In 1931, Norwegian engineer Eric Rotheim created the first design of the aerosol can.  The U.S. military in WWII used the cans to dispense insecticide.  The basic idea behind the aerosol can is that a fluid is stored under high pressure and then used to propel another fluid out of the can. Until the 1980s, chlorofluorocarbons (CFCs) were used in many aerosol cans.  CFCs were proven to be extremely harmful to the ozone layer, and in the Montreal Protocol of 1989, seventy countries agreed to phase out CFC use over the next decade.  Since then, their use in aerosol cans has decreased substantially.

Inside the aerosol can, there are two fluids: one that boils below room temperature, the propellant, and one that boils at a higher temperature, the product.  There are two systems of aerosol cans: the compressed-gas system and the liquefied gas system.  Check out How Stuff Works to find out more information on aerosol cans.  

The two systems that are used in aerosol cans to spray the ingredients inside are the compressed-gas system and the liquefied-gas system.

Compressed-gas System: First, the liquid product is poured into the can.  Then the can is sealed, and a gaseous propellant is pumped through the valve system at a high pressure in order to push the product down.  A plastic tube runs from the bottom of the can to a valve system at the top of the can.  The valve system has a small headpiece with a channel running from an inlet near the bottom of the headpiece to a small nozzle at the top of the can.  A spring pushes up the headpiece to block the channel inlet.  When the headpiece is pushed down, the inlet slides open, creating a passage.  The high-pressure propellant gas drives the liquid product up the tube and out the nozzle, and the nozzle atomizes the product (breaks it up into tiny drops). 

Liquefied-gas System: The liquefied-gas system is similar to the compressed-gas system, but is the more popular of the two aerosol can systems.  The propellant is a liquefied gas and remains a liquid at all times.  The set up of the liquefied-gas system has the same design as the compressed-gas system.  The product is poured in, and the can is sealed.  Then the propellant is pumped in under high pressure so as to prevent the propellant from expanding into gas.  Then the valve opens; the pressure on the liquid propellant decreases, causing the propellant to boil.  Particles break free to form a layer of gas at the top of the can.  This pushes the liquid product and propellant up the tube to the nozzle.  When the liquid goes through the nozzle, the propellant expands to gas to either create a fine spray with the product or form foam.  

Aerosol cans are produced though aluminum processing.  Aluminum is either made from bauxite ore (primary aluminum refining) or aluminum scrap (secondary aluminum production).  Due to the expense of refining aluminum, 40% of aluminum in the US is recovered for secondary refining.  Major primary aluminum producers locate in low energy costs areas, such as the Northwest and the Ohio River Valley, due to high-energy requirements involved in primary aluminum production.  Secondary producers locate near industrial centers like California and the Great Lakes.  The EPA explains how aluminum is processed in specific ways.

Primary Aluminum Refining

            First, alumina is extracted from bauxite ore using the Bayer Process [Finely crushed bauxite is mixed with sodium hydroxide and put in a digester and with added heat and pressure, the aluminum oxide is evaporated off and condensed.  The aluminum oxide is crystallized in a precipitation tank, and the crystals are washed and dewatered].  The aluminum oxide is reduced to aluminum metal using the Hall-Hercoult process [Aluminum oxide is placed in an electrolytic cell with molten cryolite, and a carbon rod in the cell is charged, creating a reaction.  This produces carbon monoxide, carbon dioxide, and aluminum.  The aluminum sinks to the bottom and is removed and melted].  The molten aluminum is mixed with alloys and cast into ingots (bars). 

            Pollution:  Air emissions from bauxite and aluminum oxide are usually caught by air emissions equipment, but air emissions from the reduction of aluminum oxide are usually able to escape.  These emissions consist of fluorides, alumina, carbon monoxide, and sulfur dioxide. 

Secondary Aluminum Production

            Scrap aluminum is melted in gas or oil furnaces.  Impurities are removed with chlorine or other chemicals. 

            Pollution: Air emissions depend on the scraps used, but can include hydrogen chloride and metal chlorides, aluminum oxide, and metal compounds.  Aluminum fluoride can substitute chlorine to decrease air emissions.

In addition to the pollution created by aluminum processing, aerosol cans also contribute to pollution due to the difficulty of recycling them. 

On top of the pollution created by the the production of the aerosol can, there are also environmental problems regarding the disposal of aerosol can air fresheners.  Most people throw away air fresheners, leaving them and their harmful ingredients inside a waste pile for years and years.  For those who want to recycle their aerosol air fresheners, the University of Wisconsin lays out the steps for recycling.  Consumers must puncture and drain the can, collecting all liquid.  Then they have to treat the gases and vapors with a carbon filter, which becomes hazardous waste.  Finally, the can is able to be sent to a recycling plant and recycled as scrap metal.  Transporting the aerosol cans to recycling plants creates even more pollution and environmental harm. 

The production and selling of aerosol air fresheners requires a lot of transportation.  First, the materials to produce the cans must be sent to aluminum production companies, located usually in California, the Great Lakes, the Northwest, or the Ohio River Valley.  Then the cans are transported to the air freshener manufacturers.  Febreze’s manufacturer, Procter and Gamble, is located in Cincinnati, Ohio, and Glade’s manufacturer, SC Johnson, Inc, is located in Wisconsin.  The finished products then travel all around the nation to stores, where people buy them and transport them to their homes.  Lastly, if the consumer chooses to recycle, the can must be transported to a recycling plant.  For more information on metal recycling plants, click here: Metals.

The ingredients inside the aerosol air fresheners also contribute to environmental pollution.  For more information on the ingredients, read my posts on air freshener ingredients.