Ozone Deaths Not Due to Changes in Temperature
Ozone air pollution has been associated with changes in daily mortality, but because high ozone days are generally quite hot, researchers seek to separate out the effect of temperature.
The case-crossover approach allows each person to serve as his own control, by comparing the day of death with a day when the person did not die. This controls for season as well as individual risk factors by matching the control day with the day of the event.
This technique was used in a study of over one million deaths in 14 U.S. cities: Birmingham, Boulder, Canton, Chicago, Cincinnati, Colorado Springs, Columbus, Detroit, Houston, New Haven, Pittsburgh, Provo, Seattle and Spokane.
The study found that during the summer months, after controlling for temperature, a 10 ppb increase in maximum hourly ozone concentrations was associated with a small increase in the risk of death. Researchers concluded that “the association between ozone and mortality risk is unlikely to be caused by confounding by temperature.”
Schwartz J. How Sensitive is the Association between Ozone and Daily Deaths to Control for Temperature? Am J Respir Crit Care Med 2005; 171:627-631.
For a copy of the abstract click here.
