Lecture No. : Ozone Hole
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1. Definition of ozone hole
A dramatic spring time (September-October) reduction in the total
Column ozone over the
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
Since the 1920's an average ozone loss of 3%, mostly in the
Past ten years.
(700 miles from the North Pole) Spitzbergen, Norway
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.
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.
(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
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 (
): reductions OH-
increase stratospheric ozone. OH-
(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
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
were substantially Halley Bay
Less than the 1957-73 mean, with minima around 180
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 0.26µ 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
Dobson unit or m-atm-cm:
What is a Dobson Unit?
unit is the most basic measure used in ozone research. The unit is named
The illustration above shows a column of air, 10 deg x 5 deg, over
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
NOTE: This page, including the copyrighted graphic, is
based on a page developed by Owen
· 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)