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

HEALTH IMPACT ASSESSMENT
Fig. 1. Schematic presentation of the main steps of health impact assessment
Air pollution data
Modelled levels a
(or monitored)
a If modelled data are used, the
approach can be used to assess
the impact of emission reduction
strategies on different health
outcomes.
Exposure estimate
Population risk
Overall
Susceptible groups
Impact estimate
Concentration–
response function(s)
Background data
Mortality rates
Morbidity rates
the background or reference concentration to ultimately determine the change
in air pollution being evaluated. The background level is the “natural” concentration
of the pollutant that would exist even without any man-made pollution.
The reference concentration can be an air pollution standard or goal developed
by WHO, USEPA or other governmental institutions. As an alternative, some
analysts have simply estimated the impact of some assumed percentage reduction,
such as 10–20%, from current levels. Finally, some assessments have calculated
the impacts of a specific control strategy, such as the USEPA analysis of
motor vehicle standards (5), or are based on the modelled contribution of certain
categories of pollution sources. For example, the CAFE analysis estimated the
impact of PM from anthropogenic sources (24).
Size and composition of population groups exposed to current levels
of air pollution
The relevant population exposed to the change in ambient concentrations is the
second data requirement for the assessment. Ideally, these data can be obtained
at the local level from census information or other available sources. In addition,
since some of the CR functions are specific to certain subgroups (e.g. the elderly,
asthmatics, infants and children), baseline demographic data on subgroups
would be useful.
Background incidence of mortality and morbidity
Since the epidemiological studies typically estimate relative risk (i.e. the percentage
change in health effects per unit of pollution), the third input into the analysis
is the underlying incidence of the health effect being estimated (e.g. the underlying
mortality rate in the population or deaths per thousand people). Ideally,
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