What are 'sulphate particles' in the context of atmospheric chemistry?

This informative answer describes some processes in atmospheric chemistry and mentions "sulphate particles".

Actually I realize that I don't know what a 'sulphate particle' really is, though I've heard the term many times. Sulphate is an ion, or an anion, so the term could refer to a solid particle of some sulphate salt (e.g. calcium sulphate, sodium sulphate) or balanced by some other caution in solution in a water droplet, but is there such a thing as a particle made of "pure sulphate"?

$$\hskip3.8cm$$

$$\hskip3.7cm$$above: "Sulfate-ion-2D-dimensions", from here.