HC PPM average?

All the figures that I see are grams per mile, not ppm. One reference that I came across said that the Prius has HC ppm so low that they could not be detected on an average smog testing device. I suspect you are talking about yet another 1970s Honda Civic that gets 70 MPG and is pollution free. Fess up. Which one is it?


https://www.priusonline.com/threads/co-by-the-numbers-was-prius-cleans-other-cars-exhausts.10743/post-98207

I once read a treatise on how clean the Prius exhaust was. One of the conclusions was that you would not die of Carbon Monoxide poisoning if you started the engine in a sealed garage. There was not enough CO. You would, however, eventually die of lack of oxygen since that is used up in the combustion process.

Dan

 

The whole auto industry has greatly cleaned up, such that the rate of vehicle-based CO suicides is way down, though not gone. And we have seen numerous reports of failed attempts by this means.

Though this reduction is not even come close to offsetting the increases in numerous other means this century.

 

I think a 2009 Prius was classified as AT-PZEV, which, being translated, has the same tailpipe emissions as SULEV, with some other requirements added.

I haven't even found a tailpipe HC number for in the SULEV documents I've looked at, though I did find one for formaldehyde (HCHO).

Tailpipe emissions might not even have been the biggest way HC gets from cars into the air. Plain evaporation from the fuel system is definitely another source of HC.

The requirements of AT-PZEV that go beyond SULEV tailpipe numbers include having no evaporative emissions (thanks, in the 2009 Prius, to the carbon canister system combined with the weird bladder fuel tank).

Maybe it's not always literally zero—I'd guess some vapors waft lazily away when you take out the filler cap—but close enough to satisfy a "zero" regulatory limit. That seems like an accomplishment.