A quick quiz: some vendors present their products in this way: showing zero PM2.5 reading at the air outlet of an air purifier. Does it make sense?
The answer is simple and clear. Can you keep your nose close to the air outlet of an air purifier all the time? If you can’t, the PM2.5 reading at the air outlet does not matter to you. It is the PM2.5 value of the entire space that matters to you.
What decides the PM2.5 value of the space you are in? It is the CADR of the air purifier which you are using!
CADR is given through a process called the ANSI/AHAM AC-1 standard:
How is CADR tested?
- The purifier is placed in a testing chamber of a specified size.
- Before the purifier is activated, the amount of contaminants in the room is measured.
- The purifier is activated for a period of twenty minutes, during which time the amount of contaminants is periodically re-evaluated.
- Finally, the reduction in contaminants is compared to their natural rate of decay
A sample of CADR test result:
The tested result – 23.7 m3/h, means the appliance can generate 23.7m3 clean air per hour, against the targeted pollutant of particulate matter.
Why is the purification rate of “99.xx%” not reliable?
Just by reading the end result of “99.xx%”, you do not know its testing process:
- the size of the testing chamber
- the amount of contaminants
- the working hours of the air purifier
In simple words, any air purifier can show a result of “99.99…%” if you put it in a tiny chamber and let it work long enough.
Does air freshener or air spray purify?
Here is a scientfific explanation on how air fresheners and air spray work:
Molecules that you can smell tend to be highly volatile. That is, they easily turn from liquid to gas, even at room temperature. That’s what the sense of smell is for: it’s tuned to detect the kinds of molecules that drift in the air.
Spray air fresheners are aerosols. The name “aerosol” means “dissolves in air”. That refers to the propellant, which is liquid when under pressure, but a gas at standard pressure. When allowed to escape, what are tiny particles at first quickly evaporate.
They mix in the fragrance molecules, which are carried along with the propellant as it escapes. They’re now spread out into the air, where you can smell them, and covering up whatever bad odors are in the air.
Some also include “odor counteractants”, which reduce your sensitivity to all smells. The goal is to slightly anesthetize your nose so that the bad smells don’t seem so bad.
In short and plain words, air fresheners/spray do not remove odor for you. They just mask odor, so you won’t smell it.
How to check a CADR report
- The lab should be approved by CNAS and CMA.
- The tested product should be clearly visible in the report.
- The background of the photo should have logo of the lab.
More details about CADR
Now we understand what CADR is. So, let’s dip further into this concept.
Generally speaking, CADR depends on two most important devices:
- filter: the bigger it is, the better
- motor: the bigger airflow it generates, the better
By looking at the two visible components of an air purifier, you’ll be able to estimate its airflow, and the clean airflow it can generate. A small machine with a small filter and motor is unable to generate enough CADR.
What is a reasonable CADR?
An air purifier should be able to filtrate air inside a targeted space 3-5 times per hour. Let’s say the average space inside a car cabin is 3 cubic meters. Then a car air purifier should have a CADR of 9-15 m3/h.
In many cases, people just stay in the car for only 10-20 minutes. The CADR of a car air purifier should be bigger than 15 m3/h, preferably 20 m3/h at the time of power-on, in order to purify the inside air quickly.
Limited by the size of a car cup holder, the cup-holder purifer is relatively small in size, which means the diameter of its motor and filter is small. It’s quite difficult to raise its CADR to a satisfactory level, unless you let its motor rotate at a very high speed, but its noise would be unbearable for most drivers.
What functions do negative ions have?
In the process of purification, negative ions have two functions:
Generally speaking, an air-conditioned space lacks negative ions. An area around PC monitors also lacks negative ions. Diffusing negative ions is helpful to improve air quality.
(2) dust precipitating
Particles with negative charge, attached to particles with positive charge, are easier to precipitate down to the floor.
Is negative ion able to replace CADR?
Some car air purifiers, usually small ones with small motors and filters, do not offer a tested CADR. Instead, they use negative ion as a selling point.
Negative ion is a contributing factor. However, it does not filtrate pollutants directly. So, it is unable to replace a filter.
The refreshing or dust precipitating by negative ions is rather slow. So, it is unable to replace CADR.
Moreover, negative ions do not break down pollutants. So, it is unable to replace ozone.
GEMEGA – We care