Grade 9 Science – Real world investigation (MYP)
CFC Production and the Ozone Layer
Part A: Reflecting on the impact of science (background research)
Chlorofluorocarbons (CFCs) are safe, non-toxic, nonflammable group of compounds developed in the 1930s by Thomas Midgley to act as alternatives to otherwise perilous chemicals such as ammonia and sulfur dioxide. CFCs have historically been used for propellants in aerosol sprays and as coolants in refrigeration and conditioning systems. In the 1970s, as their usage became increasingly popular over the years, gas began to leak into the atmosphere.
The specific type of chlorofluorocarbon discussed in this lab is trichlorofluoromethane (CCl3F). Trichlorofluoromethane consists of 1 carbon atom, 3 chlorine atoms and 1 fluorine atom. The chlorine within the substance has the potential to destroy and greatly affect large amounts of ozone due to ultraviolet radiation in the stratosphere breaking down the CFC and in turn, freeing the chlorine. CFC molecules released near the surface of the Earth, over decades would reach the stratosphere, where UV radiation would split off chlorine atoms. Each chlorine atom would react instantly with an ozone molecule, which then set off a chain reaction that went on to destroy thousands of ozone molecules.
The ozone layer is a deep layer in the stratosphere which is located in the Earth’s atmosphere. The ozone layer has a very important job. The ozone layer acts as a shield by protecting the Earth from harmful ultraviolet radiation that comes from the sun.
Ozone is a type of oxygen, it is made up of 3 oxygen atoms rather than 2 oxygen atoms. Typically, ozone forms when some type of electrical charge or radiation separates the two atoms in an oxygen molecule (O2), which can then, individually reconnect with two other oxygen molecules to form ozone (O3).
The ozone layer became more widely recognized by the public when it was discovered that chemicals such as CFCs were in the stratosphere creating a series of complex chemical reactions, destroying some of the ozone. Ozone molecules are constantly being destroyed and reformed naturally, however, chlorofluorocarbons within the air make it extremely difficult for ozone molecules to reform once it’s broken apart. Therefore, the ozone layer is getting thinner all the time. As a result of these findings, an international treaty was signed called the Montreal Protocol in order to greatly reduce the fabrication of these environmentally threatening chemicals.
When UV radiation comes in contact with CFC, chlorine detaches and drifts around the atmosphere until it encounters an ozone molecule. The chlorine and oxygen atom combine leaving behind diatomic (molecule composed of only two atoms) molecular oxygen. When the chlorine-oxygen compound contacts a free oxygen atom the two oxygen atoms merge and the chlorine atom go on to ravage more ozone molecules. According to the U.S Environmental Protection Agency (EPA), one chlorine atom can obliterate as many as 100,000 ozone molecules.
Chlorofluorocarbons enter the atmosphere caused by leaks in equipment. Since they are stable compound and do not dissolve in water, they tend to last from decades to hundreds of years. For the most part, ozone is continuously being formed and destroyed, nevertheless, the total amount of ozone remains at a stable, steady number. When CFCs are released into the atmosphere, they upset the balance by removing ozone faster than it can be replaced.
Some harmful effects of reduced ozone levels include; more exposure to UVB radiation causing skin cancer and cataracts, a breakdown of DNA which can result in mutant effects such as, missing or extra limbs, and slow down the physiological and developmental processes of plants.
In the early 1970s American chemists F. Sherwood Rowland and Mario Molina theorized that chlorofluorocarbons combine with solar radiation decompose in the stratosphere releasing chlorine atoms and chlorine monoxide (chlorine and oxygen) that are individually able to destroy large amounts of ozone molecules.
In 1984 a group of British Antarctic Survey scientists; Joseph Farman, Brian Gardiner, and Jonathan Shanklin discovered a recurring Springtime Antarctic ozone hole. In 1985, they published their paper, comprised of their alarming findings. Some of which included that ozone levels had 10% below normal January level for Antarctica and that if the hole continued to spread it would allow cancer-causing radiation from the sun to reach the ground. After this was discovered, NASA scientists used a satellite to confirm that not only was the hole over the British research stations but over the entire Antarctic continent. Within a few years an international treaty called the Montreal Protocol was instated which banned the manmade chemical responsible for depleting the ozone layer. The protocol is having a clear effect and the amount of ozone-depleting substances has gone down, nonetheless, chlorofluorocarbon molecules are so stable and long-lived that the hole will exist each Antarctic Spring for another fifty years.
