How record heat and monumental fireworks could spark miserable air quality for July Fourth

By Kasha Patel, CNN

(CNN) — As the United States celebrates its 250th birthday, firework celebrations are expected to bring more pomp and circumstance than ever before. But with bigger festivities and an oppressive heat dome in the forecast, millions of Americans could face a monumental double dose of unhealthy air.

Every Fourth of July, the country lights up fireworks from impromptu celebrations on the street to formal rocket shows — creating smoke pollution, sometimes rivaling what comes from wildfires, that can linger for several hours. In some cities, air quality often doesn’t return to normal until around noon the next day, and the stifling weather could reinforce this loitering.

But smoke from this year’s larger-than-normal anniversary celebrations may also multiply respiratory risks in areas already suffering from deteriorating air quality amid record-breaking temperatures this week, experts say.

Even before any firework is lit in some urban areas, the heat will have already created another type of air pollution: ozone. Scorching locations – such as Washington, DC where record-breaking fireworks show — are forecast to experience at least moderate amounts of ground-level ozone during the day. This pollutant is typically formed when chemicals from car exhaust are baked under strong ultraviolet rays on hot days .

More than 50 million people will see triple-digit temperatures this week – and at least 100 record highs are projected through Saturday, mostly on the East Coast.

“I like fireworks. I’m a patriot. I think they’re fun, and it’s worth having a little bit of extra dust in the atmosphere,” said Russell Dickerson, a professor in the department of atmospheric and oceanic science at the University of Maryland, College Park. “But this Fourth of July is going to be bad for several reasons.”

Bigger firework celebrations mean more pollutants

To celebrate 250 years of freedom, many cities are truly commemorating the rockets’ red glare and bombs bursting in air in historic fashion.

The grandest celebration will take place in the nation’s capital, where 850,000 fireworks are expected to launch in just 40 minutes from 10 sites around Washington, DC — setting a new Guinness World Record for the largest firework display. The current benchmark is 810,904 fireworks at a 2016 New Years countdown celebration in the Philippines. The capital’s spectacle will be about 10 times bigger than Macy’s Fourth of July Fireworks Show in New York, which is typically the largest Independence Day bash.

New York, too, plans to supersize and set a local record for its show, blasting 85,000 firework shells in 30 different colors. Nashville is aiming to launch an unprecedented number of fireworks — in the thousands. Boston will choreograph live music to its display. Charlotte proclaimed it will have the biggest fireworks show in the Southeast at a baseball stadium. For only the third time in history, San Francisco will launch fireworks from the Golden Gate Bridge.

But the pyrotechnic spectaculars spell trouble in the air, immediately producing smoke and microscopic pollutants known as particulate matter (PM) 2.5. They are about 30 times smaller than the width of a human hair and can cause respiratory issues and worsen heart conditions. Some PM 2.5 consists of metals that make up a firework’s color and can lodge deep into our lungs and cause irritation, coughing or shortness of breath.

In the hours after a firework show, researchers found around a 42% increase in these small pollutants.

But past extravaganzas haven’t typically been as big as this year, making air quality right after the show a large concern.

“We know that every city in the country that has a fireworks display has huge particulate matter levels as soon as the fireworks display starts,” Dan Jaffe, professor of environmental chemistry at the University of Washington, told CNN. “The emissions are going to matter. More fireworks are going to mean more PM 2.5 in the air.”

Watch for the heat dome, ozone and potential rain

To make matters worse, many locations of major firework fiestas will also be under historic heat. An area of high pressure, known as a heat dome, is planted over much of the country this week, limiting winds and trapping hot air close to the ground.

Washington, DC is expected to hit around 102 degrees to reach its hottest July Fourth on record. New York is anticipated to hit triple digits for the first time in a decade from Thursday to Saturday. Philadelphia could tie for its second hottest temperature recorded on Saturday at 104 degrees. Boston may experience one of its warmest days and nights on the Fourth of July.

Dickerson said the stagnant air will likely trap the smoke closer to the ground longer than usual — and may even obscure the fireworks. Similar conditions sullied Washington, DC’s sparkling display in 2019. Because of the high temperatures, Dickerson said people will likely be blasting their air conditioners and using more energy — also increasing PM 2.5 in the atmosphere.

“We’re not going to be able to see more than 100 yards,” Dickerson said. “If the winds are stagnant, which they might be at sunset on a hot day, it’s quite likely it could be many hours or even days before that plume fully dissipates.”

Then there is ozone, which many may recall as the gas high in our atmosphere that shields the Earth from the sun’s strong rays. But ground-level ozone, formed from the mingling of vehicle exhaust, heat and sunlight, can irritate our lungs — potentially worsening air quality before any nighttime celebrations.

“Heat exacerbates this whole problem, so that we generally see the highest levels of ozone when the temperatures get into the high 80s and 90s in most locations,” Jaffe said. “If you think of a belt of cities across the US, generally the warmer cities tend to have worse ozone pollution.”

And if firework particles linger into the next day, Jaffe said their chemicals could also react in the sunlight and add to the ozone risk on July 5.

Dickerson, who is based in Maryland, said Saturday does not seem like a good day to attempt the world record. “I wouldn’t bring my grandchildren, not this year,” he added.

Rain could help alleviate the heat and air pollution. As of late Thursday, storms are forecasted to pop up from Virginia to New England from late afternoon to the evening on Saturday. The rain could help quell ozone pollution during the daytime including in the nation’s capital, but the showers will likely end before they can wash out firework smoke that night. In Washington, DC, rain isn’t projected to return until around the following afternoon.

If the air quality index reaches “unhealthy” levels, exceeding 100, the Environmental Protection Agency advises people who are pregnant, have pre-existing conditions like asthma, or are with young children or older adults to take caution. If the air quality becomes hazardous and exceeds 300 on the index, everyone is more likely to be affected. People can wear a proper N95 mask to limit exposure to the pollutants.

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