Windscreens across Northern Ireland have been left coated in a fine layer of dust that was carried 2,000 miles on winds from the Sahara Desert.
Experts say a major dust storm swept sand in the western Sahara up into the atmosphere, where it spread westwards over the Atlantic before becoming caught up in the southerly winds, which carried it into Spain and the UK.
The dust formed a haze in the atmosphere and combined with rain droplets which then fell to earth, leaving a thin layer of dust on surfaces as they evaporated.
Drivers across Northern Ireland reported a thin layer of dust had been deposited on their windscreens over the weekend.
Meanwhile, Londoners were warned that the dust from the Saharan winds would spark one of the worst smogs of the year, with the Met Office forecasting the highest 10 out of 10 level of air pollution for today and tomorrow.
Adults and children with lung problems, adults with heart problems and older people were advised to avoid strenuous exercise, and healthy adults were warned to reduce exertion outdoors.
The Met Office's spokesman in Northern Ireland, Paul Wylie, said the dust coating windscreens across the province began its life in the Sahara Desert.
"It's just air from the far south that has come up across the UK," he said.
"You might have noticed the atmosphere has been very hazy over the last couple of days. It's a lot of dust and a wee bit of rain, and when it rains the dust goes onto the cars. It's good business for car washes.
"The dust becomes suspended in the atmosphere as it's very light. In 2012 there was an incident in which dust was carried several thousands of miles from the Sahara all the way to Florida.
"The wind currents can keep it in the high atmosphere for quite a distance and it's only when we get particularly calm conditions that it falls to the ground."
In Northern Ireland we only get the right conditions for the Saharan dust to fall about once in every four years, Mr Wylie said.
"We would only get dust like this if there is a south or south- easterly wind blowing across Europe that persists for several days," he added.
- The Sahara is the major source on Earth of mineral dust, producing 60m-200m tonnes per year.
- Saharan dust can be lifted by convection over hot desert areas, and can reach very high altitudes. From there, it can be transported worldwide by winds, covering distances of thousands of miles.
- The dust combined with the hot dry air of the Sahara often forms an atmospheric layer called the Saharan air layer, which has significant effects on tropical weather.