Effects of Ambient Ozone on Respiratory Function and Symptoms in Mexico City Schoolchildren

Abstract The effects of ambient ozone (O3) on respiratory function and acute respiratory symptoms were evaluated in 143 7- to 9-yr-old schoolchildren followed longitudinally at 1-to 2-wk intervals over a period of 6 months at three schools in Pedregal, Mexico City. The maximum O3 level exceeded the World Health Organization guideline of 80 ppb and the U.S. standard of 120 ppb in every week. For an increase from lowest to highest in the mean O3 level during the 48 hr before spirometry (53 ppb), logistic regression estimated relative odds of 1.7 for a child reporting cough/phlegm on the day of spirometry. For the full population, the mean O3 level during the hour before spirometry, not adjusted for temperature and humidity, predicted a significant decrement in FVC but not in FEV1 or FEF25–75. In contrast, the mean O3 level during the previous 24-, 48-, and 168-h periods predicted significant decrements in FEV1 and FEF25–75 but not in FVC. Ozone was consistently associated with a greater decrement in lung function for the 15 children with chronic phlegm as compared with the children without chronic cough, chronic phlegm, or wheeze. Ozone in the previous 24-, 48-, and 168-h periods predicted decrements in FEV1 for children of mothers who were current or former smokers, but not for children of mothers who were never smokers. Many of these effects were reduced in multiple regression analyses including temperature and humidity, as temperature and O3 were highly correlated. In univariate analyses, for the full population, a 53 ppb rise in mean 48-h O3 level predicted a 2% decrement in FEV1 and a 7.4% decrement in FEF25–75. These decrements in FEV1 and FEF25–75 may reflect an inflammatory process in the airways that differs from the acute physiologic response to O3 associated with a decrement in FVC and the inability to take a deep breath. These results also suggest that children with a history of chronic phlegm production or passive smoke exposure may be more susceptible to respiratory irritants.