Every EPA window sticker carries two 1-to-10 environmental scores. Greenhouse gas measures CO2. Smog measures what affects the air on the street — nitrogen oxides, particulates, carbon monoxide.
Usually they roughly agree. On 63 vehicles they don't.
| Vehicle | Greenhouse gas | Smog | MPG |
|---|---|---|---|
| 2025 Lamborghini Urus SE | 8 | 2 | 20 |
| 2022 MINI Countryman SE All4 | 9 | 3 | 29 |
| 2021 Audi A8 L | 8 | 3 | 23 |
| 2023 MINI Countryman SE All4 | 8 | 3 | 29 |
A 20 mpg SUV rated 8 out of 10 for climate
The Urus SE is a plug-in hybrid Lamborghini. Its greenhouse gas score is calculated including electric-only running, which drags the CO2 average down dramatically. Its smog score is measured when the combustion engine is working — and at that point it's a twin-turbo V8.
Both numbers are correct. They're measuring different operating modes.
Why plug-in hybrids produce this
A PHEV has two personalities. On a short commute within battery range it emits nothing locally. On a long drive with a depleted battery it's a petrol car carrying several hundred kilograms of dead battery.
The CO2 figure blends both, weighted by an assumed usage pattern. The criteria pollutant rating reflects the engine when it runs.
So the score you're shown depends on which question was asked — and a buyer glancing at the sticker sees one impressive number and one poor one without being told they describe different circumstances.
The reverse case also exists
71 vehicles score 3 or lower for greenhouse gas and 7 or higher for smog — thirsty engines with excellent aftertreatment. A large petrol engine with modern catalysts can be clean at street level while burning a lot of fuel.
Which is the general point: the two ratings measure different chemistry and don't track each other. Cars rated 7 for smog average 28.5 mpg while cars rated 9 average 27.3.
Which number should you use?
For fuel cost, neither. Use the mpg figure and the annual cost estimate — that's the money.
For local air quality, the smog rating. It's also the one that matters in states running emissions testing.
For a PHEV specifically, be honest about your driving. If your commute fits inside the battery range and you charge nightly, the optimistic number is closer to your reality. If you mostly drive further, you're operating a heavy petrol car and the smog score is the relevant one.
On a used PHEV, check battery condition first. A degraded pack shrinks the electric range, which shifts the car permanently into the mode the low score describes.
Pull the original sticker. Both scores are recorded per configuration — a window sticker lookup by VIN retrieves the figures for that exact vehicle, and a VIN check confirms the powertrain it was built with.
Frequently asked questions
Can a car be rated clean and dirty at the same time?
Yes — 63 vehicles score 8 or higher for greenhouse gas and 3 or lower for smog. The 2025 Lamborghini Urus SE scores 8 and 2, because CO2 is averaged including electric running while smog is measured when the engine is working.
Why do plug-in hybrids get contradictory ratings?
They have two operating modes. Within battery range they emit nothing locally; with a depleted battery they're a petrol car carrying a heavy pack. The CO2 figure blends both, the smog rating reflects the engine when it runs.
Which environmental score should I trust?
For fuel cost use the mpg figure directly. For local air quality and emissions testing use the smog rating. For a plug-in hybrid, the honest answer depends on whether your daily driving fits inside the battery range.
Does the opposite case exist?
Yes — 71 vehicles score 3 or lower for greenhouse gas and 7 or higher for smog. A large petrol engine with modern catalysts can be clean at street level while burning a great deal of fuel.
Denis Kataev is a serial solopreneur and the founder of ForCar. With 15+ years in software engineering and 10 years in SEO, he builds data-driven products end to end — backed by a sharp eye for design. At ForCar he mines proprietary vehicle datasets, turning raw numbers into buying advice you can actually trust.
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