Frederick's "Earth: The Atmosphere" class is the first in a three-quarter sequence ("Solid Earth" and "Evolution of Life" follow) offered as part of the College's Common Core and designed for non-
science majors. Of the 120 or so students in the room, many expect the trio of courses to be their last formal exposure to classroom science. Frederick accepts the prevailing climate.
But he also keeps an eye on the long-range forecast. He knows that it's impossible for his students to go through life without ever again hearing of floods, hurricanes, depletions in the ozone layer, global warming, or air pollution. As his course philosophy (Point No. 6 on the four-page course summary that he starts handing out) makes plain, they're going to need that formal exposure to atmospheric science: "Major decisions concerning the nation's environmental policy rest on our ability to understand these phenomena and to predict the future evolution of our atmosphere in response to natural and human influences."
Although the course's only assigned text is the weighty fourth edition of Meteorology: The Atmosphere and the Science of Weather, Frederick moves quickly to clear up any possible misunderstanding. "The lectures don't follow the text exactly. The text is much more geared to traditional meteorology. Meteorology isn't my vocation," he confesses, "and when you're done taking this course, you won't be able to forecast weather any better than you do now.
"You will, however," he promises, "know a lot more about environmental problems."
The course's material, he explains, falls into six sections, which he describes in terms of questions. For example, he says: Why should the Earth have an atmosphere? Why is the Earth's atmosphere so different from other planets in the solar system? Why does the wind blow? Exactly what is it that regulates the atmosphere and "allows people like us to run around taking classes"?
While he can't guarantee that the students will leave Phys. Sci. 109 knowing the answers to all of those questions, he ends the opening session promising to clear up conspicuous mists of ignorance: "I guarantee that you will know more than the reporters who write the stories that the politicians read and believe."
With a Ph.D. in astrogeophysics from the University of Colorado at Boulder, he's spent two decades as a researcher studying the interaction of solar radiation with the Earth's atmosphere, including high-profile work charting the effect of holes in the ozone layer over Antarctica. But his interest in the field goes back much further.
Witness the confession that he makes on the second day into the course. Upon learning as a schoolchild that the Earth's atmosphere is a mixture of 78 parts molecular nitrogen to 21 parts oxygen, he used to worry, he admits, about the efficacy of the mixing process: "What if a blob of pure nitrogen came by and suffocated me?"
A small burst of laughter interrupts his low-pressure delivery, and Frederick flashes a quick, sunny smile.
The lecture in progress-a look at Earth's atmospheric chemistry-is part of a larger attempt to try to figure out how the atmosphere evolved. Using an outsized stick of bright-yellow chalk, he quickly erases space on the chalkboard, raising a small cloud of dust in the process. "Here's part of the atmosphere right here," he jokes.
Up on the board goes a basic definition: "Atmosphere-envelope of gases and particles that surrounds a planet and is held to the planet by gravity."
"If you grabbed a volume of atmosphere right out of this room," Frederick says, his left hand reaching out to pluck the space above him, "this is what you'd get."
Turning to the board, he plots the volume of the three gases whose molecules make up the majority of dry air: nitrogen, oxygen, and argon.
But if you take a look at Earth's nearest neighbors in the solar system, he continues, you'll find a very different picture. The atmosphere of Venus is almost pure carbon dioxide, and the same is true for Mars. "Something had to happen on Earth to give us this very special mixture of molecules.
"One of the reasons," he explains, "involves life-like us." And plants. "We have oxygen because, in part, we have plants doing photosynthesis."
After outlining the three major gases, Frederick turns to another atmospheric component: "H2O-water vapor. The reason it's not on the list," he says, "is that its abundance is highly variable from one place to another." In its "typical, middle-range value," water makes up about 1 percent of the atmosphere, but in the tropics, water vapor can make up approximately 5 to 6 percent of the atmosphere. "On the hottest, most humid day in Chicago,"
Frederick adds, bringing the data back home, "the atmosphere can be 3 to 4 percent water vapor."
Just as the shower of percentages threatens to send the class into science-phobic doldrums, he shifts direction: "Why did I bore you with all these exact numbers?
"Because," he answers, "I wanted to talk about what's missing."
After nitrogen, oxygen, argon, and water vapor have been stirred into the mix, the atmospheric soup is still far from complete. "There are literally dozens of other molecules that we refer to as trace gases." Although each trace gas accounts for "much, much less than one-tenth of 1 percent" of the atmosphere's volume, some of them "are much more important to life on Earth than some of the major gases."
Frederick takes the two most highly publicized trace gases: carbon dioxide and ozone. The abundance of CO2 in the atmosphere today, he notes, is about .035 percent, or "double what existed in the atmosphere 300 years ago. Human activity created it." Although CO2 warms the Earth, too much of a good thing can be bad when it comes to global warming.
Then there's ozone. Produced by chemical reactions 30 kilometers above ground, ozone-or O3, as Frederick chalks it up on the board-absorbs the ultraviolet component of the sun's radiation, forming the "ozone shield" that protects life below.
The ozone layer, he says, is "what I do for a living…and what I do when I'm out for excitement." But back to the day's starting point: The blackboard definition of atmosphere has by now been almost lost in layer after layer of neatly lettered notes. So, with only a slight digression ("The Ultraviolet Radiation Index that became part of some daily weather reports this summer is produced by the government….It's based on one of my computer programs."), Frederick returns his students' attention to another part of the atmospheric envelope-particles.
Particles don't take up much space in the atmosphere, but size doesn't directly correlate with effect: "You need particles to build clouds. Without clouds, the Earth's climate would be very different."
Where do the particles come from? From forest fires, from chemical reactions in the atmosphere, even from one-celled plants living in the upper layers of the ocean near large land masses. Those phyloplankton "don't do much but photosynthesize." In the process, they emit dimethyl sulfide, which enters the atmosphere and creates particles-which, in turn, influence cloud formation.
"I like this," Frederick says, a small grin peeking out at the class. "That little one-celled critters in the ocean have influence on global cloud cover."
Once you know what the atmosphere is made of, the next step is another question-where did the atmosphere come from? And the answer, says Frederick, "starts right at the beginning, with where the universe came from." So, starting next class, "we're going to invent the universe."
Meanwhile, the classroom clock has reached 12:20 ±30 seconds. The blackboard is covered; notebooks are closing. "It looks like I'm out of time," he ends.
Outside Kent Hall, the air is still crisp and dry, and wisps of clouds still ride the sky: a sky that's a brew of nitrogen and oxygen, argon and water vapor, trace gases and particles-all part of an atmospheric envelope that's no longer quite so easy to take for granted.