To help inform our air purifier picks, we gathered 14 of the most popular models at the CNET Labs product testing facility in Louisville, Kentucky, where we put them through a rigorous set of tests. Our goal was to determine which air purifiers offered the best performance in terms of particle removal efficiency, energy consumption and quietness, while also evaluating their respective feature sets and value.

The particle-removal test

The air we breathe isn't just air. In truth, it's a combination of human-generated and naturally occurring particles. The former is composed mostly of urban, industrial and automotive emissions of hydrocarbons, nitrogen oxides and combustion byproducts, and the latter is mostly represented by smoke from forest fires, sulfates, soot and matter from volcanic activity around the globe. 

According to the EPA, some of these microscopic solids and liquid droplets, which can be made up of hundreds of different chemicals, are so tiny that it's almost inevitable to inhale them. PM10 and PM2.5, which are particles of less than 10 and 2.5 micrometers in diameter, respectively, pose the greatest risk to human health since once inhaled. They allocate deep into the lungs and even into the bloodstream, impairing the proper functionality of the lungs and heart.

"That's the size that can go into our body, into our lungs and go into our bloodstream," said Zhao. "That is the number one environmental risk factor globally. It kills about 6 to 7 million people a year," he said, due to cardiovascular or respiratory problems brought on by particulate pollutants.

Our custom air purifier test chamber uses a clear-view front panel made of plexiglass and gloved hand access, which allows us to manipulate the air purifiers, a particle counter holder for our control device, two fans that ensure proper mixing of the air and smoke inside the chamber, vent ports that ensure there is a small amount of fresh air at all times, an ignition port to light up the smoke bombs from outside the rig, and an exhaust port that removes the remaining smoke safely from the chamber and the building after each test.

The chamber is not hermetically sealed, but it's tight enough to ensure that no hazardous amount of smoke escapes to the surroundings. Our mission was to create an environment in which we exposed each air purifier unit to particle-saturated air of roughly the same concentration to assess how quickly and efficiently they get the air back to breathable conditions.

We made custom smoke bombs, which are made of 50% potassium nitrate (KNO3), 40% sucrose (sugar) and 10% sodium bicarbonate (baking soda) and included a safety fuse for igniting it at a distance. The sugar acts as our fuel source, while the potassium nitrate acts as an oxidizing agent and the baking soda ensures that our dry mixture sustains a slow and even burn.

Using the Temtop PMD331 Particle Counter, we were able to verify that 5 grams of our smoke bomb dry mixture produces roughly between 590 million and 610 million particles per meter cubed. The device is able to count particles of different sizes, including PM2.5 and PM10, and it logs this data once every 15 seconds. Although we're able to count particles of different sizes individually, it's the total number of particles we care about, which is the sum of all particles of different sizes.

We prepared a 5-gram smoke bomb, which is ignited via the ignition port after installing the air purifier and ensuring proper sealing. Once the air in the chamber becomes particle-saturated (greater than 580 million particles/m3) we turn on the air purifier in question. The data extracted from the Temtop allows us to accurately track the impact that the air purifier has on the particle count in real time.

Noise level

Using a decibel meter, we measured how loud the air purifiers are at their low, medium and high fan settings. This is particularly important if you plan on having your air purifier on in your bedroom overnight and you don't want it to disrupt your sleep. We performed this test in our sound-enhancing studio to make sure that the decibel meter picked up only soundwave stimuli from the air purifiers, excluding other possible sources.

Energy consumption

To answer this question, we used a device called Kill-a-Watt and measured how much power each air purifier consumed at different fan settings. Knowing the energy draw for your air purifier could make a difference to your energy bill.