Norman R. Pace, a microbiologist at the University of Colorado Boulder, pioneered the use of DNA to study microbes. He has searched for extremophiles (organisms that can exist in extreme environments) in the hot springs of Yellowstone National Park and once descended in the submersible Alvin to examine microbial life on hydrothermal vents. He greets visitors, like any microbiologist who has seen too much, with a fist bump.

Dr. Pace has also surveyed an exotic environment much more familiar to New Yorkers: the subway. The goal? To find out exactly what we’re breathing down there — and if any of its invisible critters are cause for worry. His study also provides a “pre-event” baseline, an idea of what’s normal — useful in the event of a bioterrorism attack, recent flooding or other catastrophe.