Passing Gas

Smell of Natural Gas in Manhattan reportedly not dangerous.

This reminds us of the Maple Sugar Smell Mystery!

Neither case is solved.

Then there is this: Secret 'gas' test staged at G. Central
"The Federal Department of Homeland Security released gas in Grand Central Terminal last month in a secret study of how dangerous chemicals might flow through the landmark in a terrorist attack."

What if the smells over New York are tests being run by Homeland Security to see how and where chemicals would travel in case of attack?