Beijing's municipal government says air pollution in the capital improved during the first six months of 2015.

It said the concentration of PM 2.5 — tiny airborne particles that are particularly harmful to human health — dropped by 15.2 percent from a year earlier to an average of 77.7 micrograms per cubic meter during the first half of the year.

However, that level remains higher than the 10 micrograms per cubic meter average considered safe by the World Health Organization.

The city government said the amounts of sulfur dioxide, nitrogen dioxide and PM 10 particles also decreased.

Chinese officials have vowed to clean up Beijing's notoriously foul air and have closed some polluting factories in the region.