Particulate Matter

The most effective way to improve air quality in your home is to ventilate with clean, outdoor air.  Outdoor air has 2 to 5 times fewer pollutants than indoor air.  Opening your doors and windows for 15 minutes each day can reduce indoor pollutants by bringing in cleaner, outdoor air to mix with the more polluted indoor air. However, opening your doors and windows is not recommended on days with poor outdoor air quality, if you live close to busy highways, if there is a wildfire nearby, or factories with high emissions. 

Air cleaners and specialized filters designed for use with HVAC (Heating, Ventilation and Air conditioning) systems may improve your home’s air quality. This is because most HVACs circulate and filter air throughout the entire home. These central forced air systems in homes usually accommodate a rectangular, one-inch-thick filter that slides underneath or beside the furnace fan. Use a furnace filter with a higher MERV rating, preferably 13 or above. These disposable filters cost about $12 each. Be sure to change the filter about every 30 days or when it looks dirty. How do you know when it is dirty? Compare it to a plain white sheet of paper.

Health studies show modest health improvements in individuals who consistently use mechanical, portable air cleaners in their home. This is because air cleaners, sometimes called air purifiers, remove the particulate matter from the air we breathe. Portable units are usually best for single room use, rather than multiple room or whole house uses. Large areas and homes may need more than one air cleaner.

When selecting an air cleaner for your home, select a model that:

1. Is appropriate for the size of your room.
2. Has low-cost replacement filters.
3. Has a filter with a MERV rating of 13 or higher.
4. Has a high CADR (Clean Air Delivery Rate). The CADR should be at least two-thirds of the cubic feet per minute metric (CFM).  In other words, if an air purifier’s CFM is 200, make sure the CADR is at least 133.
5. Is certified by the California Air Research Board.
6. Does not generate ozone or is an ionizer.  Never use an air cleaner that produces ozone, sometimes called an "ozone generator." Ozone is a nose, throat, and lung irritant and toxin.

Adding a charcoal filter to your air cleaner:

If you have very sensitive individuals in your home or odors that are difficult to remove, you may want to consider adding a charcoal filter. Activated charcoal filters (carbon) trap or destroy gaseous pollutants. The charcoal filter may need to be replaced often.

What about new technologies?

Both central and portable air cleaners continue to incorporate newer types of technologies to remove particles, gases and chemical vapors from the air. Newer technologies should be used only after careful consideration, as some may have potentially adverse health consequences, including ozone production or the generation of unintentional pollutants. Many of these newer technologies are still being studied and their effectiveness is unknown. There are no standards for testing these new technologies in the U.S. Testing is also very difficult and expensive, and testing in the laboratory often yields different results than found in the “real world.”

Air cleaners are available for purchase at reasonable rates. However, air cleaners may be difficult to find during some natural disasters, such as wildfires. Effective air cleaners can be made at home with materials you may already have.

What do I need?

• 1 Box Fan (manufactured in 2012 or more recent)
• 1 Furnace filter with a MERV rating of 13 or higher
• Tape, clamps or bungie cords

Download instructions

Your DIY air cleaner can be used for localized air filtration so you can move it from room to room. The filter on your DIY air cleaner should be changed when dirty, approximately every 6 months or more frequently during a wildfire.

Are DIY air cleaners safe?

The Environmental Protection Agency (EPA) has tested several DIY air cleaners to confirm that fans are safe to use and will not overheat during use. The following precautions are recommended:

1. Use a newer model fan, 2012 or more recent.
2. Use fans that are labeled with UL (Universal Laboratories) or ELT (Intertek's Electrical Testing Labs).
3. Follow the manufacturer’s instructions.
4. Do not leave children unattended while the fan is in use.
5. Do not use when you are not home.
6. Do not use an extension cord, or a damaged or malfunctioning fan.
7. Keep extra filters on hand, especially during heavy air pollution events such as a wildfire.