DIY PM2.5 Air Purifier using the fan you already own

[lsemprini]

 

Here is a public service announcement for those (including locals) who do not have enough cash/rights to leave Northern Thailand during the smog season or to buy one of the overpriced room air purifiers currently on the market.  Using the trick below, you can make a purifier with your existing floor/desk fan and some filter material.

 

Be sure to check out the English- and Thai-language images included below.

 

More info at: https://slice-of-thai.com/air

 

Please help share to all pollution-affected communities in Thailand and around the world.

 

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What are PM2.5 particles?

PM2.5 particles are the most dangerous ingredient of today’s world-wide pollution.  These tiny particles get into our lungs and blood stream.  They cause bronchitis and other lung diseases, and, over time, increased risk of heart attack, stroke, and cancer.

 

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Ways to protect from PM2.5

1 Wear an N95-rated mask.  Only N95 masks will block PM2.5 particles.  Don’t waste your money on cheap/fake masks!

2 If you have an aircon, buy a roll of 3M Filtrete and install the sheets in your aircon filter. Follow the video at: https://youtu.be/ka8aMHpddUw  You will need new sheets every 10-14 days.

3 Buy an overpriced commercial air purifier for between 2,500-14,000 THB, plus 1,000 THB for replacement filters every 2-3 months.

4 Make your own DIY air purifier for around 400 THB using the fan you already own!  Read on...

 

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DIY Air Purifier Step 1

Choose a small room (not more than 15 square meters).  Seal up windows and doors with tape/weatherstripping. Seal wood floor with carpet or linoleum.

(see pictures)

 

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DIY Air Purifier Step 2

Buy a true HEPA filter from Lazada (search for “HEPA”).  

Dimensions at least 30 x 30 cm, accordion-fold.  

Price around 200-400 THB.

(see pictures)

Example Lazada listings at this time:

36cm x 46cm one for 308B:
https://www.lazada.co.th/products/oscar-store-pm25-filter-element-hepa-element-filter-replacement-filter-low-noise-smog-indoor-air-purifier-parts-dust-air-cleaner-officehome-modern-fashion-i306902965-s534642044.html?spm=a2o4m.searchlist.list.27.33224d4dCi5Exe&search=1

30cm x 30cm DIY one for 284B:
https://www.lazada.co.th/products/diy-air-filter-hepa-dust-filter-for-air-conditioner-cold-fan-air-cleaner-fan-i262587968-s404515424.html?spm=a2o4m.searchlist.list.1.cddf66c9scd8px&search=1

Two of above for 226B each:
https://www.lazada.co.th/products/diy-air-filter-hepa-dust-filter-for-air-conditioner-cold-fan-air-cleaner-fan-buy-1-get-1-free-i285486364-s465578550.html?

Do not cheap out on the filter.  Only a true HEPA filter blocks PM2.5 particles: cloth, foam, and car air filters do not work.  You cannot make a HEPA filter yourself.

Lazada delivers everywhere in Thailand with cash COD.

Help the locals by encouraging your hardware store to stock HEPA filters too.

 

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DIY Air Purifier Step 3

Grab some cardboard and tape and make a tube behind your fan with a hole for fan neck:

(see picture)

All your tape joints should be as air-tight as possible.

 

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DIY Air Purifier Step 4

Tape another tube to the front of your fan, then tape the filter to the front of that tube:

(see picture)

Now run your fan on the highest speed and enjoy clean air!  It takes about 1-2 hours for air to become clean.  Don't open the door too often.

You will need to buy a new filter every 2-3 months.  Washing or vacuming the filter will destroy the fibers that can catch PM2.5: it never helps.

 

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DIY Air Purifier SUPER POWER

If you happen to own two fans, you can make an air purifier that is more powerful than the 6,000 THB commercial units.  Rich people will be jealous of you.

Just tape the second fan to the tube behind the first fan.

(see picture)

 

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DIY Air Purifier TESTS AND INFO

Please check out:

https://slice-of-thai.com/air

where you will find:

• more info about this DIY design
• English and Thai version of this info ภาษาไทย
• performance tests with a PM2.5 measuring device
• links to other DIY air purifier designs

Please help to share, adapt, and improve the design!

 

[vivid]

Thanks for sharing to all the folks here.  Yes this would work.   I hope that most thais has seen this and those who care have already shared on their own Thai social media platforms (I think there is something called Line i believe). 

