GE 2012 in Demo paint, what is it?

I spotted these in Flagstaff Arizona, idling all day on a side track. Note the strange exhaust stacks. GE 2012 would occasionally blow out clouds of smoke like an Alco engine.
Can anyone identify them? I'm wondering if they are some type of 'alternative fuel' testing.

 

GE

2012 is an ES44AC owned and used by GE for whatever, usually testing. The car 100 is a dynomometer car used for monitoring the locomotive and testing its abilities. The 905 is a C44-9W also owned by GE.

 

Probably emissions testing, I would bet the "thing" on top of the exhaust stack is probably a sensor to monitor how much carbon, carbon dioxide, etc. is in the exhaust emissions.

Of course, I could be wrong.

 

That's some SWEET catch there.:thumbs_up::thumbs_up:

 

Thanks for the info, always good to know what I'm actually looking at.
It was surprised to see it when I came around the corner of the mall. Just sitting. I went back later in the day and it was still just sitting there, idling still.