However, it should be noted that QA/QC programmes are currently only implemented

efficiently in a few monitoring networks, and the quality of the measurements can be

significantly improved by adoption of requirements. The following data quality

objectives that can be achieved though the implementation of this QA/QC programme


· Continuous or semi-continuous measurements: 15% (individual measurements)

· Indicative measurements: 25% (individual measurements)

· Modelling 30 - 50% (may be different for daily, monthly or yearly averages)

· Objective estimation: 50 to 100%

The time coverage for continuous measurements should be 100%, excluding

calibration time. For indicative measurements a minimum of 50% should be covered


(every second day, or at random, or 6 months per year for example). A lower coverage

can be discussed, but it must be ensured that the temporal distribution of samples

yields a statistically sound long-term mean. Minimum data capture for continuous

measurements are 90%. Breakdown of instrument , excluding calibrations, allowance

is 36 days per year.

Further details on required QA/QC will be given in the Guidance Report (van Aalst et

al. 1997).

The measurements of NO2 can be divided into three separate steps; sampling,

analysis/measurement and calibration (when the analysis method is not absolute). The

tables in Annex III give the currently used methods and their main advantages and




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