[♩INTRO].

Last week, the smoke from wildfires in the western US crossed the country. While air has cleared in some areas, fires continue to burn.

And seeing as nasty wildfire seasons are becoming our new normal, it's unfortunately always a good time to talk about smoke. So this week, we're giving you the lowdown: what it is, what it does to us, and what you can do to protect yourself when it gets smoky. Smoke that billows off of a wildfire is actually composed of lots of different things.

It's mostly water vapor, but it also contains gases like carbon monoxide, chemicals produced by the flames, and small bits of ash and other particles. In fact, those airborne particles are the main reason smoke is visible; if your view is hazy or the sky is a weird color, you can blame the particles. But we don't judge how bad the air is just by looking at the sky.

Many governments use a measure called the Air Quality Index or AQI, which is usually a color-coded scale of some sort. In the US, the AQI goes from zero to 500 and has six different ranges. And technically, this number can actually reflect any of five different pollutants: ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, or airborne particulate matter, usually abbreviated PM.

Each pollutant gets measured separately; a value of 100 corresponds to the level that's considered okay for short-term exposure by the National Ambient Air Quality Standards. Then, the highest of these is what's reported. So AQI reflects whatever is most harmful at the time and with smoke, that's usually that PM, especially small bits less than 2.5 microns in size.

Starting at an AQI of 151, anyone exposed to the air may be harmed, even people who are otherwise healthy. Common reactions to smoke exposure include stinging eyes, scratchy throat, coughing and wheezing, even chest pain. Or, you might just feel really tired.

So if you've been in an area with smoke and just don't feel 100%, that might be part of it. The good news is that these effects tend to be short-lived. People generally get better when the air quality improves.

That said, there is a possibility for longer-term harm. And that's because smoke contains a lot of nasty things. But what's most likely to cause health problems across the country are those floating, microscopic particles, which can contain some really harmful stuff.

When breathed in, they can damage or even kill cells and irritate the lungs, causing coughing, phlegm, and breathing problems. And if they don't get ousted, they can cause chronic inflammation. Essentially, your immune system launches an assault on the foreign material, and in the process, ends up harming your lung tissues.

These particles may even get into the bloodstream and set off inflammation elsewhere in the body. This is why people with conditions like asthma, COPD, and heart disease should be especially careful about smoke exposure; the added inflammation can exacerbate what they're already dealing with. And studies have tied wildfire smoke to things like increases in mortality and decreases in birth weights, though more research is needed.

Oh, and, not to freak anyone out, but smoke exposure has also been tied to infectious disease spread later on. Which isn't great at the current moment. Though, a review from 2016 called this evidence “inconsistent”.

So, jury is somewhat out on that front. Still, between the possibility of that and long-term health effects, it's probably a good idea to limit exposure. And beyond keeping indoors, there are a few things that health and safety agencies recommend for that.

Like, wearing a mask if you do have to go outdoors for prolonged periods though, you'll need a full on N95 or similar to have it make much of an impact. You can also boost the air filtration in your home, to combat anything that makes it inside. If you have a central heating and cooling system, you might make sure that your filter is up to the task.

Specifically, you will want to consider the filter's. Minimum Efficiency Reporting Value, or MERV rating. With these, higher is better.

A MERV rating of 13 or higher is ideal, as that will catch at least 90% of three to 10 micron particles, and 75% or more of smaller ones. And be sure to actually have the system running, even if it's just on circulate, so that the filter gets the chance to work. There's also the option of a free-standing air purifier.

For these, you will want a high MERV or a certified HEPA filter. That means it's passed a different test that ensures it captures 99.97% of particles exactly 0.3 microns in size so it's super good at filtering smoke, actually. You should also check out something called the “clean air delivery rate” or CADR.

This is essentially how quickly the air passes through the unit. The goal is to have the purifier pull the junk out of the air before you breathe it in, so you'll want it to refresh the total volume of the room several times an hour. Bigger rooms need bigger CADRs.

Some purifiers even list rates for different types of pollutants. Tobacco smoke represents the finest of these, so look at that if you see it. But avoid any filter that says that it uses ozone.

Remember, ozone's one of the things AQI looks for it's actually an irritant in its own right! You can even DIY a purifier in a pinch by connecting a high-MERV filter to a box fan! Finally, once you've made a clean space, it's probably a good idea not to spoil it.

So, you may want to avoid doing things that add to airborne particles, like lighting candles, smoking, using gas stoves, or frying food. And that's the quick and dirty… or, hopefully, quick and clean... on wildfire smoke. We hope it helps you breathe a little easier.

Thanks for watching this episode of SciShow News! And a special shout out to today's President of Space, Charles Szasz. We salute you, Charles!

We wouldn't be able to cover the latest science news if it weren't for patrons like Charles, so we're very grateful for their continued support. If you want to learn more about our awesome patron community and how you, too, can become President of Space, you can head on over to Patreon.com/SciShow. [♩OUTRO].