13.—(1) The Secretary of State must ensure that PM2.5 levels at each monitoring station are assessed as follows.
(2) Fixed measurements of PM2.5 must be taken either continuously or at hourly or other regular intervals which are not less frequent than once per day—
(a)in accordance with the method described in BS EN 12341:2014 (“the reference method”); or
(b)by another method which is equivalent to the reference method (“an equivalent method”).
(3) For the purposes of paragraph (2)(b), a method of assessing PM2.5 levels is an equivalent method if it gives results which—
(a)are equivalent to the results which would be given by the reference method; or
(b)otherwise bear a consistent relationship with the results which would be given by the reference method, disregarding any change to that relationship as a result of changes in the composition of PM2.5 in ambient air over time.
(4) If PM2.5 levels are assessed by a method to which paragraph (3)(b) applies, the results must be adjusted to produce results equivalent to the results which would be given by the reference method.
(5) If PM2.5 levels are assessed otherwise than in accordance with paragraph (2)(a), the Secretary of State must keep under review whether that method satisfies the requirements in paragraph (3).
(6) In this regulation “BS EN 12341:2014” means the British Standard so numbered and titled ‘Ambient Air – standard gravimetric measurement method for the determination of the PM10 or PM2.5 mass concentration of suspended particulate matter’(1).
Published by the British Standards Institution. Digital and hard copies can be purchased online from the BSI Group at http://www.bsigroup.com. Hard copies can also be purchased by post from the BSI Group Customer Services Department at 389 Chiswick High Road, London W4 4AL. A copy is available for inspection free of charge at the offices of the Department for Environment, Food and Rural Affairs, 2 Marsham Street, London SW1P 4DF.