Rethinking indoor air chemistry | Hacker News Reader

Rethinking indoor air chemistry

mpg.de

> Ozone was added to the chamber air inflow in a quantity that was not harmful for humans but representative of higher indoor levels

Just in case anyone reads this and is thinking about buying one of the ozone emitting "air cleaners":

https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-...

"The same chemical properties that allow high concentrations of ozone to react with organic material outside the body give it the ability to react with similar organic material that makes up the body, and potentially cause harmful health consequences. When inhaled, ozone can damage the lungs"

Seems a little odd. I guess they mean it's just not acutely harmful?

I have an ozone generator. I use it occasionally and never in the same room. It's pretty useful for clearing out odors as long as you air out the space afterwards to help the ozone dissipate.

> It's pretty useful for clearing out odors as long as you air out the space afterwards to help the ozone dissipate.

You can skip a step and clear the odors just by airing out the space.

If the odors are of the type and quantity that airing out the space isn't sufficient, the issue to deal with might be the source of the odors.

An air filter with activated carbon can also help reduce odors.

I had an RV which was previously housing mice. After removing and Killz, it still smelled. Two days with the ozone and it was fine after.

If it still smelled it is because the waste of the mice remained in the RV. The ozone didn't remove the waste, but probably just reacted with it to neutralize the odor causing VOCs.

If you were ok with that state, that's great, but eliminating the source of the odor tends to be more effective way to deal with it.

It kills off microbes, does it not? We live in a high humidity environment. When we shut up the house and travel for a couple weeks, there's inevitably a high amount of mildew on our return. I have been contemplating running an ozone generator on a timer while we're out of the house for an extended period to combat this.

> I have been contemplating running an ozone generator on a timer while we're out of the house for an extended period to combat this.

You would be treating the symptom, not the cause, with a harmful chemical that probably wouldn't completely eliminate the mildew, and have unknown side effects.

It would be far better to install a dehumidifier and proper ventilation to manage the mildew problem than killing it off with ozone afterwards.

The house isn't sealed to the outside, and we don't typically run AC (or heat). A dehumidifer would just run all day and produce water without affecting the humidity in the house at all (again, because it's not sealed). Very different from US or European build quality. And yes, ozone would leak to the outside, but most of the venting happens from the top of the house.

(For reference, there's a $50m house nearby for sale that has no exterior walls at all. It's being sold at a discount - only $12m! - because of a notorious incident that took place there, and the fact that the owner can't return to the country without risking arrest and a fourth trial.)

> The house isn't sealed to the outside, and we don't typically run AC (or heat).

Sounds like you are in or near the tropics. How do you control the mildew when you are at home? Presumably not with ozone, but with ventilation. Can you just have the house do that when you are not there also?

Yeah. Windows and doors open when we're home, typically (with ceiling fans to move the air). We definitely _could_ install whole house ventilation and leave that running, you're right - it'd just need to be done well, so could be spendy.

Have you considered something like Mitsubishi Lossnay[1]? The unit itself is not expensive. Also much cheaper to run than aircon and better for the environment.

We’re also in a high humidity environment with equally breezy construction standards and have struggled to keep the house mildew-free when we travel in Summer. We eventually settled on running a compressor-dehumidifier 24/7 during those times, but it’s not perfect.

We considered installing a Lossnay to create a consistent positive pressure gradient and help with humidity exchange, although in our case construction - although not extensive - is tricky as we’re quite high up. You might be better off.

[1] https://sg.mitsubishielectric.com/en/products-solutions/air-...

It looks interesting - thanks. I'll investigate further.

According to you, I should have removed every bit of structural material and flooring because the ozone "only" neutralized it? You do realize odors are VOCs, right? Ozone destroyed them. It's great.

> You do realize odors are VOCs, right?

Odors are caused by some VOCs. Some VOCs have no odor, including harmful ones.

> Ozone destroyed them.

https://pubs.acs.org/doi/full/10.1021/acs.estlett.1c00773

Conclusion:

"... this work shows that for at least some consumer-grade portable air cleaners that claim to remove VOCs from indoor air, VOC removal may actually be minimal, and the air delivered may contain additional VOCs and/or oxidation byproducts, some of which are known to be harmful to human health."

I worry about ozone generators degrading electrical components, especially wiring insulation and sensors.

