# Air Quality Regulations (Northern Ireland) 2003, Paragraph 4: Interpretation

Extent: N.I.
Status: prospective

(1) An annual mean is a mean, which is calculated on a yearly basis, yielding one annual mean per calendar year. The annual mean for a particular substance at a particular location for a particular calendar year is –
(a) in the case of lead, the mean of the daily levels for that year;
(b) in the case of nitrogen dioxide, the mean of the hourly means for that year;
(c) in the case of PM10, the mean of the 24-hour means for that year;
(d) in the case of benzene, either the mean of the daily levels for that year or the mean of the hourly means for that year.
(2) For the purpose of the calculation of the annual mean for lead, the daily level for lead at a particular location for a particular day is the level at which lead is recorded as being present in the air at that location during the week in which the day occurs on the basis of a continuous sample of air taken throughout that week (each day in that week therefore being attributed with the same daily level).
(3) For the purpose of sub-paragraph (2) “week” means a complete week beginning on a Monday, except that it also includes any period of less than seven days from the beginning of the calendar year until the first Monday in that year to the end of that year.
(4) For the purpose of any calculation of the annual mean for benzene on the basis of the mean of the daily levels, the daily level for benzene at a particular location for a particular day is the level at which benzene is recorded as being present in the air at that location during the fortnight in which the day occurs on the basis of a continuous sample of air taken throughout that fortnight (each day in the fortnight therefore being attributed with the same daily level).
(5) For the purpose of sub-paragraph (4) “fortnight” means a complete fortnight, that is a period of two weeks beginning on a Monday (no particular week in a calendar year being included in more than one fortnight), except that it also includes –
(a) in any calendar year beginning on a day other than a Monday, the period from the beginning of the year until the first Monday in that year; and
(b) in any year, the period from the end of the last complete fortnight in the year to the end of that year.

---
Source: https://www.legislation.gov.uk/nisr/2003/342/schedule/paragraph/4 (the official version)
Page: https://openlegislation.uk/air-quality-regulations-northern-ireland-2003/schedule/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.