As high-school chemistry may have taught you, it's easy to calculate the odds that a molecule you've just inhaled came from the dying breath of Julius Caesar. But imagine you need to account for the molecule's experiences in the meantime. Say you have to weigh the chances of each chemical transformation it might have undergone—as it ascended from ancient Rome, drifted through the dirt and droplets of clouds, and endured temperatures, solar rays, and collisions with gaseous chemicals in changing combinations. Now for extra credit, explain how the global distribution of gases shifts and evolves. Include all life, pollution, inanimate matter, and climate change.

You might raise your hand and ask to use a supercomputer. In fact, Don Wuebbles and Ken Patten of the University of Illinois at Urbana-Champaign and collaborator Rao Kotamarthi of Argonne National Laboratory did just that. Through simulations on an NCSA Origin2000 supercomputer, they are examining the lives of molecules in Earth's atmosphere and contemplating the planet's fate.

Most closely they are watching ozone. At stratospheric heights, ozone shields Earth from solar radiation. But lower down it is a toxin, produced when benign gases react with car and factory pollution or with lightning. In collaboration with the U.S. Environmental Protection Agency (EPA), the researchers are evaluating alternatives to such notorious ozone-destroying compounds as chlorofluorocarbons (CFCs). With other simulations, they are pinpointing the sources of plumes of pollution above the supposedly pristine south Pacific. Ultimately, they want to predict the pace at which the protective ozone layer will recover under different international emission control agreements.

The researchers comprise one of a few teams charged with testing new software that simulates the chemistry and migration of gases around the globe. This software—a revamping of the Model for OZone And Related chemical Tracers, or MOZART-2 for short—feeds on output from a global climate simulation and takes twice as much computer power as the climate simulation. The chemical transport model is a project of the National Center for Atmospheric Research (NCAR), which intends to release MOZART-2 by the end of this year.

Access Online | Posted 9-11-2001