Turns out tear gas is known to seep into food items, especially porous food like coffee and bread [1]. Not surprised at all that VOCs linger in reservoirs as mentioned in the article.
[0]: https://en.wikipedia.org/wiki/Capitol_Hill_Occupied_Protest
[1]: https://www.propublica.org/article/tear-gas-is-way-more-dang...
This is by far the most Seattle thing I have ever read.
Partitioning is the distribution of a solute, S, between two immiscible solvents (such as aqueous and organic phases). It is an equilibrium condition that is described by the following equation:
S(aq) ⇄ S(org)
Interesting to think that a surface can play a role comparable to a solvent. I wonder what a chemist would have to say about it.
I wonder which partitions more VOCs/SOCs, partition or structural walls.
-- to divide a country into parts (e.g. separate Pakistan and Bangladesh from India)
-- to divide a physical space with walls
-- to divide a population of molecules between molecules floating in the air and molecules stuck on walls
"Sheetrock" is a particular brand of drywall. For instance, see https://www.lowes.com/pl/drywall/sheetrock-brand/4294864808-...
Neither are they skimmed with plaster. They are instead faced with a very dense and flat hardboard.
It’s not very common, but it is used in some commercial settings.
A partition is an interior wall assembly typically consisting of framing, (optional) insulation, and a wall covering (like gypsum board, but this could be anything: wood, shiplap, masonry, lath and plaster, etc.)
IOW the smoke will have different affinity for different types of furniture, carpets, and window coverings, and when it comes in contact with these they soak it up like a sponge. Because the adsorbent materials are physically like a sponge more often than not, whether on a macro, micro, or molecular level.
The solvent is plain air, but the "solubility" of the raw smoke in air is not a factor because the smoke is not actually dissolved in the solvent (air) at this point, or ever really. The smoke consists of a lot of solid particles that have been forcefully dispersed into the air at uneven concentrations. The smoke itself is not a chemical contaminant that dissolves in the air, it's just dispersed in the air not much differently than an unwanted chemical, for a least a good period of time.
But the solids will eventually settle if they are not purged beforehand. What you're left with after that is then chemical equilibrium.
In a confined enclosure, static equilibrium will eventually be reached between the amount of chemical contaminants dissolved in the air at that temperature, versus the amount adsorbed onto available surfaces. After which no more odor can be released from the furniture once the air is saturated. To really get rid of the smell you're going to have to replace the saturated air with fresh air and one compete air exchange is not usually enough. Also the more efficient air exchange the better, and the fresher the better. If one person smoked one time, or you burned some popcorn and did not let out the smoke right away, that's not much contamination and it's not constant, but it's also not unusual to still smell it a week later when you first walk in from a fresh outdoor air environment. But just don't open the windows when something like a diesel truck is idling outside, new odor could then be coming in in greater quantities than the old odor can escape, one roomful at a time.
You may have grams of "odor" soaked into the carpet along with 100 grams of dirt & dust. But what if the chemical causing the odor only "evaporates" into the air a few milligrams at a time? Because the heavier the liquid, the slower the evaporation and the resulting partitioning coefficient using air as a solvent is such a low number. And it's not too unintuitive to figure that things which are semi-solid like tars or true solids like some pesticides hardly evaporate at all, but can really stink when there's only a few milligrams in the air.
Stuff like that is not going away without a solvent much stronger than air, and also a more concentrated solvent than a gaseous fluid can make contact by the gram much faster than a gram of fresh air can eventually flow by the unwanted material to be removed.
Plain water may not be any better as a solvent at dissolving cooking oils and tars than air is a solvent, but you sure can get a lot more grams into contact with a surface or macro adsorbent quicker compared to air as a gas.
Plain steam dissolves things so much better just from the added heat of the liquid turning it into a stronger solvent, plus so much of the water evaporates so fast at that temperature there is also a purging effect.
