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The Air Quality Standards (Wales) Regulations 2007

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Regulation 16(2) Regulation 17(2)(d) Regulation 19(6) Regulation 20(4)

SCHEDULE 8Data quality objectives

PART 1Group A pollutants and PM2·5

Group A pollutants (other than benzene and carbon monoxide) and PM2·5

1.  Data-quality objectives are set out in the table and paragraphs below 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—

Sulphur dioxide, nitrogen dioxide and oxides of nitrogenLead, PM2·5 and PM10
Continuous measurement
Accuracy15%25%
Minimum data capture90%90%
Indicative measurement
Accuracy25%50%
Minimum data capture90%90%
Minimum time coverage14% (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 averages50%-60%
Daily averages50%
Annual averages30%50%
Objective estimation
Accuracy75%100%

2.  The accuracy of the measurement is defined as laid down in the “Guide to the Expression of Uncertainty of Measurements” (ISO 1993)(1) 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.

3.  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

4.  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.

5.  The National Assembly may allow for random measurements to be made instead of continuous measurements for lead, PM2·5 and PM10 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.

Benzene and carbon monoxide

6.  The data quality objectives 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—

BenzeneCarbon monoxide
Fixed measurements
Uncertainty25%15%
Minimum data capture90%90%
Minimum time coverage35% at urban background and traffic sites (distributed over the year to be representative of various conditions for climate and traffic); 90% at industrial sites
Indicative measurements
Uncertainty30%25%
Minimum data capture90%90%
Minimum time coverage14% (one day’s measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)14% (one measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)
Modelling
Uncertainty:
Eight-hour averages50%
Annual averages50%
Objective estimation
Uncertainty100%75%

7.  The uncertainty (on a 95% confidence interval) of the assessment methods must be evaluated in accordance with the “Guide to the Expression of Uncertainty of Measurements” (ISO 1993) or the methodology of ISO 5725:1994. The percentages for uncertainty in the above table are given for individual measurements averaged over the period considered by the limit value, for a 95% confidence interval. The uncertainty for the fixed measurements should be interpreted as being applicable in the region of the appropriate limit value.

8.  The uncertainty 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 into account the timing of the events.

9.  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.

10.  The National Assembly may allow for random measurements to be made instead of continuous measurements for benzene if the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25%. Random sampling must be spread evenly over the year.

PART 2Group B pollutants, polycyclic aromatic hydrocarbons and total gaseous mercury

11.  The data quality objectives set out in the table and paragraphs below are provided to guide quality assurance programmes—

Benzo(a) pyreneArsenic, cadmium and nickelPolycyclic aromatic hydrocarbons and total gaseous mercuryTotal deposition
(1)

Indicative measurement being measurements which are performed at reduced regularity but fulfil the other data quality objectives.

Uncertainty
Fixed and indicative measurements50%40%50%70%
Modelling60%60%60%60%
Minimum data capture90%90%90%90%
Minimum time coverage
Fixed measurements33%50%
Indicative measurements(1)14%14%14%33%

12.  The uncertainty (expressed at a 95 % confidence level) of the methods used for the assessment of ambient air concentrations must be evaluated in accordance with the CEN Guide to the Expression of Uncertainty in Measurement (ENV 13005-1999)(2), the methodology of ISO 5725:1994, and the guidance provided in the CEN Report, “Air quality — Approach to uncertainty estimation for ambient air reference measurement methods” (CR 14377:2002E). The percentages for uncertainty in the above table are given for individual measurements, which are averaged over typical sampling times, for a 95 % confidence interval. The uncertainty of the measurements should be interpreted as being applicable in the region of the appropriate target value. Fixed and indicative measurements must be evenly distributed over the year in order to avoid skewing of results.

13.  The requirements for minimum data capture and time coverage do not include losses of data due to regular calibration or normal maintenance of the instrumentation. Twenty-four-hour sampling is required for the measurement of benzo(a)pyrene and other polycyclic aromatic hydrocarbons. With care, individual samples taken over a period of up to one month may be combined and analysed as a composite sample, provided the method ensures that the samples are stable for that period. The three congeners benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)fluoranthene where they are difficult to resolve analytically. In such cases they can be reported as sum. Twenty-four hour sampling is also recommended as advisable for the measurement of arsenic, cadmium and nickel concentrations. Sampling must be spread evenly over the weekdays and the year. For the measurement of deposition rates monthly, or weekly, samples throughout the year are recommended.

14.  The National Assembly may allow for use of wet only instead of bulk sampling if it can be demonstrated to its satisfaction that the difference between them is within 10 %. Deposition rates should generally be given as μg/m2 per day.

15.  The National Assembly may apply a minimum time coverage lower than indicated in the table, but not lower than 14 % for fixed measurements and 6 % for indicative measurements provided that it is satisfied that it can be demonstrated that the 95 % expanded uncertainty for the annual mean, calculated from the data quality objectives in the table according to ISO 11222:2002 — “Determination of the uncertainty of the time average of air quality measurements” will be met.

PART 3Ozone and nitrogen dioxide assessed at ozone sampling points

16.  The data quality objectives set out in the table and paragraphs below, for allowed uncertainty of assessment methods, and 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 measurements15%
Minimum data capture90% during summer; 75% during winter
Indicative measurement
Uncertainty of individual measurements30%
Minimum data capture90%
Minimum time coverage>10% during summer
Modelling
Uncertainty
1 hour averages (daytime)50%
8 hours daily maximum50%
Objective estimation
Uncertainty75%

17.  The uncertainty (on a 95% confidence interval) of the measurement methods must 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 should 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”(“yr amser a gwmpesir”) means the percentage of time considered for settling the threshold value during which the pollutant is measured.

20.  “Data capture” (“y data a gipir”) 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.

(1)

Copies of International Standards Organisation publications may be purchased from the British Standards Institution ('BSI') Sales Department either by telephone (0208 996 9001) or by post from the BSI, Standards House, 389 Chiswick High Road, London W4 4AL, http://www.bsi-global.com

(2)

European Committee for Standardisation (“CEN”) publication; the address of CEN is 36, Rue de Stassart, B-1050, Brussels, Belgium http://www.cenorm.be

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