# The Air Quality Standards (Wales) Regulations 2007, Paragraph 3


In this Part—
(a) all values must be expressed in μg/m3;
(b) the volume must be standardised at the following conditions of temperature and pressure: 293K and 101.3kPa;
(c) the time must be specified in Central European Time;
(d) “AOT40” (expressed in (μg/m3) hours) means the sum of the difference between hourly concentrations greater than 80 μg/m3 (which equals 40 parts per billion) and 80 μg/m3 over a given period using only the 1 hour values measured between 8:00 and 20:00 Central European Time each day; and
(e) in order to be valid, the annual data on exceedances used to check compliance with the target values and long-term objectives below must meet the criteria set out in Part 2 of Schedule 12.

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Source: https://www.legislation.gov.uk/wsi/2007/717/schedule/1/paragraph/3 (the official version)
Page: https://openlegislation.uk/air-quality-standards-wales-regulations-2007/schedule-1/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.