News for hackers. Stuff that matters.
Re:Experiments on a $50 DIY air purifier (2020) by 5e92cb50239222b on Thursday September 02, 2021 @02:22PM (#28395511)
You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.

Where did you buy air filters? I live in a third-world country and couldn't find them anywhere, so I had to buy a factory-built purifier. It really struggles to keep up when it's 1000+ µg/m³ outside. I'd like to add a second one (preferably DIY).

Re:Experiments on a $50 DIY air purifier (2020) by dynm on Thursday September 02, 2021 @02:53PM (#28395876)
> You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.

By my estimates, a lifelong exposure to 33 µg/m³ rather than 0 µg/m³ would on average result in a loss of around 1 disability adjusted life year.

https://dynomight.net/air/#a-heuristic-to-quantify-harms

Obviously this is very hard to estimate and you shouldn't trust this as anything more than at most a rough order of magnitude estimate. But it does suggest that the ambient levels they are experiencing are worth reducing if you can do it easily.

Re:Experiments on a $50 DIY air purifier (2020) by fighterpilot on Thursday September 02, 2021 @03:00PM (#28395956)
Might those numbers might be exaggerated a bit due to confounders? Specifically, the high density and traffic causing stress.
Re:Experiments on a $50 DIY air purifier (2020) by dynm on Thursday September 02, 2021 @03:44PM (#28396470)
It's entirely possible! But my perspective is that there's a very one-sided risk. It's extremely unlikely that particles are beneficial. Thus, given the uncertainty I think it's good decision theory to run a purifier, especially given how easy it is relative to other lifestyle changes that could plausibly have a benefit of the same magnitude.
Re:Experiments on a $50 DIY air purifier (2020) by emn13 on Friday September 03, 2021 @09:55AM (#28404279)
Running a purifier does cause noise however, which isn't healthy; assuming your purifier is close by. (No idea at what point those two effects are of similar impact.)
Re:Experiments on a $50 DIY air purifier (2020) by amluto on Thursday September 02, 2021 @03:21PM (#28396205)
Do you live in a place where forced-air heating is common? If so, you should be able to buy filters wherever people go to buy miscellaneous hardware for houses. In the US, they are rated on a scale called MERV. In other countries, other rating systems are used. You want something at or near the high end of the scale — getting near 100% removal with, for example, a real HEPA filter is unnecessary and potentially counterproductive, but getting to at least, say, 30% reduction in fine particles per pass is important. In the US, this is around MERV 13.
Re:Experiments on a $50 DIY air purifier (2020) by DeRock on Thursday September 02, 2021 @02:37PM (#28395700)
Sure, air quality is relative, but 100 AQI is the point where I start getting headaches. Obviously it can get much worse.

I got the air filters on Amazon, which can be US centric, but usually you would get them at a home/hardware store. They are made for slotting into a furnace/HVAC set up. For places where that is less common, they may be harder to find.

Re:Experiments on a $50 DIY air purifier (2020) by DeRock on Thursday September 02, 2021 @02:59PM (#28395947)
> It really struggles to keep up when it's 1000+ µg/m³ outside

Also worth noting that 1000ug/m³ is not accurate, maybe you are thinking of some other measurement? In the literal middle of a forest fire, you may see readings of ~300 ug/m³. No where on earth sees readings of 1000+ µg/m³.

Re:Experiments on a $50 DIY air purifier (2020) by 5e92cb50239222b on Thursday September 02, 2021 @03:07PM (#28396022)
It is very much accurate. This is a pretty typical PM2.5 level at winter time where I live. Put a few thousand houses heated with coal close together, add −30-40 °C winters, a particularly bad location where wind almost never blows (maybe ~30 days per year total), and voila.
Re:Experiments on a $50 DIY air purifier (2020) by DeRock on Thursday September 02, 2021 @03:39PM (#28396420)
In California, there is the Caldor Fire raging right now in South Lake Tahoe. Heres what it looks like on the ground: https://www.reddit.com/r/weather/comments/pfczpl/caldor_fire...

The highest purple air sensor, near/on the fire front, in raw PM2.5 ug/m³ is at 368 when I checked: https://www.purpleair.com/map?opt=1/mPM25/a10/cC0&select=735...

