I don't know. I worked for years in Pittsburgh, even lived there for a few years. A long time ago, people burned coal, numerous factories were belching who knows what chemicals into the air and cars didn't have anti-pollution devices. Sometimes the smog was thick. You couldn't go outside in a white shirt. Your shirt would turn black. Well, coal isn't used at homes anymore, most of the factories are gone and the few which are left have pollution controls as do cars. But at least once a year, some enviro-whacko group comes out with a report saying that Pittsburgh's air is getting worse. How can that be?
I think articles like this are just more propaganda from lefties eager to destroy industry, tax us to death and control our lives.