Page 109 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 3 earth’s Modern atmosphere 73
UV damage to skin and eyes can occur over a shorter time period. UV radiation varies spatially according to the amount of ozone depletion overhead, the season, and the local weather conditions.
With stratospheric ozone levels at thinner-than- normal conditions, surface exposure to cancer-causing radiation increases. Remember, skin damage accumu- lates, and it may be decades before you experience the ill effects triggered by this summer’s sunburn. See www .epa.gov/sunwise/uvindex.html for the UVI at U.S. locations; in Canada, go to www.ec.gc.ca/ozone/.
Pollutants in the Atmosphere
At certain times or places, the troposphere contains nat- ural and human-caused gases, particles, and other sub- stances in amounts that are harmful to humans or cause environmental damage. Study of the spatial aspects of these atmospheric pollutants is an important applica- tion of physical geography with far-reaching human- health implications.
Air pollution is not a new problem. Historically, air pollution has collected around population centres and is closely linked to human production and consumption of energy and resources. Romans complained more than 2000 years ago about the foul air of their cities. Filling Roman air was the stench of open sewers, smoke from fires, and fumes from ceramic-making kilns and from smelters (furnaces) that converted ores into metals.
Solutions to air quality issues require regional, na- tional, and international strategies because the pollution sources often are distant from the observed impact. Pollu- tion crosses political boundaries and even oceans. Regula- tions to curb human-caused air pollution have had great success, although much remains to be done. Before dis- cussing these topics, we examine natural pollution sources.
Natural Sources of Air Pollution
Natural sources produce greater quantities of air pollutants—nitrogen oxides, carbon monoxide, hydro- carbons from plants and trees, and carbon dioxide—than do sources attributable to humans. Table 3.3 lists some of these natural sources and the substances they contribute to the air. Volcanoes, forest fires, and dust storms are the most significant sources, based on the volume of smoke and particulates produced and blown over large areas. However, pollen from crops, weeds, and other plants can also cause high amounts of particle pollution, triggering asthma as well as other adverse human health effects. The particulates produced by these events are also known as aerosols, and include the liquid droplets and suspended solids that range in size from visible water droplets and pollen to microscopic dust. (Aerosols produced from human sources are discussed in the next section.)
A dramatic natural source of air pollution was the 1991 eruption of Mount Pinatubo in the Philippines
TABLE 3.3 Sources of Natural Pollutants
Source
Contribution
Volcanoes
Plants Soil
Sulfur oxides, particulates
Hydrocarbons, pollens Dust and viruses
Forest fires
Carbon monoxide and dioxide, nitrogen oxides, particulates
Decaying plants
Methane, hydrogen sulfides
Ocean
Salt spray, particulates
(discussed in Chapter 1), probably the 20th century’s second-largest eruption. This event injected about 18 mil- lion tonnes of sulfur dioxide (SO ) into the stratosphere.
2
The spread of these emissions is shown in a sequence of
satellite images in Chapter 6, Figure 6.1.
Wildfires are another source of natural air pollution
and occur frequently on several continents (Figure 3.5). Soot, ash, and gases darken skies and impair human health in affected regions. Wind patterns can spread the pollution from the fires to nearby cities, closing airports and forcing evacuations to avoid the health-related dan- gers. Satellite data show smoke plumes travelling hori- zontally for distances up to 1600 km. Smoke, soot, and particulates can be propelled vertically as high as the stratosphere.
▲Figure 3.5 Smoke from wildfires in Yukon. Plumes of smoke from fires near the centre of this image acquired on July 14, 2013,
are spreading toward the southeast (lower right). The 2013 yukon fire season ended in September after 176 fires had burned approximately 270 000 hectares of land. it was the fifth most severe season in
55 years. [naSa earth Observing System.]
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