TIANJIN -- The North China city of Tianjin is aiming to lower a major air pollution indicator by a quarter this coming winter, the municipal government said Wednesday.

The city plans to reduce the density of PM2.5 -- a measurement of fine particles in the air often used to gauge the severity of smog -- to 70 micrograms per cubic meters in the period between October 2017 and March 2018. This represents a 25 percent drop from the same period last year.

The number of heavily-polluted days will also be cut by more than 20 percent, the government said.

Wen Wurui, head of Tianjin Environmental Protection Bureau, said the target will be reached by closing down polluting factories, phrasing out the use of coal for heating, raising vehicle emission standards, and enforcing load shedding on heavy industry manufacturers.

The Beijing-Tianjin-Hebei region sits at the heart of the North China Plain where air pollution, particularly winter smog, often occurs as a result of the high concentration of industrial and vehicle emissions, static air circulation and the burning of coal.

All three areas have set clean air targets.

Beijing, for example, aims to lower its PM2.5 density to 60 micrograms per cubic meter in 2017, a challenging target to reach according to meteorologists.