The situation is expected to get even worse tomorrow. Ozone levels can be different according to the area where you are living, to be checked on the IRCEL map.
Yesterday was also not a good day. Ozone levels drop during the night, but climb steadily when the sun gets stronger in the morning, in order to peak in the (late) afternoon and early evening. It is advised that you avoid heavy physical exercise when ozone levels are highest, generally between noon and 10PM these days, especially children, older people and patients nursing breathing problems.
Yesterday, ozone levels peaked in Schoten (188) and Idegem (East Flanders, 186) but Wallonia and Brussels also had their fair share.