Anecdata I was living very close to a busy highway, and my young daughter was wheazing when she had a cold, we had to give her medicine via a nebulizer. When we moved out to the country more, far away from any major roads, these issues all disappeared within a couple months.
Living very close to busy highways is known to generate poor air quality. I recommend anyone in those locations buy an air purifier for their kids' rooms.
I bought a couple reasonably priced HEPA purifiers and I change the filters on schedule. Replacement HEPA filters are very cheap.
Also watch out for things that we do indoors that can generate bad air quality. I had a friend who bought a VOC meter and noticed very high readings in his kid's room. He traced the source to his chemical and paint cabinet nearby, which he never considered because he couldn't smell anything. Throwing out a lot of the old containers dropped the measurements to the unmeasurable range.
HEPA filters are counterproductive in standard air purifiers. Air purifiers pump their cleaned air directly into the dirty air of the room. It doesn't matter if that cleaned air is extremely clean, because it's immediately mixed with dirty air. What actually matters is how much clean air you produce: the "clean air delivery rate" (CADR).
The more effective the filter the more it restricts airflow. If a filter is only 99% effective instead of 99.99% but allows double the airflow, it provides nearly double the CADR. To benefit from HEPA you need a clean side and dirty side, like in a clean-room setup.
> It doesn't matter if that cleaned air is extremely clean, because it's immediately mixed with dirty air
What matters is the gradual removal of particles from the air.
The HEPA purifiers I have move enough air that everything gets scrubbed. It works.
My house has a separate central air system with a non-HEPA air filter with a decent MERV rating for the bulk filtering. The HEPA air purifiers do the scrubbing of finer particles.
Don’t overthink this. This looks like knowing just enough to be dangerous but missing the big picture.
Maybe overthink it a bit? I'm skeptical about the big picture.
You have an air purifier in your kid's room. If this is a fairly large apartment or a house, and you have central air running, how much purer is the air in that room? If your central air system is modern and continuously circulates air throughout the house at a low fan speed, you're effectively trying to purify your whole house with that low-output room-sized HEPA filter. Have you done measurements to see if it does anything?
(Not the person you replied to, but offering an anecdote)
There are ton of variables here. One is where the return air intake is. My house only has a single return air vent in the hallway on a 10' ceiling (the furnace is directly above that in the attic). I think this is not-uncommon in the western US.
I have a room-sized purifier in each room on the floor, and they accumulate considerable dust. What I don't know is how much of that would have been successfully pulled out into the hallway, if I didn't have the vacuum of the purifier.
This is impossible for me to A/B test meaningfully given all the environmental variables - wind (house isn't airtight, wind pushes into leaks harder), wind direction (wind from the desert brings sand and other small particles), humidity, etc.
If anyone has reading material on properly controlled experiments in this regard it'd be really interesting to see. I honestly don't know if they're more effective than disabling them and allowing the central HVAC a chance to pick it up sans airflow-tug-of-war. My hunch is it's not worse, though I have no expertise here.
Long-winded post but I'll close with an anecdote: when we had those wildfires in the Bay Area back during covid, they were absolutely more effective at getting the soot and smell out of all of our rooms than the status quo.
edit: One thing to be aware of if someone is evaluating these, all of the claimed numbers from manufacturers are based on you running the air purifier on the absolute highest speed it offers. Almost no one actually does this in on these consumer grade freestanding ones, especially in bedrooms, because they're quite loud.
A reasonable compromise is achieved by an air purifier that has the outlet on top because it’s blowing the filtered air well away from the inlet side and generally circulates the air in the room.
I used to work in the cleanest room in the state, that wasn’t a lab, back when I lived in Adelaide, and top-inlet button-outlet in a raised floor data centre is how the air handling units in the main data hall worked, so you can simulate that to a certain extent.
> The more effective the filter the more it restricts airflow.
This isn’t the whole story. Surface area and flow rate are factors.
A residential home is aiming to improve air quality, rather than grow flawless silicon ingots etc.
