During Wednesday night the mild southerly airflow affecting the UK spread a thin ribbon of dust, originally lifted from the Sahara, northwards across parts of England and Wales. The dust has been detected just above the surface over many parts of the south of the UK by monitoring stations.

How long will it last?

The moderate pollution levels are only expected to be short-lived. A cold front moving eastwards across the UK on Thursday will result in the wind swinging round to a ‘cleaner’ south-westerly and therefore low air pollution levels across the whole country on Friday. Southerly winds on Saturday will increase the likelihood of further patches of Saharan dust being spread across the UK with a risk once again of some moderate air pollution levels across parts of England and Wales. Sunday will then see a return to low air pollution levels across the country. The rain may lead to some deposits of dust being left on surfaces as it washes the dust from the atmosphere.

What is Saharan dust?
Saharan dust is lifted by strong winds and can reach very high altitudes; from there it can be transported worldwide by winds, covering distances of thousands of kilometres. The dust gets caught in rain droplets in clouds, falling to the ground in rain. When the water evaporates, a thin layer of dust is left on surfaces, like cars. It can also lead to vivid sunsets.

Will this lead to blood rain?
No. We rarely, if ever, see blood rain in the UK. This is because to get blood rain, when rain actually appears red, you need red dust or particles in high concentrations in the air. Even worldwide, documented cases worldwide are quite rare.

Dust and air quality
Saharan dust is a contributing factor to air quality along with pollution levels and weather conditions.

The combination of southerly winds and lifted dust is forecast to result in locally moderate pollution levels over parts of England and Wales during Thursday, but with levels falling rapidly as winds turn more westerly.

Further information including health advice on the different air pollution bands can be found on the Defra UK-air website.