If you live in the US you'll have likely seen a little badge on the back of some vehicles that reads "PZEV" which stands for "Partial Zero Emission Vehicle".
Of course the only true zero-emission vehicle is an electric car, and even then that only considers the car itself, because emissions are created during the production of electricity (to charge the car) and during the manufacture of the vehicle, so there really is no true zero-emission vehicle in existence. So what is PZEV?
It's just a marketing gimmick. PZEV is a label manufacturers can put on a car if it has no evaporative emissions from its fuel system, has a 15 year warranty on the emission control components and meets SULEV exhaust emission standards.
Let's deal with each of those one at a time.
No evaporative emissions from the fuel system. Seems logical, right? I mean you don't drive around with an open container of fuel so surely every vehicle manages to meet that criteria? It depends on what you mean by "no evaporative emissions" because as soon as you take the petrol filler cap off, petrol starts to evaporate - it's why you can smell it. If that description refers only to the car when it's not being filled up, then it applies to every car built pretty much for as long as filler caps have had bayonet fittings and rubber seals. So that items is a bit of marketing BS.
A 15 year warranty on the emission control components? Don't make me laugh. If that were true, oxygen sensors and catalytic converters would be covered by the vehicle warranty, meaning owners would not be charged for having them replaced. Clearly that's not true - go to a dealer with a 6 month old car with a dead oxygen sensor and you'll be $200 out-of-pocket. So that item is also marketing BS.
So what about SULEV? That stands for Super Ultra Low Emission Vehicle. In theory these engines produce "90% less emissions than equivalent petrol powered vehicles". That's a really woolly and vague statement, but all you need to know is that there are only 22 vehicles in existence that meet this criteria and 8 of them are either hybrids of natural gas vehicles and one of them isn't manufactured any more.
So in summary, "PZEV" really means nothing. Feel free to go ahead and remove that label from the back of your car.