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Comment by mensetmanusman | Hacker News Reader

I am still shocked: months after research has shown that SARS-CoV-2 is airborne stable in aerosol form for over 3 hours, we still aren’t telling the public that room air purifiers are a ‘good thing’ (for making indoor air like outdoor air - in regards to virion density per cubic air volume)

The filter technology is essentially the same as in the N95, orders of magnitude more effective than cloth masks.

Put these indoors, multiple per classroom/working space to help the air refresh in sub 5 minute intervals.

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Added benefit: post-covid pandemic, improved indoor air quality with all the included benefits!

Air quality associated with:

Alzheimers: https://www.scientificamerican.com/article/the-new-alzheimer...

Cancers, plural: https://www.aacr.org/patients-caregivers/progress-against-ca...

Sperm Quality: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4443398/#sec995...

Female Fertility: https://www.newscientist.com/article/2207560-exposure-to-air...

Autism: https://www.sciencealert.com/particulate-matter-in-air-pollu...

Bipolar/Depression: https://www.nationalgeographic.com/environment/2019/08/air-p...

side note: please make the ICE>Electric transition happen faster... sigh

Thanks for these links. I've saved them for future reference!

Sperm Quality? That's it - the window stays open!

My wife works in a doctors office which has stayed open through the pandemic. She sees a few people a day in a small room. The very first thing she did after the pandemic hit the US, was buy an air purifier and she runs it continually. I'm quite surprised that they aren't more common in medical offices in general. The benefits of the air filter are cumulative with other protections—particles caught by the filter can't bypass the mask.

Filters should be mandatory in any enclosed room, the fact that they don't even talk about them as part of the discussion about schools and businesses opening is mind boggling to me.

Expect we will see a repeat of the bungled rush for air purifiers as we did with ventilators.

As with the ventilators, a bungled rush for them is better than not using them at all. Obviously if they had a more ordered distribution it would be better, but any movement in the correct direction would be an improvement.

Here would could at least prioritize schools? Ventilators was only bungled because it turned out to be the wrong therapy... air purifiers is a win win win

> Here would could at least prioritize schools?

Or just mandate them in schools and let the rest of the population figure it out. Though even this would be fraught, there aren't enough air purifiers on store shelves to adequately provide for public schools.

A thing I really wish would catch on is people actually leaving their windows open to get proper ventilation of their living spaces.

Air purifiers seems like a great idea, but if the outside is the safest place in terms of the virus, bringing the outside in to you seems like a no-brainer.

In general, I'd say outdoor air beats indoor air probably 99 times out of 100.

It is all about virion particles per cubic meter (similar to how they classify class ## cleanrooms for the semiconductor, but in that case they talk about dust particles).

Outdoor air works through dilution (‘the solution to pollution is dilution’ is the phrase often used).

Indoor air being purified is often much cleaner than outdoor air (assuming CO2 levels are not of any concern), this is especially true during wildfire season.

If you purchase a PM2.5 sensor and put it in your kitchen while you make toast, you will be shocked. (do this with and without an air purifier near by to be calmed :))

> this is especially true during wildfire season

Curious what if any effect that would have over here in Iowa. I would guess negligible, but we do get high-level haze occasionally when there are wildfires in Canada.

> If you purchase a PM2.5 sensor

I have been curious about these in the past. Do you have any recommendations? I couldn't find enough info to feel comfortable that whatever I bought might actually tell me useful things.

> Indoor air being purified is often much cleaner than outdoor air

As a more or less believer in the Hygiene Hypothesis [1], I'm not convinced that this is a good thing. But I guess also most people don't have purified air in their homes so purified stale air is probably better than just regular stale air.

[1] https://en.wikipedia.org/wiki/Hygiene_hypothesis

This is a good quality particle counter for a home or school:

https://www.amazon.com/Dylos-Laser-Particle-Counter-DC1100/d...

It can be connected to a computer to record particle counts long term using the included Windows software. Useful for seeing that your Hepa air purifier is actually working. There are many brands of hand held instruments for use with HVAC systems. Their cost ranges from $100 on eBay up to several thousand dollars for high end instruments that can measure many particles sizes. They generally are not meant to be left on to take measurements over days though. There are also professional weather instruments that use a laser to count particles in the air outdoors.

Ideally people would be outside more if the air is good. When they have to be indoors, it is better to purify so we aren’t being exposed to ‘unnatural’ environments, i.e. lots of skin flakes floating around with dust mites, etc.

Also, many people in South America have shortened lives because they are indoors with wood burning stoves that are giving them lung cancer.

