Deep Dive: What you should do before the next round of wildfire smoke

Part of living through climate collapse is that we will all, periodically, have wildfire smoke blowing in from somewhere.

Since about a week ago, forests in Canada, from British Columbia in the west to Quebec and Nova Scotia in the east, have been on fire. These disasters know no borders; the smoke from these fires has made it as far south as the Pacific Northwest and the Eastern Seaboard.

Wildfires are cyclical, and that means the smoke from them is, too. Fire burns an area clean, leaving it ready for fresh growth; subsequent rains, besides causing debris flows, also begin the phase of new growth. Enough of that growth, especially coupled with drought that increases its flammability, creates the conditions for another wildfire.

Which is to say that even when historic fire seasons such as those in 2020 and 2021 are behind us, that doesn’t mean that dealing with smoke is behind us in any permanent sense. There will be another wildfire, and we will have smoke again. And this is true for everyone, everywhere.

The knowledge that we in California have gained from our encounters with wildfire smoke is knowledge that we can share with others. As we learned in 2018, 2020, and 2021, and folks on the East Coast learned this year, folks in cities are not exempt—wildfire smoke can blow into your area wherever you are.

Wherever you live, you will have smoke in your area in your future. Prepare now, and stay prepared, so that when it happens, you and your family have the best chance of making it through unharmed.

Note: This article does not contain any affiliate links or any endorsements of any product or brand. Specific products mentioned are for informational purposes only. Nobody’s paying us; this isn’t an advertorial.

Wildfire smoke: Not just unpleasant, but actively dangerous

Any wildfire smoke, even if it’s just smoke from trees and brush, largely consists of fine particulates, classified as PM2.5. These particulates—essentially an ultra-fine powder suspended in the air—can embed in your lungs and damage them, making it harder to breathe long after the smoke has moved on.

Worse, wildfires often do engulf cars or structures in their path, and then the smoke may include substances released or produced from those burning human-made objects. Those can include a wide variety of nasty things you don’t want to breathe any more than the smoke itself.

That’s why it’s important to protect yourself and your family in every way you can.

If you have central air

If you live in a house with a central air or HVAC system, replace its furnace filter with a filter whose efficiency rating is at least MERV 13. This includes “true HEPA” filters.

Check your thermostat for a “recirculate” or “fan” option that runs the fan continuously even when not heating or cooling. When the air turns smoky, turning that on will put your central air system to work cleaning the air throughout your home. If your thermostat doesn’t have this option, you may be able to replace it with one that does, even without replacing the rest of the system; if you don’t feel up to the task of doing this yourself, you could hire an HVAC technician to do it for you.

When not going through a smoke event, filters will last for a long (but finite) time, typically at least three or four months. The package should say. Mark your calendar for the next replacement date, or schedule it for something memorable such as the first day of every third month. And after a smoke event, you should consider the filters to be spent and ready to be disposed of.

Be sure to get filters in the exact right size for your system. A filter that’s too big will fit poorly, introducing gaps that compromise filtration effectiveness. A filter that’s too small will basically not filter at all. Air will go around the filter instead of through it unless the filter is the correct size.

Buy, or build, an air purifier

If you’re preparing before a smoke event, it should be possible to buy a suitable air purifier locally and have it ready. Consumer Reports has a helpful general buying guide.

You need the right type of filter. Activated carbon filters absorb odors, but don’t remove particulates such as smoke. To filter particulates, you’ll need a HEPA filter or other filter with a sufficiently high MERV rating. The package should tell you what types of particles—if any—it’s rated to remove; allergens such as pollen are large particles that require the least filtration, while viruses are tiny and require dense, electrostatic filters. Smoke falls roughly in the middle.

We mentioned viruses. Filters of MERV 13 or higher can also help reduce COVID-19 transmission risk within the vicinity of the air purifier. If you or someone living with you has COVID-19, that person should have an air purifier with a suitable filter (or UV disinfection feature) in their bedroom. When smoke isn’t a concern, ventilation can also help.

