That poster seemed to be saying that frying pan PM2.5 was not a health risk:
> Heck, my PM2.5 meter skyrockets whenever I cook anything in a frying pan, because many of the aerosolized oil droplets are PM2.5.
I'm not sure how they determined that PM2.5 is not a neurotoxin, or the full extent of their claims, but frying pans inside are a common cause of minor health problems.
> That poster seemed to be saying that frying pan PM2.5 was not a health risk
They said that the category "small particles" is not equal to the category "neurotoxic".
Much like how "Walks on Two Legs" is not "Men", there may be some overlap in the categories, but the first does not reliably indicate the second. (Or vice-versa.)
The point was that PM2.5 is a measurement of particle size, and that by itself allows no judgement about its toxicity. The same way you cannot argue that things of 5 centimeter diameter are healthy.
The toxicity judgement comes from the information what substance has the form of PM2.5, and the journo managed to omit that.
> The point was that PM2.5 is a measurement of particle size, and that by itself allows no judgement about its toxicity.
This does not logically follow at all. The size indicates where it can reach in the lungs, whether cilia can eject it, etc.
A 5cm ball shot at the head at high speed is indeed dangerous. We are talking about inhalation of particles causing irritation, and the size is indeed the major factor. Content as well, but frying pan particles filled with carbon chains that have gone through who knows what reactions are indeed of concern. Lots of extremely nasty things are easily accessible from chains of hydrocarbons, from toluene to formaldehyde.
> The toxicity judgement comes from the information what substance has the form of PM2.5, and the journo managed to omit that.
I believe the journalist is not at fault here in the least. The scientific papers I have seen usually class all PM2.5 together, and perhaps by source. But the size itself is of great concern due to the size allowing easy entry to the body that is not possible for larger sizes.
There is nothing inherently impossible about the idea that all airborne substances of some specific size are harmful to breathe. It simply requires that they be bad because they physically fit into somewhere that shouldn't have foreign substances of any kind in it rather than because of something specific to the substance.
To be just a touch pedantic, that all particles of a certain size are harmful is a silly assertion.
Water and sugar particles, for instance, are almost certainly harmless below some reasonable threshold.
Small enough particles can easily pierce the blood brain barrier. https://pmc.ncbi.nlm.nih.gov/articles/PMC10141840/ They also appear to interact with human gut microbiota. https://pmc.ncbi.nlm.nih.gov/articles/PMC11056917/
What they do there is up for further study.
Many studies show a high correlation with childhood respiratory defects and living near roads (or even attending school near roads) specifically a road with diesel truck traffic, and a recent study showed a decrease in effects when air filters are installed in the schools. https://pmc.ncbi.nlm.nih.gov/articles/PMC6949366/