When people ask "is the air bad where I live," they usually expect a yes or no. The honest answer has three numbers, and they behave differently. We now show all three for every US county on your free ZIP report, from CDC Environmental Public Health Tracking estimates. Here is what each one means and what to do about the ones that are high.
PM2.5 is fine-particle pollution - soot from traffic, industry, wood smoke, and wildfires, in particles small enough to pass deep into the lungs and into the bloodstream. Long-term exposure is the number health research cares most about: it is linked to heart disease, stroke, and lung conditions.
In 2024 the EPA tightened the annual health standard to 9 micrograms per cubic meter. Most US counties sit under it; the ones that don't cluster around dense traffic corridors, industrial zones, and California's Central Valley. If your county's average is above 9, the air on an ordinary day - not a smoke day, an ordinary one - exceeds the federal health standard, and indoor filtration stops being optional for sensitive households.
The second number counts days over the short-term limit (35 micrograms per cubic meter over 24 hours). These spikes are mostly wildfire smoke and, in some valleys, winter wood-burning trapped by inversions. A county can have a clean annual average and still rack up a brutal smoke week - Seattle's 2022 wildfire season is a textbook case.
Spike days are the ones you can actually manage: they are visible, forecast, and short. On smoke days, keep windows closed, run a HEPA purifier, and skip the outdoor workout.
Ozone is different. It is not smoke; it is a gas that forms when vehicle and industrial emissions cook in hot, sunny air, which is why it peaks on summer afternoons. The standard is 70 parts per billion over 8 hours. High-ozone counties are usually hot, sunny metros - Los Angeles remains the national example.
Ozone's practical impact lands on kids playing outside, outdoor workers, and anyone with asthma: it inflames airways at exactly the times you most want to be outdoors. The management is scheduling, not sealing: on ozone-alert days, shift exertion to mornings.
High annual average: filter indoor air year-round. A HEPA purifier sized to the bedroom and main living space, plus a MERV-13 filter in your HVAC, meaningfully cuts what you breathe for most of the day.
Smoke-day counts: get ahead of events. Sign up for AirNow alerts, keep purifier filters spare, and treat a smoke forecast like a weather forecast.
Ozone days: time-shift. Morning practice instead of afternoon; watch the AQI before sending asthmatic kids out at 4pm.
One honesty note, because it matters: these county figures are modeled estimates - the CDC combines monitor data with satellite and weather models to cover counties without monitors. They are a screening view of your area, not a sensor on your street. For today's actual conditions, AirNow.gov is the live source; our air quality guide goes deeper on all of this, and your county's radon zone sits on the same report.
Which matters more, the annual average or the bad days?
For long-term health risk, the annual average. For day-to-day decisions, the bad-day counts. High-average counties need standing indoor filtration; spike-prone counties need an alert habit.
Do air purifiers actually work for wildfire smoke?
Yes - a properly sized HEPA purifier in a closed room measurably drops fine-particle levels during smoke events. Size it to the room's square footage and run it on high while smoke lasts.
Does ozone matter if nobody in my family has asthma?
Less, but not zero. Healthy adults exercising hard on high-ozone afternoons still show temporary lung-function dips, and kids' developing lungs are more sensitive regardless of asthma. The fix is cheap: shift hard outdoor exercise to mornings on alert days.
My county has no air monitor. Are these numbers made up?
They are modeled, and labeled that way. The CDC gap-fills unmonitored counties using satellite and weather data calibrated against real monitors. It is a credible estimate, not a measurement - which is exactly how we present it.