Many motorists awoke to find their vehicles coated with the red dust.
Smog reached the top of the official 10-point scale of air pollution in Norfolk, the East Midlands and Yorkshire.
Greater London suffered with smog that reached level 7.
People with heart or respiratory conditions were urged to avoid exertion and remain indoors and to see their doctors if symptoms worsened.
The environment department said the smog was caused by pollution from Britain and industrialized areas of neighboring Europe that stayed in place because of light winds, along with the Sahara dust.
Smog Forecast Graphic: Public Health England