The Met Office said very light winds and high pressure have led to high pollution levels in parts of the UK today.
The dust blown over from the Sahara at the weekend is "lingering" as the lack of wind means there is "nowhere for it to go," a spokeswoman said.
However, a change in weather tomorrow means the air quality should be very good by Friday, she added.
Higher numbers of complaints about breathing difficulties are thought to have been brought on by record pollution levels in recent days.
Air pollution in the east of England reached the top of the scale as a 'perfect storm' of conditions blanketed parts of the country.
Our region is one of the worst-affected by "very high" levels of air pollution today, with much of the East stuck under a cloud of smog.