“Air pollution” is never written as the cause on death certificates. If it were, it would be the biggest killer in the world. Air pollution causes 6.5 million early deaths a year. That is double the number of people lost to Aids, tuberculosis, and malaria combined, and four times the number killed on the world’s roads. But driven by new data, revelations about the impact of poisonous air on virtually all aspects of health and, crucially, the increasing anger of affected people and communities, air pollution is finally getting the attention it deserves.