Then there's the carpet-cleaning liquids that can improve the partitioning coefficient of water so it will dissolve otherwise insoluble materials without nearly as much heat as steam. Like grams of detergent added to volumes of water to clean a certain area of carpet, or hundreds of grams of water-soluble organic solvent over the same area instead. Or both, simultaneously, or sequentially. Then when you do the math you see how much more effective sequentially is.
Now without doing any carpet cleaning, when you enhance the air exchange rate to do as good a job removing odors as that can accomplish, you are then trying to establish a dynamic equilibrium so odors are being purged outward at an enhanced rate due to increased fresh solvent (air) flow. Kind of like sequential carpet cleaning. One window fan blowing in and one blowing out at opposite ends of the structure can sometimes be more effective than all windows open whether or not using the same fans.
>I wonder what a chemist would have to say about it.
I wouldn't be surprised if people are still wondering :)
Edit: Hopefully they're wondering even more about a lot of things where they didn't know there were equations, actually ;)
I have a couple HEPA filters in my house that hopefully keep particulate exposure down. Does this mean that I have to run them longer? That I need more of them continuously running to keep exposure to VOCs low?
For VOCs you need activated charcoal/carbon filters usually and replace them from time to time.
Where I live all new houses are pressure tested and have a ventilation system, replacing all air once every 1-2 hours or something (I think).
> The lifetime of these compounds indoors can be extended via partitioning to the surface reservoir as modulated by ACR. Higher ACR, which may be achieved by opening windows or through mechanical ventilation, leads to shorter t_half_surf because once indoor compounds partition from the surface reservoir to the gas phase as controlled by gas diffusion across the boundary layer, they would be removed from indoor air more quickly before repartitioning to the surface reservoir.
So they do state active ventilation can help, as you reduce the vapor pressure of VOCs allowing them to partition back into the gaseous env, where they can be promptly ejected. How much exactly is hard to ascertain from their graph since I don't have the exact data they used in the plots. But from squinting at it, it seems 1 OOM change in ACR gives you close to 1 OOM change in the VOC half life, which seems substantial to me.
So adding an active ventilation system might be a good idea for this particular concern. Of course it will add to your energy bill.
Most of us don't eat wooden furniture -- granted my toddler didn't get the memo :)
Thus, continuous ventilation (while not perfect) is hopefully still a decent alternative. Probably better than active charcoal filter.
Granted I should probably out a charcoal filter on the ventilation intake to reduce pollutants coming in from nearby traffic. (All depending on your level of paranoia)
EDIT: And yes, charcoal filters aren't as effective if they're not part of your critical airflow/ventilation path. :D
And that's for the entire house, zero is such a small number.
Then when you run it 24/7 it's 24 times as effective compared to a single hour. That's an impressive multiple itself, on top of bumping the baseline above zero to begin with.
This can really add up to a lot more ventilation than commonly assumed from some of the crummiest fans.
If you can't tell the difference when you walk in, between zero and running one of these all day before you get there, you're gonna need a bigger fan.
But you may be surprised and you never know until you try.
What you're looking for are not HEPA filters but organic vapor filtering. If you were shopping for a respirator it would be easy but organic vapor extractors I think are a lot more expensive than HEPA filters. I looked in to it when I was doing a couple of oil based coatings for a home renovation project.
They won't do anything against VOCs, you need activated charcoal filters
The only difference are some materials like charcoal, which does permanently bind many substances (but as a result can also saturate).
No idea which kind lime and clay are (i.e. "absorb and permanently bind with limited capacity" or "act as a buffer both ways").
> Combined with a HEPA filter in the air circulation system
HEPA filters are not effective against VOCs.
Because carbon is such an effective adsorbent for contaminants, the partitioning coefficient for contaminants to remain in the solvent being filtered is lowered quite dramatically compared to so many other kinds of affordable alternative filtration media.
Most times people do need to afford to discard the carbon eventually, but it doesn't even really absorb contaminants like it's supposed to unless it is activated carbon to a good degree.
