Understand the Smog Score
In California all vehicles manufactured after January 1, 2009 are required to display a Global Warming Score and Smog Score as part of the Environmental Performance Label. The Smog Score is important because it gives car buyers the ability to determine quickly how much a vehicle pollutes compared to all other vehicles on the market.
There have been many advancements in clean vehicle technologies over the years, making even gasoline cars significantly cleaner than ever before. But cars and trucks are still a major contributor to smog, and pollution levels vary drastically between vehicles, even within the same make and model. Choosing vehicles with high Smog Scores is a sure way to reduce your contribution to pollution today and finding one with an 8 or higher ensures that the car meets California's strictest emissions standards.
Smog
Smog is a haze-like form of air pollution produced by the photochemical reaction of sunlight with volatile organic compounds, including Non-Methane Organic Gases (NMOG) and Oxides of Nitrogen (NOx), that have been released into the atmosphere, especially by automobile operation.
Smog Score
Smog Scores are on a scale of 1 – 10, with 10 being the cleanest. The average vehicle available in California today has a smog score of 5. The table below shows the different pollutant levels associated with each Smog Score, and how those levels relate to Federal and California certification standards.
How the Smog Score is Determined
Every car sold in California is certified by the Air Resources Board (ARB) and meets a certain emission standard. These emission standards are part of ARB's Low Emisson Vehicle program. Below is a table that provides the emission standards and the grams per mile of pollution associated with each standard. This is then associated with a certain Smog Score. The grams per mile of NMOG and NOx are the amounts of smog forming pollutants that come from the car’s tailpipe, and that evaporate from the car.
| Smog Score* | Emission Standard | NMOG + NOx (g/mile) |
| 10 | ZEV, Bin 1 | 0.000 |
| 9** | ATPZEV, PZEV | 0.030 |
| 8 | SULEV, LEV2 SULEV, Bin 2 | 0.030 |
| 7 | Bin 3 | 0.085 |
| 6 | Bin 4 | 0.110 |
| 5 | LEV 2 ULEV | 0.125 |
| 4 | LEV 2 LEV, Bin 5 | 0.160 |
| 3 | Bin 6 | 0.190 - 0.200 |
| 2 | SULEV (Medium Duty Vehicle) Bin 7 | 0.240 |
| 1 | Bin 8, LEV 2 ULEV (MDV), LEV 1 ULEV | 0.325 - 0.356 |
*Does not include upstream emissions.
**A Smog Score of 9 was given to vehicles certifying to the California PZEV and ATPZEV standards based on the longer useful life, zero evaporative emissions requirements, and extended warranty for these vehicles compared to vehicles certifying to the SULEV standards.