There’s a change at some filling stations—a new blend marketed as Unleaded 88 “Engine smart. Earth Kind.” According to Gas Buddy, it’s available in 31 states and 1,826 stations. Look closely at pump labeling. Unleaded 88 has 15-percent ethanol (E-15) and usually costs less than regular unleaded (87 octane) with 10-percent ethanol or E-10. Refiners are introducing 88 in many places, even those with problematic air pollution despite the fact it’s not strictly Clean Air Act compliant. More on this later. Thus “88” is now available in Milwaukee/Chicago, a “nonattainment area” due to subpar ambient air quality. This piece explores whether you should refuel with E-15 and how it arrived at the pumps. Let’s start with whether you should use it. This is much more complicated than you’d think. Pump labels say it’s suitable for 2001 and newer model year vehicles. It’s not appropriate for small engines used for lawn mowers and motorbikes. Ethanol in this fuel has a corrosive nature and has added oxygen. These properties aren’t kind to older machines. The EPA says E-15 has been thoroughly vetted; carmakers disagree. They claim the EPA focused primarily on the fuel’s impact on catalytic converters. It didn’t check E-15’s feasibility in a wide range of vehicles for damage to fuel senders and fuel pumps. Carmakers agree on one point: all flex-fuel vehicles engineered for E-85 can burn E-15. VW’s product specialist Mark Gillies says he’s “pretty sure all Dubs since 2014 are designed for E-15. There was an E-15 program out of its Detroit office.” Nonetheless, both Wade Newton, the Alliance for Automotive Innovation’s vice president of communications, and VW’s Engineering and Environmental Office’s Jenny Sigelko urge you to check your owner’s manual. It’s the ultimate arbiter of what fuel belongs in your vehicle’s tank. Sigelko says a blanket statement isn’t possible. Some engines, such as the one in Audi’s V-10 R8 sports car, she argues, weren’t evaluated for E-15. The 2021 Atlas’ manual says E-15 is permitted, the 2021 Mazda6 says no and the 2009 VW Rabbit’s says nothing greater than E-10, although 15-percent MTBE is acceptable. This latter blend (now banned in many regions) contains methyl tert-butyl ether, an oxygenate. It’s a controversial fuel additive, which upped octane and was part of a reformulated gas program meant to reduce ozone-forming volatile organic compounds during summer months and cut oxides of nitrogen for the entire year. After its introduction (Chicago/Milwaukee area in 1995), this additive’s proclivity for contaminating water, led to an ethanol-laced alternative: E-10. Pump labeling, itself a hotly debated topic, reflects a shift in motor vehicle fuel systems since 2000. Most late-model cars now have fast-acting oxygen sensor systems, which alter the fuel mixture to meet the ideal stoichiometric ratio of gas and oxygen for an internal combustion engine. The reason an engine’s fuel systems must tweak for this ratio is ethanol has oxygen molecules; straight gasoline doesn’t. Thus, E-15 introduced into engines designed for conventional gas or the mandated E-10 might experience “enleanment.” If there’s too much air, the resulting fuel mixture increases combustion temperature and could damage engines or emissions components. Plus, it might increase oxides of nitrogen emissions (NOx). How E-15 got to your filling station is likely just as confusing as whether you should use it. The experts I consulted couldn’t provide a definitive timeline. Thus, we might start this journey by returning to the 1980s and 1990s. Air quality in many parts of the USA didn’t meet the Clean Air Act’s standards. Therefore, regulators required a shift toward what’s called reformulated gas (RFG). These were oxygenated blends meant to meet goals mentioned earlier. These blends alter cold-engine emissions, which I’ll explain later. Another factor shifted is called volatility. Fuel blends shift seasonally because temperature has an effect on how fuels burn and volatile organic compounds (VOC). One VOC measurement is Reid Vapor Pressure or RVP. Ideally, you’d want a low vapor pressure during the summer to prevent vapor lock or gasoline turning into a vapor before it’s combined with air via the fuel system. In contrast, a higher vapor pressure improves a cold engine’s ability to start. So, refiners seasonally adjust fuel blends. And under RFG rules, one goal was improving air quality by lowering vapor pressure. Fuels that didn’t meet this requirement were banned—especially during summer months from many metro areas. Experts say E-15 exceeds vapor pressure standards. True, but so does E-10 in much of the USA. There’s a patchwork of gas blends in the USA, so there are regions with different rules. The reason it’s now available in places such as Chicago year-round is a 2019 EPA waiver. The politics behind this waiver focused on increasing the use of renewable fuels. It extends to E-15 the same increase of 1 psi in vapor pressure granted to E-10. You might point your finger at E-15 and then call it a stunt appeasing certain political interests. It is. But whether it’s good for the earth in terms of air quality is difficult to peg as vapor pressure isn’t the only factor in what forms ground-level ozone due to VOCs. Plus, the reason it’s at the pump involves the renewable fuels standards mandate codified at least 15 years ago. RFS is a federal program with policies enacted in 2005 (Energy Policy Act) and 2007 (Energy Independence Security Act) couched as weaning the USA from its reliance on imported oil. Since use of renewable fuels hasn’t met expectations, the feds added E-15 to the mix. I cannot evaluate the impact of E-15 on vehicles or the air you breathe, but we know a few things about fuel blends from university studies. Researchers focused on Milwaukee to measure whether RFG improves air quality. Milwaukee’s problematic air probably doesn’t sound as nasty as Los Angeles. But