Horse hockey!! I remember as a young buck driving along welfare alley in Michigan (Detroit to Saginaw) and you could see the foundry debris particles in the air. One area in Detroit was in the Rouge River, called Zug Island) and if you drove through it, there was so much crap in the air you needed to get a car wash when you left it. Another area between Detroit and Toledo, was a factory which made fiberglass and it was so thick in the air it felt like little pin pricks when it touch your skin.
By comparison, today's climate is pristine to those days (1960s) and I would have expected research to show that. Instead it shows the air is worse. Give me a break you money grubbing "scientists."