Nashville, Tennessee, has experienced rapid population growth and urban expansion over the past decade, bringing with it increased traffic congestion and a heightened focus on air quality. According to the Tennessee Department of Environment and Conservation, portions of Middle Tennessee, including Davidson County, have historically faced challenges in meeting federal ozone standards. In this context, flex fuel vehicles (FFVs), which can run on blends of gasoline and ethanol such as E85, have been promoted as one tool to help reduce transportation-related emissions. While FFVs are not a silver bullet, understanding their actual impact on Nashville’s local air quality standards requires a careful look at emissions science, local infrastructure, and policy frameworks.

What Are Flex Fuel Vehicles?

Flex fuel vehicles are internal combustion engine vehicles specifically designed to operate on more than one type of fuel. Most FFVs can run on conventional gasoline, ethanol-blended gasoline such as E10 (10% ethanol), or high-ethanol blends like E85, which contains between 51% and 83% ethanol depending on season and geography. The fuel system, engine calibration, and emissions controls in these vehicles are engineered to handle the different combustion characteristics of ethanol. Today, there are over 21 million FFVs on American roads, according to the U.S. Department of Energy, yet many owners are unaware of their vehicle’s flex fuel capability. Ethanol itself is a renewable fuel typically produced from corn in the United States, with smaller contributions from sugarcane and other biomass. The production and combustion of ethanol have distinct emissions profiles compared to petroleum gasoline, which is the basis for the environmental argument in favor of FFVs.

The Environmental Case for Flex Fuel Vehicles

Proponents of FFVs point to several emission reductions achieved when operating on E85 compared to regular gasoline. However, the magnitude and real-world significance of these reductions depend on vehicle technology, driving cycles, and the specific blend used.

Reduction in Harmful Pollutants

Ethanol contains oxygen, which promotes more complete combustion in an engine. This can lead to lower emissions of carbon monoxide (CO) and volatile organic compounds (VOCs). Carbon monoxide is a poisonous gas formed from incomplete burning of carbon in fuel, and VOCs contribute to ground-level ozone formation. Studies published by the Environmental Protection Agency (EPA) indicate that E85 can reduce CO emissions by 20–30% compared to gasoline, and total hydrocarbon (HC) emissions by varying amounts. Particulate matter (PM) emissions, associated with asthma and cardiovascular problems, are also generally lower when burning ethanol blends because ethanol burns with a cleaner flame and produces fewer soot precursors. In an urban area like Nashville, where vehicle exhaust is a major source of fine particulate matter, these reductions can contribute meaningfully to meeting the National Ambient Air Quality Standards (NAAQS).

Greenhouse Gas Implications

From a lifecycle perspective, ethanol made from corn can reduce greenhouse gas (GHG) emissions by about 19–48% compared to gasoline, depending on the production method and land use assumptions (Argonne National Laboratory’s GREET model). When FFVs use E85, the net CO₂ emissions per mile can be lower than gasoline, especially if the ethanol is produced with efficient farming practices. However, some studies caution that indirect land-use change—such as converting forests or grasslands to corn production—can offset these gains. For Nashville, the GHG benefit is secondary to the local air quality benefit of lower VOC and NOx emissions that directly affect ozone formation.

Nashville’s Air Quality Landscape

Nashville sits in the Cumberland River Basin, a geography that can trap pollutants, especially during hot summer days. The area has a history of non-attainment for the 8-hour ozone standard. As of the latest EPA designations, Davidson County is in attainment for all NAAQS, but the broader Middle Tennessee region continues to push the limits for ozone. Ozone forms when VOCs and nitrogen oxides (NOx) react in sunlight. Because vehicle emissions contribute a significant share of both precursors, any technology that reduces VOCs or NOx can help Nashville stay below the standard. The Tennessee Department of Environment and Conservation maintains several monitoring stations in the metro area, and data from stations like the one at the Music City Star train station in Lebanon show that ozone spikes still occur during heat waves.

How FFVs Affect Local Air Quality Standards

To directly connect FFV usage to local air quality standards, we must examine the net effect on VOC and NOx emissions. Ethanol has a higher latent heat of vaporization, which can lower combustion temperatures and reduce NOx formation. Some engine studies show a 10–20% reduction in NOx when running on E85. Meanwhile, the oxygen content reduces CO and HC (which are VOCs). However, ethanol blends can also increase evaporative emissions—fuel vapors that escape from the fuel system before combustion. Modern FFVs have improved canisters and seals to minimize this, but it remains a factor. On balance, a fleet of FFVs used as intended, with E85 available, would tend to lower peak ozone formation potential in Nashville. The EPA’s MOVES model allows regulators to estimate emission reductions from alternative fuel vehicles; if Nashville’s FFV penetration increased, the modeled emissions inventory would show declines in CO and VOCs, helping the region maintain its attainment status or even improve the margin of safety.

