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

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AIR QUALITY GUIDELINES
In addition to guideline values, interim targets are given for levels of PM, ozone
and sulfur dioxide. Th ese are proposed as incremental steps in a progressive reduction
of air pollution, and are intended for use in areas where pollution is high.
Th ese targets aim to promote a shift from high air pollutant concentrations, with
acute and serious health consequences, to lower concentrations. If these targets
were to be achieved, one could expect signifi cant reductions in risks for acute and
chronic health eff ects from air pollution. Progress towards the guideline values
should, however, be the ultimate objective of air quality management and health
risk reduction in all areas.
Th e fact that other pollutants, such as carbon monoxide, were not included
in the present review refl ects the limited resources available to the project. As a
result, the 2000 WHO guidelines (1) for pollutants not considered in the current
update remain in eff ect. Th e steering group recommends that the update of the
guidelines be expanded to include additional pollutants as soon as possible, as
resources become available.
Key scientific issues in the development of the guidelines
Th e guidelines are based on the extensive scientifi c evidence on air pollution and
its health consequences. Although this information has gaps and uncertainties,
it off ers a strong foundation for the guidelines. Several overall research fi ndings
need to be emphasized with regard to the guidelines.
First, the evidence for ozone and PM shows risks to health at concentrations
currently found in many cities in developed countries; these epidemiological
fi ndings imply that guidelines cannot provide full protection, since thresholds
below which adverse eff ects do not occur have not been identifi ed.
Second, an increasing range of adverse health eff ects has been linked to air
pollution, and at ever-lower pollutant concentrations. Th is is especially true of
airborne PM. New studies use more refi ned methods and more subtle but sensitive
indicators of eff ects such as physiological measures (e.g. changes in lung
function, infl ammation markers). Th erefore, the updated guidelines could be
based both on these sensitive indicators and on the most critical and traditional
population health indicators, such as mortality and unscheduled hospital admissions.
Th ird, the complexity of the air pollution mixture has been better characterized,
making more clear the limitations of controlling air pollution through
guidelines for single pollutants. Nitrogen dioxide, for example, is a product of
combustion and is generally found in the atmosphere in close association with
other primary pollutants, including ultrafi ne particles. It is also a precursor of
ozone and therefore co-exists in photochemically generated oxidant pollution.
Nitrogen dioxide is itself toxic, and its concentrations are oft en strongly correlated
with those of other toxic pollutants. As it is easier to measure, it is oft en used
as a surrogate for the mixture as a whole. Achieving the guidelines for individual