I recently wanted to learn more about the air purification systems used on the International Space Station (ISS). So I turned to NASA’s website to find out exactly what keeps the air inside the ISS healthy. After all, there are probably tons of contaminants do deal with in an airtight container 230-ish miles above Earth. Unfortunately what I found were a bunch of blog posts that only mention “air purification.” Others highlight a specific experiment. And surprisingly some promote things like the Airocide commercial air purifier with what comes off a little like an advertorial. So, I did what any good like minded (perhaps slightly cynical and maybe pedantic at times) would do. I spent hours combing through various scientific papers, websites, and press releases to find out exactly what is going on inside that habitat that laps our beloved planet every 90 minutes or so.
Airocide… case closed. Right?
In the upper left hand corner of the Airocide website you’ll see the tagline “developed for NASA.” Which leads me to believe that NASA put out a contract (or grant) and this company developed a product. Sounds pretty good, right? Case closed? Not really — let’s continue. Scroll down a bit and you find a beautifully designed in-home air purifier.
A little more digging around and you’ll find a nice how it works video, some beautiful photos, and surprisingly fair comparisons to other purification methods (hats off to Airocide for the honesty about Ozone producing “purifiers”). Full disclosure, by the time I got to the bottom of the page… I kind of wanted to buy one of these machines. When I read the “commercial” tab, I was even more impressed. But we’ll take a look at that another day. I’m here to figure out how the air in the ISS is “cleaned.”
Further reading (between the lines – and otherwise) reveals that the technology was in fact developed “for” NASA. But, that ambiguous “for” made me hop off the site to see if I could find anything on NASA’s enormous website. After a bit of digging I found a few blogposts about Airocide using NASA-funded technology in its purifiers. I also came across a more in-depth post about how the technology is was used to scrub Ethelyne Gas from the space station at some point. But, what I didn’t find was a clear answer to the question “how do they purify the air on the space station?” So, while Airocide does have a legit connection to NASA and a bunch of other reputable commercial customers… I’m not sure i can call it a day quite yet.
Air Purification on the ISS is… complex.
Unsurprisingly… it’s not a simple cut and dry solution. Humans didn’t just invent a box, send it to space, and plug it into the technologically advanced wall of the ISS. Space is unforgiving — so it makes sense that it is not a overly simple answer – like buying some furnace filters at Home Depot and calling it a day. The International Space Station (ISS) stands as a testament to human ingenuity and determination. It’s a freaking orbital laboratory, inhabited by astronauts from across the globe that serves as a microcosm of life on Earth (albeit with some major differences). Of course the air (and water) solutions are going to be not only complex, but highly specific and multi layered. So let’s roll up our sleeves and scratch the surface on what is likely volumes and volumes of information collected and developed over decades.
In this blog post, we will dip our toes into the fascinating world of air purification technology aboard the ISS, exploring the types of purification methods used, their development, and their vital role in supporting the astronauts who call the ISS home. Let’s go.
Differences between the ISS and your house / apt / etc.
Aside from obvious things, like one moves at a speed that allows it to lap the earth every 90 minutes of so, there are some pretty significant differences between the confines of the ISS and a structure planted to the earths surface.
The first that stands out to me is circulation. Like it or not, your home exchanges the interior air with outside air on a pretty regular basis. The space station, for obvious safety and basic science reasons, is completely sealed. That might sound obvious but a lot of challenges arise from the lack of air exchange. For example to capture carbon dioxide, air must first be dried. Which requires, according to one NASA document, up to four times more power than actually removing the carbon dioxide. At home, here on Earth, carbon dioxide makes it’s way outside pretty easily, trees consume it, and they give off nice breathable oxygen in return.
Speaking of oxygen… if you’re wondering how the make it on the ISS it’s pretty similar to the systems used in the submarines that are constantly sneaking around beneath the surface of the oceans. Electricity is passed through water separating Oxygen from Hydrogen through a process called electrolysis. There are also redundant tanks of oxygen aboard the space station, but those are cycled out somewhat regularly. Oh, and there’s another backup called the SFOG (solid-fuel oxygen generator), but since it requires fire and temps around 600 degrees Celsius… its sort of a last resort.
Monitoring Air Quality
Okay, back to the differences between your home and space. Another one is monitoring. In my home we have sensors like a thermostat, carbon monoxide detector, and even a few sensor push devices that track temp and humidity over time. The ISS is on a completely different level when it comes to monitoring air quality. This section could probably sprawl into a book of its own, but we’ll just say its more closely monitored. I highly suspect that there’s ever been a space fart on the ISS that was not detected by at least one closely monitored instrument.
Microgravity and Humidity
Beyond human… ummm emissions. There is also the gravity situation that has to be acknowledged. The ISS operates in a microgravity environment, which means that there is no natural convection of air. In a home or office on Earth, warm air rises, and cool air sinks, facilitating the circulation of air and the dispersion of airborne particles and contaminants. In microgravity, air tends to stagnate, making it easier for airborne particles to accumulate and creating challenges for ventilation. Which in turn can impact microbial growth. This growth can be more challenging to control in the confined environment of the ISS.