The point isn’t that the HEPA filter won’t work under those conditions, it’s that if you can get away with not separating the clean and dirty air, you can achieve better filtration overall with a higher flow, lower resistance filter at a lower noise level. HEPA filters shine in use cases where you need single-pass filtration, like vacuum cleaner output filters or clean room air filters. If you don’t separate clean and dirty air, the filter will still work, but you aren’t taking advantage of its main distinguishing quality, which is its single-pass filtration performance.
If you get to recycle the air through the filter several times, MERV-13 offers much better performance tradeoffs for a residential air purifier because you can recycle the air through it much faster at acceptable noise levels. My home air purifier recycles the volume of my home every 15 minutes or so, vs HEPA filters which produce totally clean air, but since it just mixes with the dirty air that doesn’t matter as much as the rate at which it cleans air.
And guess what 98% of consumer air filtering systems utilize a hepa filter. You’re really over optimizing a non problem. Unless you are constantly producing more contaminants than the system can keep up with it’s totally a fine solution.
If the purifier can filter the air more quickly than air leaves the room it'll still reduce the amount of pollutants in the air. Most people aren't going to create a "clean side" and "dirty side" setup for filtering the air in a room.
I think that is what they're saying: the point is that if you're doing this, you don't want to optimize for the cleanest air leaving the filter, but more for throughput.
The average person isn't going to have a clean-room setup and we're not looking for perfect here just marginally better when it comes to a bedroom.
If you put a standard sized air purifier with a HEPA filter in it into a room it will absolutely lower the dirty air of the room. Because over time you're lowering the particle count.
If I turn my air purifier on in my room even with the door open the air quality sensors improve their readings quite dramatically.
I can buy a HEPA filter machine off the shelf. What I can't buy off the shelf is any other non-HEPA filter machine like you're describing. So while you might be right, there's no products readily available that meet the spec you're providing. We've got to work with what we have available and what time we're able to make for this stuff.
> What I can't buy off the shelf is any other non-HEPA filter machine like you're describing
In locations with central air handlers, the filter in that handler already serves this purpose. That’s how my house is set up: Central handler has a high throughout MERV filter. Several rooms have additional HEPA purifiers.
The parent comment also has a fallacious argument in assuming that the CADR is too low if a HEPA filter is present, but even the cheap HEPA purifiers I bought have sufficient CADR to cycle the room over and over.
If you’re in a location with no central air handler (only mini splits or no air conditioning at all) and you have a giant space to cover and you have a constant exchange of air from the outside to overwhelm your filtration (must leave windows open, for example) then what the commenter above would apply. You would be better with a higher throughput, lower rated filter.
For everyone else, it’s kind of a misplaced “well actually” take that has just enough information to feel truthy but misses the bigger facts.
This reads as being overly confident and wrong. Optimizing for CADR is right but saying HEPA is counterproductive is simply wrong. We are not trying to filter out asbestos and consumer air purifiers are meant to mix the air. So long as over some acceptable period of time the air quality improves it’s a success.
If you only use 99% it means there are small particles you can't catch. Being faster is meaningless if you can never clean the air.
Air purifiers are designed to run 24/7 and all they do is catch particles. Eventually all the particles will be caught. The one I got also detects if there is a lot of particles and will spin faster accordingly.
I am specifically talking about particles in the 0.3 to 1.0 micron range which according to the graph from your link are the most difficult to filter out. Can a 99% filter catch these? My understanding of this is that they cannot.
According to hepacart [1] 99% HEPA filters do not even exist, since HEPA seems to be clearly defined:
> HEPA filter definition, which requires a filtration efficiency of 99.97% for particles as small as 0.3 microns. "HEPA-type" filters may capture larger particles but are not effective against the finer particulates that true HEPA filters excel at removing.
If you’re so inclined, you can build your own air purifier with laser cut panels or 3d printed panels and use a cheap ikea air filter and standard PC fans. All the parts are readily available, and user repairable.
If you pair if with an Apollo AIR-1 you can have home assistant ramp up and down the fans with a PC fan controller based on live readings of PM2.5 in your home. I did this with the help of Claude code.
Looks like a cool project, but the 99.97% HEPA filters are the expensive part. Building yourself only makes sense if you want to choose your own aesthetics or enjoy doing it.
