The main difference in the new new particles file is that it's twice as big as it was before (so for the default resolution, the image is 256x256 instead of 128x128). If you just want to make your old particles work, you can make a new image that's twice as big in both dimensions as the old one and put the old image in its top-left corner.
If you want to know where in the image to put the textures for the new particles, here's how you can get them from the JAR for reference:
Go to your .minecraft folder (since this is about resource packs, I'll assume you know where that is :-P ).
Open the "versions" folder.
Find the folder with the name of the version you want textures for.
Inside that folder is the JAR that you want. If you have a dedicated archiving tool such as 7-Zip, you can probably just open the JAR using that; otherwise, if you're able to open ZIP files (the normal Windows file explorer, for example, can do this), you can change the JAR's extension from ".jar" to ".zip" and open it then. You might want to rename it back to .jar when you're done to avoid having unnecessary files sitting around, but even if you don't, Minecraft will just download a new JAR and will run fine.
Does anyone the know the format for 1.13 particles because I was in the snapshot and my particles in my texture pack are all out of wack. Help please?
You can extract the .jar file of the snapshot and take a peek at the images/formats for the particles and such.
The main difference in the new new particles file is that it's twice as big as it was before (so for the default resolution, the image is 256x256 instead of 128x128). If you just want to make your old particles work, you can make a new image that's twice as big in both dimensions as the old one and put the old image in its top-left corner.
If you want to know where in the image to put the textures for the new particles, here's how you can get them from the JAR for reference:
AKA Arctenik on some websites (or Zatnik, but I'm not the only Zatnik out there)
My texture pack on Planet Minecraft