Happy 4th of July! From all of us in the StormTracker Weather Center we hope you and your friends and family have had a great day of celebrations. The forecast couldn't be better for fireworks, even after Mother Nature's own display earlier in the day. A few clouds will linger and it will be a muggy evening as the fireworks light up the sky.
Before we see all of the dazzling combination of colors and shapes, there's a lot of science that goes into putting on the perfect fireworks show. You need the chemistry knowledge for combining the right compounds, and the correct amounts, to get the right colors. There's another recipe for ensuring that the firework will go off, and not end up as a dud. Then it comes down to the physics of the explosion.
The color in fireworks is produced by pyrotechnic "stars," which give off colored light once ignited. Each star contains five ingredients - metal salts for color; a fuel (often gunpowder); an oxidizing compound, which provides oxygen for the combustion of the fuel; a chlorine-donating compound to intensify the color; and a binding compound to hold everything together. Red fireworks use strontium salts for it's star, while burning metals like magnesium, aluminum, and titanium are used for white, and copper salts are used for blue.
That's how we get the colors, but how we see those colors can be affected by the weather conditions during a fireworks show. Its not just time of day, precipitation, and cloud cover that can dampen the vibrancy of the fireworks. The colors will be appear duller on a night with higher humidity than in a drier air mass. When it is "humid" there is more water vapor in the atmosphere. That means there are more molecules that can mask the colorful explosions. Ideally you would want a light breeze during a fireworks show. Just enough wind to promptly clear the smoke. With a calm wind the plume of smoke will hang around and could limit the visibility of future explosions. A strong wind can be dangerous for those setting off the fireworks. Temperature through the different levels of the atmosphere can also play a key role. An inversion, or a rising in temperature with height, create a lid or cap in the atmosphere. It will trap the smoke, not allowing it to mix out. A shallower inversion will trap the smoke closer to the ground.