6. Recommendations for specifications of preliminary assessment

In this chapter, recommendations are provided for preliminary assessment as defined in the introduction to this report.

Two different types of recommendations are covered:

• assessment techniques to be used (measurements, emissions, modelling or combinations)
• requirements of accuracy and spatial resolution

6.1 Preliminary assessments

According to the FWD Article 5, Member States, who do not have representative measurements of the level of pollutants for all zones and agglomerations, shall undertake series of representative measurements, surveys or assessments, in order to have data available in time for implementation of the Daughter Directives.

The purpose of the preliminary assessment is to identify all areas of exceedance of the limit value, and of the upper and lower assessment thresholds where assessment in compliance with the Directives is necessary. Here, the upper and lower assessment thresholds, commonly referred to as x% and y% of the limit values, are the levels referred to in article 6.3 and 6.4 of the FWD which set out the framework for different assessment regimes, depending on the maximum pollution levels which occur in an agglomeration or other zone. For the four pollutants for which a Daughter Directive has been proposed in 1997, these levels have been calculated to provide a safety margin below the limit value to take into account interannual variability of the levels; in fact, (100-x)% is two times the standard deviation of interannual variation of the quantity or statistic under consideration.

Recommended assessment specifications are:

either: (for zones in agglomerations):

• indicative measurements on fixed positions with high resolution (see 3.4)

or: (for all zones, including agglomerations) combination of:

• emissions (minimum 50 x 50 km resolution , 5x 5 km in agglomerations, and including the largest sources (streets, point sources, or other) on an individual basis)
• modelling (background, contribution of largest sources)
• indicative measurements (see 3.3 - 3.6)

As indicated in Article 5, existing monitoring information can be used whenever appropriate.

It is strongly recommended to report the estimated total relative uncertainty of the estimated concentrations. If this uncertainty exceeds (100-x)%, while the pollution level is above y% of the limit value, it is recommended to repeat the assessment with more precise assessment tools (measurement techniques, emission inventory techniques, air pollution models). If this is not possible by available methods, this should be reported to the Commission, since in that case development of better methodology would appear to be necessary.

6.2 Criteria for judging existing assessments

Member States may have existing data on air quality for some or all zones and agglomerations. This document should provide criteria for Member States and the Commission to judge whether such existing information is sufficient for a preliminary assessment (FWD, Article 5), or whether additional work should be carried out.

In essence, the recommended assessment specification is equivalent to the case described in 6.1. It is recommended to map all areas of (potential) exceedance in the zone, with a documented total relative uncertainty of less than (100-x)% in these exceedance areas, where x% is the upper assessment threshold referred to in article 6.3 of the FWD.