THE BIG SNIFF

Smog now spreads from continent to continent. Man is trying to restore the health of the Earth's life-sustaining ozone shield by curtailing some industrial activities, only to find that he's hurting his own cause by what he's doing elsewhere. Greenhouse gases--a lot are man-made but some are from nature--are warming the lower atmosphere and changing the climate.

Discovering just how much good news and bad news there is for Earth's atmosphere--and where it's coming from--is the goal for Aura, the third spacecraft in NASA's Earth Observing Satellite series. Managed by NASA's Goddard Space Flight Center, the EOS trio is an unprecedented effort to monitor global climatic change on land, sea and in the atmosphere.

Aura is set for launch July 8 from Vandenberg AFB, Calif., on a Boeing Delta II for what is expected to be at least a six-year mission. Originally set for liftoff June 19, the flight was postponed owing to a stuck helium pressurization valve in the second stage.

Satellites have been on the front line of ozone depletion studies since the deteriorating effects of chlorofluorocarbons (CFCs) and other man-made chemicals were first recognized as an environmental scourge more than three decades ago. Their wintertime images of the swelling of the South Pole's "Ozone Hole" helped lead to the 1987 Montreal Protocol that restricted CFC production, and to the Copenhagen agreement five years later that set a schedule for the elimination of their production.

The ozone story is complicated: When it's in the stratosphere (7-31 mi. above the Earth's surface), ozone is a benefit by shielding the planet from ultraviolet radiation. But when it's closer to the surface in the troposphere, ozone is a pollutant that threatens people's health. Just as CFCs cause a chemical reaction in the stratosphere that eats ozone away, industrial activity contributes to greenhouse gases that promote ozone accumulation in the troposphere. Additionally, ozone naturally seeps down from the upper atmosphere, and natural activities--volcanoes, forest fires--contribute to the greenhouse effect. So, on balance, what's the net effect?

Ozone and greenhouse gases are just part of the environmental headlines that Aura is investigating. It's also on a smog patrol, examining the air quality of the troposphere on a global basis, not just above urban centers where there's lots of data already, but also over unpopulated land masses and the oceans.

How these and other activities contribute to global climatic change is the third big goal of the Aura mission.

The EOS series began with the 1999 launch of Terra. Built by Lockheed Martin Missiles & Space, it carries a set of five instruments that take in the whole picture of the Earth's atmosphere, land and seas, and their interaction with solar radiation (AW&ST Oct. 4, 1999, p. 54).

Aqua was next, three years later. Built by Northrop Grumman Space Technology (NGST) here, it concentrates on Earth's water cycle (AW&ST Apr. 1, 2002, p. 50). Two of its six instruments duplicate a set on Terra and illustrate the way the EOS trio complements one another.