Fighting crime via clean air - with a lag

Again, not directly about Arizona, but this is interesting from an environmental standpoint. If true, this could be a significant positive externality.

In the early 1990s, a surge in the number of teenagers threatened a crime wave of unprecedented proportions. But to the surprise of some experts, crime fell steadily instead. Many explanations have been offered in hindsight, including economic growth, the expansion of police forces, the rise of prison populations and the end of the crack epidemic. But no one knows exactly why crime declined so steeply.

The answer, according to Jessica Wolpaw Reyes, an economist at Amherst College, lies in the cleanup of a toxic chemical that affected nearly everyone in the United States for most of the last century.

HT: Instapundit