>>>By evening, the answer seemed to be a stinky gas emitted by a New Jersey swamp or marsh.
That would be Fresh Kills
Here are some aeriel shots of Fresh Kills.
http://positron.jfet.org/wtc-fk/
Now now...I know some people in New Jersey like to claim Staten Island as their own (for what reason God only knows), but last I checked it was still part of New York, and Fresh Kills landfill is located there.