The primary issue with diesel is the NOX emissions and the smell (but alot of that has been cleaned up with recent emission standards & use of cataltic convertors use). Diesels produce less CO emisions than do LP or gasoline fuel.

I have sold the Linde units with diesel engines in to warehosue applications successfully with no issues. No exhaust emission smell or smoke issues, in fact one customer told me that they can have lunch behind the units with the engine running. I would not reccommend a diesel for a stop and go applications as a diesel is more efficent when it is running continously