Tracking Air Pollution From Afar

By Chelsey Stevens

Measuring pollutants in the atmosphere from space can be akin to standing atop a very tall building while trying to count marbles located on the ground. Although this seems nearly impossible, this task is similar to what researchers from Washington State University (WSU), Pennsylvania State University, and NASA's Goddard Space Flight Center (GSFC) in Maryland hope to achieve with the next generation of space-based air pollution monitoring instruments. The team has received a $2.95-million grant to develop a proof-of-concept instrument with a higher orbit and greater sensitivity and spatial resolution than existing instruments.

Air pollutants are harmful to both animal and plant life and play a direct role in global warming. For this reason, it is especially important to measure air pollutants in the lower atmosphere, known as the troposphere. Scientists have been monitoring air pollution for years using weather balloons and ground-based equipment. This technology limited the view of pollution to relatively small areas.

The instrument in development, known as GEOSPEC for Geostationary Spectrometer, will remain stationary over a specific region, providing long-term data on movement of pollution in that region. This is yet another tool for scientists in their efforts to develop models of the complex atmospheric environment.

Set to maintain what is known as a geostationary orbit, the GEOSPEC will orbit at an altitude of 22,000 miles. The GEOSPEC is designed to scan an area the size of the Pacific Northwest in 0.6-mile chunks. Previous instruments obtained a resolution of 8-mile chunks over a 1,600-mile wide swath of land and visible only when the satellite appeared overhead several times per day. Obtaining this high resolution of pollution measurements in the troposphere from such a high altitude was not previously possible due to technology limitations.

The proof-of-concept instrument is being designed at GSFC. Upon completion it will travel to the laboratory of WSU professor George Mount, where it will be tested against field instruments. Once researchers have proven the technology, the instrumentation will be scaled down to a size small enough to fit on a satellite. It is expected that an instrument appropriate for launch may be ready as soon as 2010.

Prior to working with the GEOSPEC, Mount collaborated with the Dutch government in the development of the Ozone Monitoring Instrument (OMI). The OMI is a Dutch-designed instrument that launched on NASA's Aura satellite in July of 2004 and currently is returning data.

The GEOSPEC will use much new optical technology, but relies on lessons learned from its predecessor. Like the OMI, the GEOSPEC will measure air pollutants that have been identified by the U.S. Environmental Protection Agency as especially harmful to health and the environment. These include ozone, nitrogen dioxide, sulfur dioxide, and aerosols. The OMI works by measuring the spectrum of the sunlight in the ultraviolet and visible range as it is reflected back by the Earth. As the light moves through the atmosphere it is altered by the pollutants in the air. The alteration that occurs is characteristic of the type and amount of pollutant present. This allows scientists to determine what type and how much of the pollutants are present in the atmosphere.

Chelsey Stevens is pursuing a bachelor's degree in materials science and engineering at the University of Washington.

Image at Top:

The atmosphere is made up of several distinct layers. Human and natural sources of pollution result in the accumulation of pollutants in the troposphere and stratosphere, closest to the Earth's surface. Image: Chelsey Stevens