A spike in air pollution levels in Sheffield was caused by the same dust blowing in across the UK from the Sahara desert, experts say.
Figures from the Department for Environment, Food and Rural Affairs showed the level of air pollution recorded at Devonshire Green was unusually high on Tuesday.
Over a 24-hour period the figures – which are updated hourly – showed a measurement of eight on a scale of 10 used to monitor pollution.
Sheffield Council said the figure is more normally between two and three, and that the increase was being seen across Yorkshire.
A spokesman said it was ‘very unusual’.
Defra said ‘a combination’ of local emissions, light winds, pollution from the continent and dust blown over from the Sahara caused a spike in the UK Air Quality Index.
Dr Sotiris Vardoulakis, head of the air pollution and climate change group at PHE’s Centre for Radiation, Chemical and Environmental Hazards, said people with heart or lung conditions may experience increased symptoms.
The levels of pollution are expected to be high again today before they clear on Friday.
Dr Robert Bryant, from the University of Sheffield’s Department of Geography, is conducting research into the causes of Saharan dust being blown to the UK.
He said: “Today’s misty fog is relatively common, but what’s not so well known is the reasons behind this event, which suggest the UK experiencing similar episodes of extremely poor air quality may be something that will happen more and more in the future.
“The dust that has blown over from the Sahara and caused this mist of toxic air, which has been mixed with other pollutants from Europe on route to the UK, is largely made up of fine soil particles that are ejected into the atmosphere by the action of strong winds on the surface of the Earth.
“Once caught in the wind, these small particles can travel large distances before returning to the surface either via rainfall or simply under the influence of gravity.”
Dr Byrant said dust could also affect health conditions, transport accidents and aviation problems.
He added: “However, we also know that dust can have much wider impacts in affecting short-term climate by directly reducing average daytime temperatures and indirectly affecting cloudiness, rainfall patterns and other regional climate phenomena.”