The Ozone Layer and its recovery from CFCs

October 22, 2010 by jason

With growing pessimism over the future in a world of global warming, rising greenhouse gas emissions and dwindling oil supplies, we seem to have forgotten one of the big environmental success stories of the 20th century. I think everyone reading this will have heard of terms like Ozone Layer and CFCs. What some of you might not know, is that CFCs have been almost completely phased out, and that the damage their use has caused is on the road to reversal.

Think of this story the next time you let yourself think that humanity is doomed to self-destruction, and that we cannot possibly solve the current global warming crisis before there's no turning back. Take this as an example of how humanity can, and has done, something right, before it was too late.

Let's start at the beginning...

First there was the Ozone Layer

You can think of Ozone (a molecule of Oxygen, chemically symoblized as O3) as a filter, stopping certain frequencies of solar radiation from penetrating our earth's atmosphere and wreaking havoc on our sensitive skin. The term Ozone Layer is somewhat misleading, as it does not refer to a region of space that is thin by any means of the term. It refers to the quantity of Ozone in a region of the atmosphere called the Stratosphere, between altitudes of 10km and 50km (6-31 miles).

Although the concentration of Ozone in the Ozone Layer is at most 1000ppm (or 0.01%), it plays a hugely important role, blocking anywhere between 97-99% of the sun's high frequency Ultraviolet light.

The Discovery of Ozone

Ozone itself was discovered by a Swiss Chemist, Christian Friedrich Schonbein in 1839. However, it would be until 1918 that Ozone would actually be measured at the surface of the earth, by Robert Strutt. Strutt measured Ozone concentrations by measuring spectra from a Hydrogen lamp, with the air (and ozone contained in it) passing through 5 km of air illuminated by the lamp. It wasn't however until the 1930s, that the discovery was made that Ozone concentrations varied significantly with altitude, so much that over 90% of the atmosphere's ozone was concentrated at altitudes above 10km.

Depletion of the Ozone Layer through the use of CFCs

Ozone is a strong oxidizer, and reacts rapidly with free radical catalysts, namely Nitric Oxide (NO), Nitrous Oxide (N20), hydroxyl (OH), atomic Chlorine (Cl) and atomic bromine (Br). While these chemicals do occur naturally, their concentrations (especially of Chlorine and Bromine) increased drastically during human releases of chlorofuourocarbons (CFCs) and bromofluorocarbons.

The term "CFCs" refers collectively to a range of chemical compounds (see this wikipedia article for a list). Large-scale industrial production (or at least research into how it could be done) was probably pioneered by a man called Frédéric Swarts from Belgium. Swarts developed an exchange agent in the 1890s that could effectively replace the chlorine atom in carbon tetrachloride with flouride, allowing him to synthesize CCl3F and CCl2F2.

The use of CFCs would not begin on an industrials scale until somewhere in the 1920s, when research was being conducted into their use for extinguishing fires. Freon is a well-known CFC refridgerant used for much of the 20th century, as well as having applications as a propellant in aerosol cans. Additional well-known CFCs included Bromomethane (a widely used fumigant) and Dichloromethane (an industrial solvent).

The use of CFCs really took off during World War II, where their implementation as a firefighting tool saw growing industrial-scale production, especially in military aircraft. Their use quickly spread to civilian applications. Their use in fire extinguishers became more or less standard by the late 1960s. By the time concern began to be expressed about their effect on the Ozone layer in the late 1970s, CFCs were integral to the global economy.

The implementation of regulation and ultimate banning of CFCs

While initial concerns about CFCs had been around for most of the 20th century, it wasn't until James Lovelock proved the widespread increase in CFC concentrations that we really began to understand that they might have a negative impact. Lovelock himself however, concluded that "...the presence of these compounds constitutes no conceivable hazard". Lovelock would later admit that this was one of his greatest blunders. Nonetheless, Lovelock discovered and proved the increasing presence of CFCs in the atmosphere.

Lovelocks work allowed researchers Sherry Rowland and Mario Molina to first suggest a connection between increasing CFC concentrations and a depletion of the Ozone Layer in their first publication in 1974. Sherry Rowland and Mario Molina, along with fellow Paul Crutzen were awarded the 1995 Nobel Prize in Chemistry. The rest is history; 1987 saw the realization that Ozone levels had diminished significantly over Antarctica, and quickly lead to the creation of the Montreal Protocol. In March 1989, 12 European nations signed the protocol, agreeing to completely halt all production of CFCs by the end of the 20th century. Under the protocol, production and use of CFCs should be completely eliminated in all forms by all countries, including the 3rd world.

DuPont was probably one of the major drivers of CFC science skepticism (doesn't that sound familiar). Their patent on Freon (U.S. Patent #3258500) was set to expire in 1979, and in 1978 they pushed heavily, funding organizations such as the "Alliance for Responsible CFC Policy". By the 80s they had lost that battle, and began publicly condemning the use of CFCs.

The Happy ending?

Thanks to Lovelock and his research, we have the following plot of CFC concentrations in the atmosphere throughout the 20th century:

Source: Observed atmospheric CFC concentrations: 1930-2000

The recovery of the Ozone layer has been slow at best, and no undesputable evidence exists that it will make a full recovery. Here is an indication of the degree of response from the Ozone layer:

Source: WDC-RSAT

While this isn't exactly a happy ending, and while it might not be the best example of people getting together to find a solution, it does tell us a lot about what we're capable of. Now that we have done as much as we can do to really fix the ozone problem, we should look towards global warming and growing greenhouse gas emissions. I don't believe that people will wait until it's too late, and if given a bit of a push by science, policy makers and industry can be convinced as well. Maybe not today, maybe not tomorrow, but hopefully in 100 years we can tell a similar "almost success-story" about global warming, as I just have about the depletion of the Ozone Layer...

If CFCs had not been regulated

If the regulation on the use of CFCs had never occurred, we would be living in a very different world today, and in an even more frightening one tomorrow. NASA has done extensive research on this. I'll leave you with a hypothetical model of how things would have looked if we never took action and regulated the use and global spread of CFCs:

Hypothetical picture of CFC concentrations from 1974-2054 if CFCs had not been regulated, showing actual levels and the "world avoided" hypothetical scenario (source: NASA)