 

The only downside is that it's very power inefficient and also noisy.  But if you are looking at a quick and dirty solution that''d bring down the levels, this would work, just different to different CADRs only.  Use enough units, plug up even leaks in the house (not overly airtight though) and you are golden.  ????

 

The SmartAir Cannon, among most powerful DIY one, has been tested to have a CADR of about 233 /3hr from what i saw on a Chinese testing video, scientifically tested by chinese test agency.    Those small box fans that you use would maybe be 100 m3/h at best?

And also they were using some pretty good DIY HEPA, not in terms of H10, H11, H12 or H13, but in terms of some filter that has pretty low air resistance presenting a higher airflow.   

 

 

Just one additional snippet of info  : These DIY HEPA also are made of different media.  The $5 a pop DIY ones would be around 92% filtration efficiency (real world actual measurement on my laser particle counter) and say give a 15.5km/hr airflow speed at one spot of my AP output.  Then the $20 a pop DIY ones would be arond 96% filtration on my meter and give a 17km/h airflow at the same spot of my AP output.

 

[vivid]

One last thing, if possible try to get a prefilter on it.  Do not use those tight mesh aquarium filters as it'd drop the airflow pretty drastically, just a very coarse mesh kind of plastic filter type like the ones that you use on your AC would do fine.  In short, a prefilter is very nice, but do not overdo it.  A corase prefilter is absolutely fine.

 

Other than HEPA H10-H12 grades, you can also try other filters, like those 3M Filtrete HVAC electrostatic filters, or any other filters.

They have quite lower filtration %, eg instead of 92% of the above cheap HEPA at $5 a piece, it might be just 80% at 0.5 microns levels.  But the airflow corresponding goes up.  In fact you might get a higher CADR figure with this higher airflow figure but lower filtration efficiency % in the end.

Different filters give different performances on different fans and different type of fans give different performance results. eg box fans, standing fans, those cylindrical ones i think they are called bilge blower fans which are popular in marine applications). 

 

Enjoy DIYing!  ????

 

[vivid]

This is the one that i was talking about.  Pretty big panel, the standard size used in USA Homes HVAC AHU is enough for 4 fans.  Get the ones that has the highest microparticle filtration number, i believe the best is around 2200 (the number that you can see on the label in the picture below).

But seriously even if you cannot get the 2200, the lower spec ones like 1200, 1600 would work for PM2.5, even 0.3 microns as well.

These are electrostatic based filters.

 

BTW, i am saying this because i have tried this before and measured the PM2.5 and airflow with the meters (in fact, technically the meter is good for down to 0.5 microns sensitivity, and also is somewhat sensitive at 0.3 microns which is good enough for "home use").

 

Edited April 4, 2019 by vivid

[lsemprini]

3 minutes ago, vivid said:

Thanks for sharing to all the folks here.  Yes this would work.   I hope that most thais has seen this and those who care have already shared on their own Thai social media platforms (I think there is something called Line i believe). 

 

We also shared this on a Thai-language Facebook group in Pai.  Would appreciate knowing what is a good Thai-language Facebook group in Chiang Mai or other major Northern Thailand spots.

 

 

3 minutes ago, vivid said:

 

The only downside is that it's very power inefficient and also noisy.  But if you are looking at a quick and dirty solution that''d bring down the levels, this would work, just different to different CADRs only.  Use enough units, plug up even leaks in the house (not overly airtight though) and you are golden.  ????

 

All true, but also remember that low cost is the main goal of this particular project, so as to increase access to air purifiers to as many people as possible (see https://slice-of-thai.com/air/#intro ). Nearly everyone has one of those fans from the picture already so the only added cost is the filter and some tape/cardboard.

 

3 minutes ago, vivid said:

 

The SmartAir Cannon, among most powerful DIY one, has been tested to have a CADR of about 233 /3hr from what i saw on a Chinese testing video, scientifically tested by chinese test agency.    Those small box fans that you use would maybe be 100 m3/h at best?

And also they were using some pretty good DIY HEPA, not in terms of H10, H11, H12 or H13, but in terms of some filter that has pretty low air resistance presenting a higher airflow.   

 

Not sure if that's what you meant, but the project above does not use box fans because (while a convenient shape) they are not available in Chiang Mai.  Instead they use the plain ol' table/floor fans that everyone has, with the circular cages.  And the one in the picture is 48cm in diameter, so a lot more cross-sectional area than the little boxes used by the SmartAir Cannon.

