Aura, the third and final satellite in NASA's Earth Observing System series, will take off Monday or Tuesday, its launch delayed by at least 24 hours due to a problem with the rocket. The EOS satellites -- Terra, Aqua, and now Aura -- study the complex interaction between geophysical systems.

Aura is designed to help answer important questions about atmospheric change, with a particular focus on the ozone layer:

One question that researchers have asked is: Is the stratospheric ozone layer is recovering? International agreements, like the Montreal Protocol, have banned ozone destroying chemicals like Chlorofluorocarbons (CFCs), but scientists are unclear about the effectiveness of these treaties. Aura will accurately detect global levels of CFCs, and their byproducts, chlorine and bromine, which destroy the ozone layer.

Another question that researchers need more information to: What are the processes controlling air quality? Aura will help greatly to unravel some of these mysteries by tracking the sources and processes controlling global and regional air quality. When ozone exists in the lower atmosphere, the troposphere, it acts as an air pollutant. Gasoline and diesel engines give off gases in the summer that create ozone and smog. Aura will help scientists follow the sources of ozone and its precursors.

Finally, Aura will offer insights into the question: How is the Earth's climate changing? As the composition of Earth's atmosphere changes, so does its ability to absorb, reflect and retain solar energy. Greenhouse gases, including water vapor, trap heat in the atmosphere. Airborne aerosols from human and natural sources absorb or reflect solar energy based on color, shape, size, and substance. The impact of aerosols, tropospheric ozone and upper tropospheric water vapor on Earth's climate remains largely un-quantified, but now Aura will have the unique ability to monitor these agents.

One way that Aura will help us better understand ozone and air pollution is with the resolution of its Ozone Monitoring Instrument. Previous satellites used to monitor ozone could only resolve a regional scale of about 50x200 miles. Aura's OMI will resolve down to 8x8 miles, sufficient to monitor a single urban center. This will greatly increase the sophistication of our understanding of how local air pollution develops, propagates, and changes.

The three EOS satellites will soon form the core of the "A-Train" set of environmental orbiters, which will work together to study the planet. The next in the series is a Cloud-Aerosol satellite intended specifically to better understand the role of cloud formation in climate change.