By Nicole Soussana
When we think of fireworks, we typically think of the Fourth of July or New Year’s Eve. Scientists, on the other hand, prefer to think of fireworks in terms of their logistics. Three main aspects regarding the mechanics of fireworks can be further investigated and understood through chemistry. These categories are color, explosion, and the health and safety of our environment.
In the 1800s, the color of fireworks was due to black body radiation. This is the phenomenon that all objects radiate electromagnetic waves, and the object’s color is influenced solely by its temperature. Those fireworks were a yellow-orange color. Modern fireworks are colored by a spectral emission of excited gases. Unlike black body radiation, this is dependent on chemical composition. The electrons of a certain element become excited by an explosive burst of heat and jump to a higher energy state. When they come back down to their original state, energy is released and a characteristic color is produced.
The fireworks displays we may have seen boast an array of colors. This is because scientists formulate fireworks with metal chloride compounds, including metals of known characteristic color, upon excitation. For example, barium chloride produces a green color, strontium chloride displays red, copper is associated with the color blue, calcium with orange, sodium with yellow, and a mixture of strontium and copper will result in purple. If you’ve taken a general chemistry lab course, you might be reminded of flame test experiments. Interestingly, similar experiments are conducted to produce new firework colors.
Metal chloride compounds are combined with fuel into dough-like lumps called ‘stars.’ The fuel is an oxidizer which assists in the burning process. Potassium perchlorate is often used in star formulas because it is an oxidizer as well as a chlorine donator. The colorful dots of light in the sky are a result of exploding stars.
Physics and chemistry work together to ensure a spark at just the right moment in the sky. The speed of burning, volume of gas released, weight this volume of gas can lift, and the strength of the casing for the star must all be taken into account for a successful fireworks display. In order to send a weight soaring into the sky before it bursts, a slow burning gunpowder, which gives off gas, is used. The gunpowder is in the form of pellets in order to prolong the burn time.
There is so much thought and science poured into the beautiful fireworks we enjoy, however it is important to consider the environmental side effects of our celebratory customs. The smoke and vapors which are released during a display pollute the environment. As an example, strontium, barium, chlorine, and unreacted perchlorate used for fuel, can all be toxic fallouts. The combustion of chemicals with oxygen results in greenhouse gases and pollutants which can cause acid rain, among other negative outcomes. Additionally, exploded metals take the form of aerosols, which can poison all of our basic needs for survival: air, soil, and water. In 2018, 8.6 million kilograms of fireworks were used in the US. In 2019 after the Diwali festival of lights in India, there were certain areas that had an Air Quality Index score of 500 which is the most severe level of air pollution.
It seems as though society is unlikely to give up on its love for fireworks, and therefore the responsibility falls on scientists to create safer materials. The US Armament Research and Development and Engineering Center (ARDEC) is developing chlorine-free compositions that will produce the same colors without using harmful metals. Research has shown that boron can be used instead of barium to form a green color. High nitrogen content materials can produce red rather than using strontium, and also has a low smoke and soot content because it can contain little carbon and hydrogen.
While military pyrotechnics have already begun to establish safer measures, it might be a while until our normal celebratory fireworks adapt to a more environmentally friendly composition. It is important to note that we can greatly affect our world with our choices, whether that be by polluting it or working to cure it. We can appreciate the science which goes into a beautiful fireworks display, but it’s more worthwhile to appreciate the science that will undo the damage it has caused.