When outdoor air quality drops into unhealthy ranges, the most effective thing you can do is stay indoors with windows and doors closed and run some form of air filtration. That sounds simple, but doing it well requires a few specific steps, from sealing your home properly to choosing the right mask if you do need to go outside. The actions that matter most depend on how bad the air actually is, so checking your local Air Quality Index is always the starting point.
Check the AQI Before Anything Else
The Air Quality Index runs from 0 to 500 and is color-coded so you can quickly gauge how serious conditions are. At 0 to 50 (green), air quality is satisfactory. At 51 to 100 (yellow), it’s acceptable but may bother people who are unusually sensitive. Once you hit 101 to 150 (orange), anyone with asthma, heart disease, or other respiratory conditions can start feeling effects. At 151 to 200 (red), even healthy adults may notice symptoms. Above 200 (purple), everyone is at increased risk, and above 300 (maroon) is an emergency-level health warning.
AirNow.gov is the official source, pulling data from EPA-certified monitors that are rigorously calibrated. Updates come hourly, and the site powers most of the air quality alerts you see on weather apps. If you want more localized, real-time data, PurpleAir runs a dense network of consumer-grade sensors that update every 10 minutes. Their raw readings can run higher than official numbers because the sensors aren’t corrected for humidity and particle type. The EPA and U.S. Forest Service addressed this by creating the AirNow Fire and Smoke Map, which combines official monitor data with PurpleAir readings adjusted using a correction algorithm. That map is your best single tool during wildfire events.
Keep Outdoor Air From Getting Inside
Closing windows and doors is obvious, but homes leak air in dozens of places you might not think about. Gaps around window frames, door thresholds, bathroom exhaust vents, and dryer ducts all let smoky air seep in. Two inexpensive fixes handle most of the problem: caulk for cracks between stationary components like window frames, and weatherstripping for parts that move, like doors and operable windows. Replacing worn door-bottom sweeps with ones that have pliable sealing gaskets makes a noticeable difference. These materials typically pay for themselves in energy savings within a year, so they’re worth installing even before a bad air quality event.
If your home has a fresh-air intake on the HVAC system, switch it to recirculate mode so it’s not pulling outdoor air in. Avoid running kitchen or bathroom exhaust fans when possible, since they create negative pressure that draws polluted air through every gap in your home’s envelope.
Filter the Air You’re Breathing Indoors
If you have central heating and cooling, upgrading your furnace filter to MERV 13 is one of the most effective steps you can take. The EPA specifically recommends MERV 13 filters for removing the very fine particles found in wildfire smoke. Run your system’s fan continuously (most thermostats have a “fan on” setting separate from heating or cooling) to keep air circulating through the filter even when the system isn’t actively heating or cooling.
A standalone HEPA air purifier works well for individual rooms. Place it in the room where you spend the most time, typically a bedroom. Look for a unit with a Clean Air Delivery Rate matched to the room’s square footage.
If you don’t have a purifier and can’t find one during an air quality emergency, you can build a surprisingly effective DIY filter. Known as a Corsi-Rosenthal box, it uses four MERV 13 furnace filters taped together into a cube shape with a standard box fan on top. EPA testing measured a wildfire smoke Clean Air Delivery Rate of about 111 cubic feet per minute for a single-filter version, and the four-filter box design performs even better. The total cost is usually under $100, and the materials are available at any hardware store.
Wear the Right Mask Outdoors
If you need to go outside during poor air quality, mask choice matters a lot. N95 respirators filter at least 95% of fine particles down to 0.3 microns. Surgical masks, by contrast, only capture about 53 to 75% of those same small particles because they don’t seal tightly to the face. The difference is significant: wildfire smoke and other pollution sources produce enormous quantities of PM2.5, particles smaller than 2.5 microns that are small enough to pass through the lungs and enter the bloodstream, eventually reaching the heart and other organs.
For an N95 to work properly, it needs to fit snugly with no gaps around the nose or chin. Facial hair breaks the seal and dramatically reduces protection. KN95 masks offer similar filtration in a slightly different design. Cloth masks and bandanas provide almost no meaningful protection against fine particulate matter.
Move Exercise Indoors
Exercise increases your breathing rate and the volume of air you pull into your lungs, which multiplies your exposure to pollutants. EPA guidance for schools recommends moving all physical activities indoors once the AQI reaches the “Unhealthy” category (151 and above). For sensitive groups, the threshold is lower: at “Unhealthy for Sensitive Groups” (101 to 150), the recommendation is to reduce intensity, take more frequent breaks, and consider moving longer or more intense activities inside.
If you’re a healthy adult and the AQI is in the moderate range (51 to 100), outdoor exercise is generally fine, but consider shortening your workout or choosing a less intense activity. At any AQI level, pay attention to symptoms like coughing, chest tightness, or unusual shortness of breath, and stop immediately if they appear.
Why Bad Air Quality Hits Your Body Hard
Fine particulate matter is the primary concern during most poor air quality events, whether from wildfire smoke, industrial pollution, or vehicle exhaust. These particles are so small that they bypass your nose and upper airways, penetrate deep into the lower respiratory tract, and cross through the lung lining into your bloodstream. From there, they can reach the heart, brain, and other organs.
Short-term exposure causes eye, nose, and throat irritation, coughing, chest tightness, and wheezing. It can also trigger headaches, dizziness, and nausea. For people with asthma or chronic lung disease, even a few hours of exposure can cause a flare-up. People with heart conditions face increased risk of cardiac events. Children, older adults, pregnant women, and anyone who works outdoors are also at higher risk because of either greater vulnerability or greater exposure.
What People With Asthma Should Do Differently
If you have asthma, the CDC recommends monitoring air quality reports daily through radio, TV, or online sources, especially during wildfire season or high-pollution periods. Plan outdoor activities for times when air quality is at its best, typically early morning before traffic peaks or after rain. When wildfires are active, stay away from areas with visible smoke and remain indoors as much as possible.
Keep your quick-relief inhaler accessible at all times during poor air quality days, even if you haven’t needed it recently. Follow your asthma action plan, and if you don’t have one, work with your doctor to create a written plan that specifies exactly which medications to use and when to escalate care based on your symptoms.
Cleaning Up After the Air Clears
Once outdoor air quality improves, you’ll want to deal with any particles that settled on indoor surfaces during the event. The California Department of Public Health recommends wiping hard surfaces with a damp cloth and using a wet mop on floors. Vacuum carpets and upholstery with a HEPA-filter vacuum. The key rule: do not dry sweep with a broom. Sweeping kicks fine particles back into the air, where you’ll breathe them in all over again. Continue running a HEPA air purifier for a few hours after cleaning to capture anything that gets stirred up.
If ash has settled outdoors on your car, patio, or walkways, wet it down before disturbing it. Ash particles are extremely fine and irritating to the lungs. Wear an N95 mask during outdoor cleanup, even if the AQI has returned to normal, because the act of cleaning re-suspends settled particles right in your breathing zone.