Moderate (51-100) AQI Cities

An AQI between 51 and 100 falls into the EPA's "Moderate" category. Air quality is generally acceptable for the broad public, but pollutant concentrations are high enough that a small subset of unusually sensitive people — primarily those with severe respiratory conditions — can feel symptoms. The EPA flags Moderate days as worth watching, not as cause for general concern.

72 of 1,020 monitored US cities have a 5-year average AQI in the moderate range (51-100). That is 7.1% of the EPA-monitored cities tracked here.

Most outdoor activity is safe at Moderate AQI. Schools should run normal outdoor PE and recess. Healthy adults can train for races, bike to work, and exercise as planned. The main daily-life adjustment: people in the most-sensitive subgroups should avoid prolonged or intense outdoor exertion when AQI is in the upper end of the Moderate range (around 80-100).

Long-term residence in cities that average Moderate AQI is associated with measurably higher rates of asthma in children, accelerated lung function decline, and modestly higher cardiovascular mortality compared to Good-AQI cities. The effect is real but smaller than the difference between Moderate and Unhealthy. The biggest health upside from local advocacy in Moderate-AQI cities comes from preventing slippage into Unhealthy territory during pollution events.

A HEPA air cleaner sized to a bedroom or living area provides meaningful protection during the worst pollution windows — particularly during summer ozone peaks and wildfire smoke events. Sign up for AirNow.gov alerts at your specific zip code (city-level numbers can mask hotspots near freeways and industrial sources). For chronic respiratory conditions, talk to a pulmonologist about whether a daily controller medication makes sense given your exposure profile.

Moderate AQI is the most common reading for U.S. metros and reflects the typical blend of vehicle exhaust, industrial emissions, and seasonal pollution events (summer ozone, winter wood smoke, occasional wildfire smoke). Cities cluster in the Moderate range when their underlying emissions are average for U.S. urban areas and their geography neither concentrates nor disperses pollution unusually well.