# 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 1: Definitions

Extent: E+W+S+N.I.

AOT40 (expressed in (μg/m3) · hours) means the sum of the difference between hourly concentrations greater than 80 μg/m3 (= 40 parts per billion) and 80 μg/m3 over a given period using only the one-hour values measured between 8.00 and 20.00 Central European Time (CET) each day.

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Source: https://www.legislation.gov.uk/eudr/2008/50/annex/VII/division/A/division/1 (the official version)
Page: https://openlegislation.uk/eu-directive-2008-50/annex-VII/division-A/division-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.