China has made dramatic air quality improvements in recent years as the government has relocated and retrofitted heavily polluting coal and oil plants.

Unfortunately for residents of many industrial cities, the country’s steel mills continue to belch out health-harming particulates, sulfur dioxide and nitrous oxides. But that is now changing as hundreds of firms upgrade their factories to meet strict emissions targets, according to Jiang Wei, the deputy Communist Party secretary of the China Iron and Steel Association, an industry group.

Some 228 companies accounting for more than 60% of total crude steel production capacity “are implementing the transformation to ultra-low emissions,” Jiang said Friday at an industry conference.

China, the world’s largest steel producer, aims to bring 60% of steel capacity in “key regions” in line with so-called “ultra-low” emissions standards by the end of this year and do the same across 80% of national capacity by 2025.