BEIJING—The Chinese capital of Beijing woke on Sunday morning shrouded in thick dust carrying extremely high levels of hazardous particles, as a second sandstorm in two weeks hit the city due to winds from drought-hit Mongolia and northwestern China. Visibility in the city was reduced, with the tops of some skyscrapers obscured by the sandstorm, and pedestrians were forced to cover their eyes as gusts of dust swept through the streets. “It’s quite serious today. There’s always a day or two like this (of pollution or dust) each month,” said Mr. Fan, 39, who did not wish to disclose his full name. 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 meter in some districts. Readings of smaller PM2.5 particles were above 300 micrograms per cubic meter, far higher than China’s standard of 35 …