|A chimney somewhere in Midtown|
Although this hypothesis was sensible, I still wanted to do some research about it; in order to being able explaining this very special phenomenon to my visitors when they come to New York and ask me the question – which typically happens after one or two days.
New York, in fact, has the world's biggest steam generation system. Everyday, this system pumps steam into not less than some 100,000 commercial and residential establishments.
What is the steam for? It is mostly used to heat, cool or supply power to high rise buildings and businesses.
And regarding the mysterious steam that comes from several manholes in the City, it is mostly due to water infiltration – when water comes in contact with the hot steam pipes it causes vapor – or vapor leaks. The orange and white stacks surrounding manholes are there for our safety; they make sure people don't touch the very hot steam vapor and get burned. The cones also elevate the vapor above street level so drivers can have decent visibility.
The good thing about steam energy, other than its originality, is that it significantly increases the efficiency of fuel usage in Manhattan. It reduces the emission of pollutants in the City, as well as New York’s global carbon footprint.
Last but not least: the steam is very clean. As a proof, numerous businesses use it for cleaning, climate control and disinfection. Consequently there is no reason to worry about inhaling the vapor...