Orange Sky: Sand Storm in Lanzhou

On April 4th, 2018, the most massive dust storm in 8 years swept through Lanzhou, China. Many social media posts from the region showed a wall of red dust looming over the city. The negative effect of the dust storm had lasted for four days: the visibility was reduced to less than 700 meters; People had to cover nose and mouth walking outside. Though did not pose a threat to life or property, the dust storm caused great inconvenience to residents’ daily lives. According to Gansu Meteorological Administration, the cold air above the Gobi desert which neighbors Lanzhou triggered the event. In late March, the cold air sitting on top of the warm and dry air of desert moved westward towards Lanzhou. The outflow winds caused by downdrafts splashed against the surface and kicked all the dust off, leading to a massive dust storm.

Lanzhou is located in the northwest geographical center of China, neighboring the Gobi Desert. It is the only capital city where the Yellow River runs through from the west to east. The town is located in a curved, low, and narrow river valley where surrounding mountains cause it to be hemmed in blocking the free flow of air. Lanzhou was repeatedly ranked as one of the cities with the worst air quality in China due to not only the massive dust storms kicked up from the Gobi Desert but also its central position of heavy industry and petrochemical industry. According to the National Environmental Analysis release by Tsinghua University and The Asian Development Bank in January 2013, Lanzhou was one of ten most air polluted cities in the world. In 2011, the World Health Organization reported that Lanzhou had the worst air quality (annual mean PM10 ug/m3 of 150)  among eleven western Chinese cities. Since then the authorities have dedicated to improving the air quality. The measures have been largely successful that Lanzhou has reduced its Air Pollution Index at the fastest speed across China. It was awarded China's climate progress title in 2015.

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