Response: If your wife spends most of her time at home in one or two rooms, then placing a suitable portable air cleaner near her in each room should help reduce particle levels - and thus improve your indoor air quality. If she spends time at home in many rooms or your home has an open floor plan, portable air cleaners may not be the best solution. You may want to look at other possible solutions, such as a whole house air cleaning system. [Note that whole house air cleaning systems are not a solution for everyone, as they require a central cooling or heating system.] You should be aware that air cleaners generally don't remove everything -- most don't remove bad smells or remove all potentially harmful gases from the air — be suspicious of such claims.
Portable air cleaners are the most common type of air cleaner. They are small and plug into the wall much like a counter-top kitchen appliance or a portable heater. There are many brands and models of portable air cleaners to chose from. In choosing the best portable air cleaner for you, you should consider the following three factors: Efficiency. Most portable air cleaners use a filter to remove dust and other particles from air that is moved through the filter by a fan. The efficiency of the filter is the fraction of particles removed by the filter. The best performing portable air cleaners have HEPA-grade efficiency, meaning that they remove at least 99.97% of 0.3 micron particles from the air that passes through them.
Clean Air Delivery Rate. The performance of portable air cleaners is typically determined by its "Clean Air Delivery Rate" or CADR. Conceptually, CADR is the amount of clean air delivered each minute by the air cleaner. In practice, CADR can be calculated from the airflow rate of the fan and the filter efficiency. For example, a portable air cleaner with a flow rate of 200 cubic feet per minute (cfm) and a 50% efficient filter would have a CADR of 100 cfm. CADRs can usually be found on the box of the air cleaner. [The Association of Home Appliance Manufacturers (AHAM) provides more detailed explanation of air cleaners and lists model-specific CADRs at http://www.cadr.org/consumer/certified.html.] Notably, portable air cleaners without fans, such as many ionic type models, do not have a CADR rating because they do not have a fan to deliver air through the filter. As a result, models without fans are generally ineffective (e.g., are a waste of money) because they don't clean enough air to make a difference in your air quality.
Room Size. Portable air cleaners work best inside an enclosed space, for example a bedroom with closed doors and windows. The best air cleaner for your home will have a CADR equal to the square footage of the room that you want to clean. An air cleaner with a substantially larger CADR may be too noisy and create too many drafts. On the other hand, an air cleaner with CADR much smaller than the area of your room will not clean the air fast enough for your room size. In this case, you could purchase several portable air cleaners which together have a large enough CADR to clean the same large room. This solution may be sufficient for your needs, although testing has shown this solution to be relatively inefficient.
On a more personal note, I would stay away from ionic or electronic air cleaners that produce measureable amounts of ozone, a pollutant that has been shown to be harmful to health. Look for test results from companies making ionic or electronic air cleaners to make sure that the air cleaner does not produce measureable amounts of ozone (say over a couple parts per billion or ppb) in your living space. Some ionic or electronic air cleaners will include a scrubber to remove the ozone. I would still be wary of these air cleaners, as it is possible that faulty operation, installation, or maintenance will result in the build up of harmful levels of ozone inside your house. Since there are many available air cleaners that don't produce ozone, I don't see a reason to choose a model that may pollute your air.
Previous Ask Treehugger columns can be found here.
Helen Suh MacIntosh is a professor in environmental health at Harvard University and studies how pollution behaves in the environment and how it affects people's health. Please keep in mind that her answers are just her interpretation of available information and should not be taken as the only viewpoint or solution to a problem. Use this column at your own risk. Having said this, please feel free to post any of your environmental health questions to AskTreeHugger [[@]] TreeHugger [[.]] com (please use a descriptive email subject line and mention if you want to remain anonymous or not).