[Vigilanteman]

Plus eight of the top ten are in the southwest where naturally occurring dust is a big, if not bigger, factor than industrialization. Of the remaining two, both St. Louis and Pittsburgh are dominated by massive rivers which cause chronic flooding in low lying areas (producing mold) as well as an abundance of flora (producing pollen).

Blaming the Homer City power plant for Pittsburgh's relatively mild air pollution is idiotic as well since Homer City is mostly to the east and north whereas the worst pollution cited is mostly to the west. FWIW, our prevailing winds are mostly from the west.

[SoothingDave]

That, and the reporting station for Pittsburgh is located right next to the Clairton Coke works.