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Context: This article was originally written in 2020 after a sour smell came from new Blueair SmokeStop filters. The issue was also discussed in videos by Fran Blanche / FranLab, who had similar experiences with Blueair Classic filters. Since then, Blueair has published general support information about odors from new filters, filter media and saturated activated-carbon filters, but we did not receive a substantive explanation or useful follow-up for these specific filters through Blueair, the importer or the manufacturer. The shop where we bought this type of equipment and filters, later stopped selling these filters. The text remains relevant as a practical experience article about air filtration, carbon filters, product support, sourcing and trust in replacement parts.
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At ASK-Solutions, we purify the air we breathe. We are located in one of the older parts of the inner city, only a couple minute walk away from Haarlem central train station. We're surrounded by red brick housing, shops, workshops and small to medium industry. It's also only a couple of minutes drive to both mayor highways.
Due to a health condition, I've lived with air purifiers for nearly my whole life. Because of my constant illness, my parents bought a Mountain Breeze air purifier with activated carbon filters on three sides. Not only do I care for my own health, but also for the health of others. To be honest, I care less about myself than others; a personality flaw which is being worked on.
After years of good service from multiple generations Mountain Breeze units, it was time to look ahead. Replacement filters for the older units got a pain in the backside to obtain and on top of that the motor on one of the units burned out. After seeing a video by Fran and doing some research, I decided to get three BlueAir Classics 505. Unfortunately without SmokeStop filters; those were sold out and my supplier told it could take a few months before they would be in stock again. Luckily, Amazon.de had a couple on stock that were genuine filter sets, not the imitation filters sold on eBay.
About a couple of weeks ago I started to notice a sour smell causing me respiratory irritation, but I did not realize it could be caused by the SmokeStop filters. From experience, I knew carbon filters don't remove all smells, so I started to clean all the rooms thoroughly. Again, it was a video from Fran which pointed me in the right direction. She noticed a sour smell, only a couple of weeks after getting a BlueAir purifier fitted with a SmokeStop filter.
I switched out filters between rooms and air purifiers. The smell was definitely coming from one of the filters. The two other filters also had a sour smell, but not as strong. I contacted Amazon.de, they immediately offered me a refund but were not able to offer replacement filters.
I also contacted BlueAir, in the hopes that they knew what the problem was; especially because of all the stock problems I experienced. I clearly explained the problem and that the filters were practically new. Their reaction: "The air in a room is a complex mixture. Air purifier filters can cause smells over time, especially when they get older and need to be replaced. Some people are very sensitive in noticing those smells. You can buy new filters directly from us".
Well I'm sorry, that does not instil confidence. You could at least work with us to verify the Amazon.de bought filters are indeed genuine by asking if I've got a photo of the filters and box or having them sent in. They could have offered replacement under warranty, or shown a sign of care about our health instead of their sales.
I'm probably going to send them back to Amazon.de and claim a refund. Those filters are not worth petty cash, they're quite expensive. In fact it is undoable if you need to replace them nearly every month.
Fran made a new video about the BlueAir filter problem.
Fran has made another video about the air filter problems. BlueAir took back her BlueAir Classic filters. Fran now has new filter from Austin. These filters are classified as being industrial laboratory filters instead of personal home usage filters.
In her video, Fran states that the issues with the BlueAir filters could come from the fact that she’s not using them ‘at home’, but in her lab. I do not agree, and I speak out of a lifetime of experience with air filtration, both at home, at the office and in ‘real’ industrial and laboratory settings. I placed the word “real” in air quotes because I speak out of experience; industrial as in a floor operated with 5 to 30 people, filled with wood and/or metal working machinery, hydraulics, pneumatics, conveyor belts, welding robots, CNC machines and hydraulic presses. And I mean laboratory as in a chemical or high energy labs fitted with fume hoods, vacuum chambers, autoclaves, scanning tunneling microscopes where a couple of people work with strong smoking acids, bases and / or radioactive materials.
