You’ve either used an aerosol spray or at least seen it being used by someone at one point of time or another. From pain relievers to hair sprays, deodorants to shaving creams, canned spray paint to numerous other applications, the aerosol spray can is entwined in our everyday lives.
The modern aerosol spray can was invented in 1926 by Norwegian chemical engineer Erik Rotheim. The illustrations in his patent, in fact, have most of the elements that are found in these cans even today.
War leads to popularity
His spray cans, however, weren’t picked up immediately. It was only after World War II, when the Americans put it to use for killing malaria-carrying mosquitoes in the Pacific, did it become popular. The term aerosol, to describe an aero-solution or clouds of microscopic particles suspended in air, is first believed to have been used during the war.
Like in the case of a photo finish, the idea behind aerosol spray cans has more or less remained the same from the time Rotheim came up with it. There have been innovations to increase its applications, but the basic premise with respect to its working system has remained faithful to the original.
Propellant and product
This idea involves having two fluids, one under high pressure that is used to propel the other fluid out of the can. The fluid under high pressure, or the propellant, generally boils well below the room temperature. The other fluid, called the product and corresponding to the substance that we use, boils at a much higher temperature.
Both these fluids are stored inside the sealed metal can and are configured in two main ways for it to work. While simple designs employ a gaseous propellant to push the product through the valve, the more popular system includes a liquefied gas as the propellant.
Till the 1980s, chlorofluorocarbons (CFCs) were predominantly used as propellants in these liquefied-gas aerosols. As evidence started suggesting that CFCs were responsible for damaging the ozone layer, Sweden became the first country to ban them on January 23, 1978. Other countries joined the bandwagon and 70 countries signed 1987’s Montreal Protocol, agreeing to phase out the use of CFCs.
While CFCs have indeed been largely phased out, aerosol spray cans still remain in use as other suitable replacements have been found for the propellants. Liquefied petroleum gas, propane, n-butane and isobutene are among a variety of alternative propellants that are used these days. While they do not pose as serious a threat to the environment as CFCs did, they too increase the carbon footprint ever so slightly and also emit volatile organic compounds. Are there better substitutes that can be used as propellants? We’ll find out with time…
