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I'm way out of my domain of expertise here, not being automotively or mechanically inclined at all, so would like some brief orientation here. I'm not seeking any particular brand, only something that will work at a verified/rated quality standard.

So briefly as a back story, I'm getting sick of my Nissan Frontier (2014) allowing a certain amount of exhaust from other vehicles through the cabin air filter even after a brand new one has been installed (by Nissan themselves), and I hit a dead end with customer support who told me they have no higher grade filters than was already in it, so decided to do "freelance" research.

The Question: How can I find a grade of filter which filters out at least 95% (or better 98/99%) of pollutants or more? I don't mind paying a premium for superior quality and protection of a fine grain filter.

Though the announcement seems gimmicky because of the Coronavirus pandemic, it has been in the news lately that a Chinese vehicle manufacturer has achieved a N95 equivalent air filtration rating. As Business Insider reports: "The Icon's air filtration system is N95 certified, which means it blocks at least 95% of small particles that measure 0.3 microns." That description interests me. All I care about for purposes of this question are pollutants, not viruses, passing through the filtration system though.

I really don't want cough-inducing levels of exhaust and strong odors from the vehicle in front of me to enter the cabin when my vehicle it is pulling external air (vs. recycling internal air). Not to mention pulling external air is the default in my vehicle. Obviously nothing will achieve 100% filtration, but surely some filter can do better than what I'm experiencing.

Now, I had never heard of AZUMI (my examples are random, not preferential) or their products until today, but their blurb on their filters (though I have no idea if it reflects their quality) hits the central concern:

Air in the midst of traffic contains five times more exhaust gases, pollutants and allergens than the air you experience standing by the roadside. On top of that, airflow through a vehicle’s air ducts can go as high as 540,000litres/hour. The only barrier between healthy lungs and the cloud of pollutants during every drive is the cabin air filter that you decide to install.

A clean air filter aids in trapping pollen, allergens, smoke, fumes, and odors...

One company that looked like it actually had air filters that claimed a certain filtration percentage was Valeo, which is (for me) an international company that I'm unsure whether I can have their products shipped overseas to receive them. But even with Valeo I didn't know how to verify that a product was actually formally rated for a certain filtration percentage. A different manufacturer - by contrast - of what looked like a popular brand of air filter, to take one random example, was TYC. But they didn't list any formal filtration specs either on the product page. So where do I look to find that information?

Maybe there are more detailed 'data sheets' I'm missing on a given manufacturer's website, but if such things are available that's the kind of information I am seeking and would like to be made aware of.

How can I be assured when researching for a high grade, high filtration cabin air filter that I am getting a product that is actually rated at a certain level, to where I could actually compare it to other products to determine whether its quality is superior? Can someone give me some more objective and precise criteria and tools to use to locate high grade filters for automobiles?

I haven't the faintest idea where to start beyond my sporadic internet searches.

  • Ah, here is something where Valeo claims CN95 certification for filtration here: "The HVAC cabin air filter stops ultra fine particles (including some viral particles) with size over 0.3 microns in diameter with an efficiency above 95% according to official norms, ISO** 11155 Part 1 (with Dust ISO A2 – ISO fine dust)". valeo.com/en/cabin-air-filters – SeligkeitIstInGott Apr 29 at 13:55
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"The Icon's air filtration system is N95 certified, which means it blocks at least 95% of small particles that measure 0.3 microns."

This sounds really impressive.. and I suppose it is, from a certain perspective. However from your perspective:

All I care about for purposes of this question are pollutants

It's less impressive. Why? Because much of the pollutants you are concerned about are smaller than than the 0.3 micron level. The nasties from the vehicle in front's exhaust that you're concerned about - the nitrogen oxides, the sulfur oxides etc are in the ~2.5 micron range. So a filter that's doing a great job of blocking the 0.3 micron particles (e.g. N95 spec) makes no such promises about anything smaller. You can perhaps expect that they might do better than something that doesn't but.. it's a crapshoot basically.

Cabin filters aren't really intended for this soft of filtration - largely they're there to filter out pollen and the larger soot particles. Heck many even refer to them as "pollen filters". If you do fit a higher grade of filter you may notice some improvement, but it's likely to be slight, and it's going to come with a cost of it's own. As Solar Mike's answer excellently brings up if you have a filter that does a really good job of filtering the incoming air you're going to hamper the ability of the HAVAC fans to get air into the cabin at all. Finer filters are going to clog up faster, and need replacing sooner.

