Grade C Air Quality Cities
433 cities with average air quality
Grade C means average air quality with regular moderate-to-unhealthy days for sensitive groups. These cities are scored using 10 years of EPA Air Quality System data, weighted across 5-year median AQI (40%), trend direction (30%), unhealthy days per year (20%), and worst-pollutant severity (10%).
What "Grade C" Actually Means
A Grade C means a 5-year median AQI in the solid "Moderate" range (typically 65-80), mixed trends, and a meaningful count of unhealthy days each year. These are average U.S. cities — air quality is acceptable for the broad public but has enough pollution events to matter for sensitive groups.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst windows. People with asthma, heart disease, COPD, pregnancy, or young children should reduce prolonged or intense outdoor exertion on flagged days, and consider running indoor HEPA air cleaners during peak season.
Grade C and Daily Life
Most outdoor activity is fine on most days. Schools usually run normal outdoor recess but may invoke "indoor recess" protocols during the worst pollution days. Outdoor workers should rotate tasks or take indoor breaks on flagged days.
Long-Term Health Picture
Long-term residence in Grade C cities is associated with measurably higher rates of asthma in children, accelerated lung function decline, and modestly higher cardiovascular mortality compared to Grade A and B cities. The effect is real but smaller than the gap between Grade C and below-average grades.
Where Grade C Cities Cluster
Grade C is the most common rating for mid-size and large U.S. metros. The typical Grade C city has the standard mix of vehicle exhaust, industrial emissions, and seasonal pollution events (summer ozone, winter wood smoke, occasional wildfire smoke) without unusual concentrating geography.
Among the 433 Grade C cities tracked here, the largest concentrations are in TX (26), CA (24), WI (23), CO (19), FL (19). The dominant pollutant in these cities is PM2.5 (258 cities), followed by Ozone (171), PM10 (3).
All Grade C Cities
Frequently Asked Questions
A Grade C means a 5-year median AQI in the solid "Moderate" range (typically 65-80), mixed trends, and a meaningful count of unhealthy days each year. These are average U.S. cities — air quality is acceptable for the broad public but has enough pollution events to matter for sensitive groups.
433 of 1,020 monitored US cities currently have a Grade C Air Quality rating, representing 42.5% of all tracked areas.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst windows. People with asthma, heart disease, COPD, pregnancy, or young children should reduce prolonged or intense outdoor exertion on flagged days, and consider running indoor HEPA air cleaners during peak season.
Most outdoor activity is fine on most days. Schools usually run normal outdoor recess but may invoke "indoor recess" protocols during the worst pollution days. Outdoor workers should rotate tasks or take indoor breaks on flagged days.
Grade C is the most common rating for mid-size and large U.S. metros. The typical Grade C city has the standard mix of vehicle exhaust, industrial emissions, and seasonal pollution events (summer ozone, winter wood smoke, occasional wildfire smoke) without unusual concentrating geography.
/methodology
The this entity category groups every U.S. air quality and pollution monitoring entity sharing this attribute. The list above is the data; the paragraphs below explain what the grouping means against the broader the EPA Air Quality System (AQS) distribution and how to read the relative rankings within the category.
For readers using this category as a starting point, the per-entity detail pages linked from the table above carry the underlying the EPA Air Quality System (AQS) data in full. The category-level view is the filter; the per-entity pages are the actual answer.
Source: EPA Outdoor Air Quality Data, 2026.