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Why use an air cleaner? The air doesn’t look dirty, and I can breathe easily?!

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    SARS-COV-2, the virus that causes CoVid, is actually carried by respiratory aerosols. Portable air cleaners (also called air purifiers and air filters), work by pulling air through high-quality filters.

    As the air cleaner pulls air in with the fan contained in it, the filters attached to it clean the air. Details on how the filters work below*.

    Respiratory aerosols (emitted when we breathe, talk, laugh, yell, sing, cough, sneeze) carry SARS-COV-2 and are extremely small. The ones most likely to carry SARS-COV-2 are too small to see.

    Roughly 85% of respiratory aerosols are 5 microns or smaller. High-level tweetorial about this study.

    Just to give you an idea of how small, here are 50 micron aerosols floating:


    *How the filters actually clean the air.  The first thing to know is that while the filter appears to be flat, it is actually a 3 dimensional matrix of interwoven fibers.

    Those fibers work via the following mechanisms:

    • Inertial impaction – Occurs when a particle encounters a filter fiber due to the inertia of the particle.
      • Example: A large dust particle is unable to change direction of flow due to its inertia, so it impacts the fiber and becomes attached to it.
    • Interception – Occurs when a particle follows a the air flow happens to come in contact with the surface of a fiber.
      • Example: An intermediate dust particle that readily follows the airflow stream comes in contact with a filter fiber.
    • Diffusion – Occurs when particles do not follow the airflows as readily and are governed by random particle motion (Brownian motion of small particles).
      • Example: A small particle, such as certain exhaust particles, encounter filter fibers at random.
    • Electrostatic attraction – Occurs when an electrostatic charge on the filter fibers are present.
      • Example: Static charge on a fabric creating static cling.

    In terms of filtration, the most important filtration mechanics pertaining to everyday use are: Intertial impaction and Interception.

    The larger particles that encounter the filter tend to impact onto the exterior surface of the filter.

    The smaller particles that follow airflow streamlines tend to impact and intercept within the depth of the filter.

    Here’s a video from the NYTimes showing how the N95 masks catch viruses.  These are the same as how air filters work.

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