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How many 0.3 micron particles in 0.1L volume of room air?

  1. Apr 3, 2016 #1
    Hello all,

    I wanted to say thanks to everyone on this forum who dedicate their personal time to enlighten so many like myself. I am a fan of physics and consider myself a student for life.

    I recently bought an Indoor Air Quality (IAQ) sensor/monitor to test my air purifier and as expected, the particle count decreased when I first ran it in my bedroom with the door closed. When I moved it to the living room I was surprised that despite how long I ran it or at what speed, the particle readings did not fall. When I took it back to my room I got similar results to my original test. I then did another test with the door open and saw the numbers jumped all over the place depending where it was placed. Even when the numbers went down it seemed to hit a wall which made me wonder, if the air is truly being vacuumed why it does not continue to decrease?

    I did some research online and read claims, mainly from air purifier manufacturers of the benefits but was surprised to read healthcare and government sources unanimously admit that the benefits are inconclusive. One major OEM was warned to not make health benefit claims to which they immediately complied, while another household brand declared bankruptcy for making false claims. The most accepted industry standard is a terminology called CADR (Clean Air Delivery Rate) that is advertised on retail boxes but it merely references a square footage application with the door closed. The concern is that this standard seems to only introduce filtered air into a room which would merely dilute the air concentration allowing minimal removal of the harmful particles in our air. Worse, since these allergens are much heavier and dust naturally wants to settle, wouldn't this method actually prolong these particles time in the air?

    Particle counters being rebranded as IAQ sensors are becoming increasingly popular so I think it is time to really understand their purpose. In a dusty but normal office I get values between 200 to 500 particles of size 0.3 microns per .1L on average but I am not too sure how to put these figures in perspective. So I would appreciate help in answering the following:

    Fine dust is considered 0.3 microns and smaller and the volume relationship for many devices is 01.L (or 1/100 of a cubic foot depending on the type of particle counter used). So if the reading is 500 particles what percent of the total volume of 0.1L does this represent? In other words how many 0.3 micron particles can fit into a 0.1L volume of air to achieve 100% saturation? A simple volume calculation is straightforward but how do the air molecules relate into this calculation or do they? For starters, a rough calculation of 0.1L volume seems equivalent to 3 standard board game dice! Is this right?

    I would like to understand the relationship of the measured value as a percent of the total volume, to determine if we are talking about saturation of a pinch of sugar in a cup, a gallon or a bathtub of water? If particles are just being blown around and diluting then these sensors may lead us to falsely believe that that the harmful airborne particles are being removed. More so since the CFM is known for the fresh air how fast are these readings effected? Can all the air in the room actually be influenced in 5 minutes as so many particle counters seem to imply?

    More people die from bad air pollution than traffic accidents and the trend is only getting worse. The EPA is saying that the average indoor air in our homes is 3-5 times worse (up to 100 in some cases) than out door air, I think if these particle counters are going to be relied upon the same way canaries were used in coal mines we need to take a honest look at these devices. One thing is that a representative of a high grade measurement company said that their expensive lab grade calibrated particle counter is not recommended to be used in an environment that has artificial air movement since it may yield unreliable results.

    I would really like to encourage maximum feedback on this since I believe this will effect everyone's future. Thanks in advance.
  2. jcsd
  3. Apr 3, 2016 #2


    User Avatar

    Staff: Mentor

    Welcome to PF!

    Have a look here:

    What is the make and model of the air purifier?
  4. Apr 5, 2016 #3
    Hi thanks, I have 2 one blueair 403 and an IQair.

    I did review these specs but still just trying get a better understanding of this concentration question.
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