Respirators are specially designed to protect against small sized particles and particulates such as dusts, smokes, mists, organic vapors, harmful toxic gases, etc. Depending upon their efficiency to filter these particles and particulates these half face masks are further classified into three filtration effectiveness classes such as:-
P1 – Filters about 80% of particles smaller than 2 micrometers
P2 – Filters about 94% of particles smaller than 0,5 micrometer
P3 – Filters about 99,95% of particles smaller than 0,5 micrometer
https://mybreathbuddy.com/blogs/blog/difference-between-p1-p2-and-p3-filters