The cleaner air is the result of “international boycotts, armed conflict and related mass migration of people,” said study leader Jos Lelieveld, director of the atmospheric chemistry department at the Max Planck Institute for Chemistry in Mainz, Germany. “The changes are so large that they can be seen from space.”
and it's not just war that will clean up the air. One major source of pollution is Chinese industry.
With the economic slowdown in China, expect this industrial pollution to get better.
Of course, an economic collapse may hurt a lot of folks, and not just in China, and even lead to civil insurrections, but hey, the air will be cleaner...