Irrelevant. Electricity doesn't ACTUALLY get cheaper at night by some macick.
They're just ticking over. Demand a serious load and they'll use MORE FUEL.
You have a basic problem with thermodynamics I see and conservation of energy. I guess SCIENCE wasn't your strong suit ?
Existing cars with catalysts do fine. Even in 1993 the Saab 9000 was promoted as an 'air cleaner' in congested cities. The emissions from its tail pipe were less than in the surrounding air. Guess my car.
Graham