NASA - National Aeronautics and Space Administration

By: Jim Hodges

The answer isn't in space. It isn't on the ground, or in between.

The answer to determining air quality is a combination of all of those things, Jim Crawford told a January Colloquium audience Tuesday in the Reid Conference Center at NASA Langley.

"Satellites give us a global picture where there is none," said Crawford, a NASA Langley atmospheric chemist who was principal investigator of the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) project that flew the I-95 corridor between Baltimore and Philadelphia last summer, measuring air quality.

"We have global simulations to verify, and satellites help with that," Crawford added. "But what those satellites don't do is provide accurate and useful day-to-day information that you can map to the surface conditions."

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Jim Crawford talks about DISCOVER-AQ, which took its first of a planned four series of measurements during July 2011 over the I-95 corridor between Baltimore and Philadelphia CREDIT: NASA/Sean Smith.

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Satellites find the sources of atmospheric gasses and even track them. What they do not do is determine how those gasses are layered, particularly near the Earth, where they affect people and agriculture, the primary concerns of those who measure air quality and attempt to regulate it through legislation.

That's the job of the airplane and ground sensors – at least for now.

It was the job of DISCOVER-AQ during its July flights. Daily, "A-Train" and TERRA satellites flew overhead, and the P-3 and UC-12 aircraft of the DISCOVER-AQ mission compared data with the space birds.

"That was important to what we do, but it actually peripheral to the activity," Crawford said.

In essence, DISCOVER-AQ created its own measurement scenario, with a plane at higher altitude simulating a satellite, including taking lidar measurements. A second plane below flew between 1,500 and 10,500 feet, spiraling up and down at selected points to measure layers of ozone, formaldehyde, carbon dioxide and other parts of the atmosphere. Finally, 12 ground sensors took measurements. NASA joined with academe and industry to paint a picture that has never been painted of a section of the atmosphere.

To what end?

In part, to help develop a geostationary satellite that will keep an eye on North America – with others perhaps viewing Europe and Asia.

"When you have a satellite parked in orbit over the United States, looking all day long, we want to know what sorts of information will make us better at understanding the satellite's judgment of what's going on in the atmosphere," Crawford said.

"Also, knowing that satellites don't operate in isolation, what is the best mix of observations for that satellite to make it effective?"

The idea is to make the satellite smarter before it's sent aloft.

"You need measurements that will verify or validate what the satellite hopes to see," Crawford said. "The satellite doesn't reach down and touch the atmosphere. It's inferring from reflected light what's in that atmosphere, so you need to verify that this thing works. The aircraft has been an important part of that."

Also, satellites measure only part of what makes up the chemistry of the atmosphere.

"But from aircraft, we get into the details and processes by which the chemistry propagates, by which transport moves things between locations," Crawford said.

They are the details and processes that generate air quality legislation, which is often local, which can be troubling. That's because air quality of a one locality can depend on that of an area upwind of it.

Airplanes and satellite measurements are two legs of a three-legged stood. The third leg is the ground sensor, some of which are being used today while others are being developed. Airplane testing is part of that development, the way it's also part of satellite instrument evolution.

They are among the reasons that DISCOVER-AQ will fly again. Missions are planned next winter for California's Central Valley, where agriculture rules amid oil wells and emissions that flow south from the state's San Francisco Bay Area. And where a winter anomaly – Tule fog – offers a challenge. A February decision on that mission is scheduled.

DISCOVER-AQ also plans to survey the Houston area, where petro-chemical emissions make it among the most smog-laden areas in the country.

Another mission is scheduled for 2014 at a place to be determined.

"We're not looking to go to a location just to study it," said Crawford. "We're looking to go to a location where authorities have studied it for years and want to know more about it."

The DISCOVER-AQ project wants to know more, too, with an idea that when it learns can be used well beyond the location it studies.

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NASA Langley Research Center
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