Lungs' ozone defense defused.

• Position: Pollution

Exactly how airborne particles harm our lungs still puzzles epidemiologists, physicians, environmental scientists, and policymakers. Now researchers at the California Institute of Technology, Pasadena, have found that they act by impairing the lungs' natural defenses against ozone.

"I've long been perplexed by the inconclusive debates, based on epidemiological and clinical evidence, over whether the causative agent is particle size or some unspecified chemical component. I always felt that some missing chemistry might be associated with particle effects," muses A.J. Colussi, senior research associate in environmental science and engineering.

The researchers harnessed breakthroughs in chemistry to focus on what happens when air meets the thin layer of antioxidant-rich fluid that covers our lungs, protecting them from ozone, an air pollutant that pervades major cities. Adapting an innovation in mass spectrometry by Nobel laureate John Fenn of Virginia Commonwealth University, Richmond, the Caltech team studied how aqueous ascorbic acid, the essential antioxidant also known as vitamin C and present in lungs' fluid layer, reacts with ozone gas.

Under normal physiological conditions, ascorbic acid instantly scavenges ozone, generating innocuous by-products. However, the researchers discovered that, when the fluid is acidic--a...