July Fourth fireworks fill the skies across the nation with more than sparkling bursts of color. They spew pollution, too.

A study of 315 locations around the country found that the holiday explosions temporarily boosted the levels of airborne microscopic particles that can pose a health risk.

At 9 p.m. and 10 p.m. on July 4, levels of those particles were more than twice normal, on average, researchers found. But they tapered off overnight and fell back to normal by noon on July 5.

Smaller studies have also linked fireworks to particle pollution.

Dian Seidel of the National Oceanic and Atmospheric Administration, who reported the results recently in the journal Atmospheric Environment said the study did not look for any resulting effects on health.

But in response to the research, the Environmental Protection Agency noted Tuesday that children, older adults, and people with heart disease, asthma or other lung diseases are considered to be particularly sensitive to particle pollution. The agency recommended that they limit their exposure by watching fireworks from upwind.

"We want everyone to enjoy their local fireworks displays," the agency said in a statement.