People watch a fireworks show at night.
People watch a fireworks show in Del Mar, California, on July 4, 2017. Mike Blake/Reuters

There will be more than 16,000 fireworks displays across the U.S. this Fourth of July—enough to register a dramatic (if temporary) effect on air quality.

America’s air this Independence Day will be filled with displays of patriotism—and with potentially dangerous air pollution.

All those rockets and explosions release significant amounts of “fine particulate matter,” microscopic particles capable of penetrating deep into the lungs and bloodstream.

The annual Independence Day spike in air pollution registers on air-quality sensors, from official government sensors to private networks. CityLab analyzed data on more than 100 private sensors located around the country from the PurpleAir network, and saw the same massive spike in Fourth of July air pollution that other studies have found:

Among the 118 PurpleAir sensors that CityLab analyzed, particulate matter levels rose from an average of around 10 micrograms per cubic meter (μg/m3) early on Independence Day 2017 to highs above 70 μg/m3 around 10 p.m. local time. That’s roughly equivalent to the difference in air quality between Los Angeles and Beijing.

Those averages obscure more dramatic swings for some isolated sensors, which registered particulate matter levels above 500 μg/m3 on the evening of July 4, similar to peaks observed in other studies.  

Prolonged exposure to those levels of pollution can cause difficulty breathing, aggravate asthma, and even lead to death for people with heart or lung disease. The U.S. Environmental Protection Agency’s official standards say exposure to more than 35 μg/m3 over a 24-hour period is harmful to public health.

Some countries, including India and China, have begun to regulate fireworks in an attempt to control pollution. German officials have recommended air masks for people near fireworks shows. In the U.S., the EPA doesn’t regulate fireworks but recommends that people sensitive to pollution, such as small children or people with heart or lung diseases, “try to limit their exposure by watching fireworks from upwind—or as far away as possible.”

The good news is that, based on previous years, tomorrow’s fireworks-related pollution should subside gradually after midnight, and air quality will return to normal around noon on Thursday.

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