He created an app that put China’s worst polluters on watch

More than a million people in China died from the effects of ambient air pollution in 2016, according to the World Health Organization. It’s a shocking number, and Ma Jun is exerting steady pressure on the Chinese government and private companies to reduce it.

A former investigative reporter who wrote a groundbreaking book called China’s Water Crisis, Ma founded the Institute of Public and Environmental Affairs (IPE) in 2006. The organization aims to make environmental data accessible. “We have to involve the people in our environmental governance,” says Ma. “They must be informed.”

At first there was little data to share. But in 2013 China vowed to “declare war” on pollution and began releasing the hourly levels of PM2.5, the especially harmful fine-particle pollutants. IPE and its partners pushed for the sources of those pollutants to be disclosed. When that happened a year later, IPE incorporated this new data into an online map and phone app called the Blue Map, where users can check the air quality of more than 300 Chinese cities and the water quality of thousands of rivers.

Now Chinese citizens can see whether it’s safe to send their children outside to play—and if it isn’t, they can identify which factories are to blame. Companies are facing public pressure to clean up, says Ma. Just as important, he says, the government has been convinced “that environmental transparency will not disrupt our society.”