It also makes sense if you're worried that a proprietary filter will be yanked off the market, leaving you with an unusable item. Also, for the money, you cannot get that kind of smart functionality from my research.
My $50 (without the HEPA filter) air purifier can detect particles and change fan speed accordingly. It also has a light sensor to go into really quiet mode during the night.
Though, looking it up it seems that prices for the Winix Zero (including one set of filters) have doubled since I last bought one.
Didn’t the Apollo 13 crew make an air scrubber out of duct tape and hope? Surely a cardboard box, a box fan and a hepa filter covered in tape gets you 90% there
You are referring to a Corsi–Rosenthal Box. You are correct that they will get you 90% of the way there, but they also tend to be large, loud, and ugly. We can build better things now that we have time and resources.
I really wish the DIY folks would measure the airflow and sound levels on this sort of thing. CADR and decibels are going to vary wildly with fan choice
I came across this site which has pretty comprehensive data about PQ curves (the chart for determining CADR given filter impedance) at different noise and power levels: https://www.cybenetics.com/evaluations/fans/204/ (many other fans tested as well but I've been liking the value of P14 Pro PST)
However they look somewhat commercial and I'm not sure the funding/incentives so definitely corroborate with other sources.
DIY folks are not a commercial outfit with access to testing equipment.
Having said that, there are reviews of some DIY models reviewing CADR[1], and it's bizarre to complain about testing decibles since Arctic P14 fans, the most commonly recommended fans, are a thouroughly tested product. Running them at around 25% based on lower PM2.5 readings is almost inaudible from experience.
It's a good start, but for VOCs and gases you'll need activated carbon. Those 2-in-1 filters do exist but cost more. And many are scams because they don't have enough volume of activated carbon.
Getting rid of the VOC source, if possible, is much easier than trying to filter it.
> Those 2-in-1 filters do exist but cost more. And many are scams because they don't have enough volume of activated carbon.
Any filter with a little bit of carbon added is going to be useless after a few days, or maybe even hours.
The only VOC filters that work have multiple pounds of carbon, with the good filters having upwards of 10-20 pounds. It also has to be replaced regularly.
The pollution from highways is primarily particulate matter: Rubber from tires wearing down, brake pad dust, particles disturbed by fast vehicles and kicked into the air.
Because it’s not obvious to most customers that a corner’s been cut. Same reason most new construction in the US sucks.
You can safely put a washer and dryer on the upper floor of a house if you add a proper floor drain, but you’re unlikely to see anyone add a floor drain in new construction because buyers aren’t looking for it. Now multiply that by everything a buyer isn’t looking for and you’re talking real money.
> You can safely put a washer and dryer on the upper floor of a house if you add a proper floor drain
European here, we've always been placing washer/dryer stacks in our bathrooms without needing floor drains. We have machines with a system called Aquastop [1] that stop the water flow if the machine detects a leak inside the system.
There’s a wide range of such designs due to the various different failure modes from false positives to the kinds of leaks resulting in 10’s of thousands in damages they are supposed to prevent.
If the seal between the washing machine and the water supply fails it doesn’t matter which brand you’re using.
They have improved over time, but you need to have a drain for the washing machine anyway so the cost is quite low vs the rather extreme damage a leak can cause.
And manufacturers do a sneaky swap too, my Coway 150 which is a great air filter by the way, came with a nice thick grid of hexagonal cells each filled with carbon granules - that insert alone weighs like half a kg. I ordered official filter and carbon filter replacements off their website ....got a thin carbon "foam" that weighs maybe 50g instead.
If anyone wants to get serious about VOC filtering, these things have 7 pounds of carbon in them, they’re made for filtering the air of weed grow ops: https://terra-bloom.com/collections/carbon-filters
You have companies choosing the component that cost 10 cents instead of 15 cents even if the 10 cents component will break 10 times faster than the more expensive one.
What’s your suggestion? Just sit there and be angry that transportation exists?
You don’t think the parent commenter is also using transportation?
The pollution from transport also occurs with trains, buses, and any other vehicle that has wheels, brakes, or moves fast enough to stir up the air and kick particulates into the air.
People do what they can and control what’s within their reach.
So to give you other example. You live and nearby opens a chemical plant and starts smelling, so you just buy gas mask and hazmat suit or start complaining?
