Delaware is under a "code red" air quality index on July 16 for airborne particles and a "code orange" for ozone due to smoke from Canadian wildfires spreading south, along with high temperatures.

Millions of people in the Great Lakes, Northeast and mid-Atlantic states muddled through another day of unhealthy air from uncontrolled wildfires on Friday.

Air quality indices, which measure fine particulate matter, the tiny pollutants emitted by wildfires, surpassed historic thresholds reached in 2023 during wildfires wafting from Quebec, Canada .