Activation only means that is it porous enough to begin with so it has enough surface area to be effective, then it is heated with adequate air exchange to about 250 Celsius for as many hours as it takes for virtually all of the VOC's or moisture it may have accumulated to be baked out. Then sealed up tightly, otherwise it can sit around for ages and gradually become saturated passively with any contaminants or humidity admitted through leaks to the ambient environment.
Sometimes, you can reactivate almost indefinitely to keep reusing the same carbon, and it works with VOCs because by their volatile nature they are basically baked back out easily and virtually completely each time. Different amounts of time if using different temperatures though, if equipped.
The stronger the activation, the more tightly with higher capacity the carbon wants to absorb things it encounters that are dissimilar to the fluid being filtered.
With clay the indoor problem is more about radioactivity, but it's best in terms of humidity control. Chalk creates an alkaline environment on the surface which makes it inhabitable for mold (however the wooden furniture you put in front of it can still get mold if the indoor air humidity is too high).
For clay I know you can add color pigments to the clay itself, most likely you can do the same with stucco for some limited amount of colors. But painting over it with modern products mostly destroys the diffusion properties.
Many people put plastics or other sealing products on top of a clay or lime-based wall and it's a shame.
... so is "smooth, impermeable surfaces" the current begrudgingly-accepted model or something? because there's no way any person who has ever been in a house would think that's a reasonable model. permeable surfaces are all over the place, literally most of the place because it includes essentially all walls and therefore wall interiors. managing that for e.g. humidity is a significant part of building design because it's completely inescapable... and that's before even touching stuff like fabric where your average couch probably has more surface area than all structural surfaces combined.
Simplifying the surface makes it possible to model the system with equations that can be solved analytically--which gives theorists something to work on. Modeling more complex systems (which often happens, eventually) typically requires lots of computing power and results in a model that doesn't generalize well.
I know you have AC for the summer, where we use Lüften during the night and then close our exterior blinds. And that makes sense, as your summers are hotter in many areas and it doesn't get cool enough at night for our strategy to work consistently. But I have always assumed that everyone does Lüften in the winter, and that you guys just like the funny sounding word we use for it.
Here's another recent paper with similar findings. The persistence of smoke VOCs indoors: Partitioning, surface cleaning, and air cleaning in a smoke-contaminated house https://pmc.ncbi.nlm.nih.gov/articles/PMC10575580/
Replication and peer review are required to be very careful about believing small effect sizes that are inconsistent across populations which are so common with papers in biology and medicine measuring the effect of X on Y when it's entirely believable that the study might just be statistical error or cherry picking.
This study is measuring something pretty obvious and it's more akin to you demanding replication and peer review to your bathroom scale. There might be room for some additional studies but the conclusions here "surface areas for VOCs to stick to are much bigger than this simplified model" don't really need to be doubted all that much.
VOCs getting absorbed by surfaces was the most plausible theory in the comments there as well. Interesting to see more evidence for it.
Ozone won't stick around for very long. It is extremely reactive. With windows / doors open and vent fans running it will be cleared out in maybe a few hours max. The first few minutes is definitely overpowering though. You need to have a plan to turn the machine off and ventilate the building that doesn't involve walking through it for longer than you can hold your breath.
Household cleaning one would otherwise moderate their exposure "by smell", so I'm comfortable trusting my sense of smell through an activated charcoal filter even though it's not a listed use, is past expiration, etc.
For things (eg painting with isocyanates), I follow the directions religiously.
It's two oxygen atoms with 1.5 covalent bonds each and another one in the middle with three!
What surprises me about the linked reddit thread is that a chemist was surprised that pumping a bunch of a highly reactive oxygen species into a pile of random chemicals would…. produce a bunch of highly reactive random chemicals in return?
Ozone doesn’t make the soup of random elements disappear, it just oxidizes/reacts with them! Which eliminates odors if they’re trace volatiles (like most odors), but breaks a lot of other things down into even crazier chemicals - and if trapped in an enclosed space, can be bad.
Also, here is a cool video from a guy making liquid ozone [https://youtu.be/9EVrIcaVrqM?si=SyXBieoolcMntcaW]
https://www.youtube.com/watch?v=RYKpKMFIdGQ
Of course the FCC will probably be up your ass in half an hour if you tried it; the point is the equipment is readily available in a few clicks, no questions asked.
