Solution Makes Smog Glow

Ironically, a layer of ozone gas in the upper atmosphere protects living things from harmful UV rays of the sun, but ozone gas present at ground level is a pollutant. In fact, it is the principal component of smog. It forms when sunlight comes into contact with compounds from motor vehicle exhaust and industrial emissions.

The situation is even more ironic because ozone gas, O₃, consists of three oxygen atoms - just one more atom than the molecular oxygen (O₂) that humans need to breathe in order to survive. Although necessary for life, oxygen atoms tend to react with other compounds and damage whatever they encounter through the process of oxidation, and ozone is much more oxidative than O₂.

Kazunori Koide and colleagues at the University of Pittsburgh have developed a fluorescent solution that glows bright green in the presence of ozone. Compounds that can detect ozone and other oxidants are already in existence, but what makes this substance special is that it is specific for ozone.

Besides as a detector of urban pollutants, this probe should function as a biological sensor as well, for studies show that ozone may be produced by white blood cells in the human body as a natural weapon. However, the probes used in these studies were not specific to ozone. Because Koide’s probe is specific to ozone, it could show conclusively whether white blood cells are producing it.

“This [probe] is rationally designed,” Koide said. Ozone reacts with the probe through a process called ozonolysis, releasing aldehyde that then undergoes beta-elimination to release fluorescein, a common fluorescent dye. Fluorescein glows bright green under UV light. “Both reactions are typical undergraduate chemistry reactions,” Koide said, “but the [combination] is new.”

The researchers coated paper strips with the solution and tested it indoors in an unventilated office with two photocopiers and two laser printers. These devices produce ozone, which has a sweet aroma. “As long as your [office is] ventilated, it’s OK,” Koide said.

They also tested the solution out of direct sunlight in four high-traffic areas in Pittsburgh, which has ranked high in livability surveys in recent years, with much of its industry having been replaced by health care and technology businesses. “Pittsburgh is not really the ideal city to measure ozone outside,” Koide said. Results of a recent survey by the American Lung Association were an exception to the rule, placing Pittsburgh among the top cities in the US for particulate matter pollution, but not among the top cities for ozone pollution. That mantle belongs to Los Angeles.

Koide said that his lab will continue to pursue the three applications presented in this work: His group will calibrate the dye to ozone in the air, find out the extent to which ozone travels through the lungs of people who inhale it, and test white blood cells to see whether they really produce ozone. The researchers already have done some tests with blood serum and lung fluid.

David Shenkenberg
Features Editor
david.shenkenberg@laurin.com