Air Filtration for Your Home
How to keep your home safe from ash & smoke.
The Bay Area is experiencing a light reprieve from the heavy smoke that has been blanketing the region for about a week now. As the wildfires burn out of control, hitting the “refresh” button on air quality monitoring websites like PurpleAir and AirNow is a constant pastime for residents in the American West. Today, it is a relief to be able to spend time outdoors again after being cooped up inside because the outside air was unhealthy for humans to breathe.
The air inside has been difficult to breathe as well, with many low-rise residential spaces lacking any kind of HVAC system to filter the polluted outdoor air. A frequently cited statistic from the Environmental Protection Agency (EPA) estimates that even in the best of times, indoor air quality is 2–5x worse than outdoor air quality because of inadequate ventilation.
One solution is to purchase a standalone air purifier for your home. I’ve had a few people reach out to me for air filter recommendations given my experience working in the healthy buildings industry, so I am sharing some tips more broadly though this blog post. Some people have even taken matters into their own hands by constructing budget-conscious homemade air filter options using a box fan, a filter and a bungee cord. Given the potential of this setup to cause electric sparks, I would not recommend this option . . . unless you’re aiming to impress at your next Gender Reveal party.
Here are a few things to look for when choosing a filter:
Particulate Matter (PM)
Particulate matter, or aerosols, is a “complex mixture of solid and liquid particles that vary in size and composition, and remain suspended in the air.” This includes the ash blowing about, as well as finer particles that you cannot see. The finer the particle size, the more likely it is that the particle will enter your bloodstream and cause adverse health effects. Particulate matter is the primary concern with the current wildfires.
To address PM concerns, look for Minimum Efficiency Reporting Values (MERV) filters. MERV filters report a filter’s ability to capture larger particles between 0.3 and 10 microns (µm). The higher the rating, the more likely the filter will capture particles. See additional rating details here. So a filter with a MERV rating of 6 will capture particles between 3 and 10 microns, while one with a 14 rating will also filter out smaller particles in the .3–1 micron range.”
An even better PM filter option is a High Efficiency Particulate Air (HEPA) filter. HEPA filters can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).
Volatile Organic Compounds (VOC)
These are chemicals that have been designated as hazardous to human health. Trees and grass do not generally release a high level of VOCs, however these chemicals can be a problem when buildings and other synthetic structures catch fire. Look for carbon activated filters to remove these chemicals. Unfortunately, VOCs are not included in the EPA’s continuous air quality monitoring program because the health effects from air toxics are generally not believed to be episodic in nature. For information on concentrations of air toxics, refer to EPA’s National Air Toxics Assessment (NATA).
Another option is to look for a combined filter, which removes both PM and VOCs. These filters may be wide or have a higher filter mesh density, which can create a pressure drop when paired with a motor (fan) so they will require a more sophisticated mechanical system. This upgrade tends to be more expensive but does offer the highest quality level of filtration.
Remember to change or clean (clean only when possible according to manufacturer recommendations) your filter about once every quarter. Ash and other particulates cling to the mesh of the filter as the air passes through which reduces the efficacy of any filter. The smoke has been bad enough lately that it may be blowing holes through filters so it is worth your time to check on the filters more frequently.
A Data Science Perspective
With the severity of this year’s wildfire season, many people are scrambling to acquire or upgrade their air filters. However, with better predictive modeling, it would be easier for people to be prepared. The ability to predict when wildland fire smoke will lift from a region requires complex modeling of meteorological, environmental and satellite imagery data. Fires are considered “exceptional events” for regulatory purposes and they produce substantial amounts of PM2.5. For a forecasting program, historical data are required to investigate relationships.
The federal government is starting to open the door to additional data collection beyond the high-grade EPA air quality monitoring sites. A pilot program was announced in August of 2020 to allow low-grade sensors to collect data. For those interested in becoming a citizen scientist, you can learn more here. There are even a few options to receive air quality monitoring equipment on loan.
In the current publicly available Guidelines for Developing an Air Quality Forecasting Program (2003), the Air Quality Index (AQI) is calculated using the log-normally distributed values of ozone and PM2.5 which are entered into a multivariate regression model. At the time that this guideline was written, the neural-net model provided “only a modest improvement in forecast accuracy”, but there is a good chance that this has changed behind the scenes.
Remember, the 2020 fires will end! You can track fire containment using the resources below.
