“Public concerns/outrage over smog would never cause a technology leap to make cleaner cars and smokestacks? “
If the government hadn’t MANDATED unleaded gas be at EVERY GAS STATION some time in the 70s, we’d still be driving those smokers - there was NO WAY that the auto industry could have cleaned up their tailpipes without the government mandate, even if they wanted to (which I doubt they did).
Neither you can prove this statement nor can I disprove it. I think technology would have cured it without the EPA.