Using alcohol to improve air filter effectiveness in wildfire smoke events?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9828579/
This study says:
“3.6. Filter condition
The filter condition had a strong impact on DIY air cleaner effectiveness. The DIY air cleaner was almost completely ineffective when used with dirty filters. The CADR for the smoke loaded filter was 4.3 ± 0.9 CFM and repeated with a second smoke loaded filter (CADR = 9.7 CFM) to confirm the poor performance. The smoke loaded filters had only 10.0 ± 1.1 mg of smoke deposited and, despite being only a small mass of smoke, resulted in dark filters with a distinct smoke smell. We qualitatively assessed the air flow through the fan and found that it was largely unaffected by the smoke loaded filters. Additionally, the pressure drop across the filter was only slightly higher (0.29 ± 0.01 in H2O at 819 CFM) than the clean filter (0.27 ± 0.01 in of H2O at 819 CFM). Therefore, it is unlikely that the low CADR is due to the quantity of smoke deposited on the filter. It is likely that the low CADR for the smoke loaded filters is due to the electrostatic filters that were used in this study. Fresh smoke particles can carry charge 34 and when deposited onto the filter build up a charge on the surface that serves to repel charged smoke aerosol. This loss of effectiveness has been observed with electrostatic filters loaded with cigarette smoke 35 and the effectiveness could be restored by discharging the filter using isopropyl alcohol. 36 The loss of effectiveness through charge buildup also explains why the flow was not greatly reduced but the filter was still ineffective at reducing PM2.5 concentrations in the chamber.”
This is could explain some experiences I had with air filters during past smoke events. I’m wondering if it’s worth spritzing them with a small amount of alcohol mist?
In the past I found I had to change filters very frequently during heavier smoke events.
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Be sure to use caution alcohol is very flammable!
Do not spray a mist of alcohol anywhere you would not spray gasoline.
Walta
That’s funny, I know the lead author. I might be able to ask her. But I think this is the paper that discusses the isopropyl “recharge” method (if you can find an unpaywalled verision): https://onlinelibrary.wiley.com/doi/full/10.1002/ceat.201700105
As walta says, that stuff is super flammable so tread lightly and don’t mix alcohol and electricity.
You can ask the author on Researchgate or email them directly and they'll usually supply the paper.
Thanks for the link!
Here is their conclusion:
"4 Conclusions We have shown that recent testing standards overestimate the cleaning efficiency of mobile air cleaners if considering only particles larger than 0.3 μm. This effect is explained by a significant decrease of the CADR with decreasing particle size. Since UFP are omnipresent in indoor environments and have a higher impact on human health than larger particles, the size range below 0.3 μm should be taken into account in future standards to yield a more praxis-oriented and health- relevant measure. Furthermore, we have shown that aging with cigarette smoke strongly degrades the cleaning efficiency: Considering only particles larger than 0.3 μm and the filters tested here, already about 200 cigarettes lead to a reduction of the initial CADR by 50%. However, the effect is smaller for smaller particles, which we relate to the decreasing relative contribution of electrostatic effects to the total filtration efficiency with decreasing particle size. Finally, we have compared two different aging methods, one according to the GB/T 18801 and one self-developed. Aging according to the standard leads to a stronger aging effect for the same amount of cigarettes than the self-developed method. This is presumably related to different aerosol characteristics in terms of particle size and concentration, a higher charge state and a higher particle-to-gas emission ratio in the standardized method. We conclude that the aging method described in the GB/T 18801 does not reflect the closeness to reality it might pretend to the consumer. Moreover, it remains to be investigated how strong the dependence of the results on the burning conditions actually is, which might bring a lot of uncertainty in the testing method. Together with the further disadvantages of cigarette smoke such as its toxicity and high costs, we recommend to look for an alternative choice for future testing standards for mobile air cleaners using cheaper and non-toxic materials. Our results show that for a praxis-oriented rating of the long-term stability the considered particle size range and the conditions of aging are of great importance."
When I was younger I had a job and one small part of it was cleaning recently repaired PC boards with alcohol. There was some rush on and my immediate supervisor told me to through them in the environmental oven to speed up the drying
You know where this is going.
I cannot remember if it was the lead test tech, or my manager who walked up and asked me if I knew what the flash point of alcohol was...cue eyes open wide.
Made a mess of the lab oven.
Point being, no flame whatsoever, boom!
So, no, no alcohol on filters
Isopropyl alcohol is used for cleaning many things, in the telecom industry, we use it a lot to clean fiber optic connectors. It’s not particularly hazardous to work with, although it is flammable. I wouldn’t call it explosive though.
I’m not sure sure it’s worth trying to clean filters with alcohol. Alcohol is very volatile and evaporates quickly, so it’s not going to stay on/in the filter for long (probably only a matter of seconds to a minute or so), but it might be able to clean a filter for reuse. The alcohol might also cause the adhesives used to hold the filter together to let go though, so there is some risk of damage to paper filters.
I think it would be easier to just change the filter. If you really want to deal with smoke, use a deep pleated filter with a high MERV rating as a first stage, then follow that with an activated carbon filter. Not much will sneak through that filter combo.
Bill