Beijing sandstorm makes sun appear blue and sky yellow

Beijing is suffering its second sandstorm in two weeks, due to winds from drought-hit Mongolia and northwestern China

Mie scattering caused by a sandstorm in Beijing has reversed the colours of the sky (Barcroft Media via Getty)

Beijing is suffering its second sandstorm in two weeks, turning the sky yellow and making the sun appear blue and triggering weather warnings.

The unusual weather in the Chinese capital is due to winds from drought-hit Mongolia and northwestern China.

Images on social media show a Mars-like blue sun shining through the storm.

The phenomenon is caused by Mie scattering — a scattering pattern that occurs when there are fine particles such as sand or water droplets that absorb red light with a longer wavelength, giving the sun a blueish hue.

Since Sunday, visibility in Beijing has been low, with the tops of some skyscrapers obscured by the storm. 

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Beijing’s official air quality index reached a maximum level of 500 on Sunday morning, with floating particles known as PM10 surpassing 2,000 micrograms per cubic metre in some districts.

Readings of smaller PM2.5 particles were above 300 micrograms per cubic metre, far higher than China’s standard of 35 micrograms.

This is the second sandstorm in the city since mid-March. The first was the most severe in years, according to residents, and turned the sky orange. 

The meteorological office has said Beijing might be hit with more sandstorms throughout April, due to the favourable weather conditions.