Apr 19 2011
*Since did not have a scribe for ozone day, I pulled this post by alum Kelly Cox ’10 out of the archives.
Today during the second half of class, we discussed ozone, or O3.
The first thing to recognize when discussing ozone is that there is good ozone, and there is bad ozone. You MUST be able to distinguish between the two of these!
Good ozone (O3) is responsible for absorbing and blocking about 95% of harmful UV radiation from the sun in the stratosphere (NOT the troposphere). Good ozone is what we want to maintain in the stratosphere, obviously. Without it, humans and plants are exposed to UV-A and UV-B, which penetrate through the skin and cause DNA to lose electrons. This leads to tumors called carcinoma and melanoma. Without good ozone, we are also at risk of cataracts, severe sunburn, skin cancer, lower crop yields, and less phytoplankton which the food chain depends on.
Bad ozone is a main component of photochemical smog, and obviously we want to minimize the amount of bad ozone that is released into the atmosphere. Bad ozone irritates the eyes, nose, and lungs, and damages plant’s leaves.
One of the most common misconceptions about ozone is that there is a “hole” in the ozone layer. In reality, the issue at should be referred to as “ozone thinning.” The ozone layer varies in thickness and concentration throughout the stratosphere. Thick is obviously better because it can better protect us from UV radiation. Here is a diagram showing the varying concentrations of ozone in the stratosphere but NOTE: No where is there a “hole” or complete absence of ozone!!!
The “hole” is the largest or the most thinning occurs during the spring months (September-October) in Antarctic.
CFCs (chlorofluorocarbons) were discovered in 1928, and at first they were considered “the dream chemical” because they were useful and versatile, yet they weren’t explosive or dangerous, or so they thought. They were used for coolants in refrigerators, propellants in aerosol cans, and in plastic bubble packaging. But in 1974 research proved a reaction of CFCs in the stratosphere, which was destroying good ozone. When UV light hits CFCs, the chlorine in the atmosphere is free and reacts with O3 causing these series of reactions:
Cl + O3 –> ClO (unstable) + O2 ClO + O –> O2 + Cl….. then this Chlorine continues to react with O3 creating a vicious cycle where good ozone is being removed from the stratosphere. Once this discovery was made, a large movement to remove all CFCs from the market quickly began. Here is a good description of this reaction that takes place in the stratosphere that Mr. Willard sent me (I’m not sure who to credit this??):
The Montreal Protocol has been very successful in eliminating CFCs in most products. Almost every country has signed on to it now, and ozone remediation is working, but slowly.