If you’re shopping for an air purifier, you’ll often read and hear quite a bit about how quickly (or slowly) an air purifier cleans the air.  This seems weird: why should it matter if your air is cleaned in 20 minutes or an hour as long as it gets cleaned?  Can it really make that big of a difference?  This can be especially confusing when many of the more expensive air purifier companies tout this as a plus.

The truth is, in fact, that cleaning speed really matters.  In fact, it may be one of the most essential functions of an air purifier, besides for its overall effectiveness at removing pollutants.

Let’s examine why.

The risk of catching a sickness through airborne particles depends on the total amount of bacteria, virus, pollen or dust you inhale. Virologists define the minimum quantity of viruses inhaled to actually get infected as the “infectious dose.”

Now, the amount you inhale is affected by two things:

  1. The concentration of the infectious agent suspended in the air.

  2. The time you’re exposed to that infectious agent.

It may help to think about it in the way that nuclear radiation is often thought of in popular media: you want to get away from the infection as quickly as possible as well as remove it from the air.

As an air purifier company that works hard to develop and manufacture our own products, we’ve always emphasized that reducing the concentration as fast as possible is an important way to protect humans from exposure to bad pollutants.

Take a simple scenario, where a sick patient enters a non-ventilated operation or examination room, coughs in it, and then leaves the room. If it’s an airborne virus, micro particles created by the sick patient’s cough will linger in the room for hours if they’re not removed.

So if the next healthy patient or caretaker enters the room, he or she’s exposed to immediate risk of infection. To strongly reduce this risk of infection and make sure these rooms can be used efficiently, an air purifying system has to remove the airborne particles within the shortest time possible.

This is, in fact, exactly what hospitals do in order to minimize the risk of the spread of infection.  It’s also why hospitals, dentists, and others use these products.

A key way to measure purification speed of an air purifier is to calculate the time necessary to reduce the concentration of a pollutant to half of its initial value: the “half-life time.”

Half-life times should be compared on standardized tests, where the environment and test settings are the same for all machines.

Another important factor is the size of particles you’re testing on. The particle size should mimic the actual infectious agent. We like to compare products on 0.1 micron size as it’s equivalent to many of the common bacteria and virus sizes. One such test, the AHAM AC-1, for example, tests on 0.1 micro particles and provides the purification data for a 1008 cubic feet room.

Both our aair 3-in-1 Pro and aair lite models show excellent behaviour in this standardized test and reach a half life reduction time of 90 seconds and 3.8 minutes respectively.

What’s the link between the cleaning speed of an air purifier and the Coronavirus?

One of the things that’s gone unspoken so far, but which of course we are all deeply concerned about, is COVID-19. Do the same principles apply? If so, how?

As it turns out, a number of studies on the decay of the virus in and on different substances have been done.

The longer the overall decay of the virus takes, the higher the concentration will be in the substance. Higher concentrations of the virus in a substance also means that if being inhaled or swallowed by a human, a higher virus load is consumed which leads to a higher risk of infection. It has not been established what exact virus load for Sars-Cov-2 is necessary to infect a human being, but it’s clear that minimizing the viral load in substances exposed to humans to a minimum is essential to stop the virus from spreading.

In other words, if the virus survives in suspended air particles then it’s clear that removing these air particles or blocking those particles from being inhaled is essential for infection control.

Unfortunately, at present there is no known method to immediately remove air particles in a closed room the moment they’re created, such as when an infected person exhales, coughs, or sneezes. You can, however, reduce the amount of suspended particles in a room over time either through exchanging the indoor air with outdoor air or purifying the air through an air purification system. In both cases, an essential measurement will be the amount of time needed to remove the contaminated suspended droplets.

In other words, time matters.