You might think of gas masks as clunky, spooky, military-looking devices
only found in spy movies or World War I museums.
But you probably already own a mask that uses remarkably similar technology.
And in the near future, we may need to rely on these filters
as part of our everyday lives.
In addition to emerging diseases,
wildfire frequency has more than tripled from 1996 to 2021.
As fires burn longer and cover more land, their smoke affects more people each year.
Climate change is also causing more hot, sunny days,
which accelerates the production of toxic ground level ozone.
So, how do these masks work,
and can they protect us from new and old airborne threats?
Well, the first rule of filters is making sure you have a tight seal.
Without that, even the best mask in the world is useless.
So assuming your mask is on tight,
this technology can capture pollutants in one of two ways:
filtering them out by size or attracting specific chemical compounds.
For an example of the first approach, let’s look at wildfire smoke.
When forests burn, they generate a wide variety of chemicals.
At close range, there are so many different pollutants
at such high concentrations that no filter could help you—
this is why firefighters travel with their own air supply.
But further away, the situation is different.
While there's still a range of chemicals,
they’ve mostly aggregated into tiny solid or liquid particles
smaller than 2.5 microns in diameter.
This particulate matter is much of what you're seeing and smelling in smoke,
and it's especially dangerous for children, the elderly,
and those with respiratory or cardiovascular diseases.
Luckily, the majority of these particulates are still large enough
to be captured by the most basic filters,
which are made of polypropylene or glass strands
roughly 1/10 the width of a human hair.
Under a microscope, they look like a thick forest,
and at this scale, these branches have a special property.
Typically, when you use a sieve,
you’re filtering out objects larger than the sieve’s holes.
But these polypropylene branches can catch particles much smaller
than the gaps between them.
That’s because, when a particle collides with a thread,
van der Waals forces cause it to stick as if it were made of Velcro.
Plus, size-based filters can use electrically charged fibers
that attract particles not already on a collision course.
This is how even a simple N95 mask can catch at least 95% of particulate matter.
And why an N100 mask
or an air purifier with a high efficiency particulate air filter
can catch at least 99.97% of particulates.
With a tight seal,
this level of protection will filter out most airborne pollution.
Unfortunately, some pollutants are still too small for this approach,
including ozone molecules.
These are barely bigger than the oxygen that we need to breathe
and exposure is associated with asthma, respiratory conditions,
and even premature death.
Our best chance to filter them are activated carbon masks.
At the microscopic level, activated carbon looks like a vast black honeycomb,
and it's highly microporous structure can trap tiny ozone molecules.
But this material still needs help to capture other pollutants
like hydrogen sulfide, chlorine, and ammonia.
For these threats, we need to combine the activated carbon
with some simple chemistry.
If the pollutant is acidic, we can infuse the filter with a basic chemical.
Then when the two meet, they react, and the gas is trapped.
Similarly, we can use acids to trap basic pollutants.
Even with the right mask, it's still smart to check air quality indicators
and to stay indoors when the threat level is high.
And just like a mask, you'll want to make sure your house is well sealed.
You can do this by closing windows, turning off fans that vent outside,
and using HEPA filter equipped air purifiers
or their cheaper, DIY cousin, the Corsi-Rosenthal box.
Following these guidelines can help us breathe easy
as we work on preventing these pollutants in the first place.