Environmental Problems, Their Causes, and Sustainability 1

layer of rising and falling air currents and winds islargely responsible for the planet’s short-term weatherand long-term climate.To biologist and environmental scientist DavidSuzuki, “Air is a matrix or universal glue that joins alllife together. . . . Every breath is an affirmation of ourconnection with other living things, a renewal of ourlink with our ancestors, and a contribution to generationsyet to come.”What Is the Stratosphere? Earth’sGlobal SunscreenOzone in the atmosphere’s second layer filters outmost of the sun’s UV radiation that is harmful to usand most other species.The atmosphere’s second layer is the stratosphere,which extends from about 17 to 48 kilometers (11–30miles) above the earth’s surface (Figure 20-2). Althoughthe stratosphere contains less matter than thetroposphere, its composition is similar, with two notableexceptions: its volume of water vapor is about1/1,000 as much and its concentration of ozone (O 3 ) ismuch higher (Figure 20-3).Stratospheric ozone is produced when some of theoxygen molecules there interact with ultraviolet (UV)radiation emitted by the sun (3 O 2 UV 2 O 3 ).This “global sunscreen” of ozone in the stratospherekeeps about 95% of the sun’s harmful UV radiationfrom reaching the earth’s surface.Altitude (kilometers)403530252015Stratospheric ozoneStratosphere105Troposphere5Photochemical ozone000 5 10 15 20Ozone concentration (ppm)Figure 20-3 Natural capital: average distribution and concentrationsof ozone in the troposphere and stratosphere. Beneficialozone that forms in the stratosphere protects life on earthby filtering out most of the incoming harmful UV radiation emittedby the sun. Harmful or photochemical ozone forms in thetroposphere when various air pollutants undergo chemical reactionsunder the influence of sunlight. Ozone in this atmospherenear the earth’s surface damages plants, lung tissues,and some materials such as rubber.25201510Altitude (miles)This UV filter of “good” ozone in the lower stratosphereallows us and other forms of life to exist onland and helps protect us from sunburn, skin and eyecancer, cataracts, and damage to our immune systems.It also prevents much of the oxygen in the tropospherefrom being converted to photochemical ozone, a harmfulair pollutant.Much evidence indicates that some human activitiesare decreasing the amount of beneficial or “good”ozone in the stratosphere and increasing the amount ofharmful or “bad” ozone in the troposphere—especiallyin some urban areas.20-2 OUTDOOR AIR POLLUTIONWhat Are the Major Types and Sourcesof Air Pollution? Burning Fossil FuelsIs the Major CulpritOutdoor air pollutants come mostly from naturalsources and burning fossil fuels in motor vehiclesand power and industrial plants.Air pollution is the presence of chemicals in the atmospherein concentrations high enough to affect climateand harm organisms and materials. The effects ofairborne pollutants range from annoying to lethal.Table 20-1 (p. 436) lists the major classes of pollutantscommonly found in outdoor (ambient) air. Themajority comes from natural sources. They includedust particles blowing off the earth’s surface (Figure6-1, p. 102), volatile organic chemicals released bysome plants, the decay of plants, forest fires, volcaniceruptions, and sea spray. Most natural sources of airpollution are spread out and, except for those fromvolcanic eruptions and some forest fires, rarely reachharmful levels.Air pollution is not new (Spotlight, p. 437).Throughout human history, beginning with the discoveryof fire, we have added various types of pollutantsto the troposphere. Our inputs increased whenwe began extracting and burning coal, first for heatand later for generating electricity and producing materialssuch as steel.Burning oil, gasoline, and natural gas also addspollutants to the atmosphere. Pollutants from our activitiescan reach harmful levels in the troposphere,especially in urban areas where people, cars, and industrialactivities are concentrated.Most outdoor pollutants in today’s urban areas enterthe atmosphere from the burning of fossil fuels inpower plants and factories (stationary sources) and inmotor vehicles (mobile sources). Scientists classifyoutdoor air pollutants into two categories. Primarypollutants are those emitted directly into the tropospherein a potentially harmful form. Examples are soothttp://biology.brookscole.com/miller14435