 

If you know of any other DIY purifiers let me know because I'd like to add them alongside SmartAir and CMU at https://slice-of-thai.com/air/#other

 

3 minutes ago, vivid said:

 

 

Just one additional snippet of info  : These DIY HEPA also are made of different media.  The $5 a pop DIY ones would be around 92% filtration efficiency (real world actual measurement on my laser particle counter) and say give a 15.5km/hr airflow speed at one spot of my AP output.  Then the $20 a pop DIY ones would be arond 96% filtration on my meter and give a 17km/h airflow at the same spot of my AP output.

 

 

Interesting!  Thanks.

 

When switching between two filters in our experiments we saw vastly different flow rates.  See:

 

https://slice-of-thai.com/air/#p4

 

 

 

 

 

[lsemprini]

9 minutes ago, vivid said:

This is the one that i was talking about.  Pretty big panel, the standard size used in USA Homes HVAC AHU is enough for 4 fans.  Get the ones that has the highest microparticle filtration number, i believe the best is around 2200 (the number that you can see on the label in the picture below).

But seriously even if you cannot get the 2200, the lower spec ones like 1200, 1600 would work for PM2.5, even 0.3 microns as well.

These are electrostatic based filters.

 

Have you or anyone seen any of these on Lazada?  When I search for HEPA or Filtrete I don't see them.  For the target audience for this project (Thai people, including many who can only use a cash-based COD delivery service like Lazada offers), Lazada and local hardware store are the only option.  And at least for now, small-town hardware stores never stock HEPA filters of any kind, let alone 3M ones.  I'm hoping that distributing this type of information will help change that.

 

And the big hardware stores in Chiang Mai have a few filters but have been out of stock for pretty much the last month. 

 

 

[vivid]

Yes, i am actually residing in Singapore (Actually i am not a westerner/farang lol) and we also do not usually use box fans, though they are available.  Yes we usually use the cage type fans, be it those normal standing ones from KDK/Panasonic etc or the floor circulators which are more powerful with a higher powered motor, metal blades etc but much noisier.

 

  Even within the box fan realm, there are quite a few different types.  eg the box ones here are smaller than the ones available in the USA.

 

And yeah due to the lower income levels in N Thailand, especially those in the other districts other than CM city, these things might be a saviour for them and their kids/elderly especially due to its low cost. Not everyone can afford a Xiaomi 2S or the replacement costs. 

  It's the same in Indonesia also, in fact they use a similar type to the 3M Filtrete sheets.  It's always for the kids and elders right, esp if they are already down with some pre-existing medical condition?  ????

 

>> When switching between two filters in our experiments we saw vastly different flow rates.

Yes, different filters give different results in different fans.  So need to experiment a bit.  But of course the usual folks would not have a laser particle meter/anemometer and have access to vast different sets of filters esp if they do not have access and buy from say Taobao china "directly".

 

 

Over here, we have also tried these stuff before because of the 2013 and 2015 haze seasons, so the info has also been shared in the local forums.

Actually i believe some the Thais also ought to have been using such methods before as 2015 was similarly a very bad year for South East Asia (N Thailand and Sumatra + Kalimantan Indonesia suffered from extremely bad haze episodes).....the main factor being that it was a Super El nino year hence very dry and long dry season.

 

In short, just use whatever you have and can get hold of.  ????   

 

In our 2013 haze season which the PM2.5 transient figure was suspected to have touched very briefly 600 or even 800 ug/m3 (extrapolated from PM10, no PM2.5 official figures available then and no personal laser particle meters to even get a rough guesstimate figure).   People were desperate to just get anything they could lay their hands on, even H13 vacuum cleaners were snapped up.  Needless to say, no such thing as N95 or Air purifiers, all filtration products were emptied in the stores, ab it like a SHTF typhoon/hurricane situation. 

 

So, just use whatever it's good in Thailand.

[vivid]

11 minutes ago, lsemprini said:

 

Have you or anyone seen any of these on Lazada?  When I search for HEPA or Filtrete I don't see them.  For the target audience for this project (Thai people, including many who can only use a cash-based COD delivery service like Lazada offers), Lazada and local hardware store are the only option.  And at least for now, small-town hardware stores never stock HEPA filters of any kind, let alone 3M ones.  I'm hoping that distributing this type of information will help change that.

