Do We Need Car Air Purifiers? Do they Work?

Car air purifiers sound like a great idea. But do we need them? Do car air purifiers even work?  Soon after I started making DIYs, people emailed me asking if we could make an air purifier for their car. My initial reaction was, “Great idea!” On the highways, we’re surrounded by all of that awful pollution. Best to get a car air purifier.

But as a methodical nerd, I wanted to do some tests first. The results of those tests led me to a conclusion I didn’t expect: you don’t need a car purifier. Here’s how I got to that conclusion.

Car Air Purifier Test: Do We Need Them?

To test whether we need an air purifier in our cars, I first took to the streets of Shanghai with my Dylos DC1700 laser particle counter. (Are particle counters accurate?) Here’s what the air outside was like:

The number on the left is the number of particles 0.5 microns and above. For that channel, “safe” is somewhere around 2,500. So the air that day wasn’t pretty. The number on the right is larger particles—2.5 microns and above.

Car Air Quality Results

Next, I got into an Uber and kept taking readings. Here’s what the air was like when I just got into the car:

car air filter test wildfire

Way better! The 0.5 micron particles were only about 25% of outdoor air.

And a few minutes later:

car filter PM2.5 test China

 

Look, ma, no car air purifier! We were down to 11% of outdoor air.

So why’s the air so much cleaner?

It turns out car air systems have filters in them already, and apparently they do a pretty good job of filtering out particulate pollution. Here’s an example of a car filter on Amazon for only around $10.

 

Let’s Test Another Car’s Air

This simple test suggested to me that the car’s built-in air filtration system reduced particulate levels significantly—even the dreaded particles smaller than 2.5 microns. But was it something special about that car?

To be sure, I teamed up with Ohad, a Smart Air aficionado to do tests in his Mazda in Israel. He drives a regular 2010 Mazda 3–no special filters.

car filter test Mazda 3

Method

Ohad took his Dylos particle counter with him when he drove his car. When he got in the car, he turned on the AC, used “recirculate air” mode, and kept the windows closed. That’s it. Ohad took measurements every minute for five minutes. That’s not very long, so this is a fairly conservative test of the car cabin.

But wait, does Israel really have bad air pollution? It’s no Beijing, but several parts of Israel have recently experienced dangerous levels of smog. In Ohad’s tests, baseline 0.5 micron counts ranged from 2,464 (near the WHO limit) to over 10,000 (four times the limit). So the air has plenty of particulate to do tests.

Results

I averaged across all 8 tests, and here’s what I found:

Car air filter test air purifier HEPA

The Mazda’s built-in air filtration system drastically reduced the number of particles. When averaged over the course of 5 minutes with the fan on its maximum setting, the results showed a staggering 97% reduction of 0.5 micron particles and 99% drop in 2.5 micron particles!

But wait, savvy readers might ask: how do we know it’s the car’s air system and not just that there’s a person breathing in all those particles? Or maybe it’s because particles settle over time?

Ohad also ran an identical test with the car air system turned off. That way we can know if the reduction is truly because of the air system.

Car air filter test air purifier wildfire

With the air system off (the red line), particle levels drop a bit, probably because of settling.But with the air system on (blue line), particulate levels dropped much faster.

Across 5 tests with the AC off, particulate went down (right), but not nearly as much compared to the 8 tests with the AC on high (left):

Car air filter test air purifier PM2.5 pollution

Do Car Air Purifiers Work?

So as it turns out, most cars have their own built in air purifiers.  Smart Air tests show these built in filters work very well, reducing the need for any additional air purifier.

Bottom Line: Do We Need Car Air Purifiers?

No need to add special car air purifiers to protect against particulate pollution. The air systems already in cars dramatically reduce particulate pollution. Here’s how to do it:

  1. Keep the car windows closed.
  2. Use the “recirculate air” mode for the highest particulate drop.
  3. Turn the fan on high (at least at the beginning of the trip).
  4. Check and replace your filters every few months.
  5. Think twice about whether you really need a car purifier.

Smart Air

Exception: Gas pollution

There is one exception to these tests: Car filters capture particles, but they won’t capture gases, like NO2. Thus, it may still be worthwhile to consider using a carbon filter. (Does carbon really work?)

Are you saying no one should ever use a car purifier?

If I owned a car in China, I wouldn’t bother buying a car purifier, but I won’t say no one should buy one. For example, people who are extra sensitive to pollution or parents with small children might consider using a purifier to get extra protection.

As always, I’m making the raw data and more testing details publicly available for fellow nerds. Check that test out for a full comparison of AC high, AC low, and AC off tests.

Breathe safe!


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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.