High levels of air pollution are expected across parts of England on Wednesday.
The sudden rise in pollution is down to dust blown over from the Sahara desert in northern Africa, and pollution emissions in the air.
Over the last few days many people in the UK have found their cars covered in a layer of the fine dust.
In London, the fine sand floating in the air has triggered one of the worst smogs of the year.
Defra, the part of the Government that deals with environmental issues, has issued a warning over the levels of pollution in some parts of England on Tuesday.
They have a scale of 1-10 by which they measure air pollution - 1 meaning "low" and 10 warning of "very high" levels.
This morning they recorded a level 5 in the south East, north-east England and East Anglia - which means 'moderate'.
But forecasters think that could rise 8 or 9 by later in the day.
The elderly and those who have lung problems have been told to avoid doing heavy exercise outside.