Originally Posted By: gathermewool
While newer emissions controls are undoubtedly more expensive, they also seem to be much better, at least in the short-term, compared to cars putting around when I was a kid - 80's and early 90's cars. In today's day and age, the old schnauz can't really detect any emissions from newer gassers and diesels. We won't count warm-up time, though, as every car I've ever owned smelled at least a little rich on cold start-up.
Yes, all engines will create more HC and CO when cold, and in order to reduce that problem, auto makers create ways to make the engine warm up more quickly, locate catalytic converters closer to the cylinder head, and sometimes add electric air pumps that operate for a few minutes after startup.
I don't know which has lower cold start emissions, a modern gasoline engine or a modern diesel.