When air quality drops, the most important thing you can do is limit your exposure to outdoor air. That means staying inside with windows closed, filtering the air in your home, and wearing proper protection if you must go outside. The specific steps depend on how bad the air actually is, which you can check in seconds using the Air Quality Index.
Check the AQI Before Anything Else
The Air Quality Index runs from 0 to 500 and is color-coded so you can quickly gauge risk. You can check it on AirNow.gov or most weather apps. Here’s what each level means in practical terms:
- Green (0 to 50): No precautions needed. Go about your day normally.
- Yellow (51 to 100): Fine for most people, but those with asthma, heart disease, or unusual sensitivity to pollution should limit prolonged outdoor exertion.
- Orange (101 to 150): Sensitive groups, including children, older adults, and anyone with lung or heart conditions, should reduce outdoor activity. Healthy adults can still exercise outside but may want to shorten workouts.
- Red (151 to 200): Everyone should cut back on prolonged outdoor activity. Move exercise indoors.
- Purple (201 to 300): Avoid outdoor activity entirely if possible. This is a health alert for the general population.
- Maroon (301+): Emergency conditions. Stay indoors with filtered air.
Most “bad air quality” alerts you’ll encounter during wildfire season or smog events fall in the orange-to-purple range. The steps below apply any time the AQI is above 100, and become increasingly urgent as the number climbs.
Why Polluted Air Is Harmful
The main threat during poor air quality events is fine particulate matter, tiny particles smaller than 2.5 microns across. For reference, that’s about 30 times smaller than a human hair. These particles are so small they pass through your nose’s natural filtration, travel deep into your lungs, and can cross into your bloodstream through the air sacs where oxygen exchange happens.
Once in your body, these particles trigger oxidative stress, essentially damaging cells the same way rust eats metal. The particles carry toxic compounds on their surface, including metals like iron and copper plus chemical pollutants, which generate free radicals that inflame lung tissue. This is why even a few hours of exposure can cause coughing, throat irritation, and chest tightness in otherwise healthy people. For anyone with asthma or heart disease, the inflammatory response can be severe enough to trigger an attack or cardiac event.
Seal Your Home and Filter Indoor Air
Staying inside only helps if you keep the bad air out. Close all windows and doors. If you have a central HVAC system, set it to recirculate rather than pulling in fresh air, and make sure you have a clean filter rated MERV-13 or higher. Turn off whole-house fans, attic fans, or window units that draw outdoor air in. Stuff damp towels under doors that lead to garages or other unsealed spaces.
A portable air purifier with a HEPA filter is one of the most effective tools you can use. When shopping for one, look at the Clean Air Delivery Rate for smoke, which covers the smallest, hardest-to-capture particles (0.09 to 1.0 microns). The purifier’s smoke CADR should be high enough to cycle the air in your room several times per hour. As a rough guide, multiply your room’s volume in cubic feet by 5 (for five air changes per hour), then divide by 60 to get the CADR in cubic feet per minute you need. For a standard 12-by-15-foot bedroom with 8-foot ceilings, that works out to about 120 CFM.
If you can’t afford a commercial HEPA purifier, you can build what’s known as a Corsi-Rosenthal box for under $60. It’s a simple cube made from MERV-13 furnace filters taped around a standard 20-inch box fan. In testing published in Aerosol Science and Technology, this DIY setup delivered a clean air delivery rate of about 600 cubic feet per minute on its lowest setting, roughly double the output of the commercial HEPA purifiers it was tested against. It costs about $0.11 per unit of CADR compared to $0.74 to $0.86 for commercial units. You need five MERV-13 filters (three 20″x20″ and two 16″x20″) and a box fan. Tape the filters into a box shape with the airflow arrows pointing inward, set the fan on top blowing upward, and seal the edges with painter’s tape.
Wear the Right Mask Outside
If you need to go outside during a bad air quality day, a well-fitting N95 or KN95 respirator is the single best thing you can protect yourself with. N95s filter at least 95% of particles as small as 0.1 to 0.3 microns, and their efficiency actually improves for larger particles, reaching roughly 99.5% for particles 0.75 microns and above. That covers the full range of fine particulate matter in wildfire smoke and smog.
Surgical masks are significantly less effective, filtering about 15% fewer particles than N95s. Cloth masks are even worse. If you’re choosing between options, a KN95 (the Chinese standard equivalent) performs comparably to an N95 in filtration, though fit can vary more between brands. The key is a tight seal around your nose and chin. If air leaks around the edges, filtration percentage becomes irrelevant.
Adjust Exercise and Outdoor Plans
Physical activity increases your breathing rate and depth, which pulls more polluted air deeper into your lungs. At AQI levels above 100, sensitive groups should avoid prolonged or intense exercise outdoors. Once the AQI hits 151 or above, healthy adults should move workouts indoors too.
If you run, cycle, or do other cardio outside, the simplest rule is: the harder you breathe, the more pollution you inhale. A brisk walk pulls in far less air than a tempo run. On moderate air quality days (AQI 51 to 100), you can reduce risk by lowering your intensity and shortening your time outside. On unhealthy days, move to a gym or do home workouts in a filtered room. Swimming in indoor pools is another good option since the enclosed environment tends to have better air quality.
Protect Yourself While Driving
Your car can either shield you from pollution or concentrate it, depending on one setting: the recirculation button. When set to fresh air mode, your cabin’s particle levels reach 65% to 80% of outdoor concentrations within minutes, even with the cabin filter in place. Switch to recirculate, and particle concentrations drop to about 10% of outdoor levels.
The tradeoff is that recirculation causes CO2 to build up inside the cabin, which can reach 3,000 parts per million and make you drowsy on long drives. The practical solution is to use full recirculation during the worst stretches of your commute and briefly switch to fresh air every 20 to 30 minutes to flush CO2, then switch back.
Recognize Warning Signs
Some degree of throat irritation, mild coughing, and watery eyes is normal during bad air quality events. But certain symptoms signal something more serious. Seek emergency care if you experience chest pain, significant shortness of breath, wheezing that doesn’t resolve, confusion, dizziness, or fainting. Hoarseness and noisy breathing, particularly a high-pitched sound when inhaling (called stridor), can indicate airway swelling that needs immediate treatment.
People with asthma should keep rescue inhalers accessible and follow their action plan at the first sign of tightening. Anyone with heart disease should be especially vigilant, since fine particulate exposure can trigger cardiovascular events even before respiratory symptoms become obvious. Children and older adults tend to be affected sooner and more severely than healthy adults in their 20s and 30s, so watch them closely for any change in breathing pattern or energy level.