I always found the research on second hand smoke misleading. How can they possibly evaluate the subjects when we are all exposed daily to amounts of pollution from so many sources. There is no way to be objective about this.

Does second hand smoking causes COPD? Does walking down the street in NY for 2 hours? How about standing on top of a grill and cooking?.

Inhaling some substances IS bad. No doubt. How much and from where though, we can't possibly determine.