And yes other means of transport also does pollute, but amount is is critical here. You need much less public transport than you need individual cars.
I perfectly understand that there is no quick solution (only quick patch with air purifier) so thats why we should not normalise this and remember to complain (after buying air purifier)
I drive the car, you buy/rent cheap place because its shitty polluted noisy place, so compensate that with air purifier. There is no free lunch in healthy society, there are good reasons for rent for same amount of m2 do wildly differ across same city and its not just sunset views or distance to work
I got tired of that sort of argument when I realized that a great many of the people who argued that they have the right to tear down the side streets of walkable downtown neighbourhoods lived in unwalkable suburban neighbourhoods. Those unwalkable neighbourhoods were usually designed with a single access road to ensure there was no through traffic, so they would never have to deal with that problem. Then those same people had the audacity to ask everyone to pay for additional access roads when they realized that a single access road was a disaster when their neighbourhood needed emergency services and had to be evacuated (because it was burning to the ground). Of course, those additional access roads had to be designed to discourage through traffic.
Am I bitter about that? Yes. There is nothing wrong with wanting the best for you. There is something dearly wrong with using what's best for you to make life worse for others.
buying a new house will have $40k in reltor fees alone, $2k for movers, plus the, you know, hundreds of thousands for the new house. and what if I like my current house, it's in a busy hip area?
or should I launch a multi-year lobbying campaign in the city and/or state and/or national level to have roads moved?
Agreed, just buy air purifiers with HEPA filters and change them regularly. The main expense is buying one for every room, but it's one of those expenses you wish you had made sooner.
Since Eastern Europe is relatively poor and sensitive to energy prices a lot of households invested into insulation, new windows, etc. Last 20 years there was also a huge boom for heat recovery ventilation. Such a simple and inexpensive device that provides so much. Should be first item in every household to invest into.
Funny part is that locals here are absolutely scared of any sign of draft or direct aircon. All while it's what actually saves their health lol.
> Funny part is that locals here are absolutely scared of any sign of draft or direct aircon
I have always been and am still baffled by this. My whole family loses their minds if there is even a slight draft or AC, whether in the house or car. When my brother visits he incessantly closes car vents and windows. Parents constantly nag to put on warm clothes and avoid drafts etc., and when we inevitably get sick a few times a year mostly from school transmitted cold viruses they gloat about it.
Maybe it's a cultural thing from times without good heat/insulation where drafts meant an actual freezing house, which, yes that would actually have an impact on health.
I was in Sarajevo during COVID, I'm sure a reason the numbers were so bad there is from everyone being in enclosed spaces with no ventilation. Smoking without ventilation was bad enough, now add a virus on top of it.
I wanted to long for the time when people hated "Malaria" and wanted to move to "Beunos Aires". But they believed the arrows chase us at daytime and the plague engulf us at night, like in the Psalm.
NO2 is a very hazardous air pollutant which doesn’t get a ton of attention. The main sources are combustion engines and gas stoves. Asthma looks to be mostly caused by gas stoves.
I’ve got a sensor that can detect no2 and it noticeably spikes when using gas. Switched to induction after that.
Do you have a source for that? Because as far as I can see, asthma isn't _that_ less common in countries where gas stoves are barely used, such as germany. Still has like 60-70% of the asthma cases the US has. There's also a ton of other pollutants the US hasn't yet forbidden, but the EU has, which could also explain a lot of the difference in rates.
Don't get me wrong, it's certainly a good idea to get rid of gas stoves. I just think it's a bit much to declare them the primary cause of asthma.
> N02 is a very hazardous air pollutant which doesn’t get a ton of attention. The main sources are combustion engines and gas stoves. Asthma looks to be mostly caused by gas stoves
That makes sense but the unverified claim is that gas stoves are the main contributors to asthma.
That’s a good point, and obvious now you point it out.
On the other hand, when water turns into steam at standard atmospheric pressure, it expands in volume by about 1,700 times.
Whereas the gas in your stove is already a vapour, mostly methane, turning in to mostly water vapour and carbon dioxide. So the expansion ratio isn’t going to be anywhere near as high as that.
I’d say you’re still right.
