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It's a good question. It depends on whether we're observing arc discharge or just combustion. If it's arcing, it could surely have a significant UV component. But I suspect this is burning copper or aluminum. HV transformers are filled with some kind of cooling oil, and I suspect that just has to burn off. If it were totally uncontrolled arcing, I'd guess there would be lots of reports of broadband interference that I haven't come across.

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With that sort of light, there clearly was arcing. But most of the billowing smoke was from burning transformer oil.

And about radio interference. This is 60 Hz, so I doubt that's an issue.

A spark’s RF interference isn’t limited to the frequency of the power supply. I don’t know the mechanism, but when I was a kid I found I could hold a lightswitch in a halfway state and hear the interference on the nearby FM radio. (Classic FM, so ~101 MHz compared to UK mains at 50 Hz).

OK, fair enough. But I know what arcs look like. And I'm 100% sure that the one in these NYC videos was huge.

https://en.m.wikipedia.org/wiki/Spark-gap_transmitter

No, spark discharge EMI is a broad spectrum signal.

As I understand it, there's a lot more to spark-gap transmitters than arcs.

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