What to Do When Air Quality Is Bad: AQI Guide and Safety Tips
The air around you carries more than oxygen. On any given day, it may also hold wildfire smoke from thousands of miles away, dust blown across the Atlantic from the Sahara, ground-level ozone cooked by summer heat, and pollen thick enough to coat your windshield. When those particles reach high enough concentrations, breathing becomes work for your body. The Air Quality Index was built to tell you when that threshold is being crossed and how seriously.
How the AQI Scale Works
The Air Quality Index runs from 0 to 500. Lower numbers mean cleaner air. The scale is divided into six color-coded categories: Good (0 to 50), Moderate (51 to 100), Unhealthy for Sensitive Groups (101 to 150), Unhealthy (151 to 200), Very Unhealthy (201 to 300), and Hazardous (301 and above). AQI readings are calculated from five major pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.
According to AirNow, the EPA-operated service providing real-time air quality data, most healthy adults can go about normal activity at Moderate levels with minimal concern. The calculus shifts at 100, where people with heart or lung disease, older adults, and children should begin reducing prolonged outdoor exertion.
What Pushes Air Quality Into Dangerous Territory
Weather is the most powerful driver of air quality swings. A heat dome acts as a lid on the atmosphere, trapping pollutants near the surface and holding them in place for days. That same heat accelerates the chemical reactions that produce ground-level ozone, the primary ingredient of smog.
Wildfires are a second major driver. Once smoke enters the atmosphere, upper-level winds carry it hundreds or thousands of miles from the fire itself. Canadian wildfire smoke has pushed into the Midwest and Northeast in recent years, spiking AQI readings in cities far from any burning. Saharan dust, transported across the Atlantic on trade winds during summer, produces similar effects across the Gulf Coast and Southeast.
Not every source is dramatic. Traffic exhaust, industrial emissions, and pollen contribute too. Each season has its own pattern: winter brings stagnant air that allows pollutants to accumulate; spring adds pollen and mold; summer heat and ozone combine to produce some of the worst air quality of the year; and fall leaf burning sends a fresh wave of particles back into the air.
Air Quality Is an Indoor Problem Too
When outdoor air quality is poor, heading inside and closing the windows is the right call. But indoor air is never fully sealed from outdoor conditions, and it comes with its own pollutants. Burning candles, cooking on gas or propane, and using aerosol sprays release particles directly into the air at home. Long, hot showers raise humidity and, over time, contribute to mold growth.
The CDC advises maintaining good indoor air quality year-round and being especially attentive when outdoor conditions are poor. A portable air purifier with a HEPA filter can significantly reduce indoor particle concentration. Ensuring that HVAC filters in your home and car meet current standards provides an additional layer of protection, and replacing filters more often during high-smoke or high-pollen seasons is worth the effort.
How to Protect Yourself When the AQI Rises
The most effective step is monitoring air quality before it becomes a problem. AirNow provides free real-time AQI data by ZIP code and issues alerts when local readings reach concerning levels. Setting up those alerts means you will know to act before heading outside, rather than after.
When outdoor air quality is unhealthy, stay inside and keep windows closed. Avoid adding to the indoor particle load: skip candles, gas stoves, and aerosol sprays until conditions improve. If you must go outside, a properly fitted N95 or KN95 mask filters fine particles effectively. Standard cloth masks and dust masks do not provide meaningful protection against particle pollution.
On days when the AQI is good, open the windows. Fresh outdoor air flushes accumulated indoor pollutants and prevents them from building up over time. Heat safety and air quality often overlap in summer — the same approach that helps you survive a heat wave, staying indoors during the hottest part of the day and reducing outdoor exertion, also limits your exposure during high-AQI events.
People with asthma, heart disease, or lung conditions, along with older adults and young children, face the greatest risk from air quality events and should lower their threshold for taking protective action.
Weather changes fast, so help your community stay prepared. Share this story with friends, family, or your group chat, and keep your forecast in the now with Weather Forecast Now.