Grade D Air Quality Cities

A Grade D means a 5-year median AQI elevated above the U.S. average (typically 80-95), often with worsening trends or a high count of unhealthy days. These cities have meaningfully more air pollution than the typical U.S. metro, and the daily picture often swings into the "Unhealthy for Sensitive Groups" or "Unhealthy" range during peak season.

43 of 1,020 monitored US cities currently have a Grade D Air Quality rating, representing 4.2% of all tracked areas.

Sensitive groups — children, pregnant women, older adults, people with asthma, COPD, heart disease, diabetes — should treat AQI alerts as essential daily input. Healthy adults will start feeling effects (eye/throat irritation, mild breathing difficulty during exercise) on the worst days and should plan accordingly. Outdoor workers face the highest occupational exposure.

On flagged days, sensitive groups should avoid outdoor exertion and keep windows closed. Schools in Grade D areas often run "indoor recess" protocols and cancel outdoor sports practices when AQI exceeds 150. A HEPA air cleaner sized to a bedroom or family room is a worthwhile investment for any household.

Grade D cities typically share one of three patterns: California Central Valley geography (pollution trapped between mountain ranges with limited ventilation), wildfire-smoke exposure in the western states, or concentrated industrial and freight corridors (parts of the Ohio Valley, Houston ship channel, port-adjacent neighborhoods).