 

And the big hardware stores in Chiang Mai have a few filters but have been out of stock for pretty much the last month. 

 

 

Nope, i don't think it's available there.  Yes that's a good point made, if the Thais in CM/CR/MHS provinces only can use  COD  and not credit card, then it's not good.  Moreover, delivery services levels and effectiveness may vary a lot.  eg it's the same in Indonesia, Jakarta is not the same as some small town of just 30k pop.  Your package might just go missing for no apparent reason....unless you are doing DHL or something (even then they might hand over to some different last mile courier, or even the local post and that could be quite variable in service).;

 

 

In 2013 during the haze season, i bought it from Amazon.com USA, direct from Amazon LLC and not some 3rd party seller.  The only cool thing then was then i believe from USA to Singapore, it costed me USD 9.90.  And because it is a pretty large item (L and W are large, the D is thin), the system "automatically upgraded" me to 3-days DHL you know how Amazon works. 

 

"Unfortunately" the heavy haze days only lasted some 5 days.  So by the time it arrived after 3 days, it was already the last day so i didn't really get to use it.  But what happened after that is that i just cut it into 4 pieces, just enough to be used in my Sharp KC-840 air purifier.  

 

In short, as you'd already know by now they all work alright in an appropriately sized and non-leaky room.  It's all just a matter of sizing the devices to the room

Edited April 4, 2019 by vivid

[lsemprini]

6 minutes ago, vivid said:

 

And yeah due to the lower income levels in N Thailand, especially those in the other districts other than CM city, these things might be a saviour for them and their kids/elderly especially due to its low cost. Not everyone can afford a Xiaomi 2S or the replacement costs.

....But of course the usual folks would not have a laser particle meter/anemometer and have access to vast different sets of filters esp if they do not have access and buy from say Taobao china "directly".

 

Actually that's one of the amazing things that Lazada (now an Alibaba subsidiary) has brought to Thailand.

 

They have basically made the entire AliExpress catalog of millions of items from China available to any Thai person who has cash, even if that Thai person has no bank account or credit card.  They offer cash COD delivery.  It is hard to overestimate how empowering this can be.  The only thing the Thai person needs is an ability to use a web browser or a friend who knows how (the friend does not need to use their bank/credit either).  And even if some farmer has no computer-literate friends, the owner of his nearest hardware store probably can do it and would then be motivated to actually start stocking the filters regularly.

 

So that means we do actually have a wide variety of filters (from China) available in Thailand...but the rub is that delivery is always 2-3 weeks.  So if we had started this project earlier then we'd have more filters to test with ????.  Ah well, we'll be ready for next year.

 

[vivid]

It's actually a bit the same in rural China.  They cannot buy from Taobao, simply because of the computer literacy and access to computer/smartphone issues.  The way they buy is that they'd travel to the village's Taobao buying service point which is sort of a small family biz that has a few PCs and pax who'd buy for you, sort of a part time biz.   But nowadays, payment is usually not an issue due to the vast array of internet payment methods/gateway there (basically they'd just pay for even a pack of chewing gum or fruits via their phone in the cities).  As long as they have a smartphone, even a basic one, they are good.

 

Internet is usually not a problem also, the mobile networks/coverage there is absolutely amazing actually.   Heck, the internet should not be an issue nowadays, many small towns in most countries usually have 3.5G, towns itself might have 4G.  Unless if it's the extreme rural area.

[vivid]

Anyway, i thought that many in Thailand are already using this.  Simply coz Xiaomi replacement filters are available on Lazada TH.

 

 

 

 

[lsemprini]

3 minutes ago, vivid said:

Anyway, i thought that many in Thailand are already using this.  Simply coz Xiaomi replacement filters are available on Lazada TH.

 

Yes, the second purifier "device" (eAIR1) is available on Lazada and I'll bet a bunch of people have bought it in Thailand.  I'm skeptical though given how small the fan is.

 

There is a similar hack from Chiang Mai University here with a fun video:

 

https://slice-of-thai.com/air/#cmu

[vivid]

Anyway for anyone who is interested in some info, this is the SmartAIR HEPA that has the highest efficiency/best airflow that we are talking earlier.

rmb 295 for 4pcs.  Lot of info inside.

