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SCHEDULE 6 continued PART 5
8. In cases where zones attain the long-term objectives, the number of sampling points for ozone must, in combination with other means of supplementary assessment such as air quality modelling and co-located nitrogen dioxide measurements, be sufficient to examine the trend of ozone pollution and check compliance with the long-term objectives.
9. The number of stations located in agglomerations and other zones may be reduced to one-third of the number specified in the Table in Part 4. Where information from fixed measurement stations is the sole source of information, at least one monitoring station should be kept. If, in zones where there is supplementary assessment, the result of this is that a zone has no remaining station, co-ordination with the number of stations in neighbouring zones must ensure adequate assessment of ozone concentrations against long-term objectives.
10. The number of rural background stations should be 1 per 100,000 km2.
Regulation 15(6)(b) Regulation 16(1)
1. The following information must be compiled for zones within which sources other than fixed measurement are employed to supplement information from fixed measurement or as the sole means of air quality assessment—
(a) a description of assessment activities carried out;
(b) the specific methods used, with references to descriptions of the method;
(c) the sources of data and information;
(d) a description of results, including uncertainties and, in particular, the extent of any area or, if relevant, the length of road within the zone over which concentrations exceed the limit value or, as the case may be, the limit value plus applicable margin of tolerance and of any area within which concentrations exceed the upper assessment threshold or the lower assessment threshold;
(e) for limit values the object of which is the protection of human health, the population potentially exposed to concentrations in excess of the limit value.
2. Where possible, maps must be compiled showing concentration distributions within each zone.
3. Where an air quality model is used for assessment, references to descriptions of the model and information on the uncertainty must be compiled. The uncertainty for modelling is defined as the maximum deviation of the measured and calculated concentration levels, over a full year, without taking into account the timing of the events.
4. Where objective estimation techniques are used, the uncertainty must not exceed 100%.
5. For substances to be analysed in the PM10 fraction, the sampling volume refers to ambient conditions.
6. The following information should be compiled for zones within which sources other than measurements are employed to supplement information from measurement—
(a) a description of the assessment activities carried out;
(b) specific methods used, with references to descriptions of the method;
(c) sources of data and information;
(d) a description of results, including uncertainties and, in particular, the extent of any area within the zone over which concentrations exceed long-term objectives or target values;
(e) for long-term objectives or target values whose object is the protection of human health, the population potentially exposed to concentrations in excess of the threshold.
7. The National Assembly must ensure that maps are compiled showing concentration distributions within each zone.
Regulation 16(2) Regulation 17(2)(d) Regulation 19(6) Regulation 20(4)
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 nitrogen | Lead, PM2·5 and PM10 | |
|---|---|---|
| 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% |
2. The accuracy of the measurement is defined as laid down in the “Guide to the Expression of Uncertainty of Measurements” (ISO 1993)(12) 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.
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—
| Benzene | Carbon monoxide | |
|---|---|---|
| Fixed measurements | ||
| Uncertainty | 25% | 15% |
| Minimum data capture | 90% | 90% |
| Minimum time coverage | 35% 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 | ||
| Uncertainty | 30% | 25% |
| Minimum data capture | 90% | 90% |
| Minimum time coverage | 14% (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 averages | 50% | |
| Annual averages | 50% | |
| Objective estimation | ||
| Uncertainty | 100% | 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.
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The Air Quality Standards (Wales) Regulations 2007