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America's historic 250th Independence Day celebrations ended with an unexpected consequence as fireworks smoke blanketed several major cities, temporarily sending air pollution soaring. Washington, D.C., Detroit, Los Angeles and other metropolitan areas saw sharp spikes in PM2.5 pollution after thousands of public and private fireworks displays lit up the skies. Detroit briefly ranked as the world's most polluted major city, while parts of Washington and Los Angeles recorded hazardous air quality levels. Officials urged residents in some areas to limit outdoor activity as thick smoke lingered into the morning. Watch the dramatic visuals, air quality maps and the full impact of America's biggest Fourth of July celebration.