Yet in February, the concentrations of Nitrogen Dioxide were higher during the half term week (12 to 18 February), compared to the school week (19 to 25 February).
Ond eto'i gyd, ym mis Chwefror roedd crynodiadau Nitrogen Deuocsid yn uwch yn ystod wythnos hanner tymor (12 i 18 Chwefror), o gymharu â'r wythnos ysgol (19 i 25 Chwefror).