[Secondhand smoke from cannabis]
A study? Are you kidding?
Did you read my post?
Did you know if American it's illegal to study cannabis?
You don't need a study, if you have 4 states (and 1 DC) where it's already legal. Go see for yourself.
Over the years, at concerts and what knot, I've seen a lot of cannabis smoked. I've never ever heard of somebody complaining about your issue.