Scale particles

It depends on what you want to achieve - can you elaborate?

I had the same issue where I wanted to scale down the size of an emitter over time. I was able to partially achive the result by setting the particle size for the emitter.

https://developer.apple.com/documentation/scenekit/scnparticlesystem/particleproperty/1523860-size

It is something I need to come back to improve on.