 

I believe there is something called PET media over in China that they use for these in their HEPA, and they cost the most.

https://item.taobao.com/item.htm?spm=2013.1.0.0.47ea2d4awK0YXZ&id=528380897884&scm=1007.12144.95220.42296_0_0&pvid=401dec07-9211-4b1e-a164-e43e7f940f23&utparam={"x_hestia_source"%3A"42296"%2C"x_object_type"%3A"item"%2C"x_mt"%3A0%2C"x_src"%3A"42296"%2C"x_pos"%3A2%2C"x_pvid"%3A"401dec07-9211-4b1e-a164-e43e7f940f23"%2C"x_object_id"%3A528380897884}

 

 

I am using this type, they said that they media is PP.  A bit lower in efficiency, but cost is quite a bit lower too.

Anyway i am not anal, as long as they measure ok, i am good.  ????  Because my filters usually start to smell in around 6-9 months time of usage, i change them out every 5-6 months. 

I cut it up and use in my 7 APs (5 units in my house, 2 at my parents as they take care of my school-going kids during the day on weekdays).

So a good price matters to me.

 

rmb 28 a pc.

https://detail.tmall.com/item.htm?spm=a230r.1.14.20.589d7ab3RNzzdg&id=533065026910&ns=1&abbucket=12

[vivid]

1 minute ago, lsemprini said:

 

Yes, the second purifier "device" (eAIR1) is available on Lazada and I'll bet a bunch of people have bought it in Thailand.  I'm skeptical though given how small the fan is.

 

There is a similar hack from Chiang Mai University here with a fun video:

 

https://slice-of-thai.com/air/#cmu

I see........here's the TB link. if you are interested in more info.  Anyway, the info on the TB sites are not always 100%, but generally is ok to read and believe to a certain extent.  ???? If you are regular TB/JD/1688.com buyer (be it personal or using a 3rd party buy-for-you forwarding agent) then you'd know.  ????

 

https://item.taobao.com/item.htm?spm=a230r.1.14.60.e8546a24ZNFwG3&id=581996854197&ns=1&abbucket=12#detail

 

 

[chingmai331]

Seems with such a device that yes, you are saving your lungs but are totally restricted to spending life in a small room. Solitary confinement on its head.

[vivid]

5 minutes ago, chingmai331 said:

Seems with such a device that yes, you are saving your lungs but are totally restricted to spending life in a small room. Solitary confinement on its head.

Can't be helped.  IT's called survival.

 

In Myanmar levels peaked AQI 3350, 3000+ ug/m3 PM2.5.  In Samoeng and Mae Sa and some areas, PM comfortably over 1000 ug/m3 PM10. 

Indonesia PM10 2240 ug/m3 or around there.

 

You go out, there is nothing.  Silent Hill. 

 

This is what AQI 2000+ looks like.  Hope mods don't remove this Indonesia video.  ????

 

 

[vivid]

Oh yes, the levels of 1000+ in Indonesia lasted for weeks, AQI 2000+ for a few days.   Unofficially, many people have died from that kind of conditions.

 No air travel, if you are an expat you can't get out unless you have a car and willing to risk travelling on your own, and that is a pretty bad idea.  You gotta hire a driver, who comes by very rarely as very few wants to do a 500km drive (total of 1000km to and fro), and at a very high cost.  Or you drive to another city and hope you can air evac from there.

 

One more video.  How they can get to such high levels and affect such ultra vast areas all the way to Vietnam and Southern thailand till AQI 200+ no less, and even Guam in the PAcific OCean when a typhoon's inflow sucked in the smoke) is coz they are underground peat fires which produces a lot of smoke in addition to some being usual forest fires.  

 

 

Edited April 4, 2019 by vivid

[elektrified]

I always see posts on TV and other social media websites with people criticizing the Thais for not having air filters/purifiers and that they don't care, etc., etc.

 

Every single one of my Thai friends that I can think of, both here and in Bangkok do in fact care about their health and that of their kids, and all of them have air filters; either DIY (like we have), or expensive units from Xiaomi, etc. They all wear masks too.

 

There is so much incorrect information shared on these websites.

[vivid]

6 hours ago, vivid said:

This is the one that i was talking about.  Pretty big panel, the standard size used in USA Homes HVAC AHU is enough for 4 fans.  Get the ones that has the highest microparticle filtration number, i believe the best is around 2200 (the number that you can see on the label in the picture below).

