The FWD requires only that Member States report the methods used to carry out preliminary assessments to the Commission. Member States will need however to retain clear documentation on methods and results for their use in implementing the FWD and daughter legislation, and they may wish to share and exchange this information with other Member States.

It is recommended that the results are documented taking into account minimum quality assurance criteria: the report is dated, the authors and the competent institutions and bodies (art. 3 of FWD) and their addresses are named, and the report is explicitly authorized by the competent authorities.

7.1 Mapping of results

Results are recommended to be primarily produced in the form of maps. Such maps may be produced for each of the quantities/statistics as referred to in limit values and threshold or target values for the pollutant(s) under consideration.

A useful map has a scale such that it clearly shows the limits of the zone, in relation to national and sub-national boundaries. A practical suggestion is to use a normal map as background .

In the zone, areas of exceedance resulting from the preliminary assessment are indicated, either by isolines for the limit value, and for x% and y% of the limit value, or by grid grey scales with a scale enabling to read x%, y% and 100% of the limit value. Here, x% and y% are the upper and lower assessment thresholds levels referred to in article 6.3 and 6.4 of the FWD,

If limit values are expected to be exceeded, it is recommended to indicate the extent of exceedance by the measured or calculated maximum concentration, and/or by isolines indicating suitable multiples of the limit value. Areas of exceedance should be presented on maps with sufficient resolution to see the location of maximum concentrations, in relation to relevant sources and proposed measuring sites. It is recommended to describe and discuss the results as mapped, including uncertainties (see below). Note that different assessment techniques may be used alone or in combination for different parts of the map.

7.2 Documenting of procedures followed

It is recommended to describe and document the work that has led to the map(s). More specifically, the documentation should:

• describe assessment activities carried out;
• report specific methods used, with references to descriptions of the method;
• report sources of data and information.

7.3 Documenting uncertainties

It is desirable to report the most likely total uncertainty in the concentration, either in absolute concentration units, or in relative terms. Uncertainties in, and resulting from emissions, measurements and model results may be presented and discussed separately, and the uncertainties in the mapped quantities (isolines, grid grey scales) may also be estimated. Methodology for this is to be further developed on the basis of expertise and experience in the Member States.

7.4 Updating procedure

It is recommended to update each assessment at the latest 5 years after the date of the initial assessment carried out under the requirements of the FWD, or earlier, if the air quality situation changes appreciably or, in case of revision of the limit or target values.

Appreciable changes to be considered are:

• changes in the zone of more than (30) % in human activities relevant to emission of the pollutant(s) (traffic volume, industrial production, population number, energy consumption, tourist visits, etc.) or changes smaller than this if they are likely to lead to an exceedance of a limit value or of an upper or lower assessment threshold.
• major changes in the distribution of emission sources (redesign of road or highway network, closing or establishing of major industrial plants, etc).

Annex 4.1 SNAP 97 SUBSECTOR DEFINITIONS (SNAP LEVEL 2)