5 ms·

Focusing on PM 2.5 makes sense because anything that size and smaller tend to cause the most harm. [1] [1] https://www.epa.gov/pm-pollution/particulate-matter-

Focusing on PM 2.5 makes sense because anything that size and smaller tend to cause the most harm. [1] [1] https://www.epa.gov/pm-pollution/particulate-matter-pm-basics https://www.epa.gov/pm-pollution/particulate-matter-pm-basic... > Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles less than 10 micrometers in diameter can get deep into your lungs and some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as fine particles or PM2.5, pose the greatest risk to health.

BobaFloutist 2y ago
Presumably smaller particles are also more difficult to filter (and therefore more likely to make their way indoors without dedicated filtration), and also expected to remain airborne for a greater distance and duration (because of square cube things).
- hedgehog 2y ago
  PM2.5 is around the hardest size to filter, I don't understand the physics but both larger and smaller are actually easier to remove from the air. Given that 2.5 is a useful estimate of worst case performance for a given setup.
  - TylerE 2y ago
    Basically a HEPA/electrostatic filter works in two ways. As a “physical” filter (think fishing net), works well on big particles. As an electrostatic filter, works best with really small, works by electrically attracting particles and having them stick. 2.5 micron is in the middle crossover range where total net effectiveness is worst. Respirators are rated at the same size for the same reason.
- LordDragonfang 2y ago
  >Presumably smaller particles are also more difficult to filter So, that may or may not be true for just passive filtering (like door and window frames), but it's actually not true for actual hepa-style filters, because the physics of particulate filtering is totally unintuitive from the macro level -- past a certain point, finer particulates actually become easier to filter, because the physics is dominated by two different effects at different sizes. https://dynomight.net/ikea-purifier/#on-physics https://dynomight.net/ikea-purifier/#on-physics
  - tsimionescu 2y ago
    I don't think it's all that un intuitive, as long as you know that there is an electrostatic effect used for filtering. We all know that it's easier to attract a lighter object with an electrostatically charged ruler, so it's quite easy to imagine that very fine (so, light) particles are easier to to attract than larger heavier ones as well.
4death4 2y ago
Yes, but isn’t lead getting into your bloodstream worse than pollen? I mean oxygen gets into your bloodstream via inhalation…
- bluGill 2y ago
  Worse in what way? Lead is a long term neurotoxin, but pollen triggers the immune system and makes you miserable. Both are bad but in different ways.
  - 4death4 2y ago
    It’s really unclear to you why a long term neurotoxin that leads to lifelong disability is worse than allergy producing pollen?
    - bluGill 2y ago
      It isn't clear until you are suffering from allergies, and notice that old people who used to chew on lead fishing weights are not all that bad off. Most people with high lead in their bodies don't realize the issue nor to the people they know.
      - alright2565 2y ago
        > used to chew on lead fishing weights Chunks of lead just aren't that bad. https://doi.org/10.2146/ajhp060175 https://doi.org/10.2146/ajhp060175 lists common sources of lead poisoning, and none of them are lead weights. Common sources involve things like airborne lead powder (from grinding or smelting), lead compounds dissolved in food & water, paint, and lead in soil.
- wnevets 2y ago
  Which plant produces pollen at PM2.5 tho? Pollen usually isn't entering your bloodstream through your lungs, its too large.
  - 2y ago

BobaFloutist 2y ago

Presumably smaller particles are also more difficult to filter (and therefore more likely to make their way indoors without dedicated filtration), and also expected to remain airborne for a greater distance and duration (because of square cube things).

hedgehog 2y ago
PM2.5 is around the hardest size to filter, I don't understand the physics but both larger and smaller are actually easier to remove from the air. Given that 2.5 is a useful estimate of worst case performance for a given setup.
- TylerE 2y ago
  Basically a HEPA/electrostatic filter works in two ways. As a “physical” filter (think fishing net), works well on big particles. As an electrostatic filter, works best with really small, works by electrically attracting particles and having them stick. 2.5 micron is in the middle crossover range where total net effectiveness is worst. Respirators are rated at the same size for the same reason.
LordDragonfang 2y ago
>Presumably smaller particles are also more difficult to filter So, that may or may not be true for just passive filtering (like door and window frames), but it's actually not true for actual hepa-style filters, because the physics of particulate filtering is totally unintuitive from the macro level -- past a certain point, finer particulates actually become easier to filter, because the physics is dominated by two different effects at different sizes. https://dynomight.net/ikea-purifier/#on-physics https://dynomight.net/ikea-purifier/#on-physics
- tsimionescu 2y ago
  I don't think it's all that un intuitive, as long as you know that there is an electrostatic effect used for filtering. We all know that it's easier to attract a lighter object with an electrostatically charged ruler, so it's quite easy to imagine that very fine (so, light) particles are easier to to attract than larger heavier ones as well.

4death4 2y ago

Yes, but isn’t lead getting into your bloodstream worse than pollen? I mean oxygen gets into your bloodstream via inhalation…

bluGill 2y ago
Worse in what way? Lead is a long term neurotoxin, but pollen triggers the immune system and makes you miserable. Both are bad but in different ways.
- 4death4 2y ago
  It’s really unclear to you why a long term neurotoxin that leads to lifelong disability is worse than allergy producing pollen?
  - bluGill 2y ago
    It isn't clear until you are suffering from allergies, and notice that old people who used to chew on lead fishing weights are not all that bad off. Most people with high lead in their bodies don't realize the issue nor to the people they know.
    - alright2565 2y ago
      > used to chew on lead fishing weights Chunks of lead just aren't that bad. https://doi.org/10.2146/ajhp060175 https://doi.org/10.2146/ajhp060175 lists common sources of lead poisoning, and none of them are lead weights. Common sources involve things like airborne lead powder (from grinding or smelting), lead compounds dissolved in food & water, paint, and lead in soil.
wnevets 2y ago
Which plant produces pollen at PM2.5 tho? Pollen usually isn't entering your bloodstream through your lungs, its too large.
- 2y ago