If cars were running solely on straight ethanol E100, there would still be some pollution, but the emissions would be significantly reduced compared to gasoline-powered vehicles. Ethanol is a renewable fuel that can be produced from various sources such as corn, sugarcane, and other agricultural products, and it has lower emissions of harmful pollutants such as carbon monoxide, particulate matter, and volatile organic compounds than gasoline.
However, catalytic converters would still be necessary to further reduce emissions of pollutants such as nitrogen oxides (NOx). NOx is a harmful pollutant that contributes to smog and acid rain, and it is produced when the temperature inside the engine exceeds 2500 degrees Fahrenheit. Catalytic converters help to reduce NOx emissions by converting the NOx to nitrogen and oxygen gases that are harmless to the environment.
Therefore, even if cars were running on straight ethanol E100, catalytic converters would still be necessary to reduce NOx emissions and meet the emissions standards set by regulatory agencies. However, the use of E100 as a fuel would significantly reduce the overall emissions of harmful pollutants from cars.