Updated April 2026 · EPA Air Quality System
Air Quality Report Card
Search for any US city to see its Air Quality Grade, median AQI, 5-year trend, and unhealthy day count based on 10 years of EPA data.
This Air Quality Report Card looks up any of 1,020 U.S. cities tracked by EPA monitoring stations and returns an A-F Air Quality Grade, the current and 5-year median AQI, the 10-year trend direction, and the dominant pollutant. The national average across tracked cities is a 5-year median AQI of 39.
According to EPA Air Quality System data analyzed by AirHistory.org, air quality grades are calculated from 10 years of AQI monitoring data, weighing average AQI (40%), trend direction (30%), unhealthy days (20%), and worst pollutant severity (10%).
How to Read the Air Quality Report Card
The report card returns four headline numbers plus a letter grade. The 5-year median AQI is the typical air quality reading for that city across the past five complete calendar years of EPA data — a more reliable signal than any single day or month. The current median AQI shows the most recent year on file. The 10-year trend labels the city as Improving, Stable, or Worsening based on a linear regression slope across the past decade. The dominant pollutant identifies which of the six EPA-regulated pollutants drove the highest subindex on the most monitored days.
EPA categorizes any day with AQI 0-50 as Good, 51-100 as Moderate, 101-150 as Unhealthy for Sensitive Groups, 151-200 as Unhealthy, 201-300 as Very Unhealthy, and 301+ as Hazardous. The report card surfaces the count of days in the Unhealthy for Sensitive Groups category or worse over the past five years, which is the count most relevant for residents with asthma, COPD, heart disease, pregnancy, young children, or older adults.
What This Tool Does Not Show
The report card is not a real-time monitor. For hour-by-hour readings at your specific zip code, use EPA AirNow — AirNow streams live data from federally certified monitors and is the right tool for daily exercise or commute decisions. The bulk historical files this tool builds on come from the EPA Air Quality System Annual AQI by County program.
The report card also does not measure indoor air quality, which can deviate sharply from outdoor readings depending on cooking sources, ventilation, and HEPA filtration. The World Health Organization air quality guidelines publish health-protective concentration thresholds for the same pollutants the EPA tracks, generally tighter than U.S. National Ambient Air Quality Standards.
How the A-F Grade Is Calculated
Each city's Air Quality Grade is a weighted composite of four signals taken directly from the EPA AQS dataset: 5-year median AQI (40 percent), 10-year trend slope (30 percent), unhealthy days per year (20 percent), and dominant pollutant severity (10 percent). The composite produces a 0-100 score that maps to a letter grade: A (80-100), B (65-79), C (50-64), D (35-49), F (0-34). Read the full methodology for definitions, edge cases, and update cadence.
Frequently Asked Questions
How do I check the air quality in my city?
Type your city name into the search box above. The tool searches across 1,020 U.S. cities tracked by EPA monitoring stations and returns an Air Quality Report Card with the city's current median AQI, 5-year median AQI, A-F grade, and 10-year trend direction. Results draw directly from the EPA Air Quality System (AQS) Annual AQI by County dataset.
What does the Air Quality Grade mean?
The Air Quality Grade is a 0-100 composite score that condenses a decade of EPA monitoring data into a single A-F letter. It weights the 5-year median AQI at 40 percent, 10-year trend slope at 30 percent, the count of "Unhealthy for Sensitive Groups" days per year at 20 percent, and the dominant pollutant type at 10 percent. Of the 1,020 cities in the dataset, 50 earn an A and 4 are graded F.
Why is my city showing a different AQI than AirNow.gov right now?
AirNow shows real-time hourly readings from individual monitors near you, while this tool reports a 5-year median computed from EPA's annual aggregate data. A single afternoon ozone spike or wildfire smoke event will appear on AirNow but will not move the long-run median much. Use AirNow for "should I run outside today" decisions and use this tool for "is this city's air reliably clean year-round" decisions.
How often is this air quality data updated?
The dataset refreshes whenever the EPA publishes a new Annual AQI by County file, typically once per year covering the prior calendar year. The current dataset was last refreshed April 2026. Historical readings are stable and do not change retroactively unless the EPA reissues a corrected dataset.
What pollutants does the AQI track?
EPA computes the Air Quality Index from five regulated pollutants: ground-level ozone, fine particulates (PM2.5), coarse particulates (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and sulfur dioxide (SO2). The AQI for any given day is the highest single-pollutant subindex measured. Most cities are dominated by either PM2.5 (combustion, wildfire smoke) or ozone (summer photochemical formation), and the report card identifies which pollutant drives that city's grade.
This Air Quality Report Card looks up any of 1,020 U.S. cities tracked by EPA monitoring stations and returns an A-F Air Quality Grade, the current and 5-year median AQI, the 10-year trend direction, and the dominant pollutant. The national average across tracked cities is a 5-year median AQI of 39.