My patients frequently ask me whether they should purchase an air filter, and generally the answer is somewhat nuanced depending on who they are, what illnesses they have, where they live, and the limitations of the data we have so far. However, the air quality maps out West are currently horrific. I am certainly very grateful for our home air filtration system- we even had to change the filter with the particulate matter burden outside. Many people will also appropriately want to lower the particulate matter in their homes by use of air filters, but the array of options on the market is dizzying and the science on their effects and how to pick an air purifier is evolving.
There is also little regulation on the health claims these filters make. A particularly dangerous category are the “ozone” filters. Please make sure to avoid these if you are going to purchase an air purifier or filter. Ozone is “good up high, bad nearby.” Why would someone be interested in ozone as an air purifier in the first place? You can read some truly creative pseudoscience about this. They may use confusing terms referring to ozone as “activated oxygen,” or “energized oxygen.” Ozone (O3) is made of three atoms of oxygen (as opposed to the oxygen (O2) we breathe, which has two atoms of oxygen). That third oxygen can detach from the other two atoms and attach to another substance, therefore altering its composition and potentially “removing it” from the air. There are many health claims made about this that have not been endorsed by the EPA or any other health organization, and in fact these devices are likely at best useless and more likely harmful. Furthermore, there are no studies showing that these actually work for cleaning up the air, despite some slick marketing materials.
However, just like ozone can react with other particles, it can also react with your body. Specifically, ozone can damage the lungs. Ozone from traffic-related air pollution has been shown to cause emphysema, for example, and it likely worsens other lung diseases as well.
If you are going to purchase a new air filter, a good resource is the California Air Resources Board. It explains different considerations and actually has a list of what is permitted for safe air filters in their state, and you can search for specific models on their website before you purchase one yourself. Most importantly, they also explicitly list some filters to avoid, since the marketing on ozone filters can be misleading. The EPA also has more information available, including summaries of the studies showing a lack of significant effect for ozone air filters as well as more details on the health effects of ozone.
Sadly, as part of climate resiliency, I think we are going to need more air filters for these catastrophic wildfires in the future. Hopefully we will also develop more robust science to guide our decisions regarding filters as well as working to address climate change and improve wildfire management. Overall, the best way to ensure clean air in your home is to avoid air pollution in your home in the first place, by avoiding smoking and indoor fires, ensuring good housing with adequate ventilation and minimal water and mold damage, as well as by working for cleaner air and reduced traffic and wildfire pollution outside.
But since you’re not going to solve climate change this weekend, if you decide to buy an air filter, make sure it does not generate harmful ozone as a byproduct or as part of its mechanism of action. Also ensure it reduces PM2.5, which is the main concerning particulate currently, and is sized appropriately for the room you are trying to clear. Specifically, make sure that it has a CADR (Clean Air Delivery Rate) of 2/3 the area you are trying to clear (or more if have cielings over 8 feet). It should also state its particle removal efficiency, and should be able clean the room volume around two to three times per hour.
Look for the certification seal from AHAM (the Association of Home Appliance Manufacturers) which should have different CADR numbers for tobacco smoke, pollen, and dust. The analogy for wildfires is closer to tobacco smoke (FYI 10 min of 4 people smoking pushes PM2.5 levels over 600ug/m3, so don’t smoke!!!). Ensure the one you choose is rated to clear tobacco smoke from at least 2/3 of the area of the room at least 2-3 times per hour.
- Pay careful attention to air quality, and invest if you can in an approved, non-ozone generating air filter sized for the area you wish to clear
- Ensure you have an adequate supply of your rescue and maintenance medications. If you are in or near an evacuation area, keep your medications handy so you can take them with you
- Make sure that you talk to your doctor about having an emergency plan
- Consider an N95 mask if need to go into unhealthy air
Resources-
California Air Resources Board- general information on air filters
EPA– Information on ozone generating air “purifiers”
AirNow.Gov– Wildfire Smoke: A Guide for Public Health Professionals– very detailed information for public health professionals (that is becoming all of us these days); has information on health effects and air filters in Chapters 1-3
DIY purifier box fan– From Puget Sound Clean Air Agency
Working on a mask post for nuances of respirators, but if you use one, make sure it’s as close to fitted correctly as you can get! More info towards bottom of this CDC blog.
Please see prior post on other ways you can help and places to donate.
