Bay Area Earth Science Institute (BAESI)
San Jose State University,
January 24, 2004
Weather and Climate 1
How is ozone produced?
Ozone is produced and destroyed naturally
– It is formed when oxygen absorbs solar radiation
O2 +UV radiation O+O
O+ O2 O3
Ozone reacts with various other chemicals, and thus
is highly reactive (i.e.) O + Cl ClO + O
ClO + O Cl + O2
Net : O3 +O 2O2
One Cl atom can destroy ~100,000 ozone molecules
Weather and Climate 2
Ozone, the good and the bad
Ozone is often
The ozone layer
What affects the amount of UV radiation hitting the Earth?
Time of year
Time of day
Weather and Climate 7
Weather and Climate 10
Concept Map Terms
Weather and Climate 11
History of Ozone Depletion
Chlorofluorocarbons (CFCs) developed in 1940’s
and 50’s as:
– Refrigerants, propellants, fire retardants
1970’s CFCs detected in upper atmosphere.
– Many of these have long atmospheric lifetimes:
–(10’s to 100’s of years)
– 1974 Rowland and Molina propose that CFC’s
can destroy ozone in the stratosphere.
– CFC contain chlorine (Cl)
– Chlorine can destroy ozone rapidly
Weather and Climate 12
What causes the ozone hole?
Ozone Hole Recipe (make your own!)
– 1. _____________________
– 2. _____________________
Formation of Polar Stratospheric Clouds (PSC’s)
– 3. ______________________
Sunlight to activate chemistry
Winter Polar Vortex is region of strong winds forming
an isolated ‘container’ from the middle latitudes.
– This produces cold temperatures.
– Allows chemistry to develop undisturbed.
Weather and Climate 15
Is the ozone hole getting much
No, not over
the last few
Weather and Climate 17
What is being done about ozone
Montreal Protocol ~ (1988) international agreement
to phase out ozone depleting chemicals
Further amendments accelerated the phase out.
– Developed countries have switched to HCFC’s
(more ozone friendly!)
– Developing countries have until 2004 to phase
Weather and Climate 18
Is the Montreal Protocol working?
Seems to be…
Recent observations indicate that chlorine is
beginning to decline in the atmosphere.
Weather and Climate 19
Weather and Climate 20
What is the connection between ozone
depletion and global warming?
No direct connection between these environmental
However: Global warming may enhance
Global warming produces:
– Tropospheric warming & stratospheric cooling
– Therefore, if the stratosphere cools, then ozone
destroying chemistry (e.g. ozone hole), will
Weather and Climate 21
What are predictions for the future?
Model simulations suggest:
– atmospheric chlorine will return to pre-80’s level
In next 50 years or so
A slow ozone recovery should follow
decreasing chlorine concentrations!!!
– Uncertainties still remain:
Phase out of CFC’s
Influence of global warming
Weather and Climate 22
Concept Map Terms
Sun Dobson Unit
Gas Total Ozone
Skin Cancer Tropospheric ozone
Summer Good ozone
Winter Stratospheric ozone
Spring Bad ozone
South Pole TOMS
Ozone hole 2050
Chlorine Cold temperatures
Weather and Climate 23
present in is a causes
is present in the
is depletion of protects the
earth from produce
Good Ozone Bad
CFC’s may cause
has has Warming
is the column
is measurement of Ozone
Ozone depletion and global warming often
– Ozone depletion – CFC’s (aerosols, refrigerants)
– Global Warming – burning of fossil fuels
Some student ideas
– Hole in ozone hole allows more heat into
– Automobile exhaust responsible for ozone
Weather and Climate 25