I have a friend who runs a smog shop. One day when I had to get my truck 2004 Duramax emission tested, we where chatting about the difference between gas and diesel and the difference in emissions.
We decided to stick the sniffer in and see what the machine would read. Since the machine didn't have any settings for testing the emissions of a diesel we ran it as a gas engine. I dont remember exactly what the readings where now but HC was 0 or below detectability, it of course couldn't read particulates, CO was also real low. The rest, NOx, CO2, etc where all within the limits of a gas engine and would have passed.
He was very surprised considering all of the bad press surrounding diesel emissions.
My truck tested had a straight pipe exhaust, blocked EGR, and was tuned by me with EFI Live