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Lazarus Long Profile picture
@LazarusLong13
Aug 11, 2021 • 29 tweets • 14 min read • Read on X
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A mega thread on the ultimate DIY air filter known as the Corsi/Rosenthal Box (@CorsIAQ/ @JimRosenthal4).

Take it into work. Donate a couple to your school classroom if they'll let you.

Illustrations beautifully done by @ughberta, discovered through @kprather88.

Image
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But my little angels don't transmit CoVid!?

They have ACE2 receptors, which SARS-COV-2 targets.

They get it and transmit it.

And those little bodies have a thermal plume wafting CoVid up to you.

. link.springer.com/article/10.100…
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Always a typo, no matter how many times you go over it....

Sorry - @Poppendieck has a great FAQ here - used up above!



Another classic FAQ is one maintained by about 10 aerosol scientists.


poppendieck.com/IAQ/COVID19%20…
tinyurl.com/FAQ-aerosols
Above...about 40,000 tweets ago, you mentioned 5 microns...and seemed excited about it. Why?

Respiratory aerosols (emitted when we breathe, talk, laugh, yell, sing, cough, sneeze) carry SARS-COV-2.

And 85% of them are 5 microns or smaller.

Corsi/ Rosenthal boxes in action!

Classroom








Used for wildfires:


For STEM fair





Used for Bacon. Gets it's very own tweet. Mmmmm. Bacon....

For sports palace.


For no reason given
















Pulling this up into the thread for optimum visibility.

Thank you, David!

(A great follow!)
A great resource for clean air:

Your lungs will thank you!

Next tweet...this is the hand sanitizer for the lungs you've always needed. Just without that bad smell...

This spacing is really excellent.

The one thing I would change, based on @Poppendieck's recommendation is to flip the box to be pointed up.

So any dried respiratory aerosols (carrying SC2) on the ground are not lifted off the ground (re-aerosolized).


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Would these help in a hospital with already great ventilation?
(H/T
)

Yes.

Preprint, but Dr. Marr is serious money:



Great discussion of why they still help in such already great ventilation:


And that tweet author is the lead on this study showing basically the same:


Same study, but a great tweetorial, too.

Ontario, Canada bringing in 20,000 portable air cleaners.
Someone asked how to dispose of the filters.

Put on your N100 elastomeric respirator (more comfortable than N95).



Carefully, pick up the Corsi box and gently take it outside.

Since you used painter tape, gently peel it back to get the fan off.
Separate the filters and gently place in a garbage bag. Do not shove them in as might have virus in them and don't want the garbage bag blowing the virus back on you.

Tie the bag tight. Toss into garbage.

Make new box!

Why not spray disinfectant on it?

Because by the
time the garbage bag degrades the virus will have been activated...

nejm.org/doi/full/10.10…
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Corsi/Rosenthal Thread Update:

Some folks, (mostly teachers) cannot bring in an air cleaner. But can bring in a fan.

Here's a fan that has a filter built into it! So, a stealth air cleaner.

"Lasko FF305 Air Flex 2-in-1 20-inch Box Fan and Air Purifier in One with MERV10 Image
Air Purifying Filter"

Won't be as good - but something is better than nothing!



H/T @kprather88 for this. She is NOT endorsing it - I am just thanking her for the knowledge of its existence, and I am the one suggesting it would make a great stealth one.walmart.com/ip/Lasko-FF305…
The filters here: are 13-A - so I would buy one and swap out the MERV 10 that it comes with.



No affiliation, just these are hard to find.
@Al_pha_Q2 @CorsIAQ @JimRosenthal4 @ughberta @kprather88 @CathNoakes might require slower air to do its job. Not as familiar with that tech, so happy to stand corrected if wrong.
@Debbie_Winslow_ @ManTh1ng @tafkak @CorsIAQ @JimRosenthal4 @ughberta @kprather88 @DavidElfstrom But ...I am NOT the expert here, so if any of the actual experts could "like" the above tweet, or otherwise correct my ruminations, I'd be most appreciative :). .
@Karthik07720496 @CorsIAQ @JimRosenthal4 @ughberta @kprather88 improved by implementation of 2 portable air cleaners.

Dr. Schofield's excellent study here - with an explanation of why:


And yes, it will reduce virus transmission by removing the respiratory aerosols that carry SARS-COV-2.

&

@dgurdasani1 @laineydoyle @DavidElfstrom @fischelfe @CorsIAQ @JimRosenthal4 @ughberta @kprather88 @CathNoakes @Poppendieck But round fans are addressed here with some examples:


Overall FAQ here - includes all build instructions for 5/4/2/1 filter versions. (Actually working on finishing up the 5 version).

cleanaircrew.org/boxfanfilterfa…
cleanaircrew.org/boxfanfilterfaq
Mega Corsi/Rosenthal Box Thread Update:

David Elfstrom has done a fantastic triangle filter build with estimated CADR.


It, along with everything else, is now in the FAQ:


One of the FAQ's is the Gallery - check it out!
cleanaircrew.org/boxfanfilterfa…
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Mega Corsi/Rosenthal Box Thread Update - Adding the Baskett Box (3 filter build).

Wow! An update to the Mega Corsi/Rosenthal Box Thread that kind of went a little viral.

Here's a fan that has a filter built into it! So, a stealth air cleaner.

"Lasko FF305 Air Flex 2-in-1 20-inch Box Fan and Air Purifier in One with MERV10."

Next tweet - a surprisingly Image
good performance.

I AM impressed!

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More from @LazarusLong13

Lazarus Long Profile picture
Feb 27
From the ZeroCovid sub on Reddit.

