High-Energy physicists can play with these, they don't affect the types of filters that we are talking about. The next group of particle comprises of whole atoms, then whole molecules. Even these are almost infinitely smaller than the tiniest particle that our filters can deal with. A small anomaly exists when defining the size of a particle. Engineers tend to talk about 'diameters'.
Particle physicists talk about particle radii.
In truth it doesn't really matter one way or the other, because particles are very rarely round, and who is going to argue about the exact size and shape of a bit of material which is only 0.01 micron in diameter, or radius. However - For those of us that do want to argue, the following definitions of size are available. This is depicted as dimension 'B' , it is the length of a theoretical horizontal line, which passes through the centre of gravity of the particle, to touch the outer boundary walls of the particle. Projected Area Diameter. This is depicted as dimension 'C' and is the diameter of a theoretical circle, which would contain the same projected area as the irregular particle.