The microgravity environment, combined with higher humidity levels (about 60 percent according to a few sources I encountered) and the presence of organic materials, can create conditions conducive to the growth of mold and bacteria. When you spill a glass of water in your kitchen its probably not a big deal. But in space a lot can go wrong if water gets loose.
Types of Purification Technologies aboard the ISS
The foundation of air purification on the ISS is the High-Efficiency Particulate Air (HEPA) filtration system. HEPA filters are designed to trap and remove tiny particles from the air, such as dust, microbes, and allergens. These filters consist of a dense mat of fibers that create a net-like structure. Particles are trapped as air passes through. HEPA filtration serves as the first line of defense. Above all else it ensures the air inside the ISS remains clean and safe to breathe. Interestingly, scientists developed HEPA during World War II, And, future scientists made significant improvements to meet the rigorous standards required for space travel. NASA worked closely with engineers and scientists to enhance filter efficiency and durability. These advancements ensured that HEPA filters could effectively remove particles as small as 0.3 microns. Which is crucial for maintaining clean air aboard the ISS.
HEPA filters work through a combination of three mechanisms: interception, impaction, and diffusion. This trio captures even the tiniest particles, leaving the air clean and safe to breathe.
Engineers included 21 HEPA filters in various locations throughout the ISS. Not only do the make the air more breathable… they protect important equipment from contamination.
Activated Carbon Adsorption
While HEPA filters are highly effective at capturing particulate matter, they are less efficient at removing things like Volatile Organic Compounds. To address this challenge, the ISS employs activated carbon adsorption technology. Activated carbon is highly porous and has an immense surface area, making it ideal for adsorbing volatile organic compounds (VOCs) and other gases. The carbon acts like a sponge, attracting and trapping these molecules, thus purifying the air of any unwanted odors or potentially harmful substances. As air passes through the carbon bed, gas molecules are physically adsorbed onto the carbon’s surface, effectively removing them from the air stream. This process continues until the carbon becomes saturated and requires replacement or regeneration.
The carbon filters on the ISS are housed in Aluminum frames and are attached to similar looking frames that house the advanced HEPA filtration units. Without getting too deep into the weeds one of the main objectives of the carbon filters on the ISS is to absorb siloxanes… a compound off-gassed by sealants and materials used in the construction of the space station.
Photo Catalytic Oxidation
Well… here we are back where we started (sort of) with the tech used in Airocide purifiers. Photo Catalytic Oxidation traces its roots back to labs in Japan circa the late 1960’s. To oversimplify a technology that is still evolving after 5 decades of work… this process involves passing air through a catalyst, typically consisting of noble metals like platinum or palladium. These catalysts facilitate chemical reactions that break down harmful gases and pollutants into harmless compounds. Catalytic oxidation plays a crucial role in maintaining a healthy atmosphere inside the station. The development of catalytic oxidation technology for space applications involved extensive research into catalyst materials, reactor design, and performance optimization.
Engineers and scientists focused on creating compact and efficient catalytic systems that could reliably purify the air in the confines of the ISS. One of the key gasses targeted by this tech is the same gas that makes fruit ripen and rot. The biggest is that like their earth-based cousins…. The ISS PCO units require periodic replacement of the catalyst. Scientists are currently working on resolving that problem with air scrubbers that last long enough to support trips to places like Mars and beyond.
How does Air Purification on the ISS relate to the consumer….
The importance of air purification is evident both in space and at home. In space, on the International Space Station (ISS), maintaining pristine air quality is a matter of life and death for astronauts. The closed environment of the ISS necessitates advanced air purification systems to ensure the removal of harmful substances and maintain a safe breathing atmosphere. But as we can see from the ISS simple methods like activated charcoal and HEPA filters do wonders.
Likewise, on Earth, air purification plays a crucial role in our daily lives. In homes, schools, and workplaces, air purification systems help reduce indoor air pollution, allergens, and pathogens, thus promoting a healthier and more comfortable living environment. Especially in urban areas with high levels of outdoor pollution, home air purifiers provide a sanctuary of clean air, offering relief from respiratory issues and allergies. The shared importance of air purification in space and at home lies in its capacity to protect human health, create a clean and comfortable living space, and ultimately enhance our overall quality of life.
Unfortunately, many purifiers currently sold to the general public do not face the same scrutiny that a multinational… multi-decade space mission does. And that means you’ll need to approach your in-home air quality with at least some degree of critical thought and research. But, you’re not alone. We’re always here to help separate the “wheat” from the “chaff” since there is so much bad purifier information floating around the vast and harsh environment of the interwebs.
- Design and Implementation of Combination Charcoal and HEPA Filters for the International Space Station Cabin Air Ventilation System – https://ttu-ir.tdl.org/handle/2346/84608
- International Space Station (ISS) Bacterial Filter Elements (BFEs): Filter Efficiency and Pressure Drop Testing of Returned Units – https://ntrs.nasa.gov/citations/20170008803
- Airocide Air Purification Units Use NASA-Funded Technology – https://www.nasa.gov/offices/oct/images/airocide-air-purification-units-use-nasa-funded-technology
- Health Research off the Earth, for the Earth – https://blogs.nasa.gov/ISS_Science_Blog/tag/education/