(c) Limitations of the Indicator: Measurement limitations relate to detection limits,
interferences, time resolution, ease of operation and cost. Evaluation of the accuracy
of model results is critical before model output can be relied on for decision making.
To compare the indicator values obtained from different cities, countries should
ensure that monitoring networks, monitoring strategies, measuring methods, etc., are
compatible. (d) Alternative Definitions/Indicators: A composite indicator that weighs and sums
the main pollutants (e.g. PM10/2.5, nitrous oxides) into one measure could possibly
be used, but only if data for all pollutants were regularly available. However, the
recommendation of a European Environment Agency (EEA)/WHO workshop in
Berlin in 2002 was that this approach should not be used for indicator purposes. ASSESSMENT OF DATA (a) Data Needed to Compile the Indicator: Data must include time and spatially
representative concentrations, such as mean annual concentrations (mean
concentrations of the pollutant of concern, averaged over all hours of the year) or
percentile concentration (concentration of the pollutant of concern exceeded in 100 –
x% of hours, where x is the percentile as defined by the relevant standards). In
addition, information must be available on site location and type (e.g. industrial or
residential area). (b) National and International Data Availability and Sources: Data on ambient air
pollution concentrations are often routinely collected by national or local monitoring
networks. Universities and research institutes often also collect data for research
purposes. In addition, industry collects many data. Data on concentrations of major air
pollutants are available for major cities in Organisation for Economic Co-operation
and Development (OECD) countries, but more work is needed to improve
international comparability and to link these data to national standards and to human
health issues.
