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Understanding the Smog Index on new vehicles

nozferatnozferat Posts: 11
edited March 2014 in Honda
Every time I see this sticker on cars, it makes me want to question how good the information is we are being fed about smog and emissions.

Example: How can a 270 HP, V6 Nissan Altima have far less smog index values than a 177 HP, 4 cylinder Nissan Sentra SER?

V6 Altima = 0.29/1.0
SER = 0.49/1.0

Does this make sense to anyone? And this is only one example. VW's 2.5L V5 engine has something like a 0.09/1.0?

Come on


  • larsblarsb Posts: 8,204
    Under the new system, two scores-one for smog-forming emissions, one for carbon-dioxide-will be given on new-vehicle window stickers. Both will be have a simple score system from 1 to 10, with 10 being the cleanest.

    The new Smog Scores will correspond to real emissions classifications. For instance, a ULEV vehicle will receive a 5, PZEVs will be 9, and ZEVs will get a 10. Based on 2007 model year vehicles, most vehicles rated 4 and 5, though the numbers will migrate upward. The system is set to be revisited for 2012.

    With the so-called Global Warming Score, it would be the first notification of any sort to be required on new U.S. vehicles that directly associates carbon dioxide emissions with global warming.

    From This Page (hope that helps)
  • Thanks for the response.

    How do they determine the 0 to 1 score then that is placed near the sticker of the car?

    So is it safe to say that the smaller engine is more dirty than the larger V6? It doesn't make sense.
  • larsblarsb Posts: 8,204
    This is what Ken G said over at when you axed this que4stion there:

    The Smog Index sticker only appears on California cars and a few other states that have recently adopted it. A quick google search will reveal that this index is strictly a measure of hydrocarbons, with no other pollutants factored in. The index is not a direct measurement. It is a rating of a cars position relative to a standard for it's class. That's why the Altima scores better than a Sentra with the same engines. The Altima is compared to other cars in it's size class that generally have larger engines.

    Adding to that fact is that the V6 Altima and the 4-cyl Sentra SER score the same at in the Air Pollution score. Nissan made that V6 Altima pretty darn clean for it's class.
  • The index is not a direct measurement. It is a rating of a cars position relative to a standard for it's class.

    Somehow that doesn't make sense because the rating for ALL cars is 0.38 for the 2007 year. Not just in that class. That number is on all cars for some reason.

    It's still wierd if you ask me.
  • larsblarsb Posts: 8,204
    I think this will finally "clear the air" in regard to the Smog Index (Dang, I crack myseff up !!!)

    Read this PDF

    and this doc:

    Click Me
This discussion has been closed.