You may need to buy multiple air purifiers, depending on the size of your home. Each unit will have a “clean air delivery rate,” or CADR, that indicates how many cubic feet per minute (CFM) of air the unit can clean. Measure the width and length of the room where you’ll put the air purifier, multiply them to get the area, and buy an air purifier whose CADR is at least two-thirds that number.

Retail (not homemade) air purifiers are meant to run continuously; you don’t need to turn them off when you leave the home. Leave them running so the air is still clean when you come back.

Caveat: Beware of ion generators (“ionizing purifiers”)

Some air purifiers have an ion-generating feature, which emits ions into the air to cause small particles—such as those in smoke—to be attracted to surfaces and thus be drawn out of the air. (The worst of these don’t even have a filter—they’re just ion generators.)

Ion generators are also ozone generators, and ozone is a pollutant and a lung irritant. People with asthma will especially want to avoid these, as the ozone so produced can set off an attack.

Ion generators, in trapping smoke but producing ozone, effectively trade one pollutant for another. The EPA says that “the levels [of ion generation] needed to [effectively remove odors and pollutants from the air] are above those generally thought to be safe for humans.”

If you can’t find an off-the-shelf air purifier

Particularly when smoke is already affecting your area, retail air purifiers—or replacement filters for them—may be hard to come by.

Back in the 2018 wildfire season, people started developing methods for building a homemade air purifier out of a 20-inch box fan and one or more 20-inch furnace filters. The COVID-19 pandemic brought a lot more people into that work, as air cleaning is, as we mentioned above, an effective method of reducing viral transmission within an indoor space. There’s now a large body of knowledge about homemade air purifiers, and plenty of design variations to choose from.

The basic ingredients are a 20-inch box fan, at least one 20-inch furnace filter, and duct tape. You’ll also want to use the box the fan came in to make a shroud for the fan—covering the area outside of the fan blades—to improve filtration efficiency. Common Humanity Collective has a write-up of one method that uses a single filter, and regularly organizes builds in the East Bay of these air purifiers to distribute in mutual aid. The EPA has an article presenting research on these DIY air purifiers, including their own how-to for the one-filter model.

The filters can be purchased from Target, large hardware stores, or Costco (which actually has a four-pack of suitable filters on sale as we write this). Make sure you get the right size; 20-by-20 will exactly fit a typical 20-inch box fan, while some designs permit use of longer filters such as 20-by-25.

The CADR will be hard to pin down, as it’s highly dependent on both total filter area (the product of filter size times the number of filters) and fan speed.

Advantages

  • When retail air purifiers are hard to find, you can still generally find the materials to make your own.

  • Homemade air purifiers are considerably cheaper; costs vary depending in part on size, but a retail air purifier can be over $100, and replacement filters in the $20–50 range.

  • Furnace filters come in standard sizes and never stop being made. A retail air purifier typically only works with filters specifically designed for it; if the manufacturer stops making those filters or goes out of business entirely, your retail air purifier spontaneously becomes e-waste, whereas you’ll always be able to duct-tape a new filter to your box fan.

Disadvantages

  • They’re relatively loud compared to a retail air purifier. If you’ve ever used a box fan, you have some idea of how noisy they can be, and adding a filter isn’t going to help that. (There are kits you can buy that use computer fans instead, which are much quieter, but they cost significantly more and are more work to put together.)

  • Procuring the materials and putting them together will cost you more time than buying something already assembled.

  • Replacing the filter (or filters) isn’t as easy on the homemade designs that have you duct-tape the filter(s) to the fan; you’ll need to cut that duct tape and then tape the new filter(s) on.

  • The single-filter design scores pretty poorly on CADR; a UC Davis study found a CADR of roughly 45–80, depending on fan speed (and thus airflow). The other common design using four filters scored much better, at roughly 165–250, but that does increase your filter spend (though it’s still competitive with retail air purifier filters) and the labor of putting it together. It’s a tradeoff.

If you need an air purifier right now and can’t find one to buy, building one is better than breathing smoke. A homemade air purifier will keep your home and lungs clear until the next time you can buy a quieter, easier-to-use retail model.

Filter replacement

Filters are a consumable, and particularly after a smoke event, you should consider the filters to be spent and ready to be disposed of.

