Air Pollution Ozone
3. How are we exposed to Ozone (O3)?
- 3.1 Critical sources of Ozone responsible for health effects
- 3.2 Relationship between ambient levels and personal exposure to Ozone
- 3.3 Short-term exposure to high peak levels or exposure in hot spots of Ozone
3.1 Critical sources of Ozone responsible for health effects
Ozone is a secondary
pollutant produced by
photochemical activity in
the presence of precursors.
is also subject to long-range atmospheric transport and may be
considered as a trans-boundary problem.
The same information on
3.2 Relationship between ambient levels and personal exposure to Ozone
Can the differences influence the results of studies?
exposure measurements are not
well correlated with
concentrations measured at
To account for this, additional information (e.g., activity
patterns) was used in some studies to improve personal
exposure estimates based on
fixed site measurements. As
is a highly reactive gas,
concentrations indoors are
generally lower (less than 50%) than those in
ambient air. There are very
few indoor sources (such as photocopiers or
electrostatic air cleaners)
in most homes. Outdoor
ozone levels vary across
city areas because ozone is scavenged as it reacts with
Early morning and late night exposures outdoors are lower
because of the daily cycle of ambient ozone concentrations.
Thus, for ozone, cumulative daily or long-term average exposures
are largely determined by exposures occurring outdoors in the
afternoon. Exposure underestimations may occur in studies on
human populations when
outdoor ozone concentration
measurements are used to estimate short-term personal ozone
exposure. Such misclassifications may cause true effects to
appear less strong or be concealed.