| a Member States may apply random measurements instead of continuous measurements for benzene, lead and particulate matter if they can demonstrate to the Commission that the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25 % and the time coverage is still larger than the minimum time coverage for indicative measurements. Random sampling must be evenly distributed over the year in order to avoid skewing of results. The uncertainty due to random sampling may be determined by the procedure laid down in ISO 11222 (2002) ‘Air Quality — Determination of the Uncertainty of the Time Average of Air Quality Measurements’. If random measurements are used to assess the requirements of the PM10 limit value, the 90,4 percentile (to be lower than or equal to 50 µg/m3) should be evaluated instead of the number of exceedances, which is highly influenced by data coverage. | ||||
| b Distributed over the year to be representative of various conditions for climate and traffic. | ||||
| c One day's measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year. | ||||
| d One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year. | ||||
| Sulphur dioxide, nitrogen dioxide and oxides of nitrogen and carbon monoxide | Benzene | Particulate matter (PM10/PM2,5) and lead | Ozone and related NO and NO2 | |
|---|---|---|---|---|
| Fixed measurementsa | ||||
| Uncertainty | 15 % | 25 % | 25 % | 15 % |
| Minimum data capture | 90 % | 90 % | 90 % | 90 % during summer 75 % during winter |
| Minimum time coverage: | ||||
—urban background and traffic | — | 35 %b | — | — |
—industrial sites | — | 90 % | — | — |
| Indicative measurements | ||||
| Uncertainty | 25 % | 30 % | 50 % | 30 % |
| Minimum data capture | 90 % | 90 % | 90 % | 90 % |
| Minimum time coverage | 14 %d | 14 %c | 14 %d | > 10 % during summer |
| Modelling uncertainty: | ||||
| Hourly | 50 % | — | — | 50 % |
| Eight-hour averages | 50 % | — | — | 50 % |
| Daily averages | 50 % | — | not yet defined | — |
| Annual averages | 30 % | 50 % | 50 % | — |
| Objective estimation | ||||
| Uncertainty | 75 % | 100 % | 100 % | 75 % |
The uncertainty (expressed at a 95 % confidence level) of the assessment methods will be evaluated in accordance with the principles of the CEN Guide to the Expression of Uncertainty in Measurement (ENV 13005-1999), 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 averaged over the period considered by the limit value (or target value in the case of ozone), for a 95 % confidence interval. The uncertainty for the fixed measurements shall be interpreted as being applicable in the region of the appropriate limit value (or target value in the case of ozone).
The uncertainty for modelling is defined as the maximum deviation of the measured and calculated concentration levels for 90 % of individual monitoring points, over the period considered, by the limit value (or target value in the case of ozone), without taking into account the timing of the events. The uncertainty for modelling shall be interpreted as being applicable in the region of the appropriate limit value (or target value in the case of ozone). The fixed measurements that have to be selected for comparison with modelling results shall be representative of the scale covered by the model.
The uncertainty for objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered, by the limit value (or target value in the case of ozone), without taking into 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 following information shall be compiled for zones or agglomerations within which sources other than measurement are employed to supplement information from measurement or as the sole means of air quality assessment:
a description of assessment activities carried out,
the specific methods used, with references to descriptions of the method,
the sources of data and information,
a description of results, including uncertainties and, in particular, the extent of any area or, if relevant, the length of road within the zone or agglomeration over which concentrations exceed any limit value, target value or long-term objective plus margin of tolerance, if applicable, and of any area within which concentrations exceed the upper assessment threshold or the lower assessment threshold,
the population potentially exposed to levels in excess of any limit value for protection of human health.
that all measurements undertaken in relation to the assessment of ambient air quality pursuant to Articles 6 and 9 are traceable in accordance with the requirements set out in Section 5.6.2.2 of the ISO/IEC 17025:2005,
that institutions operating networks and individual stations have an established quality assurance and quality control system which provides for regular maintenance to assure the accuracy of measuring devices,
that a quality assurance/quality control process is established for the process of data collection and reporting and that institutions appointed for this task actively participate in the related Community-wide quality assurance programmes,
that the national laboratories, when appointed by the appropriate competent authority or body designated pursuant to Article 3, that are taking part in Community-wide intercomparisons covering pollutants regulated in this Directive, are accredited according to EN/ISO 17025 by 2010 for the reference methods referred to in Annex VI. These laboratories shall be involved in the coordination on Member States territory of the Community wide quality assurance programmes to be organised by the Commission and shall also coordinate, on the national level, the appropriate realisation of reference methods and the demonstration of equivalence of non-reference methods.