Still, I wonder to what extent an exhaust fan does help.
If the exhaust fan can vent x cubic feet per minute and the room is y cubic feet in volume then it takes z minutes to full ventilate the room, etc etc.
I’ve never once been in a property that had an exhaust fan sufficient. I’ve had the exhaust on full blast and the spike on the air quality sensor on another floor of the house is rapid and massive.
I suspect a sufficient ventilation would require something more like a lab fume hood that can pull a negative pressure on the area around the stove.
And from what I have seen, a good number of exhaust fans are straight up fake and just ventilate back in to the room rather than ducted outside.
They contain a feels good filter to make you think something is happening. But to actually filter the pollution you'd need a activated carbon filter for the n02 and a hepa filter for the smoke. Which none of them contain and would clog rapidly.
It's massively easier to just not create the no2 by replacing gas with induction, and to vent the smoke outside rather than trying to trap it in a filter. I think the introduction of cheap consumer air quality sensors like from IKEA will start to make this problem a lot more visible to people.
It squeezes me with approximately the weight of an elephant sitting on my chest. But humans are adapted to this and don't notice. It helps that the insides of my lungs are being squeezed outwards by the same force. Otherwise I surely couldn't breathe.
I am indeed wrong. Air pressure is about 100kPa, which is to say 100 kilonewtons per square meter, which is about the weight of 10 kilokilograms or tonnes per square meter, and the surface area of a human is about a square meter, so the air pressure force acting on a human is about 10 tonnes, and an elephant weighs about 5 tonnes, so it's actually the weight of two elephants.
A friend of mine does research on air pollution from cars - the TL;DR is you should not live within a third of a mile of a highway. The falloff is pretty sharp, but you don't want to be in that zone.
Generations of men have been taught that when walking with a woman on a pavement, they should always take the side closer to the road allowing her to keep further away from the traffic.
But Dr Iarla Kilbane-Dawe claimed that Londoners should avoid walking too near the kerb because on busy streets, air pollution can be up to a third higher than on the inside of the pavement.
Shame you cant remember the source. Ive long since wondered if its actually more deleterious for my health to cycle to work in London due to air quality. I came to the conclusion that youre damned if you do and damned if you dont in the end, as in London at least, many of the tube lines have particulates higher than is considered safe
Probably depends on the tube line; one of them, can't remember which now as I left the country in 2018, left me with black snot on each use. Cycling wasn't that bad, but neither were the other lines.
Notably, most major cities have been building tons of housing (especially ‘affordable housing’) right next to highways, as it is the only areas that aren’t already built out with tons of high value houses.
Developers build apartments where they can make money from them, in other words where they can rent them for enough that they'll make back their investment. It's very expensive to build housing, so the only way to make the investment back and have low rental prices is to try to make the building costs as low as possible. A big part of those costs is the price of land.
Or, the only places to build houses with reasonable costs are in areas that weren’t already built out with very expensive houses.
Which will tend to be less desirable areas, by definition.
One approach, of course, would be to also make existing houses less expensive/desirable. Notably, wealthy people tend to have the resources to fight efforts to do that.
The other approach is to expand what land is available to build on. I understand that in the UK, farmers consider it a lottery win if they get planning permission for some of their farmland to become housing.
Despite what many in the UK think about it "being full", this is mostly an illusion from how cramped are the parts in which the houses are allowed to go; the country as a whole is mostly undeveloped.
(There are of course other considerations, with "why did you build on a flood plain?" being one of the failure modes in the UK).
Well, letting people build houses right next to freeways and/or on things like earthquake faults or flood plains is what is being done here. Which is, uh, also a problem. Since those people are now at much higher risk, eh?
Building on farmland has national security concerns (as countries are slowly realizing), as the country ends up dependent on foreign food imports after awhile. Can't grow food effectively when there is a subdivision there instead eh?
In most high demand areas (which are the ones everyone is complaining about, generally), all the decent land (or even just 'normal' land) is already developed.
Bonus - next time around, even the flood plain land might be 'too expensive' to develop on, and folks will only be able to afford houses at the dump, or in a swamp, or the like. Yay.
