Air Quality Guidelines Global Update 2005 - World Health ...

OZONE
was associated with an increase of 62.9% (95% CI 18.4–124.1) in illness-related
absence rates, 82.9% (95% CI 3.9–222.0) in respiratory illnesses, 45.1% (95%
CI 21.3–73.7) in upper respiratory illnesses and 173.9% (95% CI 91.3–292.3) in
lower respiratory illnesses with wet cough (29). A time series study conducted in
the Republic of Korea reported an increase in absenteeism in elementary school
children in association with ozone (1.08 relative risk for an increase of 32 μg/m 3 )
(30). The public health significance of excess school absence, and its impact on
cost–benefit analyses for air pollution control effects, has been discussed by Künzli
et al. (31).
Tracking the severity of respiratory symptoms in asthmatic children is another
approach to determining the acute health effects of ozone. In a study conducted
in the New Haven, Connecticut area, ozone was significantly associated with respiratory
symptoms in asthmatic children; a 100-μg/m 3 increase in 1-hour ozone
was associated with increased likelihood of wheeze (by 35%) and chest tightness
(by 47%) (32). Within a cohort of 846 inner-city asthmatic children aged
4–9 years in seven American communities, an increase in ozone of 30 μg/m 3
was associated with a higher risk of morning symptoms (odds ratio = 1.16; 95%
CI 1.02–1.30) and with a 0.59% decline in morning peak expiratory flow rates
(PEFR) (95% CI 0.13–1.05) (33). In the same population, children born prematurely
or with low birth weight had greater declines in morning PEFR (1.8%) and
a higher incidence of morning symptoms (odds ratio = 1.42) (34). In a cohort of
children with asthma in 12 southern California communities, respiratory symptoms
were associated with the yearly variability of ozone (odds ratio = 1.06 per
2 μg/m 3 ; 95% CI 1.00–1.12).
There are large multi-city studies relating numbers of hospital admissions
for respiratory diseases (35) and COPD (36) to ambient ozone levels. Such associations
were robust enough to persist after controlling for temporal trends in
admission rates, day-of-week and seasonal effects, gaseous and particulate air
pollution, and climatic factors. Effects of ozone on respiratory admissions seem
stronger during warmer weather. The results of some representative studies relating
ozone to hospital admissions are briefly summarized in Table 2 of Annex 1.
A smaller number of studies looked for associations between ambient ozone levels
and cardiovascular conditions. Almost all the studies listed considered other
pollutants in the analyses. The vast majority of the studies obtained positive and
significant associations between variations in ambient ozone levels and increased
morbidity. The effects were manifested among children, elderly people, asthmatics
and those with COPD. The magnitude of the risk for respiratory morbidity
associated to an increase of 20 μg/m 3 ozone ranged from none to 5% (37). There
is some evidence of a threshold in the dose–response functions relating ozone to
respiratory disease, the lowest effect level being around 150 μg/m 3 .
Ten of the 15 studies focusing on cardiovascular diseases in Table 2 of Annex 1
showed no significant effects of ozone. In addition, there is no clear positive
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