Page 62 - Fundamentals of Air Pollution 3E

38 3. Scales of the Air Pollution Problem

IV. CONTINENTAL

In a relatively small continental area such as Europe, there is not much
difference between what would be considered the regional scale and the
continental scale. However, on most other continents there would be a
difference between what is considered regional and what continental. Per-
haps of greatest concern on the continental scale is that the air pollution
policies of a nation are likely to create impacts on neighboring nations.
Acid rain in Scandanavia has been considered to have had impacts from
Great Britain and Western Europe. Japan has considered that part of their
air pollution problem, especially in the western part of the country, has
origins in China and Korea. Cooperation in the examination of the North
American acid rain problem has existed for a long time between Canada
and the United States.

V. GLOBAL

The release of radioactivity from the accident at Chernobyl would be
considered primarily a regional or continental problem. However, higher
than usual levels of radioactivity were detected in the Pacific Northwest
part of the United States soon after the accident. This indicates the long-
range transport that occurred following this accident.
One air pollution problem of a global nature is the release of chlorofluoro-
carbons used as propellants in spray cans and in air conditioners and their
effect on the ozone layer high in the atmosphere. (See Chapter 11.)
Some knowledge of the exchange processes between the stratosphere
and the troposphere and between the Northern and Southern Hemispheres
was learned in the late 1950s and early 1960s as a result of the injection of
radioactive debris into the stratosphere from atomic bomb tests in the
Pacific. The debris was injected primarily into the Northern Hemisphere
in the stratosphere. The stratosphere is usually quite stable and resists
vertical air exchange between layers. It was found that the exchange pro-
cesses in the stratosphere between the Northern and Southern Hemi-
spheres is quite slow. However, radioactivity did show up in the Southern
Hemisphere within 3 years of the onset of the tests, although the levels
remained much lower than those in the Northern Hemisphere. Similarly,
the exchange processes between the troposphere and the stratosphere are
quite slow. The main transfer from the troposphere into the stratosphere
is injection through the tops of thunderstorms that occasionally penetrate
the tropopause, the boundary between the troposphere and the strato-
sphere. Some transfer of stratospheric air downward also occurs through
occasional gaps in the tropopause. Since the ozone layer is considerably
above the stratosphere, the transfer of chlorofluorocarbons upward to the