I need help with additional particle expiry conditions

I have global variable which is by now already getting used by my mod for some random world events,  and i want to implement a fog system which works on that. I only need to figure out how can i prevent this particles that i selected on biome generation to not spawn when i dont need them for example i want them to spawn when my variable is true but i

i dont need them when its false.

Because so far using return blocks is not working for me:

https://ibb.co/2Ms6Nw9