Mapping a picture of Earth’s minute particles from the sky

In a little conference room in an airplane hangar in Northern Virginia, about a half a dozen government scientists spent much of this past weekend analyzing the air around and above the nation’s capital as hundreds of thousands of people arrived to celebrate President Obama’s inauguration.

For hours each night, a pilot flew a 1968 Aero Commander dual propeller airplane, crisscrossing the skies around the Capital Beltway. But because of what it carried, the plane actually is the only one of its kind in the country.

Inside, there’s a collection, among other technology, of infrared and gamma-ray spectrometers, a neutron detector, scanners, cameras and broadband satellite equipment that remotely transmit chemical and radiological data back to the scientists on the ground.

The little known crew of scientists responsible for the equipment has deployed more than 125 times since 2001 for special events such as Super Bowls, inaugurations, political conventions and natural and environmental disasters, including the BP oil spill and Hurricane Katrina.

“This is commercial, off-the-shelf technology, it’s state of the art and almost all other foreign countries that are flying, they’re flying these very same systems,” said John Cardarelli II, a health physicist with the Environmental Protection Agency.

“Here’s the difference,” he said. “The detectors and the hardware, that’s the body. Really, where the trick lies is the software, that’s the brains.

“We feel we’re cutting edge in that area simply because we’re able to take this hardware and pull signals out at much higher sensitivity that anyone else out there. That’s one of the things that makes us unique is our algorithms, the brains of pulling this information out.”

In the middle of the plane, a powerful telescope looks down for tell-tale infrared signatures of various gases, while another camera points up to account for radon in the atmosphere. The equipment is so sensitive that it detected the ethylene gas emanating from the flowers and plants used in the floats for the Rose Bowl Parade.

The crew also was able to map out atomic bomb fallout that occurred more than 60 years ago from far above the Nevada test site.

“You can go down and walk around there,” program manager Mark Thomas said. “The stuff has decayed down to the point where it’s there but it’s in very small quantities. But you still have the ability to fly over in an aircraft and make that detection.”

Toward the back of the plane, radiological detection equipment offer scientists what they call a spectral picture, or fingerprint, of what’s causing radioactivity seen below.

With the airplane and pilot stationed in Dallas and scientists scattered across the country, the crew arrived in the Washington area for an environmental assessment of the air above the nation’s capital that already had been planned, but also to be on standby in case of an unforeseen chemical or radiological incident during the inauguration.

Developed by government scientists, the program is known as Aspect, for Airborne Spectral Photographic Environmental Collection Technology. Mr. Thomas said the idea for it began in 1994 when he was an EPA on-scene coordinator after an explosion at an ammonia plant in Iowa that released a 50-mile plume and forced the evacuation of 2,500 families.

“We were driving around in 2 feet of snow with hand-held detectors trying to measure a plume, and I though there’s got to be a better way,” Mr. Thomas said.