Re:Experiments on a $50 DIY air purifier (2020) by 5e92cb50239222b on Friday September 03, 2021 @02:43AM (#28401115)
Well, if you find it hard to believe, I welcome you to visit us and live here for a year or two. Don't forget to bring a good supply of spare lungs.

These measurements are supported by the official (state-sponsored) air quality monitoring.

I am not saying we have 1000+ micrograms 24/7. The daily average in winter time is closer to 300-500, depending on your location. However, I see such extreme measurements pretty much every single evening, with some going above 1500 µg/m³.

Back in the days of the great London smog particulate concentrations were going up to 5 _milli_grams per cubic meter:

https://sci-hub.se/https://pubmed.ncbi.nlm.nih.gov/29596258/...

It's not impossible or even particularly unusual.

Re:Experiments on a $50 DIY air purifier (2020) by s0rce on Thursday September 02, 2021 @08:00PM (#28398898)
I don't think the purple air sensors (laser scattering plantower sensors) are very accurate at such extreme measurements. There are numerous laboratory permanent sensors deployed by various state, federal and local authorities that you can compare. I've seen purple air at much more extreme values. Still terrible.
Re:Experiments on a $50 DIY air purifier (2020) by coryrc on Thursday September 02, 2021 @07:40PM (#28398742)
I expect there are a lot of particles bigger than 2.5 um?
Re:Experiments on a $50 DIY air purifier (2020) by Charybdis on Thursday September 02, 2021 @03:11PM (#28396074)
I think you have us all curious now - where do you live? Sounds like Siberia, except I'd expect there to be more wind.
Re:Experiments on a $50 DIY air purifier (2020) by 5e92cb50239222b on Thursday September 02, 2021 @03:13PM (#28396096)
Relatively close, but no cigar. I'll quickly deanon myself if I describe the exact place, there's not many HNers here.
Re:Experiments on a $50 DIY air purifier (2020) by bluGill on Thursday September 02, 2021 @04:09PM (#28396754)
> You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.

Everyone should have filters. Filters are for more than dust, they have also been shown to greatly reduce the amount of COVID in the room air. (i would assume flu and other viruses as well). Cheap and easy, with no stupid controversy like masks or a vaccine (even though both are better than an air filter, every little bit helps)

Re:Experiments on a $50 DIY air purifier (2020) by Bertio on Thursday September 02, 2021 @09:24PM (#28399466)
I live in an area that had over about 6 weeks with us pm2.5 aqi above 300 almost every day and many days exceeding 400 and it shocks me how many people still don't have filters of any kind and see this kind of DIY fan as excessive and silly. Ok, more filters for me I suppose.
Re:Experiments on a $50 DIY air purifier (2020) by stjohnswarts on Friday September 03, 2021 @11:54AM (#28405824)
Not sure how this helps. As soon as your kid sneezes near you, you're gonna catch covid. Air quality seems like a solid usage but in your house vs covid/flu? Your fan is gonna lose. Covid from outside your home? It's a non-issue and doesn't happen.
Re:Experiments on a $50 DIY air purifier (2020) by bluGill on Friday September 03, 2021 @02:37PM (#28407748)
> As soon as your kid sneezes near you, you're gonna catch covid

That isn't for sure. Last I checked (over a year ago, so different variants) 50% of spouses sleeping together didn't catch COVID.

We are reasonably sure that amount of virus particles you are exposed to is a factor on if you will get COVID. So the more you can eliminate the better your odds are.

Re:Experiments on a $50 DIY air purifier (2020) by stjohnswarts on Sunday September 05, 2021 @01:43PM (#28426128)
Delta is at least twice as virulent as the old strains.
Re:Experiments on a $50 DIY air purifier (2020) by OJFord on Thursday September 02, 2021 @06:01PM (#28397928)
'Masks', as worn by most, are assuredly not.

Edit: I'm not anti-mask. I would love it if you explained how ill-fitting cloth in a single pass is better than multi-pass HEPA or equivalent filtration rather than (or even as well as) down-voting, though.

Re:Experiments on a $50 DIY air purifier (2020) by JohnBooty on Thursday September 02, 2021 @09:39PM (#28399546)
Sure, yeah.

