Residents of Washington, DC, on Sunday briefly experienced the worst air quality of any major city in the world, according to a company that ranks pollution globally, as the capital reckoned with the aftermath of a massive, 40-minute Fourth of July fireworks show.

City officials issued a Code Red Air Quality Alert, asking residents to limit time outside, with a warning that the air is “unhealthy for seniors, kids, people with medical conditions” and that the general public may experience health issues.

DC slipped down to No. 26 on the air quality monitoring platform, IQAir, by 5:30 p.m. ET Sunday.

The fireworks show, organized by Freedom 250, a Trump-backed nonprofit tasked with putting on a series of semiquincentennial events, came as DC — and the Northeast more widely — suffered under an extreme heat wave. The district saw a triple-digit high temperature on Saturday, which primed the atmosphere for thunderstorms that saw the National Mall evacuated before the fireworks show.

Dr. Kisha Davis, chief health officer of nearby Montgomery County, Maryland, told CNN before the fireworks show Saturday that, “The air quality today is like running a marathon while smoking a cigarette,” adding that the 850,000-firework display around the National Mall would make matters worse.