Air quality across the Washington metropolitan area dropped sharply a day after the United States marked the 250th anniversary of the Declaration of Independence with what officials described as the largest fireworks display in history. Local authorities issued health warnings on Sunday after pollution levels rose significantly following the celebrations.

Air quality maps showed several hotspots with high levels of fine particulate matter, known as PM 2.5, across the region, reported PTI. Some of the highest pollution readings appeared near Capitol Hill and surrounding neighbourhoods.

According to the Environmental Protection Agency’s Air Quality Index (AQI), Washington recorded an AQI reading of 171 on Sunday. The level was more than double the reading recorded a day earlier and falls within the “unhealthy” category, where everyone may begin to experience health effects.

The decline in air quality came after the National Park Service organised a nearly 40-minute fireworks display on Saturday night to celebrate the country’s milestone anniversary.

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Around 860,000 pyrotechnic shells were launched from barges on the Potomac River as crowds gathered and chanted “USA, USA,”, reported PTI. Officials described it as the biggest fireworks show ever organised for the national celebration. By comparison, 2025’s display lasted about 10 minutes and used around 7,000 fireworks shells.

Air pollution increases after fireworks

Fireworks release large amounts of smoke, fine particles and gases into the atmosphere. These tiny particles, especially PM 2.5, can remain in the air for hours and travel across nearby areas. Following the celebrations, the Metropolitan Washington Council of Governments issued a Code Purple air quality alert for the District of Columbia and Northern Virginia.

A Code Purple alert means pollution has reached levels that can affect everyone’s health. Children, older adults and people with asthma or other breathing problems face a higher risk of illness when air quality reaches these levels.

The warning also came as temperatures climbed close to 100 degrees Fahrenheit, creating even more difficult conditions for people spending long periods outdoors.

The American Lung Association warned that fireworks release harmful gases such as sulfur dioxide, carbon dioxide and carbon monoxide, along with fine particles that can affect the lungs, reported PTI. “Inhaling any of these chemicals can irritate the lungs, making it hard to breathe and causing serious health problems, which is why it is important to avoid firework smoke whenever possible,” it stated.