Statutory Instruments made by the National Assembly for Wales

"the 1995 Act" ("Deddf 1995") means the Environment Act 1995,

"air quality objective" ("amcan ansawdd aer") has the meaning given by regulation 4 of these Regulations,

"the Schedule" ("yr Atodlen") means the Schedule to these Regulations,

"substance" ("sylwedd") means a substance listed in the left hand column of the Table, and

"the Table" ("y Tabl") means the Table in Part I of the Schedule.

(a) the level at which that substance is recorded as being present in the air at that location during the hour on the basis of a continuous sample of air taken during that hour for at least 30 minutes; or

(b) the mean of the levels recorded at that location on the basis of 2 or more samples of air taken during the hour for an aggregate period of at least 30 minutes.

     2. A running 8 hour mean is a mean which is calculated on an hourly basis, yielding one running 8 hour mean per hour. The running 8 hour mean for a substance at a particular location for a particular hour is the mean of the hourly means for that substance at that location for that hour and the preceding 7 hours.

     3.  - (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 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; and

(c) in the case of PM10, the mean of the 24 hour 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) "PM10" means particulate matter which passes through a size-selective inlet with a 50% efficiency cut-off at 10µm aerodynamic diameter.

    (4) 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 or from the beginning of the last Monday in the calendar year to the end of that year.

     4. An hourly mean is a mean calculated every hour. The hourly mean for a substance at a particular location for a particular hour is the mean of the levels recorded, at a frequency of not less than once every 10 seconds, for that substance at that location during that hour.

     5. A 24 hour mean is a mean calculated every 24 hours. The 24 hour mean for a substance at a particular location for a particular 24 hour period is the level at which that substance is recorded as being present in the air at that location on the basis of a continuous sample of air taken throughout the period.

     6. A 15 minute mean is a mean calculated every 15 minutes. The 15 minute mean for a substance at a particular location for a particular 15 minutes is the mean of the levels recorded, at a frequency of not less than once every 10 seconds, for that substance at that location during that 15 minutes.

     7. The reference to a number of micrograms or milligrams per cubic metre of a substance is a reference to the number of micrograms or milligrams per cubic metre of that substance when measured with the volume standardised at a temperature of 293 K and at a pressure of 101.3 kPa.