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Smog Rating Helps You Choose a Cleaner Car for Cleaner Air

By Ashley Miller, Guest Blogger

DEQ invites guest bloggers to share their thoughts on issues that impact our environment. We appreciate their insights and the opportunity to broaden the conversation with others in the community.

EPA smog rating vehicle sticker
EPA smog rating on the window sticker, located in the lower right-hand corner

There were many things that drew me to Utah, but the incredible skiing, beautiful mountains, and incredibly light snow were high on the list. But with this beauty comes a unique challenge: our mountains shape our living space into a bowl, and our cold temperatures create inversions that trap emissions in that bowl, keeping us in a thick soup of particulate pollution until a storm blows it away.

On the average day along the Wasatch Front, vehicle emissions from mobile sources account for nearly half of our air pollution — about 48 percent in winter, and 45 percent in summer. Utah is experiencing vast population growth, and vehicle miles traveled are expected to double by 2040. Transportation and air-quality challenges come with population growth, so we have to think very carefully about how we can minimize the air-quality impact from more people with more cars.

One thing that we can do individually is to consider air quality when we purchase a vehicle. Here are a few simple ways to find a clean vehicle that meets your needs.

Check out the window sticker

Look for an Environmental Protection Agency (EPA) label on the vehicle’s window sticker. There you’ll find information about the car’s fuel economy, greenhouse gas emissions, and most importantly, a smog rating. The smog rating scale is based on the U.S. Vehicle Emissions Standards, which incorporate specific thresholds for nitrogen oxides, non-methane organic gas, carbon monoxide, particulate matter, and formaldehyde. The rating is on a scale of one to ten, and vehicles that score a ten are the cleanest.

Purchase a vehicle with a “high” smog rating

Ashley Miller with her RAV4. It has a smog rating of 8!
Here I am with my RAV4. It has a smog rating of 8!

With smog ratings, higher is better: the higher the number, the cleaner the car. What does a better smog rating mean for our air quality? A vehicle with a smog rating of “8” emits about one-fifth of the emissions of a vehicle with a smog rating of “5.”

If buying a brand new car off a dealership lot isn’t right for you and your family, you can still find the smog ratings for used cars. Go to fueleconomy.gov, find the type of car you want, compare cars side-by-side, and find the cleanest car that meets your needs.

If you’re looking at buying a car from a private-party seller, the emissions information can be found on fueleconomy.gov or on the spot right under the hood. Cars have a Vehicle Emissions Control Information placard, and with your smart phone you can do a quick search to find out what the numbers mean. And even if you’re looking for a much older vehicle, with this information you can make a choice based on that car’s impact to our airshed. Remember, each number higher on the smog rating scale means dramatically fewer tailpipe emissions and cleaner air in Utah.

Consider your options

Electric vehicles (EVs)

All-electric, or battery-electric vehicles, have a smog rating of 10 and are the only vehicles with zero tailpipe emissions. The emissions from electricity generation are an important part of the equation, but even in regions dominated by relatively dirty power like coal, the emissions produced by the electricity drawn charging an EV are less than the emissions of the average compact, conventional vehicle. And as America’s electricity grids become cleaner and fueled by more renewables, charging EVs will become even cleaner.

If you’re thinking about making the switch to an electric vehicle, there is no better time than now. With so many makes and models available today, going electric is a much easier decision than even just a few years ago. EVs are coming down in price and are significantly cheaper to fuel than their gas counterparts. The average price of electricity has remained fairly static over the last decade, while oil prices to rise, drop, spike, dip and rise again over the same time period. EVs are remarkably simple to maintain because an electric motor has fewer moving parts compared to a combustion engine. This means that you’ll also be saving money on maintenance over the life of the vehicle.


If you’re still not quite ready to make the switch to an all-electric car, there are many other options out there. Hybrids are a great choice and come in a variety of makes and models. The best part about hybrids is they almost entirely eliminate idling by switching to battery power when the vehicle stops in traffic. Being idle-free is a great way to reduce vehicle emissions, and hybrids do the work for you. Many hybrids and plug-in hybrids have a smog rating of 8. And if your car has a smog rating of 8 or higher, you can apply for Salt Lake City’s Green Vehicle sticker, which allows you to park free on the street at the meter for two hours.

When you are in the market for your next car, be sure to look at the smog rating. The decisions we make every day can make a big difference in our air quality and our health.

Want to know more? Check out the EPA’s Green Vehicle Guide to learn more about green vehicles, how to help make transportation greener, and transportation options for the future.
Ashley Miller

I am an attorney originally from Lake Tahoe, California. I am the Policy Director for the local, nonprofit air-quality advocacy group Breathe Utah. My passions run deep in all things outdoors, like skiing and mountain biking. I was recently appointed by Governor Herbert to the new Air Quality Policy Advisory Board. I am also a member of the Salt Lake County Health Department Environmental Quality Advisory Commission, and the Volkswagen Environmental Mitigation Plan Advisory Committee.

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