to see Interstate 5 and its air-pollution impacts," Mount says. "You're starting to talk pretty doggone small."

After calibration and testing, OMI should begin sending data to Earth early next year. Mount says all data will be posted for the public on NASA's Web site.

Jim Downing: 206-464-2164 or jdowning@seattletimes.com

Copyright © 2004 The Seattle Times Company

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