# Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe, Division A: Data quality objectives for ambient air quality assessment Extent: E+W+S+N.I. 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. Distributed over the year to be representative of various conditions for climate and traffic. One day's measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year. 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 measurements 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 % — — — industrial sites — 90 % — — Indicative measurements Uncertainty 25 % 30 % 50 % 30 % Minimum data capture 90 % 90 % 90 % 90 % Minimum time coverage 14 % 14 % 14 % > 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. --- Source: https://www.legislation.gov.uk/eudr/2008/50/annex/I/division/A (the official version) Page: https://openlegislation.uk/eu-directive-2008-50/annex-I/division-A Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.