Aerosols and the Ozone

The aerosol industry in South Africa (and in most developed countries) has always maintained a high profile on environmental issues (remember the prompt and responsible reaction to the CFC crisis).

Initially aerosol products made use of chlorofluorocarbons (CFCs) as its gas propellant. However, in 1974, Nobel Prize winner Dr. F. Sherwood Rowland and his colleague Dr. Mario Molina proposed a theory that chlorofluorocarbons (CFCs) damage the stratospheric ozone layer. At the time, CFCs were being used in refrigerators, air conditioners, industrial processes and as propellants for some aerosol products. The scientists were worried about the stratospheric ozone layer because it consists of a particularly active form of oxygen that filters out much of the sun’s harmful ultraviolet radiation.

American aerosol manufacturers were the first to switch from CFC propellants to suitable alternatives. By 1978 when the U.S. EPA banned the use of CFC propellants, most of them had already voluntarily stopped using CFCs.

Developments in technology allowed the shift of numerous aerosols to hydrocarbon propellants. Thereby reducing the use of CFCs to less than 25% by the early 1980’s.

In 1980, the European aerosol industry signed a voluntary agreement with the EC to reduce the annual CFC use by 30% compared with 1976 and not to exceed this level despite market growth. By 1987, the United Nations Montreal Protocol was signed which laid out plans to phase out all ozone depleting substances by the end of 1995 for most products. Under this agreement the production of CFCs was to be phased out of industrialized nations by January 1, 1996 and developing nations by 2010.

In 1988, the UK aerosol industry also committed to phase out CFCs by the end of 1989 in all retail products, which made up 90% of the total. Similar action was taken at that time by the rest of Western Europe. CFC’s were only used in medical aerosols from 1990 onwards with the intention to phase these out once a suitable, cost-effective alternative had been confirmed. Currently, the use of CFCs is prohibited throughout Europe.

The Australian aerosol industry also voluntarily stopped its use of CFC propellants before the end of 1989.

Chlorofluorocarbons (CFCs) were very stable man-made chemicals. Their stability meant that they were not destroyed in the troposhere but instead drifted upwards to the stratosphere, where they were broken down by the strong sunlight. This then released chlorine, which added to the natural depletion cycle of the ozone.

From the early 1980’s, hydrocarbons started to replace CFCs as aerosol propellants and today are used in the majority of aerosols. Hydrocarbons consist entirely of carbon and hydrogen. They do not contain chlorine. The majority of naturally found hydrocarbons occur in crude oil. These hydrocarbon propellants only have a life span of a few days and therefore they contribute little to global warming. Although they are considered to be volatile organic compounds (VOCs), they make virtually no contribution to ground level ozone, which causes smog. The main source according to U.S. EPA research, of manmade VOCs, which do contribute to smog are vehicle emissions, combustion and industrial emissions.

The majority of aerosol units make use of hydrocarbons, carbon dioxide and nitrogen. Hydrocarbons are liquefied petroleum gas (LPGs). Liquefied propellants are gases that exist as liquids under pressure. Because the aerosol is under pressure the propellant exists mainly as a liquid, but it will also be in the headspace as a gas. As the product is used up as the valve is opened, some of the liquid propellant turns to gas and keeps the headspace full of gas. In this way the pressure in the can remains essentially constant and the spray performance is maintained throughout the life of the aerosol. The propellant is an essential element in the formulation.

Compressed gases are an environmental alternative to the LPGs. Carbon dioxide and nitrogen are compressed gases. Compressed gas propellants really only occupy the headspace above the liquid in the can. When the aerosol valve is opened the gas ‘pushes’ the liquid out of the can. The amount of gas in the headspace remains the same but it has more space, and as a result the pressure will drop during the life of the can. They therefore have limited use. Spray performance can however be maintained by careful choice of the aerosol valve and actuator.

Other alternatives are hydrofluorocarbons (HFCs). They were developed as replacements for CFCs. They are none ozone depleting, have low toxicity and low flammability. HFC 134A is the only non-flammable liquefied propellant available today. It is used in a small percentage of aerosol units, where user safety is critical. For example they are used in aerosols for marine and safety alarms where they are used predominantly in emergencies.