But seriously even if you cannot get the 2200, the lower spec ones like 1200, 1600 would work for PM2.5, even 0.3 microns as well.

These are electrostatic based filters.

 

BTW, i am saying this because i have tried this before and measured the PM2.5 and airflow with the meters (in fact, technically the meter is good for down to 0.5 microns sensitivity, and also is somewhat sensitive at 0.3 microns which is good enough for "home use").

 

 

 

3M Microparticle rating 2200 new filter vs old filter, just about 2 weeks old only in the Sharp air purifier (with aircon type mesh prefilter).  And at levels several far lower than that of Chiang Mai province.  This 3M filter is something like a H11 type of HEPA, but with higher airflow capability, ie higher CADR then the H11 HEPA.   But after it gets "used up", the % drops drastically but airflow still maintains, coz as the filter fibers get stuck with PM, there is less electrostatic forces to attract more PM.  HEPA filters, the airflow would drop, but the filtration efficiency maintains.

 

Edited April 5, 2019 by vivid

[vivid]

MY setup many times ago.  Need the velcro as well.  ????

 

[vivid]

Also have these. But never got to use them.

 

[vivid]

Just a few hours of operation in heavy haze of around AQI 250.   That's the issue with no pre-filter......and operating with the above green prefilter would get you too low an airflow.

 

[vivid]

After putting it in front of the fan, i also used it in the air purifier.  Stuff it in, cut it up, and the sides just put some tissue paper or wrapped up bubble wrap and seal the gaps.  Doesn't need to be 100% "HEPA seal", even 98% is fine.

 

[vivid]

Honeywell H13 "True" HEPA filters in my Sharp KC-840.  The bloody originals are way too expensive, $98 a pop.  ????

 

Just stuff up the gaps with tissue paper. It'll do.

 

Honeywell filters are cheap via Amazon, Singapore also had free shipping then too (for orders that total > usd 125). 

Some usd 11 per filter.  I needed to use 3 filters in the Sharp KC840.

 

 

 

Edited April 5, 2019 by vivid

[vivid]

The "joke" in my country about Hazardous range and 24-hr health advisories.

 

Anyway, that was a PM10 PSI 401 3hr moving average index figure (called PSI) that we were using then, and it was later calculated via extrapolation that we might have hit AQI 600-800 thereabouts for 1hr.

 

That short 30-60 mins exposure is still enough to easily trigger somewhat dangerous symptoms in some allergy cases, needing a trip Accident and Emergency.

 

TLDR - You do not need a 24-hr full exposure to high levels of haze in order to have a dangerous/hazardous situation surfacing.

 

 

Edited April 5, 2019 by vivid

[vivid]

Some 3M Filtrete on the aircon FCU.  Figures for your reference.   I didn't manage to start off with say 250 ug/m3, but just to serve as a general reference. 

 

But do note, make sure your aircon FCU is clean and can maintain a very good airflow in max fan setting.  Else you risk screwing up the aircon FCU coz of insufficient airflow through the evaporative coils, the drainage due to extra condensation etc.   Ok, CM is pretty dry, but in my tropical country it's always very humid.

 

[vivid]

Another DIY HEPA that i took out from the Samsung AX40 air purifier.  After around 6-9 months, general weather here in SG, ie not hazy usually.

 

[vivid]

Size difference between my Samsung AX40 air purifier filter (305mm x 285mm x 38mm for the HEPA portion) vs a half-size Cleanroom FFU H13 HEPA.  The FFU filter costed me $45 including shipping to get it over from TB to SG.  

 

Unfortunately it's not really usable, the filter media is very much softer than the DIY HEPA type filters, one touch and it'd partially disintegrate after dismantling the protective plastic grille.  Lost 45 bucks on this one.  Had to throw it away.  The pressure drop is quite a bit higher as well.

 

 

 

https://item.taobao.com/item.htm?spm=a230r.1.14.41.215778a75r1os9&id=561886719512&ns=1&abbucket=12#detail

 

This is only half the size, the big Cleanroom FFUs are 2X this size.

 

 

 

[sfokevin]

How difficult would it be to attach a 3M filter to one of these?...

 

[Trujillo]

I imagine that this would be more efficient if the fan it pulling the air through the filter, rather than trying to push it through, so putting the filter on the back of the fan seems better to me.