Lecture No. : Ozone Hole
The color statements (except for Links) indicate quiz questions.
Please click on the world Links on the top of the screen (in Content 
Modules) for more information. Ozone hole online textbook:
1. Definition of ozone hole
 A dramatic spring time (September-October) reduction in the total
 Column ozone over the Antarctica.
2. The ozone hole extended to 45 oS.
3. The ozone hole (reduction in ozone) occurred most significantly in 
the lower stratosphere (10-20 km).
 Elevation of stratosphere: 10-50 km (6-30 miles).
4. The drop of ozone began in late August or early September as 
sunlight returned to the polar region in the South Hemisphere, 
following the end of polar night:
 Average drop of 1% per day in mid-September and bloomed over the 
Next 20 to 30 days, until the ozone content of the hole had 
dropped by about 40%.
5. The ozone holes in the other areas
 (1) Arosa, Switzerland
 Since the 1920's an average ozone loss of 3%, mostly in the 
 Past ten years.
 (2) Spitzbergen, Norway (700 miles from the North Pole)
 A. The average ozone loss has been 1.5% a year recently.
 B. This location fits the models of CFC-caused loss of ozone.
6. causes of ozone hole
 (1) CFC (Chlorofluorocarbons) theory
 A. Chemicals (CFCs-11 and 12) used as spray-can propellants,
  refrigerants, and industrial solvents.
 B. Free chlorine and bromine atoms from CFCs and halons
  catalytically destroy ozone.
 (2) weather
 A. A prevalence of polar stratospheric clouds(PSCs)that can 
 participate in the heterogeneous processes chemically. 
Heterogeneous means that the reaction does not occur only 
in the gas phase but instead requires a condensed phase 
(liquid or cloud)in order to proceed.
 B. dynamic effect
  vertical motion carrying tropospheric air with low ozone 
 into the stratosphere.
 C. An isolated antarctic air mass (cold and stable) prevents
  horizontal mixing between the polar and low latitude air.
 (3) climate
 A. Greenhouse effect
  (A) A tropospheric greenhouse warming would be 
 Accompanied by a stratospheric cooling, therefore, 
 increasing polar stratospheric clouds (PSCs).
  (B) PSCs are formed only under very low temperatures 
 and are an important media in reactions that cause 
 ozone depletion.
 B. release of methane from warming wetlands (boreal bogs)
  (A) breakdown of methane in the stratosphere increases 
 watervapor levels which through the PSC route deplete 
  (B) scavenging of methane by hydroxyl (OH-): reductions 
 Of OH- increase stratospheric ozone.
 (4) solar activities
 A. Periodic increases in solar and cosmic-ray activities may
  give rise to a greater quantity of nitrous oxide (N2O),
  through the ionization of atmospheric gases, that
  catalytically destroy ozone.
 B. 22-years solar activity cycle
  Ozone may vary by 12%.
 C. Elimination of solar activity theory
  Recently measurement at McMurdo station in 1986 indicated
  that the level of nitrous oxide in the ozone hole is very
7. Ozone has dropped since 1978 with a high rate since 1982.
8. Total ozone measurements 
(1) instruments: 
 A. Dobson spectrophotometer: surface observation.
 B. TOMS (Total Ozone Mapping Spectronmeter): Satellite 
 C. OMI (Ozone Monitoring Instrument): Satellite Observation.
 (2) 1957-1973 measurements at the British stations
 A. Faraday: 65.25 oS and 64.25 oW
  September: 330 matm cm
  late November: 400 matm cm
  after March: 300 matm cm
 B. Halley: 75.5 oS and 26.75 oW
  October 1 and March 10: 300 matm cm
  At the end of November: 375 matm cm
 (3) 1980-84 measurements (Sept to March)
 A. Halley station
  Start at 220 matm cm, peak at 340 matm, fall off more
  gradually to 270 matm cm.
 B. Faraday station
  270, 350, 275 matm cm
 C. Daily value of October at Halley Bay were substantially 
 Less than the 1957-73 mean, with minima around 180 
 matm cm.
9. Effects of the reduction of ozone
 (1) rule of thumb
 A. The ultraviolet radiation reaching the ground increases 
About 2% for each 1% decrease in the atmospheric ozone.
 B. The UV with wavelength equaling 0.26 attacks DNA or
  reproductive molecules in all living systems.
 (2) EPA estimated that a 1% drop in the global ozone could cause
 20,000 additional skin cancers in the US annually.








Dobson unit or m-atm-cm:

What is a Dobson Unit?

A dobson unit is the most basic measure used in ozone research. The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not.


The illustration above shows a column of air, 10 deg x 5 deg, over Labrador, Canada. The amount of ozone in this column (i.e. covering the 10 x 5 deg area) is conveniently measured in Dobson Units.

If all the ozone in this column were to be compressed to stp (0 deg C and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3mm thick.

1 Dobson Unit (DU) is defined to be 0.01 mm thickness at stp; the ozone layer over Labrador then is ~300 DU.

NOTE: This page, including the copyrighted graphic, is based on a page developed by Owen Garrett for the Centre for Atmospheric Science at Cambridge University, UK. The center has kindly given us permission to reproduce it. (Take their excellent Multimedia Ozone Hole Tour!)








Earth Probe TOMS to be turned off.
The transmitter on Earth Probe has failed. So the spacecraft will be turned off later
this spring (2007). For details, see the description on our News page.
Near-real-time operations with the Ozone Monitoring Instrument (OMI) data
continue on as normal.
High-Resolution OMI Data for the entire OMI mission (August 17, 2004 through
to the present) are Now Available


Please click the following URL for more information (Optional):


http://jwocky.gsfc.nasa.gov/ (TOMS Home Page)






























http://www.esa.int/esaKIDSen/SEM4HC7X9DE_Earth_1.html (for kids)