SALT LAKE CITY — John Miller has been in the auto dealership business for 15 years, and until recently, even he didn't think about the U.S. Environmental Protection Agency's smog rating system for vehicles.

So the assistant general manager and an owner at Mark Miller Toyota in Salt Lake City said he decided go down the "rabbit hole" of learning more about the grading system for vehicle tailpipes.

"It is not as simple as people would think it would be," he said. "It takes up very little real estate on the window sticker and is confusing."

Earlier this year, Miller joined with Envision Utah, UCAIR and the Utah Division of Air Quality to embark on a pilot project to educate potential new vehicle owners about the importance of smog ratings and how they affect Utah's summer ozone levels and winter's PM2.5, or fine particulate levels.

Miller's dealership painted a mural on the wall of a full-service coffee shop that artfully explains smog ratings and their connection to air quality and Utah's inversions. The mural also points out which vehicles on the lot — seven models — have the "cleaner" smog ratings.

Those vehicles are also adorned with an eye-catching and colorful window sticker the team designed that details how a vehicle's smog rating impacts pollution levels.

EPA bases its grading system on the levels of nitrogen oxides and volatile organic compounds the vehicle emits per mile. The higher the smog rating, the fewer the emissions.

The average Tier 3 vehicle that came online in 2017 or after is markedly cleaner than those automobiles manufactured previously, said Glade Sowards, a policy analyst with the Utah Division of Air Quality.

Sowards said the goal has always been to accelerate the adoption of Tier 3 vehicles by the car buying public because of its impact on air quality — the older vehicles belch out five times the emissions.

"It would be great if we could get people to understand what those ratings mean. It is a pretty dramatic change. We want people to get the car with the best smog rating, but one that still meets their needs."

Ari Bruening, president and chief operating officer of Envision Utah, said the planning team focused on promotion of smog ratings because most of the consuming public do not know what they mean, and the numbers are counterintuitive.

"It is not readily apparent if high is better than low."

Miller said it has been an educational process for him, the sales staff and the buying public, but anecdotally, he believes the pilot project has been well received.

"It's had an impact. Hybrids for us are huge part of our inventory. We lead Utah in selling the most hybrids out of this store."

The dilemma, however, is that for the consumer, there are five models in which there are both gasoline and hybrid versions available. The hybrids cost several thousands of dollars more, and with gas prices being what they are at the pump, Miller said consumers will often not recoup those costs.

When consumers learn about the hybrid's better smog rating, Miller said it makes a difference.

"Customers have said they didn't realize hybrids would have that kind of impact."

Smog ratings are a tricky thing to learn, and not always what you'd think they'd be, he emphasized, and are not related at all to a vehicle's fuel economy and greenhouse gas rating, which is derived from the amount of carbon dioxide that is emitted.

As an example, he points to the Toyota Corolla, which has great fuel economy in the upper 30s for miles to the gallon, but only gets a smog rating of three because emissions control equipment is expensive — and Toyota keeps those vehicles inexpensive.

The Toyota Tacoma truck, on the other hand, gets in the upper teens for fuel economy. It has a smog rating better than the Corolla — a score of five.

As the public, and the industry, continue to become more educated about smog ratings, pilot project participants hope to spread the program to other parts of the Wasatch Front and hope the stickers catch on.

"Basically you're buying a cleaner car that will be better for Utah's air," Miller said.

People can look up emission scores and fuel efficiency information at fueleconomy.gov.