> The other approach is to expand what land is available to build on. I understand that in the UK, farmers consider it a lottery win if they get planning permission for some of their farmland to become housing.
I've seen that mentality in other parts of the world. The thing is that agricultural land is often protected because it is good agricultural land. It is literally the reason why the cities were built where they were built, since that land provided for the cities. Unfortunately, good agricultural land also tends to be easy to build on and we have a tendency to ignore features that may make it a poor decision to build on. (Such as the flood plains you mentioned.)
Woke activists love the word "systemic" for a reason.
If a bunch of good people acting in good faith produce a result an evil mastermind would want does it matter if they are good? On many levels obviously yes, on some practical levels the system and the incentives still need to change.
EV's have 100% reduction of NOx/tailpipe VOCs, 100% reduction in soot/tailpipe particulates, 70% reduction in brake pad dust (due to regenerative braking), in exchange for 25% increase in tire wear.
Vehicles are capped at emissions of 3mg/mile of particulates and 30mg/mile of VOC's. Something like 1-2mg of tire material actually becomes airborne PM10 particles every mile (and only about 10% of that for PM2.5 particles).
So, EV's really do a great job reducing emissions from 35mg/mile to <2mg/mile (PM10) or even <0.1mg/mile for PM2.5. A 95%-99.8% reduction in air pollution near highways would seem absolutely fantastic for me and my children!
> EV's have 100% reduction of NOx/tailpipe VOCs, 100% reduction in soot/tailpipe particulates, 70% reduction in brake pad dust (due to regenerative braking), in exchange for 25% increase in tire wear.
I replaced the tires on my Tesla model 3 at 74,000 km and they still had tread above the indicator bars. I'm now at 140,000 km and the tires look great, the back ones look like they're only about halfway done. I might be an outlier but my previous Subaru needed tires every 50,000 to 60,000 km.
Needless to say, the brake pads have never been touched and when I saw the left front one at around 110,000 to 120,000 to patch that tire, it looked like it was just installed. The regen braking almost completely eliminated the brake pad or rotor as a wear item.
Yeah, aren’t the EV tyre’s compounded differently in some way to account for the extra weight?
If the weight on each wheel is greater I’d have assumed the tyre would need to be harder, for the same performance.
I would have assumed that would counter the otherwise additional wear, but I keep hearing EV tyre pollution is higher and yet everyone who owns one has always said they aren’t changing tyres an more than they did on their combustion cars.
Given that tires have a range of warranties from 40,000 miles to 80,000 miles ... it's possible that the tires are wearing 25% faster but the consumers aren't noticing because it's still around the normal 40k-80k mile range.
No matter the warranty - I still notice when I replace them.
And the warranty requires proof of periodic rotation. If the tires are wearing evenly, as is the likely case for a new vehicle, then rotation costs significantly more than the pro-rated rebate.
One might similarly note the awe-inspiring destructive power demonstrated by tanker trucks of fuel catching fire and causing interstate bridges to collapse.
You're speculating about something that hasn't happened, using something that doesn't exist; no body is driving batteries large enough to destroy a bridge about.
They are driving liquid fuel tankers that can do that around regularly.
Also consider that as battery tech improves new chemistries lower the risk of fire even more. E.g. sodium batteries are very stable right now and solid state will improve that further. There's no way you can make petrol less flammable.
You're going to have to face facts, battery powered vehicles are safer than petrol powered one.
Consider that every single human being on the planet carries around a lithium battery in their pocket, at a large percentage of those batteries have experienced such damage that would destroy the glass screen on those devices, and yet people are not bursting into flames regularly, and even the defective batteries that Samsung distributed for a while only made events extremely rare.
I don't understand why we keep on building right next to highways which are some of the worst things for our health. You don't need to live in the countryside for that. Just stay roughly 1km away from them and the situation is significantly better.
There is evidence of a lot of ugly diseases caused by this, without even mentioning the constant 40+ dB background noise.
Are we classing A-roads as "highways" now? If not, I have no idea what you mean when you say you're never far from a highway in London. There are no motorways through London.
Same. I visit my family in London and my sleep improves because of no hay fever. Though then I get black boogers, horrible chalky hair, a renewed sense of misanthropy etc