That's generally a non-issue if used occasionally and at reasonable levels.

Worked well for me as well in mildew-y car, still had a smell after replacing all carpet and cleaning every reachable surface. Ozone with air running for an hour resolved it nicely.

The ozone will destroy the odors, where the filter just traps some.

It doesn't destroy odors in the air. It reacts with them to turn them into something else which maybe you can't smell. Moreso it can cause the creation of formaldehyde when it reacts with some chemicals in the air.

It also inhibits the sense of smell and it can cause the accelerated release of VOCs from materials, which then enters the air.

https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-...

If it works for you, great, but it doesn't destroy anything.

If it turns one molecule into another then that's basically destruction.

"It reacts with them to turn them into something else..."

Lol what do you think destroy means?

Do you think the byproducts that result from the reaction with ozone are safer to breathe? If not, then you need to air out the room or filter the air, so why not just do that in the first place?

Just because you can't smell something because it has been "destroyed" by being converted to something else doesn't mean it's not harmful to health.

Again from the EPA:

https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-...

"First, a review of scientific research shows that, for many of the chemicals commonly found in indoor environments, the reaction process with ozone may take months or years (Boeniger, 1995). For all practical purposes, ozone does not react at all with such chemicals. And contrary to specific claims by some vendors, ozone generators are not effective in removing carbon monoxide (Salls, 1927; Shaughnessy et al., 1994) or formaldehyde (Esswein and Boeniger, 1994)."

"Second, for many of the chemicals with which ozone does readily react, the reaction can form a variety of harmful or irritating by-products (Weschler et al., 1992a, 1992b, 1996; Zhang and Lioy, 1994). For example, in a laboratory experiment that mixed ozone with chemicals from new carpet, ozone reduced many of these chemicals, including those which can produce new carpet odor. However, in the process, the reaction produced a variety of aldehydes, and the total concentration of organic chemicals in the air increased rather than decreased after the introduction of ozone"

"Third, ozone does not remove particles (e.g., dust and pollen) from the air, including the particles that cause most allergies. "

Airing out the room won't remove the sources of odor. This can be stuff like smoke residue, stuff the carpet cleaner couldn't pick up, etc. I clearly advocated for airing the room out afterwards.

Name me something physical that is actually "destroyed" (mind the laws of Physics). The use of the word is used to describe the destructive process that causes a specific thing to not exist, and almost always means it was turned into something else.

> Airing out the room won't remove the sources of odor. This can be stuff like smoke residue, stuff the carpet cleaner couldn't pick up, etc

The source needs to be cleaned from surfaces, encapsulated (i.e. by painting over it), or removed by disposing of uncleanable materials like smoke residue on carpets.

> Name me something physical that is actually "destroyed" (mind the laws of Physics). The use of the word is used to describe the destructive process that causes a specific thing to not exist, and almost always means it was turned into something else.

I don't think we disagree about the physics, only about whether the byproduct of the conversion resulting from oxidation with ozone can be harmful or not.

If the citations I've provided haven't convinced you of the risks of using ozone generators for air quality, then by all means enjoy whatever methods work for you.

Who says the oxidation isn't encapsulation? If you aren't disturbing it, there will be an oxidized layer surrounding whatever is making the smell

ozone kills bacteria that cause odor

Maybe they can be used while rooms are not occupied? That said, would there be any wear/damage on items within the room?

> Maybe they can be used while rooms are not occupied?

Yes, but a simple exhaust fan in a window could also be used without any risk to the occupant. If there's no window, then one should definitely not introduce ozone.

> That said, would there be any wear/damage on items within the room?

"Ozone can cause substantial damage to a variety of materials such as rubber, plastics, fabrics, paint and metals. Exposure to ozone progressively damages both the functional and aesthetic qualities of materials and products, and shortens their life spans."

https://ww2.arb.ca.gov/resources/fact-sheets/ozone-effects#:....

It does much more than airing out. It will completely clear up cigarette smell from an apartment that had indoor smoking. It neutralizes. All the gunk that built up from it, similar to how it degrades rubber.

> It does much more than airing out. It will completely clear up cigarette smell from an apartment that had indoor smoking

As will surface cleaning and repainting porous surfaces that held the cigarette tar, but without the side effects of ozone like the release of additional VOCs from other materials it reacts with. Either way, completely airing out the space is a necessity.

