Exposure to ozone and particulate matter of 2.5 µm or less (PM2.5) in air at levels above current US Environmental Protection Agency
(EPA) standards is a risk factor for respiratory symptoms in children with
To examine simultaneous effects of ozone and PM2.5 at levels
below EPA standards on daily respiratory symptoms and rescue medication use
among children with asthma.
Design, Setting, and Participants
Daily respiratory symptoms and medication use were examined prospectively
for 271 children younger than 12 years with physician-diagnosed, active asthma
residing in southern New England. Exposure to ambient concentrations of ozone
and PM2.5 from April 1 through September 30, 2001, was assessed
using ozone (peak 1-hour and 8-hour) and 24-hour PM2.5. Logistic
regression analyses using generalized estimating equations were performed
separately for maintenance medication users (n = 130) and nonusers (n = 141).
Associations between pollutants (adjusted for temperature, controlling for
same- and previous-day levels) and respiratory symptoms and use of rescue
medication were evaluated.
Main Outcome Measures
Respiratory symptoms and rescue medication use recorded on calendars
by subjects' mothers.
Mean (SD) levels were 59 (19) ppb (1-hour average) and 51 (16) ppb (8-hour
average) for ozone and 13 (8) µg/m3 for PM2.5.
In copollutant models, ozone level but not PM2.5 was significantly
associated with respiratory symptoms and rescue medication use among children
using maintenance medication; a 50-ppb increase in 1-hour ozone was associated
with increased likelihood of wheeze (by 35%) and chest tightness (by 47%).
The highest levels of ozone (1-hour or 8-hour averages) were associated with
increased shortness of breath and rescue medication use. No significant, exposure-dependent
associations were observed for any outcome by any pollutant among children
who did not use maintenance medication.
Asthmatic children using maintenance medication are particularly vulnerable
to ozone, controlling for exposure to fine particles, at levels below EPA