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.