Air Quality Guidelines - World Health Organization Regional Office ...

184 chapter 7
Table 23. Health outcomes associated with changes in ambient ozone
concentration in epidemiological studies
Health outcome
Change in ozone
concentration (µg/m 3 )
Averaging Averaging
time time
1 hour 8 hours
Increase in symptom exacerbations
among adults or asthmatics
(normal activity):
25% 200 100
50% 400 200
100% 800 300
Increase in hospital admissions for
respiratory conditions: a
5% 30 25
10% 60 50
20% 120 100
a Given the high degree of correlation between the 1-hour and 8-hour ozone concentration in field studies,
the reduction in health risk associated with decreasing 1-hour or 8-hour ozone levels should be almost identical.
based on controlled exposure experiments, may be expected. The concentrations
presented in this table have been established by experts on the basis
of collective evidence from numerous studies and linear extrapolation in a
few cases where data were limited.
Epidemiological data show relationships between changes in various health
outcomes and changes in the peak daily ambient ozone concentration. Two
examples of such relationships are shown in Table 23. Short-term increases
in levels of ambient ozone are associated both with increased hospital admissions
with a respiratory diagnosis and respiratory symptom exacerbations,
both in healthy people and in asthmatics. These observations may be used
to quantify expected improvements in health outcomes that may be associated
with lowering the ambient ozone concentration. The values presented
in the table assume a linear relationship between ozone concentration and
health outcome. Uncertainties exist, however, concerning the forms of
these relationships and it is unclear whether similar response slopes can be