You're not going to repaint carpet.

No, but deep cleaning it with a machine or replacing it are possible.

Possible...and way less convenient and way more expensive than just putting some ozone into the air.

They are undoubtedly different solutions with very different outcomes. This discussion has been good for laying out the pros/cons.

Do you seriously leave smelly carpet from previous owners in place?

If it was visually fine, id rather use ozone to fix it than replace.

Somewhat illogical that after more than two years into the pandemic HEPA filters are still a rare sight to be seen indoors.

So chemical compounds in general yes, but especially aerosols-as-viral-vector still pose a threat:

https://elpais.com/especiales/coronavirus-covid-19/a-room-a-...

> Somewhat illogical that after more than two years into the pandemic HEPA filters are still a rare sight to be seen indoors.

I think we'll look back at this particular thing as one of the greatest public health failures in quite some time.

Can you name a greater one?

Not banning smoking probably is up there.

Really? I feel like they've popped up everywhere, never seen so many air filters in my life.

I feel like every doctor's reception area, daycare, dance studio, meeting room... every little public room that doesn't have HVAC has a little air filter in the corner or on a side table. Often one the Levoit air purifiers that got so crazy popular on Amazon.

As to whether they replace the filters regularly enough, I have no idea... I also figure they have little-to-no effect when 20 people are in the room and its fan is on its weakest (quietest) setting.

That sounds great, I guess it depends on local context then. Agree on maintenance and adjusted usage.

Granted that not everyone lives in a friendly climate:

* What's the effect of occasionally opening a window? I'm not talking about all day when it's 20F or 105F outside, but for half an hour at least.

Not exactly what you're asking but here's an anecdote:

I recently got an air quality monitor because I was worried about CO2 levels in my apartment having the windows closed and AC running all day every day. It turns out the levels were higher than I'd like (nearly 2000 PPM) and just cracking a few windows open very slightly, less than an inch, is enough to reduce the concentration to between 400 (outside air) and 900 depending on how many people are home. The window AC unit was still able to handle cooling the apartment with a relatively small change in usage.

I also run an air filter constantly so my PM2.5 and PM10 levels were already near-zero, but I'd imagine cracking a window helps with that.

I'm just waiting for a "green building" code to specify "all windows shall open."

Imagine the panic that would cause in the construction industry.

Building codes already require operable windows, and some local codes now require active ventilation systems.

The stock of office buildings probably turns over fairly slowly. I've actually never worked in an office where the windows opened.

I think generally "green building" (at least the mainstream stuff) focuses on insulation + air tightness, and then mechanical ventilation. In that context, operable windows would be mostly be a "just in case of overheating" or similar, and the expectation would be CO2 et al would be managed by the ventilation.

I went down a similar journey over the last couple years (CO2, VOC, PM1.0/2.5/10 sensors). In my apartment I sit around zero for particulate with windows closed. I jump up significantly with windows open unfortunately (for my allergies) in the midwest.

I do wish my AC/Heat had more air exchange, similar to your space my CO2 levels rise dramatically after an hour or two of occupation with windows closed.

Any recommendations on a good air quality monitor? It's been in the back of my mind for a while, but I haven't looked into it much. Ideally it'd be something that doesn't use or at the very least require a cell phone app.

I chose the Qingping Air Monitor Lite ($100) specifically because it can connect to HomeKit, but it doesn’t require it and you can use it totally fine without ever connecting it to the network! Though you might need to connect it once if you want to modify default settings like changing it to Fahrenheit. I actually find the device to have a really responsive offline interface that you can use by swiping the top of it.

To give you an idea of why I wanted a “smart” one because I know on HN it’s a polarizing topic: I can include it in my HomeKit dashboard and see it from the other room or when I’m not home, get alerts when it reaches a certain level, record data automatically, and trigger automations like turning on my air filter.

I wouldn't overthink it. Opening windows frequently is a good thing. Doing it during winter is even better. Oh and use crbon/hepa air filtering in bedrooms while sleeping.

Could the shift away from full spectrum incandescent bulbs have any affect on the "air cleaning" process indoors?

I think my potent chemicals are coming from sources other than my skin and breath.

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