7
THE ANTARCTIC HOLE
THE ANTARCTIC HOLE CHEMIC
CHEMICAL
AL OZONE DESTR
OZONE DESTRUCTION PROCESS
UCTION PROCESS
October 1981 October 1991
IN THE STRAIN THE STRATOSPHERETOSPHERE
Altitude
Australia Australia
Kilometers
Tasmania Tasmania
50
South America South America
Antarctic
40
STRATO
Antarctic UV rays
HOLE
HOLE
2 -...RELEASING
1 - UV RAYS
CHLORINE
BREAK DOWN
CFC MOLECULES...
Cl
30
SPHERE
Total ozone column: 220 310 390 430 Dobson Units
(monthly averages)
O
Ozone
3
Less More ozone layer
20
3 - CHLORINE
BREAKS DOWN
September 24, 2006
CFCs
OZONE MOLECULES
10
ODS release
TROPO
HCFCs
N
2
0
Methyl
Halons
0
bromide SPHERE
220 0 10 20 30 40
Dobson
Units Ozone amounts Pressure, milli-pascals
HOLE
stratospheric ozone,
tropospheric ozone and
the ozone “hole”
Ozone forms a layer in the stratosphere, thinnest
in the tropics and denser towards the poles. The
amount of ozone above a point on the earth’s sur-
From September 21-30, 2006, the average area of the ozone hole
was the largest ever observed.
face is measured in Dobson units (DU) – it is typi-
cally ~260 DU near the tropics and higher elsewhere,
Source: US National Oceanic and Atmospheric Administration (NOAA) using Total Ozone
though there are large seasonal fluctuations. Ozone
Mapping Spectrometer (TOMS) measurements; US National Aeronautics and Space
Administration (NASA), 2007. is created when ultraviolet radiation (sunlight) strikes
the stratosphere, dissociating (or “splitting”) oxygen
molecules (O
2
) into atomic oxygen (O). The atomic
oxygen quickly combines with oxygen molecules to
form ozone (O
3
).
The ozone layer over the Antarctic has been thinning
steadily since the ozone loss predicted in the 1970s
The ozone hole is defined as the surface of the Earth
was first observed in 1985. The area of land below the
covered by the area in which the ozone concentra-
ozone-depleted atmosphere increased steadily to en-
tion is less than 220-Dobson units (DU). The larg-
compass more than 20 million square kilometres in the
est area observed in recent years covered 25 million
early 1990s, and has varied between 20 and 29 million
square kilometres, which is nearly twice the area of
square kilometres since then. Despite progress achieved
the Antarctic. The lowest average values for the total
under the Montreal Protocol, the ozone “hole” over the
amount of ozone inside the hole in late September
Antarctic was larger than ever in September 2006. This
dropped below 100 DU.
was due to particularly cold temperatures in the strat-
osphere, but also to the chemical stability of ozone-
At ground level, ozone is a health hazard – it is a
depleting substances – it takes about 40 years for them
major constituent of photochemical smog. Motor
to break down. While the problem is worst in the polar
vehicle exhaust and industrial emissions, gasoline
areas, particularly over the South Pole because of the
vapors, and chemical solvents as well as natural
extremely low atmospheric temperature and the pres-
sources emit NO
x
and volatile organic compounds
ence of stratospheric clouds, the ozone layer is thinning
(VOCs) that help form ozone. Ground-level ozone is
all over the world outside of the tropics. During the Arctic
the primary constituent of smog. Sunlight and hot
spring the ozone layer over the North Pole has thinned
weather cause ground-level ozone to form in harmful
by as much as 30 per cent. Depletion over Europe and
concentrations in the air.
other high latitudes has varied from 5 to 30 per cent.
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