Here is a rather well done but simple and understated short video on the consequences of a high altitude nuclear burst over the USA. Many pundits, very well versed ones in fact make the claim that Iran is working in three shifts to achieve exactly this with their nuclear weapons program. A sky burst for the EMP effect would be orders of magnitude more damaging than merely detonating a nuke on a city.
A Hiroshima sized nuclear weapon detonated on LAX airport Los Angeles would in fact destroy the airport but probably nothing outside the fence delimiting the property edge of the airport concession. Many wouldn’t know it went off in greater Los Angeles till they heard about it on the news.
If the same weapon where detonated in space at the right altitude, there would be no news. No TV etc.