Published April 5, 2026 · Updated monthly
What Is a Good AQI Score? Air Quality Index Ranges Explained
A good AQI (Air Quality Index) score is between 0 and 50, classified as "Good" by the EPA. At this level, air pollution poses little or no risk. The AQI scale runs from 0 to 500, divided into six color-coded categories that indicate increasing levels of health concern.
The Six AQI Ranges
The EPA's Air Quality Index is the standard measure for communicating daily air quality. Each range corresponds to a different level of health concern:
| AQI Range | Category | Color | Health Impact |
|---|---|---|---|
| 0-50 | Good | Green | Air quality is satisfactory. No risk. |
| 51-100 | Moderate | Yellow | Acceptable. Some risk for sensitive individuals. |
| 101-150 | Unhealthy for Sensitive Groups | Orange | Children, elderly, and those with lung disease affected. |
| 151-200 | Unhealthy | Red | Everyone may experience health effects. |
| 201-300 | Very Unhealthy | Purple | Health alert. Serious effects for entire population. |
| 301-500 | Hazardous | Maroon | Emergency conditions. Everyone affected. |
What Each Range Looks Like in Practice
Numbers are abstract until you see them in context. Here are real US cities that typically fall into each AQI category based on their 5-year median AQI from EPA monitoring data:
Good (0-50): Cities With Clean Air
Cities in the "Good" range have consistently clean air year-round. These are typically coastal cities, northern communities, or areas with low industrial activity.
- Caguas, Puerto Rico, PR — 5-year avg AQI: 10, Grade: A
- Alexandria City, Virginia, VA — 5-year avg AQI: 6, Grade: A
- Cook, Minnesota, MN — 5-year avg AQI: 12, Grade: A
- San Juan, Puerto Rico, PR — 5-year avg AQI: 10, Grade: A
- Carbon, Wyoming, WY — 5-year avg AQI: 16, Grade: A
Moderate (51-100): Most American Cities
The majority of US cities fall in the Moderate range. Air quality is generally acceptable, but some pollutants may pose a moderate health concern for a very small number of people who are unusually sensitive to air pollution. This is where most mid-size metropolitan areas land.
Unhealthy for Sensitive Groups (101-150): Cities That Struggle
Cities in this range regularly trigger health advisories for children, the elderly, and those with asthma or heart disease. Wildfire smoke, industrial emissions, and heavy traffic are the usual culprits.
- Maricopa, Arizona, AZ — 5-year avg AQI: 90, Grade: F
- BAJA CALIFORNIA NORTE, Country Of Mexico, MX — 5-year avg AQI: 81, Grade: F
- Inyo, California, CA — 5-year avg AQI: 57, Grade: F
- San Bernardino, California, CA — 5-year avg AQI: 82, Grade: F
- Los Angeles, California, CA — 5-year avg AQI: 75, Grade: D
How AQI Is Measured
The AQI is calculated from five major air pollutants regulated by the Clean Air Act: ground-level ozone (O3), particle pollution (PM2.5 and PM10), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2). The EPA converts pollutant concentrations to a standardized 0-500 scale so the public can easily understand air quality conditions.
Each city's AQI reflects the worst pollutant reading at any given time. If ozone is at 65 and PM2.5 is at 42, the reported AQI is 65. Our Air Quality Grade goes further by weighting the 5-year average AQI, trend direction, unhealthy day count, and worst contaminant into a single A-F score.
Why AQI Matters for Your Health
Long-term exposure to elevated AQI levels is associated with increased rates of asthma, cardiovascular disease, and premature death. The American Lung Association estimates that over 137 million Americans live in areas with unhealthy air quality. Even Moderate AQI levels (51-100) can affect sensitive populations over time.
If you are considering relocating or want to understand your area's air quality trends, check our cleanest air cities ranking or look up your city comparison to see how your area stacks up.
Frequently Asked Questions
An AQI of 0-50 is considered safe for all outdoor activities. At 51-100 (Moderate), most people can still exercise outdoors, but unusually sensitive individuals should consider reducing prolonged exertion. Above 100, sensitive groups should limit outdoor activity.
The average median AQI across all monitored US cities is approximately 40-45, which falls in the Good range. However, this varies dramatically by region — cities in the West often have higher AQI due to wildfire smoke, while coastal cities tend to have lower readings.
Technically, AQI readings above 500 are considered "Beyond the AQI" and indicate emergency conditions. This has happened during extreme wildfire events in California and Oregon, where PM2.5 readings pushed AQI well above 500.
The EPA updates AQI readings hourly at monitoring stations across the country. Our Air Quality Grade uses annual averages from the EPA Air Quality System (AQS) database, covering 10 years of data from 2014-2023.
/methodology