> "...SARS-CoV-2 is airborne stable in aerosol form for over 3 hours..."

see, this is the kind of insinuation that does none of us any good. it's like doing PCR to connote live virus particles live for 17 days on surfaces (spoiler: they don't).

with that said, i'm down for air purifiers in living spaces† for a whole host of good health reasons, but most commercial spaces and public buildings (like schools) already have HVAC systems incorporating HEPA filters (as good or better than N95 masks). whether the operators change the filters on an appropriate schedule is a different matter however. residential HVAC systems, at least in newer construction, also tend to have HEPA filters (but not always).

† i have a blue pure 211+ for my apartment: https://www.blueair.com/us/air-purifiers/blue-pure-211-plus/...

> most commercial spaces and public buildings (like schools) already have HVAC systems incorporating HEPA filters (as good or better than N95 masks).

So, here's some anecdata. I have a PM2.5 sensor; not a great one, but good enough to measure relative changes. After buying an air purifier the PM2.5 count in our house dropped dramatically and consistently. Whereas the lower end before was a "2", now it reaches to "0"; I'd never seen the sensor register 0 before this. And the spikes from cooking are quickly scrubbed, whereas before they would cause a lingering increase in PM2.5 for the rest of the night.

Even though I spend extra to get the higher grade filters for our HVAC, an air purifier still seems to have objectively improved the air quality far beyond what our HVAC was doing.

In other words, I'm not sure an HVAC is a good replacement.

This, it is amazing how long small particles linger. It’s like looking in a sun beam and seeing floating fibers near the couch.

A very fun experiment to show children is to use a green laser pointer near a carpet floor so it is floating across the floor a couple inches.

Then have the children hit the carpet around the beam and the beam will suddenly appear as the light scatters from the micron-sized dust particles. You can see how long it takes them to resettle, and point the laser anywhere to count a crude interaction/second with the light beam to get a sense of how dirty the air is (laser light volume is quite small :))

that could be, but i'd note that a 2->0 PM2.5 count drop is likely not material to health as opposed to, say, a 20->2 drop. and furthermore, the time-averaged PM2.5 count while home is more relevant than the minimum absolute value.

If you are in the USA, I don't believe your claim that most commercial or schools have HEPA in their air filtration system, and know it isn't true for new residential in the PNW.

The school I attended as a child didn't have any filtration at all, for example.

there's certainly variation, regional, by quality level, as well as generational. class A commercial will almost certainly have filtered hvac, for example. my 1930's vintage high school most certainly didn't.

Filtered, yes, but not HEPA.

Opening the windows more often may also help a lot. This is a very simple method to reduce risk of spreading. It is free and especially useful for places like schools. But I do not think I read about this in mainstream media. It's all about masks and social distancing.

I am concerned about winter, because we have to prep now for that.

On the northern hemisphere we still have a few months (actually, two or three only). That's why the article is correct, we urgently need to talk about airborne transmission.

I've been saying this from the start - should be mandated in public transport.

> we still aren’t telling the public that room air purifiers are a ‘good thing’ (for making indoor air like outdoor air - in regards to virion density per cubic air volume)

> The filter technology is essentially the same as in the N95

So, due to the very small size of this virus, in microns. Most air filters on the market are still not good enough. HEPA isn't good enough, is it better than nothing? Yes but not much. A MERV 14 isn't good enough. I've seen some promising UV light tech but...AC units are pretty ill equipped for this virus.

I'm even curious if studies have been done in hospitals have the equipped AC filtering system to stop this virus. Air flow and filtration is a tradeoff currently. Try to blow out a candle with an N95 mask. It's extremely difficult. The filter technology is not the same.

> orders of magnitude more effective than cloth masks

Cloth masks help about 40% reduction, surgical masks 80%, and N95...95%. I find it very annoying that governments are encouraging cloth masks because they could be use their size and buy surgical masks for everyone at a very cheap cost (economies of scale).

Also, the creator of N95 masks got out of retirement and found that if hospital workers had 7 masks, one for each day. Just rotating them in the storage closet is very effective to reusing them without contamination.

The virions initially travel in large droplets of water that eventually turn into small micron-sized water droplets, these happen to overlap with the high filter efficiency regime.

For aerosol filtration, cloth masks are not very effective, much less than 40% has been measured.

You can also get air purifiers that run the air past a UVC lamp to kill viruses:

https://www.amazon.com/gp/product/B01JKDAN2M

Does anyone know how effective home filter purifiers are? I have been going to my office because of AC.

I am about 20 feet from my partner. He keeps his door closed I keep mine open. I bought two purifiers/filters one for each. they say HEPA but I have no idea if that's true. I keep mine running all the time even overnight. I'm young and healthy so likely risk is low but still being hot might be a worthy trade off.

One commenter below says HEPA isn't even effective

If they can't put these everywhere they should at least target the minority's in our country who are most susceptible; specifically, people over the age of 75.

> is airborne stable in aerosol form

AKA, it's not airborne. If it requires water particles to host the virus, its not airborne.

We need good diagrams that show the virus in a small drop of water with labels showing what we mean :)

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