If you visited or lived in the Los Angeles area many years ago, you why it was called, unofficially, the City of Smog. In the early 1970s, I attended the LA Zoo with my third grade classmates on ...

Since 1997, nitrogen oxides have decreased 70% in the air basin ... plan to achieve federal smog standards. This story originally appeared in Los Angeles Times.

This article was originally published on mentalfloss.com as The Great Smog Descended on London More Than 70 Years Ago—And its Cause Took Almost As Long to Discover.