There are two main criteria for choosing an effective air pollution mask:
1) High filtration efficiency against the most hazardous air pollutants (PM2.5), and
2) An airtight fit to ensure that air does not leak around the sides.
1) High filtration efficiency against hazardous air pollutants (PM2.5)
Since particulate matter is the most widespread and hazardous pollutant affecting human health around the world, it is important to choose a mask with a high filtration efficiency to protect against particulate matter, especially PM2.5 or “fine particulates”, which are a microscopic <2.5 microns in diameter and therefore can penetrate deep into the human system, and even bloodstream, causing a wide range of health effects.
There are a range of standards available to measure the filtration efficiency of respiratory masks. KN95 is a widely-recognized industry standard which indicates a filtration efficiency to remove >95% of airborne particle pollution under standard testing conditions. It is important to choose a mask with a high efficiency of at least 95% filtration rate for particle pollution.
2) An airtight fit to prevent air leakage
It is important to check that your air pollution mask has a good seal around the face, and particularly around the nose. When wearing your mask, you should not be able to feel any air escaping around the sides when you exhale. One good test is to try wearing glasses or sunglasses above your mask, and if they fog up, this suggests that too much air is escaping from your mask. Air leakage indicates that your mask is not able to effectively filter all the air which reaches your body through inhalation.