Math Models Could Help Clear the Air

The Code Red and Code Orange air-quality advisories that plague urban areas nationwide each summer mean hazy skies, scratchy throats, and wheezing coughs to most people. But to Dr. Montserrat Fuentes, a professor of statistics in the College of Physical and Mathematical Sciences, they also mean an increased risk of death for some people.

Fuentes was a member of a National Research Council panel that last spring established a cause-and-effect link between ground-level ozone and mortality rates. She also serves on a science advisory board which has recommended that the U.S. Environmental Protection Agency (EPA) slash the ozone standard in the Clean Air Act from 85 to 65 parts per billion. The recommendation is based on a cost-benefit analysis pitting human lives against the economics of meeting tougher restrictions. “The government has never taken mortality into account when setting air-quality standards,” she says. “Officials say there’s not enough evidence to connect pollution
and mortality.”

Fuentes has worked for years to prove such a connection. She has used statistics to solve environmental problems since working at the National Center for Atmospheric Research in Boulder, Colorado, almost a decade ago, and she now splits her time between NC State and EPA labs in Research Triangle Park. In recent years, she has developed complex statistical models to examine the relationship between short-term exposure to ozone and fine particles in air—soot, dust, and pollen—and health problems like asthma and heart disease. “It’s much more complicated than just seeing that the ozone level is high and this person died,” she says, noting weather, exposure levels, and factors like smoking need to be considered.

“The government has never taken mortality into account when setting air-quality standards.”

Epidemiologists at UNC-Chapel Hill and Duke, along with Drs. Chris Frey and Yang Zhang of NC State, provide the inputs for her models. Frey, an environmental engineering professor, helps determine pollution exposure using data from hundreds of air-quality monitoring stations nationwide. Zhang, an assistant professor in the Department of Marine, Earth and Atmospheric Sciences, uses his own models to characterize the pollution, including the types of particulate matter in the air, which can vary from one region to the next.

Plugging that data into her equations, Fuentes has determined that reducing daily ozone levels by 10 parts per billion would cut mortality rates by about 1 percent. Likewise, her models have shown a 6.6 percent jump in mortality when the monthly average exposure to fine particulate pollution increases by 10 parts per billion. With grants from the EPA and the National Institutes of Health, she now is examining particulate pollution more closely. “Instead of setting an air-quality standard based on the total level of particulate matter,” she says, “we should be regulating the sources like vehicle emissions and industrial plants.”


Dr. Montserrat Fuentes serves on national panels that established a link between ground-level ozone and mortality rates, and that recommended slashing allowable levels of ozone under the Clean Air Act.