Don't get me started on the instantly-blind-yourself-and-everyone-else lasers you can buy on eBay (they'll sell you matching counterfeit laser goggles too).
If you buy it on Amazon, it's "the Americans will sell you anything". If Amazon is too lazy to do due diligence on their third-party sellers, the blame should fall on Amazon if the item turns out to be illegal or dangerous.
Amazon chose to make direct fulfilment almost indistinguishable from third-party fulfilment. Don't want to be treated like a regular store? Then don't make your marketplace behave exactly like a regular store for the buyer!
I like listening to pirate radio but it's mostly shortwave and mediumwave via an SDR, more or less anoraks broadcasting to other anoraks. I know FM pirates are still operating in London but I've never heard any in my current city.
I have a cheap ozone generator I've used for cleaning cars and boxes of used books. Used at the right concentrations and durations, it's magical! Run it outside or in a sealed tote.
But yeah, they'll sell them to just anyone. Electricity and air go in, and ozone (a reactive, toxic chemical) comes out for as long as you leave it plugged in.
DRM-free, too, and made from an eco-friendly carbohydrate foam!
And you can resell it or lend it out to a friend.
I informed the owner, who exasperatingly told me he's been scrubbing them down for weeks but it won't stop. Every time it got hot outside the walls would start again. Apparently his parents smoked heavily in that bedroom for decades.
The confusion with ozone generators is understandable but very unfortunate here.
So yeah, smoking in a house is insanely destructive and takes a long time to actually remove the odor forever.
Also, check all of the drains (including floor drains) to ensure there is water in the trap.
I'd feel embarrassed if I was their alma mater reading that.
- - -
First, the quality of a modern American education.
Let's assume 2000sqft house with 8.5ft ceilings = 17k cu ft or ~500 m3, 1-0.1 μmol/mol ozone produces irritation to respiratory passages, so we need 1-0.1g total ozone left in 500m3 of house.
"170g of a highly reactive gas is generated over two days in a house full of organic materials. The windows are open and the heat is on; after what time will less than 0.1g gas remain?"
Make virtually _any_ assumptions and the answer could not possibly be longer than "minutes."
Mind you, I used very generous numbers and assumptions here. Mexico City averages over 0.1 μmol/mol and seconds of Mexico City air does not "totally destroy" anyone's lungs or cause you to cough up green phlegm.
In other words, with a few seconds of basic math and two basic facts about ozone it is trivial to see that the ozone is effectively gone. This guy has a university biochem degree and experience with organic synthesis? He's on there calling for an "atmospheric chemist" and thinking up ideas to fill the entire house with aerosolized cooking oil (!?!?!?) What is it that makes so many people today entirely incapable of critical thinking? Mind you, this guy literally once had a professor give him a hands-on demonstration of the rapid reaction of ozone - the sort of hint you would give if a student somehow failed the above question - and he still somehow couldn't get it after a week of Googling and reading "the literature."
How do we teach critical thinking?
- - -
Second, the modern synthetic chemicals we live with.
Ozone is always present around us, sometimes at quite high concentrations, depending on your environment. Obviously (... perhaps not always too obviously ...) it is always reacting around us. Most people own hundreds to thousands of pounds of modern synthetic materials. Innovative new chemistries. Formulas changed yearly. Those things are not static, they are off-gassing, they are reacting, they are releasing compounds unknown into the air we breathe. Just your mattress alone might have a hundred pounds of polyurethane foam, the precise composition of which is unknown to any one individual. Perhaps it is enclosed in a polyester cover, and then likely one treated with a fire retardant. Perhaps the corner protectors are recycled plastic of unknown origin, and then maybe they contain an odor-reducing additive. How do all these things react with the air around us? How do they interact with each other? I suspect that when we eventually study this better we are not going to like what we find - but for now, why do we allow plastics manufacturers to use us all as guinea pigs?