How DO we do it?

Hyper vigilance, constant exposure calculations, discussing and taking precautions?

How do I do it?

Quick thread. I would like to hear covid conscious folks opinions on this: I have long covid (mecfs + pots + mcas). I’ve been sick to varying degrees since 2022. My life has been severely affected by this. At this point, I can’t work. I am mostly housebound, recovering slowly but I still have to spend some days in bed. Recovery from this is awful, especially because it’s not widely understood. With all that said. I still feel like, for me, a life full of hyper vigilance, constant exposure calculations, discussing and taking precautions…I can’t do it. I don’t want to live that way. How can I approach t...
I don't do it.

I don't do exposure calculations.

I don't have hyper vigilance.

I am Vax, Mask, and Relax.

For me, it's just a series of habits now. Drive to the wherever, hit parking lot, put on N95. Get out of car. Stays on until I get back into the car.
A new vaccine comes out? I get it.

I go stay in a hotel?

2nd floor Motel 6 with no shared HVAC (has the PTAC) . Open door/windows for one hour until complete air exchange.

Go through a drive through? N95 on before window is rolled down. Drive away? I roll down both to
Read 6 tweets
Lazarus Long Profile picture
Feb 26
After reading a study, and reaching for my phone, if the first thing I do is check to see if I have @'d someone in the past?

That's not a good sign.

I have never @'d them, and this is not directed @ them.

But this IS a debunk thread.

And it starts with who.

/1
Study here. Before you read it?

This thread is about providing context. Read the thread, @SalvMattera's comments, AND THEN, read the study.

0/10 from me.

thelancet.com/journals/lanep…
Who paid for it? The Dutch government - who has been spectacularly almost Tegnell-like in their downplaying of LongCovid and masks.

Lead authors are from RIVM, their CDC.

RIVM was antimask even when they FINALLY recommended masks in OCTOBER 2020.

nltimes.nl/2020/10/03/dut…Image
Image
Read 13 tweets
Lazarus Long Profile picture
Dec 21, 2025
Oh, we are cooked. Just cooked.

"Brain Mitochondrial dysfunction, known for ~20 years is finally recognized as a central upstream driver of Alzheimer’s disease (AD), not just a downstream effect."

And SARS2's targeting of mitochondria is well-known.

Even in the brain.
/1 We identified dysregulation of mitochondrial and synaptic pathways in deep-layer excitatory neurons and upregulation of neuroinflammation in glia, consistent across both mRNA and protein. Remarkably, these alterations overlapped substantially with changes in age-related neurodegenerative diseases, including Parkinson’s disease and Alzheimer’s disease. Our work, combining multiple experimental and analytical methods, demonstrates the brain-wide impact of severe acute/subacute COVID-19, involving both cortical and subcortical regions, shedding light on potential therapeutic targets within pat...
@LauraMiers, in case you don't have it.

nature.com/articles/s4358…
@LauraMiers This is yet another reason why I N95.

Read 6 tweets
Lazarus Long Profile picture
Dec 17, 2025
@neiljshaw - — a few tips on your excellent article from a clean air advocate

"Consider Wearing a Mask" ?

No, "It is incredibly important to wear a well-fitting mask such as a N95, KN95, or KF94, for the best protection."

You two are doing Image
public health with this article.

Public health is best done with simple clear instructions.

No:
"These masks act as a barrier, reducing the spread of respiratory droplets when people talk, sneeze or cough."

Yes:
"These masks act as a HEPA air cleaner for the face,
cleaning the air of respiratory aerosols when people breathe, talk, sneeze or cough."

The barrier carries the idea of an immovable wall. Unable to be penetrated by things like oxygen and CO2 - which feeds antimaskers.

As an who debunks antimaskers, it is
Read 9 tweets
Lazarus Long Profile picture
Dec 11, 2025
As an anonymous clean air advocate, I've put a bit of thought into how to present, well, my expertise.

If someone were to say, "How do I know you know what you are talking about? Are you a doctor, or a virologist?"

To which, I would say...."No, but that's a good thing.
/1
I have focused on aerosol and masking science. Because it is those fields that give us the most information on how airborne particles, aerosols, get from Person A to Person B.

My expertise is derived from the great studies of Dr. Lindsay Marr, MacArthur recipient. Dr. Prather,
double National Academy member, Dr Milton, inventor of the Gesundheit, aerosol scientist and medical doctor; Dr Coleman whose group found that duckbill N95s captured 98% of emitted respiratory aerosols, and more excellent individual aerosol scientists.
Read 17 tweets
Lazarus Long Profile picture
Nov 22, 2025
I am not a fan of nasal sprays to stop The 'Vid, but I respect you having it as a layer in the Swiss cheese package.

But, some people have said they got bloody noses.

While at the ER yesterday, I picked up a pretty good at home technique. Let our $1,000 lay-out
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save you money.

Use tongue depressors to make a nose pinch clamp.

Leave it on for 30 minutes. Still a problem? Two sprays of Afrin, and re-apply nose pinch clamp. Wait 30 minutes.

Still a problem? Cotton balls sprayed with Afrin, clamp, 30 minutes

aliem.com/trick-of-trade…Image
Image
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Afrin- in generic form is $3.32 at Walmart.

Also, put a ice compress at the back of the neck, while doing the above.

"Cooling the nape of the neck is said to induce reflex constriction of the mucosal vessels of the nose"

✅ I agree with the authors.

pubmed.ncbi.nlm.nih.gov/1568881/Image
Image
Read 6 tweets

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