Beijing’s environmental protection bureau has released monitoring data that measures particles of 2.5 micrometers or less, known as PM 2.5. These particles are the smallest, and most dangerous pollution particles in the air.

Research done by Beijing authorities shows that 60% of the PM 2.5 in the city comes from coal burning, vehicle emissions and industrial production. 23% comes from dust, and 17% from the use of solvents.

PM 2.5 in Beijing has been decreasing over the past ten years, its annual intensity is 100-110 micrograms per cubic meter in 2000, 80-90 micrograms per cubic meter in 2005, and further decreased to 70-80 micrograms per cubic meter last year.

But the authorities also admitted that the annual intensity of PM 2.5 still doubles the cap set by World Health Organization.