Methane has no Nitrogen in it. All of that would have to come from the air. It's famously very very hard to react Nitrogen that way, I'd be surprised if gas turbines produced it in noticeable quantities.
EDIT: didn't see your edit until now. Heh it shouldn't be too hard to scrub out if it were really a problem. That seems like a better way to handle it than this weird exemption process that seems to be in place now.
EDIT: didn't see your edit until now. Heh it shouldn't be too hard to scrub out if it were really a problem. That seems like a better way to handle it than this weird exemption process that seems to be in place now.