[nikkwong]

I've looked into this as well; and from my understanding the amount of physical activity New Yorkers undergo by walking everywhere may offset the detrimental effects of the city's pollution; leaving New Yorkers with an average life expectancy that mirrors (or may be a bit higher) than the rest of the nation. It goes to show you how important regular, several times per day, low intensity exercise may be for human health.

Maybe also, the relative windiness of the city leads to less accumulation of road dust than you'd have in other areas? (Totally just conjecture).

[rtkwe]

I bet part of it is also that most of the traffic is actually moving quite slowly so you don't get nearly as much tire or brake wear dust in the pollutants.