LONDON -- Parts of the UK were warned Thursday about moderate pollution levels caused by a mix of dust blowing in from the Sahara Desert and diesel fumes, with the pollution set to return over the weekend.
Despite some headlines claiming that "blood rain" would come down and the UK would be "smothered" in a toxic cloud, the Met Office said that blood rain -- rain coloured red from pollution -- is quite rare because it takes a high concentration of particles in the air to cause it.
Officials warned that people with lung problems should reduce their physical activity outdoors in the warned areas on Thursday.
They said that pollution levels would rapidly decrease in southern, central and eastern England on Thursday afternoon and would be low on Friday. Southerly winds on Saturday would bring back the dust to England and Wales and then levels would return to normal on Sunday.
These same winds will bring in unusually balmy temperatures for the weekend, with temperatures as high as 10 to 15 degrees Celsius above average for this time of year.
Despite fears that Saharan dust could impact air travel, the main influence of such dust is to limit visibility, which can cause flight delays. The dust, unlike volcanic ash, does not pose a danger to aircraft engines.
“Across Europe, Saharan dust is mainly an air pollution problem for Mediterranean countries, especially those in the east Mediterranean where episodes have caused air pollution to reach 10 times the EU limits,” Dr. Gary Fuller of King's College London told the Guardian.
December has been unseasonably warm across the UK, with average highs around 15 C (59 F). Forecasters say it's been one of the mildest starts to December in 50 years.