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Ozone and mortality

Freeway filled with cars

Ozone is not emitted directly by car engines, but rather is formed in the atmosphere when nitrogen oxides and volatile organic compounds react in the presence of sunlight. Thousands of sources contribute to ground-level ozone, including motor vehicle exhaust and chemical solvents. (Photo by Carlye Calvin, ©UCAR)

Ground-level ozone, an air pollutant that is monitored by the Environmental Protection Agency (EPA), damages human health by irritating the respiratory system, reducing lung function, damaging lung cells, and aggravating asthma and other chronic conditions. In March 2008, the EPA strengthened ozone standards by lowering acceptable limits from 84 parts per billion to 75 parts per billion.

NCAR postdoctoral researcher Yongku Kim is using epidemiologic data to study the effects of ozone regulation on human health. He’s leading an assessment of how various regulatory standards for ozone may affect non-accidental mortality, including respiratory-related deaths during ozone season. The assessment uses statistical methods based on hierarchical Bayesian models to predict the potential effects of the different regulatory standards. It also analyzes the variability of the results and how they are impacted by different modeling assumptions. Although other papers have detailed the relationship between ozone and human mortality, Kim's assessment is unique for its technical and statistical approach to assessing the relationship between new ozone regulations and mortality.

Kim’s research shows a statistical correlation between ozone regulations and mortality, with lower limits of acceptable ozone linked to a decrease in deaths. His projections show that, if levels were decreased to 70 parts per billion, mortality would decrease by approximately 1.40–2.78 deaths per 1,000 total deaths; if levels were reduced further to 60 parts per billion, a reduction of approximately 2.50–4.81 deaths per 1,000 total deaths would be expected.

“The mortality reduction is clear,” Kim says. “Policymakers can use this output to make decisions.”