WHO has defined its hort term limit guideline a maximum value, while the present

EU limit value is a 98-percentile. The maximum value is very sensitive to

measurement errors, but the 98-percentile is difficult for the public to understand. The

majority of the working group has recommended to define the short term limit value

as a value, which can be exceeded 8 times per year (99.9-percentile). In the

discussions in the Working Group and in the Steering Group, the question of

introducing a lower concentration with compliance at the 98- percentile has been

discussed several times. With respect to air quality the 99.9-percentile on 200 mg/m3

corresponds to a 98-percentile on 90-120 mg/m3, somewhat varying between areas

depending on emissions and other pollution characteristics. The Auto Oil report

(1996) estimates the corresponding 98-percentile 93 mg/m3. At the same time the

Working Group recommend, that the member states should apply additional tools for

quality control and the assessment of exceedances in addition to measurement data,

e.g. statistical methods, emission inventories and air quality models, comparisons

between different stations etc. These topics will be treated in chapter 3

“Measurements and assessment of concentrations” of this position paper. The

exceedances of the air quality standards must be assessed by the Member States and

reported to the Commission. Not only exceedances should be reported, but also

statistical parameters of the concentration frequency distribution, e.g. percentiles,

averages etc., i.e. for comparison with the present limit values.

The long term limit values are recommended as annual averages.

 

 

 

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