What Wrong With My Canary?

A mysterious gas odor has got Manhattan in a panic. Sirens, evacuations, breathless news coverage. The gas is bothering people from downtown to Harlem to Jersey City. We can faintly smell it here on the 26th floor above Grand Central, but we've just heard that Rockefeller Center (six blocks away) has been evacuated, and the PATH trains have been shut down. Weird.

UPDATE: Natural gas has no odor. Foul-smelling methyl mercaptan is added to natural gas so that leaks can be identified. According to the mayor, it is possible that a leak of the additive has occurred, as air sensors show no unusual levels of natural gas.