When the Air Quality Index (AQI) crosses into “unhealthy” territory (151 or above), your priority is reducing how much polluted air you breathe. That means getting indoors, filtering the air around you, and limiting physical exertion until conditions improve. The steps you take in the first few hours matter, especially if you have asthma, COPD, or young children at home.
Check the AQI and Know What It Means
Before deciding how aggressively to protect yourself, check the current AQI at AirNow.gov or through a weather app. The scale runs from 0 to 500, and the categories that require action start at “Unhealthy for Sensitive Groups” (101 to 150) and escalate through “Unhealthy” (151 to 200), “Very Unhealthy” (201 to 300), and “Hazardous” (301 and above). At 151, everyone can experience symptoms like coughing, throat irritation, and shortness of breath, not just people with lung conditions.
If you want hyperlocal readings, low-cost sensors like PurpleAir can fill gaps between official monitoring stations. The EPA has developed correction equations that adjust these sensor readings so they’re comparable to data from regulatory-grade monitors, meaning you can trust the numbers on the AirNow Fire and Smoke Map even when they come from community sensors.
Get Indoors and Seal Your Space
The single most effective step is moving inside and keeping polluted air out. Close all windows and doors. If your home has visible gaps or drafts, stuff them with damp towels. Turn off exhaust fans and range hoods except for very brief use, because they create negative pressure that pulls smoky or polluted air in from other parts of the house.
If you have central air conditioning, switch it to recirculate mode so it’s not drawing in outside air. Look for a “fresh air” setting or intake damper and make sure it’s closed. Then set the fan to “On” rather than “Auto” so air continuously passes through the filter, even when the system isn’t actively heating or cooling. For window air conditioners, close the outdoor air intake and run the unit normally. Avoid single-hose portable air conditioners during smoke events, as they also pull outside air in.
Create a Clean Room
If you can’t filter your whole home, designate one room as a clean room. Pick a bedroom or other space where you can close the door, seal it well, and spend most of your time. The EPA recommends choosing a room that’s comfortable to stay in for hours, with easy access to a bathroom and no fireplace. Run a portable air purifier or a DIY filter box in that room and keep the door shut.
Filter the Air You’re Breathing
A portable air purifier with a HEPA filter is the gold standard for a single room. If you don’t have one (and stores are sold out, as often happens during wildfire season), you can build a surprisingly effective alternative in about 15 minutes.
A Corsi-Rosenthal box uses four MERV-13 furnace filters (20 by 20 inches), a standard 20-inch box fan, duct tape, and a piece of cardboard. Tape the four filters together into a cube with the airflow arrows pointing inward, seal a piece of cardboard across the bottom, and mount the box fan on top blowing outward. Testing has shown these DIY purifiers deliver clean air delivery rates comparable to commercial units costing several hundred dollars. They’re loud, but they work.
For your central HVAC system, upgrading to a MERV-13 filter improves particulate removal significantly. One caution: not every system can handle the increased airflow resistance of a denser filter. Check your HVAC manual or call a technician before making the switch, since a filter that’s too restrictive can strain the blower motor.
Protect Yourself Outdoors
Sometimes you can’t avoid going outside. A well-fitting N95 respirator is your best option. These masks filter at least 95% of fine particles down to 0.1 microns, and their efficiency climbs to roughly 99.5% for larger particles. The key word is “well-fitting.” Gaps around the nose or cheeks let unfiltered air bypass the mask entirely.
KN95 respirators are a reasonable alternative, though their filtration efficiency is more variable, ranging from about 80% to 97% depending on the specific product. Surgical masks filter roughly 15% less than N95s. Cloth masks made from cotton or polyester filter about 70% less than N95s, making them largely ineffective against fine particulate pollution. If you’re going to bother wearing a mask on a bad air day, make it an N95 or KN95.
Limit Physical Activity
Exercise dramatically increases how much air you pull into your lungs. During moderate exertion, your breathing rate can double or triple, which means you inhale two to three times as many pollutant particles as you would sitting still. When the AQI is in the unhealthy range, move workouts indoors or skip them entirely.
People who are older or unusually sensitive to pollution should consider scaling back outdoor exercise even when the AQI is in the moderate range (51 to 100), according to EPA guidance. For everyone else, anything above 150 is a clear signal to avoid running, cycling, or other vigorous activity outside. If you coach youth sports or manage outdoor workers, cancel or relocate activities when the AQI hits unhealthy levels.
Reduce Pollution Sources Inside Your Home
Indoor air quality can deteriorate on its own if you’re adding pollutants while everything is sealed up. Avoid burning candles, using gas stoves more than necessary, smoking, or vacuuming without a HEPA-filtered vacuum. Frying food at high heat generates fine particles that compound whatever pollution is seeping in from outside. If you need to cook, keep it brief and low-temperature when possible.
Protect Yourself While Driving
Your car cabin can accumulate high concentrations of particulate matter, especially in traffic. Switching your vehicle’s ventilation to recirculate mode makes a measurable difference. With a new cabin filter and 70% recirculation, in-cabin PM2.5 drops by about 55% compared to pulling in outside air. Even with an older filter, recirculation still cuts particle levels by roughly 39%. Keep your windows up and your recirculation button on until conditions improve.
Replace your cabin air filter regularly, especially if you live in an area with frequent smoke or pollution events. A clogged or aged filter loses a significant portion of its filtration capacity.
Who Faces the Highest Risk
Children, older adults, pregnant people, and anyone with asthma, COPD, or heart disease are more vulnerable to the effects of poor air quality. Children are at particular risk not because their lungs are weaker in the short term, but because they tend to be more active outdoors and because long-term exposure during childhood can impair lung growth over time.
If you have asthma, follow your asthma action plan closely on bad air days. Make sure rescue inhalers are accessible and not expired. Common symptoms during high-pollution episodes include coughing, chest tightness, wheezing, shortness of breath, and unusual fatigue. These symptoms are your signal to reduce exposure further, not to push through.
Know the Symptoms to Watch For
Short-term exposure to unhealthy air typically causes irritation in the eyes, nose, and throat. You may notice a scratchy throat, a dry cough, or a slight burning sensation in your chest when breathing deeply. Some people develop headaches or feel unusually tired.
These symptoms generally resolve within a day or two once air quality improves and you’ve limited your exposure. If you experience significant shortness of breath, chest pain, or worsening symptoms despite being indoors with filtered air, that warrants medical attention, particularly if you have a preexisting heart or lung condition. Persistent coughing or breathing difficulty that continues after the air clears is also worth following up on.