In those environments you need totally different multistage filters, often with part of the system inside and part of it outside the building. Fran's lab is more comparable with our office. Our soldering, wood and metal working takes place in a separate building. We use completely different filters there. In fact, the BlueAir filter that smelled the most sour, was the filter fitted in a quite part of the office where few people come. The less smelly SmokeStop filter was in the office with only desks and a maximum of three people doing deskwork there at the same time. We've run a single 3D printer in the office whilst the BlueAir SmokeStop filter was present. It's print time, whilst the BlueAir was present, was only a few hours with a good quality PLA filament.
I've also got years of experience in similar setups with Mountain Breeze carbon filters and nobrand carbon filter and DIY modified filters to fit in the older Mountain Breeze units. Including experience of hours of soldering next to one of those filters. I've had three bad experiences with carbon filters in my life:
In the meantime, BlueAir, or the official distributor in our country has not contacted us. I've not heard back from BlueAir at all. I'm going to ask around again and also contact the distributor directly. I've still not sent back the sour filters. I've placed them in an empty vented room in direct sun light. I'm curious to what happens, as some people have suggested that can help. I'm also wanting to experiment with one of our UV-C lights, and see what happens.
One year later, we still tried to get a substantive response by telephone and email through the importer and the manufacturer. We did not receive a clear technical explanation, useful follow-up or an answer that allowed us to determine whether this was a production fault, storage problem, transport damage, material property or another issue with these specific filters.
That eventually became the main point for us. An air-quality filter is not a decorative consumable. If an new activated-carbon filter itself causes a clear sour smell and respiratory irritation which it continues to produce, a manufacturer or importer should be able to do more than explain in general terms that filters may start to smell over time or that new materials can have their own odor.
The practical situation did not improve afterwards. The shop where we bought this type of equipment, together with dehumidifiers, fans, air heaters and other indoor-climate equipment, later stopped selling these filters. For us, that confirmed the sourcing problem that was already visible in the original article: even when a device remains technically usable, trust in the system can disappear when good filters are difficult to obtain, when the origin or condition is unclear, or when support does not produce a substantive answer.
Blueair has since published general support information about filter odor. It states, among other things, that new products and replacement filters may emit an odor, that filter materials have their own smell, and that ventilation or placing the filter near an open window before use may help. Blueair also writes that used or saturated filters can start to release a smell and that filter lifetime can depend strongly on the environment in which the purifier operates.
That general explanation does not fully explain our case. Our complaint was specifically about almost-new SmokeStop filters, one of which smelled clearly stronger than the others, while the filters were used in an office environment. For us, this therefore remains not a general complaint about activated carbon, but an example of what goes wrong when a manufacturer treats a practical problem with consumable filters mainly as normal wear, sensitivity or a new sales opportunity.
On October 5, 2021, we ordered three new SmokeStop filter sets. These sets came from a different batch and did have the normal activated-carbon smell we expected. For us, that strengthens the impression that the original problem was not simply “sensitivity to filter odor”, but was probably related to that specific batch or the way it had been handled.
On December 5, 2024, BlueAir published a support blog about odors from filters. That explanation still frames the issue in general terms: new filter materials, ventilation, sensitivity, or saturation of used filters. That does not fit our experience well: all SmokeStop filters from the same batch had a sour smell, with one filter smelling very strongly.
We have now been using the BlueAir Classic units for several years with generic unbranded activated-carbon filters. They are much cheaper and have worked well for us so far. They have the normal smell we expect from activated carbon, without the sour odor we experienced with the SmokeStop filters.
The one clear disadvantage that remains for us with this model is the fan-speed spacing. The low and medium settings are close together, while the high setting is far above both and immediately adds a lot more noise (whisper-quiet versus very loud). Fran also noted this and found it annoying. For us, the noise on the high setting is not a major problem, but an extra intermediate setting or a slightly higher medium speed would have been more practical.
| FranLab / Fran Blanche | 2020 | Video that helped lead to considering Blueair Classic 505 air purifiers |
| FranLab / Fran Blanche | 2020 | Video in which Fran discusses a sour smell from a Blueair SmokeStop filter |
| FranLab / Fran Blanche | July 7, 2020 | The BlueAir Filter Problem |
| FranLab / Fran Blanche | July 18, 2020 | Follow-up video about the Blueair filter problem and replacement filters |
| Blueair Support | December 5, 2024 | My Blue filter has a smell |
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