# The Air Quality Limit Values Regulations 2001, Part I: Data-quality objectives


The following data-quality objectives for the required accuracy of assessment methods, of minimum time coverage and of data capture of measurement are laid down to guide quality-assurance programmes.
Suphur dioxide, nitrogen dioxide and oxides of nitrogen
Particulate matter and lead
Continuous measurement
Accuracy
15%
25%
Minimum data capture
90%
90%
Indicative measurement
Accuracy
25%
50%
Minimum data capture
90%
90%
Minimum time coverage
14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)
14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)
Modelling
Accuracy:
Hourly averages
50%–60%
Daily averages
50%
Annual averages
30%
50%
Objective estimation
Accuracy:
75%
100%
The accuracy of the measurement is defined as laid down in the ‘ Guide to the Expression of Uncertainty of Measurements ’ (ISO 1993) or in ISO 5725-1 ‘ Accuracy (trueness and precision) of measurement methods and results ’ (ISO 1994). The percentages in the table are given for individual measurements averaged, over the period considered, by the limit value, for a 95% confidence interval (bias + two times the standard deviation). The accuracy for continuous measurements should be interpreted as being applicable in the region of the appropriate limit value.
The accuracy for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking account the timing of the events.
The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation.
The Secretary of State may allow for random measurements to be made instead of continuous measurements for particulate matter and lead by methods for which accuracy within the 95% confidence interval with respect to continuous monitoring has been demonstrated to be within 10%. Random sampling must be spread evenly over the year.

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Source: https://www.legislation.gov.uk/uksi/2001/2315/schedule/5/part/I (the official version)
Page: https://openlegislation.uk/air-quality-limit-values-regulations-2001/schedule-5/part-I
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.