Page 117 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 3 earth’s Modern atmosphere 81
Atlantic Ocean
Western Sahara Mauritania
N 100 km
N Cape Verde
(a) Typical wind-carried dust moves off West Africa in October 2012 (b) Dust plumes rise out of the White Sands dune field, New Mexico, over the Cape Verde islands and across the Atlantic. in 2012. Driven by winter winds, these plumes stretch eastward
more than 120 km over the Sacramento Mountains.
▲Figure 3.6 Winds carrying dust in the atmosphere. [(a) lanCe MODiS rapid response Team, naSa gSFC. (b) iSS astronaut photograph iSS030-e-174652, image Science and analysis laboratory, naSa/JSC10.]
There is no comparable haze over the Antarctic con- tinent. Based on previous page discussion, can you think of why Antarctica lacks such a condition?
Local and Regional Landscapes Local and regional landscapes are another important factor affecting the movement and concentration of air pollutants. Moun- tains and hills can form barriers to air movement or can direct the movement of pollutants from one area to an- other. Some of the worst air quality results when local landscapes trap and concentrate air pollution.
Places with volcanic landscapes, such as Iceland and Hawai‘i, have their own natural pollution. During periods of sustained volcanic activity at K¯ılauea, some 2000 tonnes of sulfur dioxide are produced a day. Concentrations are sometimes high enough to merit broadcast warnings about health concerns, as occurred in 2011, 2012, and 2013. The resulting acid rain and volcanic smog, called vog by Hawaiians (for volcanic smog), cause losses to agriculture as well as other eco- nomic impacts.
Temperature Inversions Vertical differences in tem- perature and atmospheric density in the troposphere also can worsen pollution conditions. A temperature inversion occurs when the normal temperature, which usually decreases with altitude (normal lapse rate), re- verses trend and begins to increase at some point. This can happen at any elevation from ground level to several thousand metres.
Figure 3.7 (page 84) compares a normal temperature profile with that of a temperature inversion. In the normal profile (Figure 3.7a), air at the surface rises because it is warmer (less dense) than the surrounding air. This ven- tilates the valley and moderates surface pollution by al- lowing air at the surface to mix with the air above. When an inversion occurs, colder (more dense) air lies below a
warmer air layer (Figure 3.7b) that halts the vertical mix- ing of pollutants with other atmospheric gases. Thus, in- stead of being carried away, pollutants are trapped under the inversion layer. Inversions most often result from cer- tain weather conditions, discussed in Chapters 7 and 8, or from topographic situations such as when cool mountain air drains into valley bottoms at night (see discussion of local winds in Chapter 6).
Benefits of the Clean Air Act
The concentration of many air pollutants declined over the past several decades because of the U.S. Clean Air Act (CAA) legislation (1970, 1977, 1990), saving trillions of dollars in health, economic, and environmental losses. Despite this well-documented relationship, air pollution regulations are subject to a continuing political debate.
Since 1970 and the CAA, there have been significant reductions in atmospheric concentrations of carbon mon- oxide (–82%), nitrogen dioxide (–52%), volatile organic compounds (–48%), PM10 particulates (–75%), sulfur ox- ides (–76%; see Focus Study 3.2, Figure 3.2.2), and lead (–90%). Prior to the CAA, lead was added to gasoline, emitted in exhaust, and dispersed over great distances, finally settling in living tissues, especially in children. These remarkable reductions show the successful link- ing of science and public policy.
For abatement (mitigation and prevention) costs to be justified, they must not exceed the financial ben- efits derived from reducing pollution damage. Com- pliance with the CAA affected patterns of industrial production, employment, and capital investment. Al- though these expenditures were investments that gen- erated benefits, the dislocation and job loss in some regions caused hardships—reductions in high-sulfur coal mining and cutbacks in polluting industries such as steel, for example.
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San Andres Mountains
Carrizozo lava field
Sacramento Mountains
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