Imagine trying to measure a needle in a haystack from an overflying airplane. That’s similar to the task researchers in the Laboratory for Atmospheric Research (LAR) at Washington State University are hoping to accomplish with new instrumentation to measure precise levels of ground-level air pollution.
George Mount, professor of civil and environmental engineering at WSU and a faculty member in the LAR, has been working with the Dutch government since 1998 to develop the OMI, or Ozone Monitoring Instrument. Launched on the NASA AURA satellite in July 2004, the instrument measures such air pollutants as nitrogen dioxide, ozone, formaldehyde, and sulfur dioxide in 64-square-mile chunks (eight miles by eight miles) over an area the size of the Pacific Northwest. The observation area sweeps by under the instrument as the satellite orbits the Earth.
Satellite-based air pollution instrumentation previously in use enabled measurement with far less spatial resolution than what the OMI can deliver, resulting in difficulty distinguishing point or mobile sources and blurred images of urban landscapes such as the Seattle airshed (the air over Seattle, plus the currents that flow into and out of it). The OMI will provide data on a grid of much higher resolution than these older systems, as well as accurate data on air pollutants moving into and out of the airshed.
The OMI measures the spectrum of reflected sunlight scattered off the surface of the earth. Depending on the type of pollutants present, the sunlight gets modified as it passes through the atmosphere and as it is reflected up to the satellite. Once the researchers measure the atmospheric spectrum, they can deduce the pollutant concentrations, determining how much ozone, formaldehyde, or other chemicals are present in the airshed, and they can track its motion with time as the satellite orbits the Earth. Overall, such observations from space allow air pollution to be measured worldwide and enable better predictions of pollution effects than are possible with ground-based instruments.
Now Mount and his collaborators are hoping to develop a new instrument to measure ground-level air pollution with even greater precision than the OMI, executing rapid scans of a 350-mile by 350-mile area every few minutes. They also want to be able to measure air pollutants continuously over a given area-not just in the every-90-minute snapshot a passing satellite provides from its orbit-by putting their new instrument on a satellite that will be in geostationery orbit, remaining continuously above one part of the earth. That means moving the instrument from hundreds of miles up, where OMI lives, to 22,000 miles away, where the satellite that will carry the new instrument will revolve around the Earth at the same rate as the Earth itself rotates.
Mount, together with colleagues from the NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, and Pennsylvania State University, recently received a $2.95 million grant to begin building a prototype instrument capable of accurately measuring pollution in 0.36-square-mile (1-km2) chunks over an area the size of the Pacific Northwest, rather than the OMI’s 64-square-mile resolution over an area of similar size. The prototype will be built at GSFC and tested at WSU.
As for how to see such a large area with one-kilometer spatial resolution from so far away with a time resolution of minutes, Mount says it requires “very fancy optics and weird mirrors.”
“This is going to be an earth-shattering instrument,” he adds. “It is the wave of the future for space based measurement of air pollution.