Jon Shanklin of the British Antarctic Survey wants the public to know that the real lessons of the story have yet to be learned, “Yes, an international treaty was established fairly quickly to deal with the ozone hole, but really the main point about its discovery was that it shows how incredibly rapidly we can produce major changes to our atmosphere and how long it takes for nature to recover from them” 1.
Reduced ozone layers have and will continue to dramatically affect the Earth. The ozone molecules in the stratosphere absorb most of the sun’s ultraviolet rays. Unfortunately, as ozone levels decrease, there are less ozone molecules to absorb the ultraviolet rays and therefore allowing a greater amount of them to reach the biosphere. The overexposure to UV radiation can cause a variation of health effects such as, skin damage, eye damage, and the under-development of the immune system. As stated by the U.S Environmental Protection Agency, by the year 2165 actions to protect and rehabilitate the ozone layer such as the Montreal Protocol will have saved 6.3 million U.S lives from skin cancer.
Also, UV radiation can damage fragile crops like soy beans and can reduce crop yields.
It is believed that exposure to UV radiation can affect the orientation, motility, and stress levels of marine phytoplankton. This is an issue because phytoplankton form the foundation of aquatic food webs. These matters could have profound effects on the food chain and food productivity.
The increase in ultraviolet radiation also increases disease amongst animals. Some examples of these diseases include non-pigmented areas in cats, cattle, sheep and horses as well as Uberreiter’s syndrome in dogs.
Over the past two decades the EPA and its partners has eliminated the mass production of ozone-depleting substances such as CFCs and have developed more environmentally friendly options that are safer for the ozone layer.
The United States, historically one of the world’s largest consumers of ozone-depleting substances, has met all of their commitments to the Montreal Protocol (an agreement that was designed to reduce the production and consumption of several types of CFCs. The protocol went into effect January 1, 1989). Along with the United states, 70 nations agreed to sign this protocol and eliminate the threatening substances. Once the protocol was instated, researchers found an available substitute called hydrofluorocarbons (HCFCs).
When CFCs were first introduced, it was believed that they were safe, harmless, revolutionary chemicals. Until scientists discovered that chlorine was not commonly found in the stratosphere because by itself, it’s very reactive. However, CFCs are very stable and able to survive and reach the stratosphere. When UV rays from the sun hit a chlorine atom, it breaks away from the molecule allowing it to be free and come in contact with ozone molecules.
Scientists then discovered that the reason for significant ozone depletion occurring above Antarctica is because in the Spring, the region can reach temperatures as low as – 80 Celsius. In extreme conditions like this, clouds called polar stratospheric clouds form. On the surface of these clouds, chemical reactions occur with the chlorine compounds. As the air begins to cool, the cloud sinks and begins to create a vortex. The vortex traps the chlorine atoms, which allows them to intensify, therefore, making the center of Antarctica vulnerable to significant ozone depletion.
Once it was discovered that CFCs were ozone-destroying substances, it was evident that we needed to find an immediate replacement to avoid any further depletion. The first available replacement was carbon tetrachloride, however, that was also an ozone depleting substance. The plan is that every substance has a phase-out date as long as that particular material depletes the ozone. Some of the substances that have replaced CFCs in the past include; hydrobromofluorocarbons (HBFCs), methyl chloroform, chlorobromomethane, and methyl bromide. The replacement for CFCs in the meantime are hydrochlorofluorocarbons (HCFCs), which also deplete the ozone. Essentially, hydrofluorocarbons (HFCs) will replace HCFCs when they have completed their production phaseout in 2030.
