City AQI Rankings

The Air Quality Index (AQI) is a standardized measure developed by the U.S. Environmental Protection Agency to communicate how polluted the air is and what associated health effects might be a concern. The index runs from 0 to 500 — higher values indicate worse air quality and greater health risk. An AQI below 50 is considered "Good," meaning air pollution poses little or no risk. Values above 100 are "Unhealthy for Sensitive Groups," and above 200 is "Very Unhealthy" for everyone.

City rankings are determined by the dominant pollutant at each location — typically PM2.5 (fine particulate matter) or ground-level ozone. PM2.5 is the most widespread and dangerous air pollutant globally, responsible for millions of premature deaths each year. Cities with high industrial activity, heavy traffic, or exposure to wildfire smoke tend to rank worst. Coastal cities with strong sea breezes and cities surrounded by forests often rank best due to natural air cleaning.

These rankings update in real time from monitoring stations worldwide. For a deeper understanding of what each AQI level means and how to protect yourself, read our Air Quality & Health Guide or explore the AQI Scale reference.