We investigated the relations between ozone (O-3), nitrogen dioxide (NO2),
and respirable particles less than 10 mum in diameter (PM10) and school abs
enteeism in a cohort of 4th-grade school children who resided in 12 souther
n California communities. An active surveillance system ascertained the num
bers and types of absences during the first 6 months of 1996. Pollutants we
re measured hourly at central-site monitors in each of the 12 communities.
To examine acute effects of air pollution on absence rates, we fitted a two
-stage time series model to the absence count data that included distribute
d lag effects of exposure adjusted for long-term pollutant levels. Short-te
rm change in O-3, but not NO2 or PM10, was associated with a substantial in
crease in school absences from both upper and lower respiratory illness. An
increase of 20 ppb of O-3 was associated with an increase of 62.9% [95% co
nfidence interval (95% CI) = 18.4-124.1%] for illness-related absence rates
, 82.9% (95% CI = 3.9-222.0%) for respiratory illnesses, 45.1% (95% CI = 21
.3-73.7%) for upper respiratory illnesses, and 173.9% (95% CI = 91.3-292.3%
) for lower respiratory illnesses with wet cough. The short-term effects of
a 20-ppb change of O-3 on illness-related absenteeism were larger in commu
nities with lower long-term average PM10 [223.5% (95% CI = 90.4-449.7)] com
pared with communities with high average levels [38.1% (95% CI = 8.5-75.8)]
. Increased school absenteeism from O-3 exposure in children is an importan
t adverse effect of ambient air pollution worthy of public policy considera
tion.