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

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AIR QUALITY GUIDELINES
In Europe the criteria that guide the quantification of data quality objectives
are defined such as to permit:
• comparison of air quality across Europe;
• detection, over a reasonable period, of the trends in air quality in Europe as
well as in each area where stations are located; and
• assessment of exposure.
Data quality objectives may also include specifications of accuracy, precision,
area of representativeness and temporal coverage. Setting quality objectives and
following a well-defined quality assurance and quality control (QA/QC) programme
are essential for obtaining good quality data and comparable information.
The measurement methods used and information concerning data quality
requirements have not always been reported and controlled. Data quality may
thus vary from one city to another and from region to region.
Representativeness of data
Information about the ambient air pollution levels have been based on measurements
representative for different types of area and microenvironment, such as:
• traffic, near roads and in streets;
• urban areas, representative for the kilometre scale inside the urban airshed;
and
• rural areas, away from local sources representative for residential areas.
The selection of representative measurement sites, as well as the use of different
measurement methods, has made the interpretation and comparisons of the data
difficult. Concentration levels presented in this book must thus be looked on as
indicative of the air quality to be expected in different urban areas, in different
regions and on different continents. Fig. 1 illustrates typical average concentrations
of nitrogen dioxide, PM10 and ozone in rural, urban and traffic environments
in Europe.
The ranges of concentration shown in Fig. 1 illustrate the variability in concentrations
between different measurement sites, different environments and different
cities. Sources of PM10, nitrogen dioxide and other pollutants are normally of
local origin, and concentrations often increase the closer one is to the source. For
ozone, the picture is more complicated owing to chemical reactions involved in
the build-up of ground-level ozone concentrations. Various factors independent
of the air quality may affect the data, and therefore it is important to have information
about site locations, measurement methods and data quality assurance
procedures when evaluating air pollution levels in different cities and countries.
Megacities of the world
Air pollution in megacities around the world has been an issue for several years.
At the turn of the century there were 24 megacities each with more than 10 million