While filming in New York, the production teams for both Ghostbusters films were able to get away with a lot, even shutting down roads temporarily (and inconveniencing one Issac Asimov* in the process.) But you can only do so much in the city that never sleeps, and cutting a big hole in the middle of a road isn't one of them.
So when they needed to go looking for slime under 1st Avenue, the producers swapped out the actual 1st Ave where Dana's baby buggy stopped (and where the Ghostbusters used their PKE meters to track the source of badness) and let East 8th Street in LA take it's place!
It works like a charm - by not bothering to light the street past a couple of buildings, you can't tell there isn't a typical New York street canyon in the distance. And by dressing up a local menswear store to look like a New York flower stand and corner grocery - complete with the plastic stall curtains to keep out some of the New York winter chill - and dressing everybody for the brisk weather back East, it's the perfect stand-in for New York.
Sadly, the street has changed a bit - Libby's Cafe, which was what initially made identifying the location possible, is long gone now, as it and the parking lot next door were developed into a small retail mall. But you can still see the apartment in the background, and even recognize bits of the corner store, even without the curtains!