Forecasters say Central Maryland's air will be unhealthy for children, the elderly and people with respiratory problems today, the area's fourth straight day of high pollution levels.

Ground-level ozone, the main ingredient in smog, reached "code red" concentrations at monitoring sites on Padonia Road in Timonium and in Upper Marlboro yesterday. Code red is considered unhealthy for everyone. Levels in most of the rest of the state were "code orange" - unhealthy for sensitive groups.

Hot, still weather has kept ozone at unhealthful daytime levels since Sunday. Today's forecast is code orange.

People in the vulnerable groups are advised to stay indoors. State officials are asking everyone to limit driving, which helps keep ozone levels down.