Up to 32 students
Some people may think that given the addition of carbon monoxide and other gases into the atmosphere that a hole in the ozone may be a good thing, mistakenly thinking that the heat can escape through the hole, common misconception. Another common misconception that ozone produced by motor vehicles and other machines will help replace the loss and is a good thing, ozone within the lower atmosphere is toxic to life forms in the lower atmosphere. Ozone upper high is good, ozone down here is bad.
The chemical reactions that occur with CFC’s and the atmosphere are very advanced and not necessary to go into in this lesson. The simplest way to describe it is as follows:
Cl + O3 ? ClO + O2
ClO + O3 ? Cl + 2 O2
This reaction occurs most efficiently in the spring time when the sun’s rays begin to concentrate over the northern or southern hemispheres. There are ozone holes over both
hemispheres in the spring times, though the hole over the southern hemisphere is notably larger.
The amount of ozone in the atmosphere is measured in Dobson Units (DU). The Dobson unit (DU) is a unit of measurement of atmospheric ozone, specifically ozone in the stratospheric ozone layer. One Dobson unit refers to a layer of ozone that would be 10 µm thick under standard temperature and pressure. For example, 300 DU of ozone brought down to the surface of the Earth at 0 °C would occupy a layer only 3 mm thick. One DU is 2.69×1016 ozone molecules per square centimetre, or 2.69×1020 per square metre. This is 0.447 millimoles of ozone per square metre.
A baseline value of 220 DU is chosen as the starting point for an ozone hole since total ozone values of less than 220 Dobson Units were not found in the historic observations over Antarctica prior to 1979.)
There is little ozone in the atmosphere, but what is available is extremely important. Similarly to the gases mentioned in the prior lesson ozone (O3) has a very special frequency that stops damaging UV light from making its way to the Earth’s surface.
There are several types of UV light, A, B and C. Ozone traps all of UVC and a good amount of UVB light. UVB and UVC are the most damaging to all life on Earth. As we move from infrared, to visible light, to UV light we are moving towards X-Rays and Gamma Rays, these are well known to be harmful. So maintaining even the small amount of ozone in the upper atmosphere is imperative to maintain life.
1. Apply understandings from prior lesson to ozones ability to block damaging UV light.
2. Understand that infiltration of excessive UV light is damaging to all life forms.
3. Understand that ozone high in the atmosphere is beneficial but ozone low in the atmosphere is detrimental to life forms.
What is ozone? Why is ozone important?
Laptop or Smart Board
Internet Connection or downloaded video
Activity 1: Exploring Ozone Video
Direct student to watch the NASA video on ozone and jot down questions and notes on the ideas presented in the video.
Activity 2: Think, Pair, Share
Have students work in pairs or small groups to discuss their ideas, concerns and questions about ozone that are derived from watching the video.
Conclusion and Wrap Up:
Clarify misunderstanding and misconceptions on CFC's, ozone and the ozone hole as a class.
Have students add to their LINK.
New York Scope and Sequence:
Intermediate and High School Science Standards
Key Idea 2.1a - 2.1c