Beijing was hit by a light sandstorm on Monday morning, as the air quality index exceeded 500.

A blue-level warning for sand and dust was issued by the Beijing Meteorological Station at 12 am Monday. According to the Beijing Environmental Protection Bureau, the major pollutant is PM10 - particles smaller than 10 micrometers in diameter, the concentration of which hit 800 micrograms per cubic meter.

Statistics show that April and May are the peak months for sand and dust in Beijing — an average of 6.1 days in April and 3.9 days in May, according to records from 1951 to 2017. In the past decade, the number of days of sand and dust has seen a remarkable reduction.