Suzhou has set a target to reduce PM2.5 density by 7 percent this year, according to a recent meeting of the city's environmental protection bureau.

The bureau made PM2.5 density a key index in its annual environment evaluation of districts and cities under the Suzhou government. Those reporting a rise in PM2.5 density will get no point for this index.

PM2.5 stands for air-borne pollutants smaller than 2.5 micrometers in diameter. PM2.5 density is one of the nine indexes in the evaluation. Other indexes include industrial upgrade, coal reduction, industrial emissions, construction dust, phase-out of polluting vehicles, and boiler modification.

District and city leaders will be openly criticized if any of their indexes is below 70 points. The bureau said Suzhou aims to cut PM2.5 density by 20 percent in 2017 from this year's level.