All masks will reduce in efficiency over time with usage.
A mask
only rated for PM2.5 isn't going to effectively filter out this virus. PM2.5 particles, where it is most efficient, are (surprise) 2500 nanometres in size. This coronavirus is going to have dimensions of something like 100-150 nanometres. The mask you describe will probably filter some of the virions but with much reduced efficacy (varying with mask manufacturer). Much better if it is rated N99 or FFP3; then it will provide some degree of protection if fitted properly (tight seal around the mouth and nose with no leakage) - the vast majority of people will have masks that either don't fit properly, or they do not know how to fit them properly, or they readjust them for comfort whilst wearing them, leading to poor fitting.
Any mask (even a clogged one) will however reduce (see
previous other discussion) your ability to touch your mouth and nose, so reducing the likelihood of virion ingress through those entry points (which just leaves your eyes, which clearly nothing other than a full face respirator helps protect).
In summary: wash hands regularly, thoroughly, don't touch them to the soft wet entry points (wear a mask if this helps achieve that), know where your food came from/who prepared it, and try to avoid other people.