I can say this because I live in Atlanta, and I know when the Olympics were here, there was no pollution and no traffic.
This is a picture of Chinese soldiers removing huge amounts of algae from a beach near the Olympics Sailing Centre in Qingdao where the clean-up pressure is on.

How many people will watch the China Olympics on TV and say, “That looks nice. We should add Qingdao to our travel plans next summer, dear.”

I wonder how long it will take to regrow all that algae?