This Action Level refers to the annual average concentration as measured using two detectors (in a bedroom and living room) over three months, to average out short-term fluctuations.
Asesir y targed hwn gan ddefnyddio mesur llymach sy'n ystyried pobl sy'n gadael cyrsiau'n gynnar (yn ystod yr 8 wythnos gyntaf) a phobl sy'n trosglwyddo rhwng cofnodion prentisiaeth.