Earth Sciences and Ecology Question #198

Eric Chan, a 17 year old male from the Internet asks on October 10, 2001,

I am considering an idea to measure the effects of ozone depletion. I intend to use an ozone making machine in my school, and mix ozone with say, CFCs or other man made chemicals that have been known to deplete the ozone. I then intend to measure just how much ozone has been degraded, as Ozone is chemical formula O3- and if it's been degraded, I should be able to detect other chemicals as well (for example it may degrade to regular oxygen O2). My question is- do you think there are methods available to a high school student in detecting the amount of 'residue' chemicals- is there a method to detect the amount and kind of chemical left after the ozone has been degraded? On a second note, do you think it's possible for me to measure just how effective the ozone is in blocking out the various rays that the sun emits?

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The answer

James Robert Bolton answered on October 10, 2001

First, a high school student should exercise extreme caution in experimenting with the generation of ozone - this is a TOXIC gas, and should only be generated under carefully controlled conditions. Ozone can be detected with a spectrophotometer by observing its absorbance at 260 nm (254 nm from a low pressure mercury lamp will do). It can also be detected by bubbling the gas through a concentrated solution of KI (Potassium Iodide). This generates the triiodide ion, which can be detected at 352 nm by a spectrophotometer.

Ozone (O3) does not react directly with CFCs. CFCs bring about a depletion of ozone in the upper atmosphere by a mechanism that starts with the photodissociation of CFC's (by the far UV rays of the Sun) in the upper atmosphere. This generates free chlorine atoms that then react with ozone in a chain reaction culminating in its conversion to oxygen (O2).

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