What we said above for HVAC filters applies here too: When not going through a smoke event, filters will last for a significant (but finite) time, typically three or four months. The package should say. Mark your calendar for the next replacement date, or schedule it for something memorable such as the first day of every third month.

Have at least one N95 or better respirator on hand per person

Sooner or later, you will have to go out for groceries or other necessary errands. (Save other outings for another time.) 

Many of us went into the COVID-19 pandemic with a supply of N95s already on hand from the 2018 wildfire season. Today, the shoe might well be on the other foot: The masks you wear to inhibit the spread of COVID-19 will also help protect you from smoke.

As with air purifier filters, you’ll want to change out your N95 masks (or replaceable filters, if you have such a mask) more frequently as they get saturated with smoke particles. If the mask or filter is visibly soiled or becomes difficult to breathe through, that’s a good sign that it’s time to throw it out. Don’t try to clean your masks or filters—there is no way to do that without compromising effectiveness.

If you’ve been wearing a non-N95 mask such as a “surgical” mask or a fabric mask, you’ll need to upgrade, at least for however long the smoke lasts. When there isn’t smoke, people often wear less-protective masks for comfort reasons, but when smoke arrives, the smoke is itself a source of discomfort (in the form of choking on smoke) and therefore the most protective mask is also the most comfortable mask.

It’s important that your mask make a good seal against your face. This is one difference between N95 respirators and other designations such as KN95: N95 respirators have upper and lower elastics, rather than earloops, specifically in order to maintain the right amount of pressure against the face. If you have facial hair, you may also need to change your facial hair style to ensure the area where the mask meets your face is clean-shaven.

If you wear glasses, you may want to look for N95s with an exhalation valve, such as this Milwaukee model, to reduce fogging.

Lastly, remember that N95 respirators do expire. (In particular, the elastic straps can lose their elasticity over time.) The box yours came in should have an expiration date printed on it. If your masks are expired, they’re better than nothing, but should be replaced ASAP.

When it’s smoky: Seal out smoke at doors and windows

When the air outside is smoky, you’ll want to keep all doors and windows closed. You won’t be able to open a window to let fresh air in, because that air won’t be fresh.

Also check your exterior doors. If there’s a gap at the bottom that lets outside air in, you may want to put damp towels or T-shirts behind that gap to prevent smoke from intruding.

If you need to bring in fresh air (because of stuffiness, CO₂ levels, a gas stove, etc.), open one window a very small amount and put your air purifier immediately under it. This will be imperfect, but it will bring in fresh air when you need it while limiting how much smoke is allowed to spread into your home.

Start keeping live houseplants

This one doesn’t directly help with smoke, but helps make staying inside with windows and doors closed more bearable.

Live plants—i.e., not plastic fakes—grow by photosynthesis: the conversion of sunlight, water, and carbon dioxide to new plant material and oxygen.

When you’re keeping your home sealed up, all of the carbon dioxide that you’re exhaling accumulates inside your home. The typical concentration of CO₂ in outdoor air is roughly 420 parts per million (as of last year; it is, notoriously, climbing every year); for a single individual at home with all the doors and windows closed, CO₂ concentration can climb over 1000 ppm. If you have other people living with you, that number increases further.

CO₂ is not just a greenhouse gas; it’s also a pollutant with cognitive effects. If you’ve ever felt tired during a long drive or after a full day in class or at work, part of that is the cumulative effect of hours spent breathing air with too much CO₂. Even before you get anywhere near OSHA’s Permissible Exposure Limit of 5000 ppm, it simply gets worse the higher concentrations go.

So it’s important to get rid of the CO₂ you exhale. Normally, you can do that by ventilation—introducing fresh air to displace stale air. But when that isn’t an option, plants can consume the CO₂ you produce and produce oxygen for you to consume.

So-called “snake plants,” also known by the Latin name of sansevieria, are a particularly easy-to-care-for and easy-to-obtain plant family. A medium-sized plant of at least a foot in height is a great start. Keep it near a window where it can get plenty of sun, and water it in the morning whenever the soil gets dry. That might be as often as twice a week or as rarely as every two weeks, depending on weather (especially humidity or lack thereof), what kind of pot it’s in (terra cotta evaporates moisture while plastic or glazed pots trap it), and size (small plants need to be watered more often).