meteorologist Robin Marshment says Milwaukee’s micro climate on Lake Michigan’s “fresh coast” generates an ozone situation during summer months; polluted air from nearby Chicago migrates north. This leads to unhealthy smog levels at testing stations nearly 40 miles north of Milwaukee—an area of low vehicular traffic. Fuels with lower vapor pressure were evaluated in California and other regions. Maximillian Auffhammer (UC Berkeley) and Ryan Kellogg (University of Michigan) examined US gas regulations (2011). What they found might surprise you. Their study focused on VOCs, NOx and ground-level ozone pollution. Their conclusion was simple: implementation of federally mandated RFG did not improve air quality because the feds allow flexibility in choosing a compliance mechanism. Therefore, refiners opt for the cheapest mode of reducing VOCs, which does not reduce ozone. In California, however, where VOC rules specifically target known harmful compounds air quality did significantly improve. Reid Vapor Pressure Regulations RVP, measured in pounds per square inch, gauges the intensity with which VOCs are emitted from gasoline. These emissions occur either on the road, via vehicle exhaust or through evaporation. The fumes you smell when fueling a vehicle are an example of evaporative VOC emissions. Regulations meant to target ground-level pollution through RVP began in 1989. Standards varied based on EPA modeling with the longer trend toward mandating tighter 7.8 psi summer RVP. Some areas implemented stricter limits, as low as 7.0 psi. Refiners often met this rule by reducing the concentration of butane in the gas they sold. Federally mandated RFG under the Clean Air Act Amendments of 1990 led the EPA to enforce RFG in 1995 in areas designated with severe ozone problems (Milwaukee and Chicago, say). These rules placed caps on how much benzene (no more than 1 percent)—a VOC—and this fuel must contain at least 2 percent oxygen with the goal of cutting VOCs. Furthermore, under federal rules RFG’s NOx emissions could not exceed those of conventional gasoline. The NOx/benzene standards were year-round, with the VOC standard applied during the summer ozone season. California’s Air Resources Board and Arizona regulators implemented their own RFG programs. Benzene rules were like the federal standards, whereas VOC targets, were tougher with a seasonal 7.0 psi RVP limit requiring cuts in olefins and aromatic hydrocarbons—both more reactive than butane in forming ozone. Sulfur content was further reduced to control sulfur dioxide and NOx. While this is weedy, and scores of graphs, charts and stats compare air pollution in various areas. For instance, evidence shows the area just east of St. Louis with lower RVP fuel accomplished via methods not as closely linked to ozone as CARB’s did not reduce ozone concentrations. Researchers noted similar findings for Chicago, Houston, Philadelphia and New York—although decreases in ozone in Delaware and New Jersey were better explained by local and upwind NOx emissions controls. In California, however, the 1996 CARB standards did significantly decrease ozone concentrations in VOC-sensitive parts of the state. In sum, this study found the failure of RVP and RFG to reduce ambient ozone concentration centers on the flexibility granted to refiners in meeting VOC emissions. The rules capped the overall rate of VOC emissions for gasoline, which refiners met by removing butane. Since butane isn’t highly reactive in forming ozone, its reduction doesn’t translate into reductions in ground-level ozone. Since Unleaded 88’s RVP is higher than federal standards for straight gasoline, it could, depending on its compounds, increase ground-level ozone pollution. Yet, its RVP is the same as currently used E-10. In contrast, those promoting ethanol argue it’s possible to design engines with higher compression ratios for greater thermal efficiency and therefore take advantage of this additive’s higher octane. Since ethanol is less energy dense than gasoline, fuel economy suffers. Here, again, engines engineered for optimal use of higher ethanol blends would fare better. Theresa Foley, Craig Rendahl and Donna Kenski published a technical paper on the effect of RFG on carbon monoxide concentrations in Southeastern Wisconsin (Journal of Air & Waste Management, 2003). They compared the Milwaukee area with a control city Madison, which didn’t have RFG during the study period. Their conclusion based on a six-year study was RFG introduced to lower CO, VOCs and thus ground-level ozone, did decrease ambient CO concentrations during the winter (twice as much in Milwaukee), but summer data showed no statistically significant change. RFG did not have the impact the federal modelling predicted—likely a variation of the same results found in the Auffhammer study—only RFG created to cut known ozone producing compounds achieves year-round benefits. Other matters studied included Southeastern Wisconsin’s vehicle inspection program—less effective than anticipated—evidence pointed to several factors including motorists who shifted their vehicle registrations to areas outside the program area. Winter reductions in CO emissions were likely because the slight “enleanment” caused by RFG reduces vehicle CO emissions after a cold start and before the catalytic convert reaches optimal temperature for oxidizing CO into carbon dioxide. Since air quality in Madison without RFG improved. Researchers theorize fleet turnover—fewer vehicles on the road built before 1978–especially carbureted autos, was a factor. Unleaded 88 is here. You can use it in some but not all late-model cars. At some stores, Unleaded 88 replaced mid-tier E-10, 89 octane gas. Those marketing 88 claim it’s cleaner, improves engine performance and costs less. You can still fill’er up with regular unleaded. Just use the appropriate pump nozzle. It’s likely a wash on whether you’ll save money.