Challenges and Limitations

Despite the theoretical benefits, several practical challenges limit the real-world impact of FFVs on Nashville’s air quality.

Limited E85 Infrastructure

As of 2025, Nashville has only a handful of E85 fueling stations—perhaps a dozen within Davidson County—compared to hundreds of conventional gas stations. Without convenient access to E85, most FFV owners simply use regular gasoline, negating any emissions benefit. The Alternative Fuels Data Center maps only 11 E85 stations in the entire Nashville-Davidson metropolitan area. Expanding the network is capital-intensive because E85 requires dedicated tanks and pumps that must be resistant to ethanol’s corrosive properties.

Fuel Economy and Energy Content

E85 contains roughly 27% less energy per gallon than gasoline. As a result, FFVs running on E85 get about 15–25% fewer miles per gallon. This means drivers must refuel more often, and while the price of E85 is often lower than regular gasoline, the cost per mile may not always be favorable. The lower energy density also means that, per mile, the vehicle may emit more total mass of pollutants if the combustion efficiency does not compensate fully.

Ethanol Production and Land Use

Ethanol production from corn requires significant agricultural land, water, and fertilizer. The environmental footprint of corn farming—including nitrogen runoff that contributes to Gulf hypoxia—can partially offset local air quality gains. Moreover, the production process itself emits VOCs and NOx from fermentation and drying operations. A true net benefit analysis requires a regional, not just tailpipe, perspective.

Vehicle Age and Maintenance

Older FFVs may not have the sophisticated engine management systems of newer models, meaning they may not achieve the optimal emissions reduction when using E85. Proper maintenance is critical; misfiring spark plugs or dirty fuel injectors can increase emissions regardless of fuel. Many FFVs in Nashville are older, used vehicles that may not be maintained to the highest standard.

Policy and Incentives in Tennessee

Tennessee has not adopted California-style clean fuel standards, but it does benefit from federal policies. The Renewable Fuel Standard (RFS) mandates a certain volume of renewable fuel be blended into the transportation fuel supply, which has directly increased ethanol availability. Additionally, the federal Alternative Fuel Vehicle Refueling Property Credit provides a tax incentive for businesses to install E85 infrastructure, though its intermittent expiration has slowed investment. At the state level, Tennessee offers grants through the Tennessee Department of Environment and Conservation for clean diesel and alternative fuel projects, but these have primarily targeted heavy-duty trucks and public transit, not light-duty FFVs. Nashville’s Metro Government has also introduced a Fleet Sustainability Policy that encourages the purchase of alternative fuel vehicles, including FFVs, for municipal operations. However, the current fleet of city-operated FFVs is small.

To accelerate FFV adoption and realize air quality benefits, policymakers could consider:

  • Expanding state tax credits for E85 station construction
  • Offering reduced registration fees for FFVs
  • Including FFV promotion in the State Implementation Plan (SIP) for ozone
  • Partnering with local utilities to offer discounted electricity for E85 pump operation

The Road Ahead

Flex fuel vehicles are not the future of personal transportation—that role increasingly belongs to battery electric vehicles (EVs), which produce zero tailpipe emissions. However, FFVs can serve as an important transitional technology, especially for the existing fleet of internal combustion engine vehicles. For Nashville, the most effective strategy to meet and exceed federal air quality standards will be a multi-pronged approach: promote EVs for new car buyers, incentivize FFV owners to actually use E85, and simultaneously invest in public transit and active transportation to reduce overall vehicle miles traveled. Since FFVs are already on the road and most drivers are unaware of the capability, a simple education campaign—perhaps paired with a discount at the pump—could yield immediate, low-cost emission reductions.

The Nashville Area Metropolitan Planning Organization has set ambitious goals for reducing transportation emissions by 2050. Incorporating FFV-specific strategies into the regional Transportation Improvement Program could help bridge the gap until EV adoption reaches critical mass. Moreover, as cellulosic ethanol technologies mature (using agricultural waste rather than food crops), the lifecycle emissions profile of ethanol will improve, making FFVs even more attractive from a climate and air quality perspective.

Conclusion

In summary, flex fuel vehicles offer a measurable, though incremental, benefit to Nashville’s local air quality standards. By reducing emissions of carbon monoxide, volatile organic compounds, and nitrogen oxides—especially when operating on high-ethanol blends—FFVs can help Middle Tennessee stay in attainment for ozone and particulate matter. However, the magnitude of this benefit is constrained by limited E85 infrastructure, suboptimal fuel economy, and the lifecycle emissions of corn-based ethanol. To maximize the impact, Nashville should pair FFV promotion with robust infrastructure investment, consumer education, and complementary policies that encourage all forms of low-emission transportation. While not a standalone solution, flex fuel vehicles remain a relevant part of the city’s broader clean air strategy.