Researchers are working to reduce the pollution left by the shooting stars and bursting bombs that spangle skies in fireworks displays.
Efforts by Walt Disney and the military are driving the changes, according to a report by Bethany Halford in Chemical and Engineering News.
Fireworks have become more colorful within the last two centuries, but the basic technology hasn't changed much in 800 or more years since early forms of gunpowder were likely used in rituals and battles in China.
Staple ingredients are a fuel to create heat and an oxidizer to accelerate burning. Additional chemicals slow the burn, making the light show last longer.
Pyrotechnic cocktails borrow from the Periodic Table of the Elements for color.
Strontium and lithium may be used for red, barium and copper lead for green, and sodium glows golden. Calcium deepens colors. Zinc makes smoke clouds, aluminum sparkles, and antimony adds glitter.
In the past, lead and mercury were in the mix.
Among the toxic culprits being addressed lately, potassium perchlorate is a reliable and inexpensive oxidizer, but it has been connected to cancers and thyroid problems.
Environmental Protection Agency analysis of an Oklahoma lake between 2004 and 2006 found that levels of perchlorate rose in some instances as high as 1,000 times above normal after fireworks shows.
And fireworks can lead to hazier summer days, exacerbating asthma sufferers.
Scientists in Germany and at Los Alamos National Laboratory have explored reducing perchlorate, smoke, and carbon by using substances rich in nitrogen.
Los Alamos researchers responded to complaints some 10 years ago from Anaheim, Calif., residents about pollution from fireworks shows every night at Disneyland.
The theme park in 2004 announced it was adopting safer air cannons that use compressed air instead of a chemical propellant, eliminating black smoke.
DMD Systems of Los Alamos, N.M., uses nitrocellulose to create fireworks with less smoke and more eye-popping colors.
More customers are asking DMD for low-smoke fireworks, which are ideal for indoor displays, Halford noted.
Unless demand expands for eco-friendly pyrotechnics, which can cost twice as much as the majority (which are assembled cheaply in China), they probably won't splash in the skies any holiday soon, Halford told CNET.
Scientists at the University of Munich and Vienna University are thus focusing on low-smoke military flares rather than recreational fireworks.
There appears to be no solid estimate of how much pollution fireworks cause, but the ecological damage is relatively minimal, Halford added.
For instance, most releases of perchlorate come from rocket fuel and other military uses. And heavy metals from fireworks tend to disperse quickly in the environment.
Improperly-handled explosives likely pose more imminent dangers.
The U.S. Consumer Product Safety Commission counted fireworks-related injuries in 9,600 people in 2004. The rate of injuries per amount of fireworks released has declined in the early 2000s to nearly one-third the level of the early 1990s, according to the National Council on Fireworks Safety.
These tips for "greening" Independence Day celebrations come from the Environmental News Network.