Wildfire Smoke & Air Quality: What to Do When the Sky Turns Orange

Wildfire smoke isn't just regular air pollution

On a smoggy commute day in Houston or Los Angeles, the EPA might log AQI in the 80s. On the morning a wildfire plume settles over your neighborhood, that number can hit 300 in an hour. The composition is different too: where urban smog is mostly ozone and nitrogen dioxide, wildfire smoke is dominated by extremely fine particulate matter — PM2.5 — laced with carbon monoxide, formaldehyde, and benzene from incompletely burned wood.

The size is what makes it dangerous. PM2.5 is so small it bypasses the nose, the throat, and the bronchioles, and lodges deep in the alveolar sacs where oxygen and carbon dioxide are exchanged. From there, the smallest fraction passes directly into the bloodstream — which is why bad smoke days correlate with heart attacks and strokes, not just coughs.

The AQI scale, decoded

The Air Quality Index is a 0–500 scale designed by the EPA to make particle and ozone measurements legible to non-scientists. Six bands. Six colors. Each band is keyed to a public-health response — what's safe, who's at risk, what to do.

What each band actually feels like

Numbers are abstract. Here's a translation: at AQI 50, the air is clean enough that you can't smell smoke or taste it. At 150, you'll notice a slight scratchiness in your throat after an hour outside, and the sky has a visible orange-gray cast. At 300, the smoke is so thick the sun looks red, breathing feels like effort, and visibility drops below half a mile.

PM2.5 vs PM10: why the small stuff matters more

"Particulate matter" is a category, not a substance. PM10 includes coarse stuff — pollen, dust, mold spores — that mostly stops in your upper airway, makes you sneeze, and gets cleared. PM2.5 is the fine fraction that wildfires generate in obscene quantities, and it's the one that does the damage.

For scale: a single human hair is around 70 micrometers across. PM10 is one-seventh that. PM2.5 is one-twenty-eighth — small enough to pass through the cellular junctions in your lung tissue and into your blood. This is why the standard surgical mask, which does a fine job catching respiratory droplets at 5–10µm, fails on wildfire smoke.

Should I go outside? An interactive answer

The honest answer depends on two variables: today's AQI and how vulnerable your lungs are. Pick yours.

Activity guidance by AQI level

Same logic in matrix form, adapted from EPA AirNow's official activity-guide table. Use it to plan a day, plan a week, or figure out whether soccer practice should be cancelled.

When to call a doctor

Most smoke symptoms — burning eyes, sore throat, mild cough, headache — fade within hours of getting to clean air. Call a doctor if you have chest pain, persistent shortness of breath, dizziness, or a cough that doesn't ease after several hours indoors. For asthma, follow your action plan; if your reliever inhaler isn't working, that's an emergency.

Masks that actually work against smoke

One number matters: filtration efficiency at 0.3 micrometers, the hardest particle size for any filter to catch. N95 respirators clear that bar by definition. The rest of this hierarchy follows.

How to fit-check an N95 in 10 seconds

Strap goes high on the back of your head, second strap goes around the base of your neck. Pinch the nose wire to the bridge of your nose. Cup both hands over the mask and exhale sharply — if you feel air rushing past your cheeks or eyes, the seal is wrong. Reposition. The most common mistake is leaving the lower strap on top of the ears; it has to sit below them to seal the chin. Beards break the seal regardless of mask quality.

Sealing your home: the "clean room" method

You can’t fully seal a whole house — there are too many leaks. So don’t try. Instead, pick one small room, seal that, and run a purifier inside. Everyone (and pets) rides out the smoke event there. Click through the walkthrough to see how.

Build a Corsi–Rosenthal box-fan purifier

In 2020, Richard Corsi and Jim Rosenthal published the design that proved a $80 stack of HVAC filters and a box fan could match the clean-air delivery rate of a $700 commercial purifier. It's the single highest-leverage thing you can do for indoor air quality during a smoke event.

How long does it last?

Filters last 6–12 months in normal use; the fan lasts as long as any box fan would (years). Replace filters when they're visibly grayed or after a heavy multi-day smoke event. Run the unit on medium — high speed actually drops filtration efficiency because air rushes through the pleats too fast.

Stockpile the filters before fire season, not during

MERV-13 filters sell out instantly when smoke hits a major metro. Buy four sets in April for whatever fire season is in your region — May–October in the West, year-round in California, mostly summer in the South.

Smoke and vulnerable groups

The thresholds in the AQI scale are calibrated to "healthy adult." Some groups feel smoke harder, sooner. The rule for all of them: drop the threshold by one band.

When smoke means evacuate, not shelter

Most of the time, smoke is a sheltering problem, not an evacuation problem. But there are three scenarios where leaving is the right call.

You can't keep indoor air clean. If your indoor AQI stays above 200 despite a sealed room and filtration running, the smoke is winning. Get to cleaner air — often that's just a few hours' drive.

Anyone in the home has worsening symptoms. Persistent cough, shortness of breath, chest pain, dizziness — if a clean room doesn't ease them within an hour, leave or get medical care.

The wildfire itself is approaching. If you're getting smoke this thick, check the active-fire map for your region. If a perimeter is within 20 miles and winds are pushing it your way, smoke is the warning shot. Don't wait for the evacuation order — sensitive groups should leave proactively.

See active wildfires near you →

After the smoke clears

When AQI drops below 50 for a sustained period — typically a day or two of clean wind — you can open up. But "clean outside" doesn't mean "clean inside." A week of smoke leaves a residue you'll want to deal with.

The day-after checklist

Open every window for at least an hour to flush stale indoor air. Wipe hard surfaces with a damp cloth — dry dusting just resuspends the particles. Vacuum upholstery with a HEPA-filter vacuum if you have one; a regular vacuum can blow PM2.5 right back into the air. Wash bedding and curtains in soft fabrics. Replace your HVAC filter. Consider professional duct cleaning only if you ran central HVAC heavily during the smoke event without a MERV-13 filter installed.

Symptom timeline

Most healthy adults feel back to baseline within 24–48 hours of getting to clean air. Linger past that — persistent cough, exercise intolerance, chest tightness — and it's time to see a doctor. The chart below sketches symptom severity vs. exposure duration at common AQI bands.

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