> The US is also much more concerned with air pollution that affects human health.
What makes you say that? The EU has made plenty of decisions that are aimed at improving air quality which has a direct impact on health, I don't see the US taking the lead here, in fact there are quite a few cases where the EU has lead and the US has definitely not followed.
There is a strong push from US automotive companies against diesel simply because they don't really have the engines, the ones they do sell are quite often sourced from other companies (such as Cummins, which is definitely a fine engine). In the US diesel is for trucks and tractors and gas for light vehicles with only some pick-ups and large SUVs available with both fuel options from domestic manufacturers.
The VW scandal is definitely very bad for the diesel engine but it's not the engines per se that are the problem here, diesel can run clean, it's just that VW decided to cut corners and then cheat on the tests when they found that their corner cutting made it impossible to comply (what amazes me about the whole thing is that it took this long to find out they cheated so massively).