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In-the-Air-Challenge: Air filter checking with a home-built laser+photodiode dust counter

janisalnis

Previous post: In-the-Air-Challenge: Laser-based dust counter using a photodiode, IoT connected

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Air in a laminar flow box with 99.999% filter

 

I have attached a small speaker to the photodiode amplifier of the home-made laser dust counter described in the previous post. Speaker clicks after every dust particle and click loudness is proportional to the dust size. Dust content outside the window in the city is similar to what we have in the room and speaker clicks with similarity to a Geiger counter near a radioactive source. Video shows that inside a laminar-flow class-6 cleanroom box there are practically no clicks. So the air filter works. Sorry, the speaker is too small to be heard in video as the air fan is making noise. Can hear clicking around second 40.


 

 

HEPA anti-alergy filters of vacuum cleaners

 

HEPA - High Efficiency Particle Air filter.

 

With a dust home-made dust counter described in previous post, I checked air coming out from a vacuum cleaner with HEPA filter on the output. Filter was labeled as Class 13 and should stop 99.95% of dust. Filter has been in use for several months, nevertheless there was practically no dust leaking through it.

 

There are also dirt collection bags marked as Anti-alergy  S-bag by Electrolux. I put one of such bags on the output of air ventilation. Such bag filters air very good and, practically, stops all dust.

Air filter of the cars did not stop the dust. and could possibly be used as a pre-filter before a HEPA filter.

 

One of drawbacks is that HEPA filter needs high pressure air fan to get much air through.  In the vacuum cleaner power is >1000W. I use vacuum cleaner from Electrolux Ultrasilencer that is made to be very silent compared to regular models.  In home-built filters, probably, one should use large size HEPA filters to get more air through.

 

Probably vacuum cleaner with a HEPA filter could be used instead of expensive HEPA laminar flow module in the optics lab.

If I fill a 250 liter plastic bag from a vacuum cleaner then the air inside is clean. But just blowing the air in a whole lab is not making air much much cleaner. As there  is wind blowing dust into the room through wooden window isles and doors.

Since one year I have started a laser spectroscopy lab in Riga, Latvia and dust here is a major problem as it deposits on the optics and laser power drops within days. It would be nice to make overpressure in the whole lab, but it is easier to build a clean air cabin around the optical table using greenhouse plastic sheets.

 

 

I need to solve the problem how to callibrate click counts into ug/m3. I plan to get in touch with some people having a commercial particle counter.

 

 

Exercise: How much dust a person inhales in one year. If air contains 50ug/m3, I get ca 0.3 kg/year. This would become ca 15 kg over lifetime. Can lungs clean themselves or get congested after decades.

 

 

 

Fine dust regulations and situation in Europe

 

As a fine dust are called particles smaller than 10 microns in size PM10. Generally, the smaller are the particles, the deeper they can penetrate into lungs. WHO suggests limit of 20 ug/m3 averaged over year. EU limit is double as high 40 ug/m3 which many experts critisize already for longer time. Studies show that exposure to particulate matter  leads to increseased lung cancer risk rougly 1% for every 10 ug/m3: "Outdoor Particulate Matter Exposure and Lung Cancer: A Systematic Review and Meta-Analysis"

 

Particulate Matter (PM10): annual mean concentrations in Europe  —  European Environment Agency (EEA)             

SPIEGEL article describes that values are above threshold, for example in German cities Berlin, Munich, Stutgart.

Feinstaub-Prognose: Die schmutzigsten Städte Europas - SPIEGEL ONLINE

 

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  • in reply to janisalnis

    IIRC, according to Scientific American, some dust is cosmic in origin, but nowadays, in cities, it is roughly 25% ground-up automobile tires.  I notice that dust in my city apartment, where it accumulates enough, is spongy and black like tire rubber.

  • in reply to D_Hersey

    This was a surprise to me that other people already use air filters so  much. In Latvia we are way behind.

    Larger size filter needs less electric power and does not need replacement so often.

     

    I found a really nice explanaition about filters why I saw no effect using a car motor filter.

     

    In a room one cubic meter can contain 1 million and more particles. Largest part of soot particles are too small to be stopped in

    kitchen air cleaner and vacuum cleaner filters. If an air filter is stopping particles larger than 5 microns, then it will stop

    80% of particles by weight, because large particles like hair, cotton patches, are heavy. But if we would count number of

    particles then it will appear that only 0.2% have been filtered out, because 99.8% of all particles that fly around in a room,

    like pollen, mold spores, are smaller than 5 microns. 99% of dust is smaller than 1 micron.

    For example, excrements of dust mites are 0.3 microns, tobakoo smoke 0.01 microns. 80% of dust is visible only under a

    magnification. Smaller dust particles get deeper into lungs and weaken the immune system. Indoor air is polluted mostly by

    carpets, domestic animals, hermetically unsealed insulation wool material, tobacco smoke, mold spores.

     

    Some interesting youtube videos:

    What Air Purifier Companies Won't Tell You

    https://www.youtube.com/watch?v=gnOK6tMl4Sc

    http://aliveairpurifier.com/

     

    Probably I am going soon to buy or to make a filter for home use.

  • in reply to janisalnis

    My cohabitant has one up front in her end of the (apartment) place, when I am up there to watch TV with her, I turn it off, because I don't like the O3.  Theory is it works on the finer stuff better, I'm told.  At the house I use a homemade rig constructed of a quiet blower, a big plywood box, a (paper) furnace filter acting as a prefilter for a big, industrial HEPA.  The cheap prefilter really ads life to the rather pricey HEPA filter.  I like the result, the only seeming downside is that it uses a fair amount of power.

     

    I find it easier to sleep if my air is clean, I think.

  • in reply to D_Hersey

    There is a nice electrostatic smoke precipitator video

    https://www.youtube.com/watch?v=x5YFK8mmeRQ

    I would like to build high-voltage negative supply and see if can filter dust. For example described here Make an ioniser.

     

    People write that there is corona discharge. It probably produces noise and ozone in small quantities. Ozone is higly reactive and kills germs. But it might irritate the lungs. Might need to send ar throug a active coal filter.

     

    I have once seen a HV brush thing at home. The ceiling above it was black like a chimney.

    In my childhood we had a black&white TV and on the glass creen of it was collecting dust.

    Nowadays people write that they are too lazy to clean electrosstatic filters and prefer throw-away HEPA filters.

    There are commercial models for example: Philips Air purifier AC4074/00 CADR 270 m³/h PM2.5 removal rate >99%.

  • Perhaps electrostatic precipitation would help with the smaller particles.