Global Stratospheric Ozone Reduction - Air Pollution and Global Warming: History, Science, and Solutions - page 238

same number of molecules as a column of air 2.92 mm
high at 1 atm of pressure and 273 K (near-surface condi-
tions). Figure 11.1 illustrates ozone column abundance.
Figure 11.2 shows the variation in the ozone column
abundance with latitude (zonally averaged, or averaged
overall longitudes) and day of the year in 2010. It
exhibits the following features:

Top of the atmosphere

293-Dobson unit column of ozone
=293 10 16 molecules cm -2

=2.93-mm column of air at 273 K and 1 atm

× 2.7 ×

Stratosphere
and above

2.93-mm high
column of air

Troposphere

A year-round equatorial ozone minimum due to
upward motion of ozone-poor air from the tropo-
sphere that displaces ozone-rich air horizontally to
higher latitudes. The column abundance over the
Equator is typically 250 to 290 DUs all year.

Surface

Figure 11.1. Example of globally averaged column
abundance of ozone. The number of ozone molecules
per unit area of surface in a 293-DU column of ozone
is equivalent to the number of air molecules in a
2.93-mm-high column near the surface.
(The figure is not to scale.)

ANorthern Hemisphere (NH) spring (March-May)
maximum, ranging from 350 to 460 DUs, near the
North Pole. The maximum is due to the northward
transport of stratospheric ozone from the Equator. As
ozone converges at the pole, it descends, increasing
the ozone column abundance.

column abundance in Dobson units (DUs). Thus, 1 DU
equals 2.7

10 16 molecules of ozone per square cen-
timeter of surface. The DU is named after Gordon M.
B. Dobson (1889-1976), a researcher at Oxford Uni-
versity, who, in the 1920s, built the first instrument, now
called a Dobson meter, to measure total ozone column
abundance from the ground. In 2010, the globally aver-
aged column abundance of ozone from 90 ◦ Sto90 ◦ N
was 291.5 DUs. This column abundance contains the

× A Southern Hemisphere (SH) spring (September-

November) subpolar (60 ◦ S-65 ◦ S) maximum, usually
ranging from 350 to 440 DUs. The maximum is due to
the southward transport of ozone from the Equator.
As the ozone moves south, much of it is forced to
descend in front of the polar vortex ,apolar front jet
stream wind system that travels around the Antarctic
continent in the upper troposphere and stratosphere.

Ozone (DU) by latitude/day of year 2010 (Global: 291.5)

90

400

300

0

200

100

-90

0 90 180 270 360

Figure 11.2. Variation in zonally averaged ozone column abundance with latitude and day of year during 2010.
Blank regions near the poles indicate locations where data were not available. Data for the figure were
obtained from the satellite-based Total Ozone Mapping Spectrometer (TOMS) and made available by NASA
Goddard Space Flight Center, Greenbelt, Maryland.