I think your assessment of the efficacy of masks is a bit facile. From what I understand, most airborne viral particles will tend to float on aerosolized matter, much of which is over 2.5 microns.

Filtration is a statistics game and so is catching a virus. The more particle exposure you get, the more likely you are to get infected. The more mask material you have between you and the particles carrying the virus, the fewer reach your body.

As far as I understand, if one is in the same physical distances with the same frequency to others with a mask (a cheap one, not an N95 that is properly put on), then the mask does not make much difference for the healthy person, but it does for the person expelling viruses.

But people are also expelling viruses while you have no symptoms, so lots of people who appear healthy are expelling viruses, and since they appear healthy, they are probably not going to wear masks.

For example, if you fly a lot in cramped air cabins, then wearing a cheap mask is not going to do much. What would do something is if every single person wore a mask all the time, since that would capture all the people who appear healthy but are shedding viruses, but that is obviously not realistic.

And if you hang out with a toddler that goes to daycare, no amount of masking makes any difference.

I agree that some particulate matter in the air that is larger than 2.5 microns contains viruses, as does some that is smaller.

Please provide some data as to how many virus particles we inhale in particles larger than 2.5 microns and in particles smaller than 2.5 microns.

I am not aware of anyone having that data, therefore COVID-19 masks seem like guesswork without sufficient science to back them up.

“When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarely, in your thoughts advanced to the stage of science.” ― Lord Kelvin

So you're saying that your test showed that above 2.5um the masks you tested did do something?

So the masks were helpful (because respiratory droplets range from <1um to >100um). [1][2]

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7805396/#sec2ti...

[2] https://royalsocietypublishing.org/doi/10.1098/rsfs.2021.004...

> So you're saying that your test showed that above 2.5um the masks > you tested did do something?

They blocked almost all of the particles larger than 2.5 microns, which surprised me.

The masks did nothing to block particles even a bit smaller than 2.5 microns. I checked the presence of particles at 1.0 microns or larger, and the after-the-mask number was only smaller by the number of particles 2.5 microns or larger that the mask had blocked. The ability of Chinese factories to make masks that filter that precisely surprised me even more.

> So the masks were helpful (because respiratory droplets range from > <1um to >100um).

They did something, but I do not have numbers on what quantity of virus particles we inhale from droplets in each size, so I can not do math or science on this.

“When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarely, in your thoughts advanced to the stage of science.” ― Lord Kelvin

This is correct but I find it very confusing why this information (that masks prevent respiratory droplets rather than virus particles) wasn't more widely known during the pandemic. It felt like it was reported in thousands of news articles.

> That was when I started laughing at the whole thing.

In the GPs case I suspect they knew what result they wanted to find and avoided any articles about how masks worked, let alone checking the scientific literature.

>> That was when I started laughing at the whole thing.

> In the GPs case I suspect they knew what result they wanted to find and avoided any articles about how masks worked, let alone checking the scientific literature.

I spent a lot of time checking the literature and did better testing in my high-school classroom (as a teacher) than the CDIC did.

What is CDIC? How have you judged that you managed to do better testing than them? There have been a lot of tests of the efficacy of masks, not just from one organisation. Especially during the pandemic; there were many organisations across the world doing studies.

If you didn't manage to discover that the main benefit of lower grade masks is to restrict respiratory droplet movement then your literature search was very ineffective.

I don't know much about gas analyzers, but I do know about measurements hardware in general, and there is no chance that this particle size sensor is anywhere close to accurate. Accurate sensors will cost $500-$10000. Why? Because that's the cost for accuracy.

It depends on what you consider “accurate”. For home/diy usage, +/-10% may be absolutely sufficient as long as the error is stable (i.E: it always is a similar offset). For lab/industrial usage, 0.1% may be too far off. There’s a large gap in engineering effort that drives up the prices for more precise sensors.

> there is no chance that this particle size sensor is anywhere close to accurate. Accurate sensors will cost $500-$10000. Why? Because that's the cost for accuracy.

Did you use circular reasoning?

I would love to see some comparisons between cheap and expensive gas sensors. It's probably out there.

"started laughing at the whole thing" sounds extremely arrogant, when your results seem to show that the masks would likely work great. The masks I was wearing filter to about 0.3 micron... including comfortable lightweight ones made specifically by covid by some outdoor clothing companies.

There is also a pretty reasonable argument that the main benefit is slowing down the velocity of air breathing out, keeping particles from spreading as far.

> The masks I was wearing filter to about 0.3 micron

I might vaguely recall some masks claiming such filtration and failing miserably in my testing.

I would love to find such a mask that actually works. Can you please post a brand and model, or a link?

It's easy for anyone here to test them with the setup I described above.

I wanted to build a product a few years ago that would hang on the back of an aquarium like a hang-on-back filter, but instead of being a filter it would test dozens of parameters and send the results to a phone app.

You could fill up an aquarium, wait a week, then ask your phone what fish would like it. It might tell you to dechlorinate it and start it cycling before asking again.

It might know what fish you later put in it, and suggest things that would make the water better suited to those fish. If you need to raise the PH for African Cichlids, it might suggest crushed coral and show a paid advertisement for just such a product.

A continuous water quality system for fish tanks would be excellent, I'm not sure if the appropriate direct sensors actually exist at low cost- but I do think you could basically make it automatically read physical dip-in test strips. I find using, interpreting, and logging the test strips to be a pain- it would be really cool to have it automatic and just pull up the data in a spreadsheet, or get a push notification if the water is having a problem.

> I'm not sure if the appropriate direct sensors actually exist at low cost

In some cases the sensors do not exists, at least not at low cost.

Sensor life is also a problem.

Part of my plan was to have some parts that used long-lasting color-changing sensors with color detectors to read the colors, and the system would prompt me to change them occasionally. SeaChem's Ammonia Alert is an example. I could not find a cheap electronic sensor that would test ammonia levels in water that would work in my system.

Another part of my plan was to have replaceable sensors (if possible) so a fish breeder or reseller with 100 tanks could move a few hang-on-back water testers to one tank and see if one of them has a reading that disagrees with the majority, and swap or replace cheap sensors as required. Replaceable sensors are hard to waterproof, but it is possible. I do not know if we can hobbyist-proof replaceable waterproof sensors. The first version would probably have to be disposable.

> I do think you could basically make it automatically read physical dip-in test strips

The issue with automatically using dip-in test sticks is you do should not return the water from the dip-in test strip to the tank. You end up with a significant amount of wastewater and used test strips that the customer must empty, and then they must refill the test strips that are not supposed to be exposed to air or water. That kills the system's marketability.

A search on Amazon for "blood test" also returns an array of cool results.