PM 2.5 Filters
PM 2.5 Filters can be added to the inside of existing masks. They are considered disposable and the length of use depends on multiple factors. A good rule of thumb is - as they become more difficult to breathe through when you wear them, it is time to replace them.
Learn more about Fine Particles here: https://www.health.ny.gov/environmental/indoors/air/pmq_a.htm