another Nemo tunnel view i have found.
(http://members.trainorders.com/debutts/sr3135nemo.jpg)
Cool shot!
Nice photo!
It is interesting, as the tunnel face looks pretty clean in this view. More recent pics of that same portal have a lot of soot built-up right above the entrance. That either means today's diesels burn "dirtier" or that this photo was taken after a storm (when the rain cleared off the southern exposure into the mountain). My guess is the traffic is heavier these days, and more powerful locomotives means more smoke.
RDS