If you're looking to see a real improvement in the air quality when you're stuck in traffic the solution is there for you already - hit the recirc button on your HVAC controls before you get a face full of fumes. That's literally why it's there, let it fulfill it's life's dream and protect you from the unpleasantness.

Pᴀᴜʟsᴛᴇʀ2 brings up something I forgot to mention:

I think the best which can be done is by getting a filter with charcoal built in, but who knows how long they actually last.

An activated charcoal filter would do a decent job of scrubbing NOx and SOx but as you touched upon longevity is the issue. Activated charcoal removes NOx, SOx and various others by chemically reacting with them and bonding with them - essentially capturing them out of the flow of air, this works well (it depends upon filter design, and the quality of the activated carbon but I've seen figures of up to 60% removal of NOx) but (brace yourself - it's a big but, and I like big...), it actually does such a good job of capturing the nasties that it never lets them go (well not without certain treatments which are impractical for doing at home).

So for a given amount of material there's a finite number of bonding points and once they're all used up the carbon is just so much dead weight from a filtration point of view and new nasties just flow right on past it.

This is why they aren't particularly great in this application - cabin filters aren't huge, they're constrained to the dimensions available and they can't be completely made of the stuff so in general activated carbon cabin filters just don't contain enough of it, they can't contain enough of it for it to be effective for much more than a few weeks - a few months at the outside.

How long will vary based on the individual filter, the amount of activated carbon it contains and obviously how much bondable particulates/gases they encounter. If you are driving in heavily polluted (particularly with NOx) environs day-in, day-out you're most likely going to be measuring that life in weeks and after that it's just a regular old "normal" cabin filter, if you want that special sauce effect back you're going to need to replace the filter. Replacing a cabin filter every few weeks is going to get impractical, and expensive fast.

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  • Thank you. This is quite helpful as an orientation. I had seen that about "pollen filters", and yeah I suspected that 95% was still lacking. Here is Valeo's page with details about their 95% filtration. It seems to fit with your analysis of the micron size and the charcoal filters too (which sound like something I need generally - but with the caveat of changing more frequently): valeo.com/en/cabin-air-filters – SeligkeitIstInGott Apr 29 at 14:11
  • And yeah, haha, I obviously get the utility of hitting that recycle button ASAP, but as I complained to my manufacturer my truck FORCES outside air for the floorboard air (when floorboard alone, not when combined with the air directed at passengers) and any combination that involved the windshield. So, have a cold day and the windshield is fogging up? Yep... outside air for me. It aggravates me that some vehicles do that. Have you experienced that with any vehicles you have operated? – SeligkeitIstInGott Apr 29 at 14:14
  • @SeligkeitIstInGott I've encountered cars that default to outside air upon first selecting a windshield setting and cars that enforce it if you're using the the specific demist setting. But not the combination you have, and yeah I can see that being aggravating! A decent charcoal filter as a "see how well it solves it and how long it lasts" experiment is probably worth a go - then you can make a call whether the increased change frequency is worth it for you personally. – motosubatsu Apr 29 at 14:47
  • I'll give the charcoal filter option a go! – SeligkeitIstInGott Apr 29 at 14:58
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The higher the performance of the filter, the more work is required to pull air through it. Once you exceed the capability of the fan then you won’t get fresh air in the cabin.

So, you may have to improve the fan, or perhaps fit a second, to put a really high quality filter in your system.

There are data sheets for fans showing the inlet or “suction” performance as well as the “pressure” side performance usually referred to as head.

There are also data sheets for filters and part of the information is about the “pressure drop” or head loss they cause.

There are sites showing example calculations, search for terms like flow loss, pressure drop, head loss etc.

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  • Thanks for that tip. Since I've never really tried "after market" mods on a car, I'm wondering: is it likely that adding a custom fan would void the manufacturer warranty (I'm nearly past the major warranty mile markers based on my odometer anyway, but...)? – SeligkeitIstInGott Apr 29 at 14:23
  • Let me also ask this, in the spirit of the original question: how are you going to determine "higher... performance" in a filter as you mentioned, objectively speaking? Have you actually seen filters claim higher than 95% filtration? – SeligkeitIstInGott Apr 29 at 14:36

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