The Air Quality Standards Regulations (Northern Ireland) 2007

PART 3 Ozone and nitrogen dioxide assessed at ozone sampling points

16.  The data quality objectives set out in the following table, for allowed uncertainty of assessment methods, of minimum time coverage and of data capture of measurement, are provided to guide quality-assurance programmes—

	For ozone, NO and NO2 assessed at ozone sampling points
Continuous fixed measurement
Uncertainty of individual measurements	15%
Minimum data capture	90% during summer; 75% during winter
Indicative measurement
Uncertainty of individual measurements	30%
Minimum data capture	90%
Minimum time coverage	>10% during summer
Modelling
Uncertainty
1 hour averages (daytime)	50%
8 hours daily maximum	50%
Objective estimation
Uncertainty	75%

17.  The uncertainty (on a 95% confidence interval) of the measurement methods shall be evaluated in accordance with the principles laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993), or the methodology in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994) or equivalent. The percentages for uncertainty in the table are given for individual measurements, averaged over the period for calculating target values and long-term objectives, for a 95% confidence interval. The uncertainty for continuous fixed measurements shall be interpreted as being applicable in the region of the concentration used for the appropriate threshold.

18.  The uncertainty for modelling and objective estimation means the maximum deviation of the measured and calculated concentration levels, over the period for calculating the appropriate threshold, without taking into account the timing of events.

19.  “Time coverage” means the percentage of time considered for settling the threshold value during which the pollutant is measured.

20.  “Data capture” means the ratio of the time for which the instrument produces valid data, to the time for which the statistical parameter or aggregated value is to be calculated.

21.  The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or normal maintenance of the instrumentation.