You can also buy a CO₂ monitor to keep track of CO₂ levels in your home. Some, like the Aranet4, are portable, while others, like the AirVisual Pro, can also track PM2.5 (so, smoke). A CO₂ monitor can give you an idea of what your CO₂ production/accumulation is like before acquiring plants, and after acquiring them and getting into your plant-keeping routine.

If you have enough plant coverage, you should be able to track the day/night cycle by CO₂ levels, as your plants begin photosynthesizing when sunlight starts coming in and stop as the sun goes down.

Again, plants won’t directly help with smoke. Staying inside, with the windows closed and your air purifier running, does. Plants can help you do that.

Keep an eye on air quality—and the wind

This is a good habit to get into in normal times, so that you’ll be the first to know when smoke might be headed your way—even before any official announcements or news reports.

Start with your local air quality conditions. The Bay Area AQMD will issue a Spare the Air alert when air quality is poor, and offers a variety of ways to get notified of Spare the Air alerts. AirNow is the EPA’s site that aggregates air quality readings from official sources such as the Bay Area AQMD. PurpleAir is crowdsourced; it shows air quality readings from thousands of internet-connected air quality monitors owned by people like you. (Don’t get too hung up on any individual sensor’s reading; pay more attention to the general level of air quality over an area.) The latter can be particularly helpful here due to the City’s topography; sometimes, depending on wind direction and smoke origin, one half of the City might be in smoke while the other might be clear.

That brings us to weather conditions. Smoke can be blown for hundreds of miles; consider, this year, the smoke being blown into our Pacific Northwest from British Columbia, or down the Eastern Seaboard from Quebec and Nova Scotia. That means a wildfire far away can be the cause of smoky conditions here.

The LA Times maintains a map of active wildfires and air pollution that can help you figure out where smoke might come from. (AirNow has a similar map.) Windy shows wind speed and direction worldwide. Once you know where smoke is likely to come from and which way it’s likely to go, you’ll have a better idea of whether or not you’re in its path.

You don’t necessarily need to check these resources every day. Pay attention to news reports of wildfires, even if they’re far away. That’s when you’ll need to start monitoring for whether smoke might be coming.

When it’s smoky: Cook at home

You might be used to eating out or getting food delivered. The former requires going out into the smoke, and the latter means putting other people’s health at risk.

So, as much as you can, cook your meals at home. This may mean stocking up on groceries when smoke is on the way.

Note that some cooking methods will produce smoke; while your air purifier will help with that, you probably want to minimize that to the extent possible. If your kitchen has a vent hood that exhausts to the outside, use it. If not, you may want to avoid smokier cooking methods, at least until the outdoor smoke has passed and you can open windows again.

It’s even worse if your stove burns gas, due to the pollution those stoves generate when cooking and even when off. You probably shouldn’t cook with it at all until you can open a window. Longer-term, if you own your home, consider replacing your gas stove with either kind of electric.

Help each other

No person is an island and we don’t have to go through wildfire smoke events, or other symptoms of climate collapse, alone.

The easiest thing is to spread actionable knowledge, such as this article or specific resources cited within it. Don’t spread fear or doom—equip people with knowledge they can use to protect themselves and others. This is especially important if you know anyone in an area going through this for the first time—because it will not be the last.

If you’re in the Bay Area and want to help build homemade air purifiers for people in need, you can sign up with Common Humanity Collective. If you’re not in the Bay Area, see if there’s something similar in your area, and if not, maybe start something like it locally.

Also, Mask Oakland helps distribute N95 masks and CHC’s homemade air purifiers to people in need. Both CHC and Mask Oakland accept monetary donations to buy supplies; donate to CHC here, and donate to Mask Oakland here.

In summary

Know that you will have to deal with wildfire smoke again. This is the new normal of our climate emergency, and a big part of why we need policy that will help stop and reverse global warming with all of its effects.

Enjoy clear air while you’ve got it, and take this time to prepare for the next time smoke blows your way.

Resources

Deep DiveKathy LassEnvironment, Climate