The sixth-biggest cause of death globally is small-particle pollution, chemical specks that enter the lungs and can contribute to cardiovascular diseases, lung cancer, and infections. It led to more than 4 million deaths in 2016. Ninety-nine percent of children 5 years old and younger in South and East Asia breathe unhealthy air.

● Much of China’s particulate pollution comes from industrial facilities, especially coal-burning power plants. In India, PM2.5 comes not only from motorbikes, cars and coal-fired...