A simple cloth mask doesn't really protect the wearer; it protects others from the wearer. It slows droplets down as you exhale them. So they travel X feet, instead of X+Y feet. Depending on air currents and other variables the level of protection this offers others will range from "nothing at all" to "some".

Obviously, a HEPA filter is orders of magnitude better. But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?

Re:Experiments on a $50 DIY air purifier (2020) by OJFord on Friday September 03, 2021 @01:44AM (#28400800)
> A simple cloth mask doesn't really protect the wearer; it protects others from the wearer.

Sure. I'd call that 'different' rather than 'better', but I suppose it's subjective.

> Obviously, a HEPA filter is orders of magnitude better.

You would think, and yet my comment saying so, objecting to 'masks are better than an air filter' (when qualified to ill-fitting cloth as worn by most) is apparently highly objectionable.

> But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?

Not a comparison I made, but yeah, if I went to a supermarket (I'm not, because I almost entirely had groceries delivered pre-pandemic, so now easily enough entirely) I would wear an FFP3 dust mask rather than ill-fitting cloth, which is two nines to HEPA's 3.5.

(More than that is probably not justified since fit won't be perfect, some leakage. Industrially etc. where there's a need for greater filtration I expect that's when you have to step up to fully enclosed hoods. I digress..)

Re:Experiments on a $50 DIY air purifier (2020) by JohnBooty on Friday September 03, 2021 @01:51PM (#28407224)

   > Not a comparison I made
Sure, but it's the relevant one.

   > if I went to a supermarket [...] I would wear an FFP3 dust mask 
   rather than ill-fitting cloth, which is two nines to HEPA's 3.5.
Good. That would be very safe. Ideally everybody would do that. I'll let you think about how feasible that is.

I mean, your entire argument seems to be that cloth masks aren't perfect, I guess?

They sure aren't. But that's not the claim anybody is making. The evidence-backed claim is that they are better than nothing -- and "doing absolutely nothing" is apparently the hill that hundreds of millions of Americans have chosen to (literally) die upon We are trying to take a step forward from that, via a simple harm-reduction method that almost anybody can afford.

Let me ask you something. How effective would a public health measure need to be before you'd endorse it?

1%? 10%? 99%? 100%?

There have been 40 million confirmed cases in America, and likely several times that amount in reality. Over half a million deaths. Each single percentage point improvement in prevention represents > 400,000K cases and > 6,000 deaths.

Re:Experiments on a $50 DIY air purifier (2020) by bluGill on Friday September 03, 2021 @08:50AM (#28403454)
Anything is better than nothing. Even if half the air isn't filtered because of bad fit, that is still half the air that is filtered.
Re:Experiments on a $50 DIY air purifier (2020) by Bertio on Thursday September 02, 2021 @09:17PM (#28399428)
During fire season this year, living in one of the cities with the worst air quality in Canada this year, I had to double up my fans to keep up when it reaches 400+ US pm2.5 aqi in my home office that is about 300 sq ft. I am using filtrete 1900 20x20x1 from amazon (Canada)

I also have a Dyson air cleaner and it works for moderate to light smoke but it's just not enough for heavy smoke.

Re:Experiments on a $50 DIY air purifier (2020) by SilverRed on Thursday September 02, 2021 @07:50PM (#28398826)
I haven't been able to prove this well yet but I got the dyson air purifier and it seems to have done really well at reducing my hey fever. Even when leaving home it seems to be not much of an issue. Possibly just reducing the allergens in the air for most of the time makes it not an issue when I experience them outside for short periods.
Re:Experiments on a $50 DIY air purifier (2020) by manmal on Thursday September 02, 2021 @08:02PM (#28398918)
Hay fever that’s caused by particulates in your house sounds weird. Maybe get a check for mold?
Re:Experiments on a $50 DIY air purifier (2020) by SilverRed on Thursday September 02, 2021 @09:35PM (#28399526)
The pollen comes in through the windows and gets me hard. While I'm at home I have no issues, when I go outside I start to get hit with them but by the time it's really kicking in I'm usually on my way home again anyway.

It's hard to actually prove the air filter did anything since a lot of factors for me have changed since last season but this year I am affected far less than I was last and not feeling any effects right now while some coworkers are.