I think that I've figured it out:
Nonetheless, even when the CEL does not illuminate on the non-FFV burning E85, proper catalytic operation of the catalytic converter for a non-FFV burning higher percentages of E85 may not be achieved as soon as necessary to prevent the emission of some pollution products resulting from burning the gasoline contained in the mixture, especially upon initial cold engine start. This is because the catalytic converter needs to rise to an internal temperature of approximately 300 degrees C before it can 'fire off' and commence its intended catalytic function operation. When burning large amounts of E85 in a non-FFV, the cooler burning characteristics of alcohol fuel than gasoline fuel may delay reaching the 'fire-off' temperature in a non-FFV as quickly as when burning gasoline. Any additional pollution, however, is only going to be emitted for a very short distance when burning E85 in a non-FFV, as the catalytic converter will nonetheless still 'fire off' quite quickly and commence catalytic operation shortly. It is not known whether the small amount of pollution emitted prior to catalytic converter 'fire off' may actually be reduced even during the cold startup phase, as well as once catalytic operation commences, when burning E85 in a non-FFV. Likewise, even once the catalytic converter 'fires off', operation with the CEL illuminated will still result in excess amounts of nitrous oxide being released, greater than when operating the engine on gasoline. The solution is simply to add gasoline, and extinguish the check engine light (CEL), at which time exhaust pollutants will return to within normal limits.
For non-FFVs burning E85 once the CEL illuminates, it is the lessened amount of fuel injection than what is needed that causes the air fuel mixture to become too lean; that is, there is not enough fuel being injected into the combustion process, with the result that the oxygen content in the exhaust rises out of limits, and perfect (i.e., stoichiometric) combustion is lost if the percentage of E85 in the fuel tank becomes too high. It is the loss of near-stoichiometric combustion that causes the excessive loss of fuel economy in non-FFVs burning too high a percentage of E85 versus gasoline in their fuel mix.
Man, the EPA is being a bunch of Nazis because of some cold start emissions?
Well, I stand corrected. Running more than E10 will delay the cat from hitting its light off temperature. There is no doubt about that, at least theoretically.
However, I still contend that, if this were a reality, the second O2 sensor, which monitors the performance of the cat, would know that the cat isn't performing correctly, and throw a CEL.