What sort of identification do you get from panel data if effects are long-term? Air pollution and cognition example.

Don MacLeod writes: Perhaps you know this study which is being taken at face value in all the secondary reports: “Air pollution causes ‘huge’ reduction in intelligence, study reveals.” It’s surely alarming, but the reported effect of air pollution seems implausibly large, so it’s hard to be convinced of it by a correlational study alone, …