Hotdog stands and mobile fish mongers selling fresh fish outside supermarkets are all hooked up to main power in Denmark.

I’m surprised that a wagon that sits in the same place every day in New York can’t get a line of power. Surely the food vendors must be paying rent and permits for the spot, so it’s not like anybody is surprised that a power outlet is needed.

They probably don't pay rent for the spot. The point of a food truck is that it's technically just a vehicle, and vehicles are allowed to move and park whenever there is parking. I'm sure there are rules about how long a vehicle can stay in one location and other restrictions, and there are fights about which food truck was "there first", but I don't think they pay rent in the traditional sense in public areas.

> replacing small gasoline generators with silent, emissions-free electricity.

I know more and more electricity these days is produced by green sources, but the statement above which I read often, is never strictly true.

When I had a job at a power plant near where I live, one of the engineers there pointed at the big chimneys and said (I translate:) "what comes out of those chimneys is cleaner than the air around us". They filter out everything except CO₂ with good efficiency and have big, heavy, expensive machinery and engineers onside 24/7 to monitor that it works.

A 5kg motor, optimised for portability, isn't going to be like that.

CO2 is the problem, and it still remains, even in your best case scenario.

The problem? As in, the only one?

A matter of opinion. As I see it the several carcinogenic components of ICE exhausts are problems. Dying of cancer may be a small problem compared to an uninhabitable planet and I can see how one might consider it insignificant in comparison, but in my opinion, cancer is a real problem, including cancer caused by smog.

Where are the emissions generated? Far away from the population of millions.

And much more cleanly/efficiently than a small gasoline-powered generator, regardless of the energy source.

Coal-powered steam turbine is not that more efficient than a portable gas generator so considering coal is more carbon-intensive it's actually about the same or even worse in terms of emissions if you consider coal burning also produces mercury. Now nat gas-powered CCGT - different story. Good news is NYC is mostly powered by the latter and there's zero coal.