Thanks to the sale of some furniture as well as a monetary gift from some friends, we were able to purchase air filters. This was a hard purchase for me because the best of the best are thousands of dollars, and the science behind some air filtering methods is controversial at best. Also, just like water filters, many are restricted and unable to be purchased for shipment to California. We ended up with two - one that is in the main living area and one in the girls' bedroom. These are doing a good job of keeping up with the toxins in the house as well as things like the wretched stench from outside in the evenings (oh! We have moved! Guess I should do that blog post next). This has been one of the ways we know they are working! No smell in the house.
The amount of research I did was quite extensive, and absolutely exhausting, so I thought I might share a little to save someone some time.
Here are the basic filtration systems currently being used in air purifiers:
1. pre-filter. This is a plain filter that works to capture large particles before they hit the more important filters. It extends the life of the other filters and is rather important.
2. HEPA filter. HEPA filters are the most efficient for catching large particles such as dust, dander, and even some bacteria. They work against mold, but there are studies showing that HEPA filters can also get mold within them and have issues so it is recommended that you remove the mold source before using the HEPA to clean it up. Just a HEPA filter is not enough because it only removes airborne particles down to .3 microns. Most household contaminants (VOC's) such as formaldehyde are smaller than this.
3. activated carbon filter. This is probably (in my opinion) the most important thing to look for in an air filter. The efficiency and size of the activated carbon in the air purifier will determine what particles smaller than .3 microns are removed. From what research I did, it appears that activated carbon filters are effective down to .1 microns.
Most of the super expensive filters stop here and use the first three filtering systems. Just like with a water filter, the more activated carbon there is for the air to move over, the more effective it is. These expensive filters are large boxes of activated carbon with HEPA filters. Most of those filters cover one average sized room and cost around $1000. We obviously could not afford this, and I also wondered about the particles smaller than .1 microns that would be missed. However, any additional filtration methods came with controversial reports regarding safety.
4. UV Lamp (germicidal). This filter gets a bit tricky. It kills micro-organisms like mold, germs, etc. and also has several variations whose safety are questionable. In general, there are either UV lamps that kill germs with ultraviolet radiation, or those that generate ozone. Both have risk factors. If the cover comes off of the ultraviolet radiation lamp you can receive dangerous exposure. On the other hand, there is still much controversy over appropriate levels of ozone. It is hard to find an air purifier that does not have one of these, so we chose one with the light instead of one that produces ozone into the air.
5. Ionizer. This is one of the components that caused me the most stress when researching; I really did not like what I read. An ionizer changes the charge of ions in the air so that particles which are normally airborne become heavy and fall to the ground. Theoretically you then sweep or dust them up, or they become airborne again where they are then again made heavy and fall to the ground. Many say ionizers are great, are not problematic and have improved their air quality tremendously. Ionizers produce ozone at varying levels. There are also some studies showing that those exposed to ionizers have particles in their lungs that are not normally found there. This made me uncomfortable for the girls' bedrooms where they would be lying flat and breathing the filtered air. For this reason I purposefully searched out filters that had extremely low (virtually no) ozone production, and was excited that the one we purchased for their bedroom has the option of turning the ionizer off.
6. Electrostatic filter. An electrostatically charged grid traps particles and is very effective.
7. Photocatalytic Oxidation (TiO2) filter. This technology is used by NASA and the newest. This filter is 99.99something-crazy% effective for cleaning the air of VOCs. The potentially questionable part is how it does that. This filter oxidizes the particles and destroys them. Extensive tests have shown that what goes in does not come out and chemicals are indeed destroyed. The problem is that there are not conclusive studies on what comes back out of the filter. The chemicals are destroyed and changed into something else, but I could not find any studies saying that the new particles being inhaled were actually safe. If formaldehyde is destroyed, what does it become? There are no answers for that yet.
There you have it. More information on air purifiers than you have ever wanted to know. We ended up with two filters that include a combination of the above systems and are proving to be very effective. If you are in the market for an air filter I recommend checking out Friends of Water who have already done the narrowing down of choices for you. We purchased some great options there for very reasonable costs.