Ever since the implementation of the Montreal Protocol on ozone depleting substances such as CFCs, the atmospheric levels of these substances have decreased substantially over the past two decades. Nonetheless, it is a slow recovery due to the substance’s stability. We are expected to have a full recovery by the middle of the 21st century, possibly 2070. As the levels of these harmful chemicals have decreased in the past 14 years, the ozone hole has seen slight improvement. However, these improvements may not be completely attributable to the elimination of ozone depleting substances. The Earth’s rising temperatures may also contribute. The ozone hole is the smallest it has been since 1988.
Part B: Hypothesis:
Hypothesis: CFCs are the main cause of ozone depletion
Table 1: The table displayed below presents the data regarding CCI3F amount, production and ozone level versus year.
Figure 1: The graph above illustrates the fluctuating yearly production rates of the ozone depleting substance CCI3F.
Figure 2: Figure 2 displays ozone levels per year before and after the implantation of the Montreal Protocol
Figure 3: Figure 3 demonstrates a yearly recording of the amount of CCI3F in the stratosphere
Based on the data shown in the graphs and table above I can conclude that as the production of trichlorofluoromethane (CCI3F) increases, the greater the amount of trichlororfluoromethane in the stratosphere, therefore maximizing ozone levels. Both the production and ozone level have a strong correlation and show an obvious trend. However there seems to be an approximate ten-year period until the effects of the production impact the ozone levels in the stratosphere. This data suggests that it takes several years for trichlorofluoromethane molecules produced on the ground to reach the stratosphere. Similarly, it takes time for the concentration of this molecule to decrease in the stratosphere after production was decreased as stated by the Montreal Protocol.
Although the amount variable and production are correlated, their correlation with ozone level variable is not as evident. As the production of CCI3F is decreased, Canada’s ozone level decreases. However, as the production of CCI3F increases, the ozone level continues to decrease. This may be an anomaly with the data.
Conclusion & Evaluation
The validity of the hypothesis “CFCs are the main cause of ozone depletion” is somewhat accurate. Based on the data given, I can deduce that CFCs are the main contributor to ozone depletion. Yet, as the quantity of CCI3F produced and CCI3F in the stratosphere decreases, ozone levels proceed to decrease. This indicates that there may be another main cause of ozone depletion other than CFCs. Another possible cause could be volcanic eruptions.
Comparable to the correlation between production and amount, there could potentially be a certain number of years that it takes for the ozone to begin to recover to its formally stable state. In order to fully comprehend and demonstrate this hypothesis to be true or false, subsequent data is necessary due to the amount of CFCs in the stratosphere only decreasing in the late 1990s. Thus, the statistics should be observed for a few more decades to fully validate the hypothesis.
The data used to form my table and graphs was collected from our textbook. This is a valid source as various authors, editors, and publishers have checked it. The book was also developed by the student advisory panel, which guarantees that the information in the book is true.
The data that I used was also relative to the topic of ozone depletion rates, CFC production rates and the amount of CFC in the stratosphere. I made sure to repeat pertinent information throughout my background research to ensure that the reader fully understands all of the main concepts mentioned in this lab.
The data was taken over the span of 60 years, which is beneficial to see how the ozone has been impacted over time. When I plotted my graph, I chose to use a line graph which displays an evident correlation between information on the graph. This strong correlation displays the validity of the claim that CFCs do affect ozone depletion.
One way in which this project could be extended is by investigating other greenhouse gases and their effect on the ozone, looking further into the question, “what will replace CFCs?”. For improvement in methodology, I could collect data from outside sources, perhaps from countries or institutions that do not believe in climate change, to eliminate any form of bias. The source I used may have bias because it comes from a Canadian textbook, a country in which climate change is commonly believed as true. By using a source or multiple sources from countries or institutions where climate change is not the common belief, the results may be different. By comparing different data set, I would be able to model a more global representation of how CFCs affect ozone depletion. I could expand on this experiment by observing amount of green energy used versus ozone depletion. This expansion would demonstrate the connection between ozone depletion and the use of CFCs even further. Another way that I could improve this project is by modelling the effect of CFCs on the ozone layer, thus creating a visual representation of the evidence shown in this report. Lastly, I could improve and extend this experiment by extrapolating these data to see the effects of CFCs on the rate of ozone depletion may have in the future.