Environmental Problems, Their Causes, and Sustainability 1

UltrafineParticlesSea salt nucleiFineParticlesCarbon blackPaint pigmentsTobacco smokeCombustion nucleiOil smokeMetallurgical dust and fumesPhotochemical smogFly ashCement dustMilled flourCoal dustInsecticide dustsLargeParticlesPollens0.001 0.01 2.5 10.0 100.0Average particle diameter (micrometers or microns)Figure 20-6 Suspended particulate matter consists of particlesof solid matter and droplets of liquid that are small and lightenough to remain suspended in the atmosphere for some period(the larger the particle, the sooner it usually falls to earth).Suspended particles are found in a wide variety of types andsizes, ranging in diameter from 0.001 micrometer to 100 micrometers(a micrometer, or micron, is one-millionth of a meter,or about 0.00004 inch). Since 1987, the EPA has focused onfine particles smaller than 10 microns (known as PM-10). In1997, the agency began focusing on reducing emissions ofultrafine particles with diameters less than 2.5 microns (knownas PM-2.5) because these particles are small enough to reachthe lower part of human lungs and contribute to respiratorydiseases.suspended droplets of sulfuric acid (H 2 SO 4 ). Some ofthese droplets react with ammonia in the atmosphere toform solid particles of ammonium sulfate [(NH 4 ) 2 SO 4 ].The tiny suspended particles of such salts and carbon(soot) give the resulting industrial smog a gray color,explaining why it is sometimes called gray-air smog.Today urban industrial smog is rarely a problemin most developed countries. This has happened becausecoal and heavy oil are burned only in large boilerswith reasonably good pollution control or with tallsmokestacks that transfer the pollutants to downwindrural areas.However, industrial smog is a problem in industrializedurban areas of China, India, Ukraine, andsome eastern European countries (especially the“black triangle” region of Slovakia, Poland, Hungary,and the Czech Republic), where large quantities of coalare burned with inadequate pollution controls.In addition to providing electricity and runningindustries, coal is burned for heating homes and cookingby millions of poor families. As a result, China hassome of the world’s most polluted indoor and outdoorair. This explains why many residents of Beijing developserious respiratory problems and some die prematurelyfrom the coal-generated air pollution. Afteronly a few days in this region visitors often suffer fromcoughs and bronchial irritation.Some Chinese cities have so many smokestacksand home chimneys belching coal smoke that residentssee the sun for only a few weeks a year. This is similarto conditions in many U.S. cities a hundred years agoand earlier in many European cities (Spotlight, p. 437).What Factors Influence the Formationof Photochemical and Industrial Smog?Rain, Wind, Buildings, Mountains, andTemperatureOutdoor air pollution can be reduced by precipitation,sea spray, and winds and increased by urban buildings,mountains, and high temperatures.The frequency and severity of smog in an area dependon local climate and topography, population density,the amount of industry, and the fuels used in industry,heating, and transportation.Three natural factors help reduce outdoor air pollution.One is rain and snow, which help cleanse the airof pollutants. This helps explain why cities with dryclimates are more prone to photochemical smog thancities with wet climates. A second factor is salty seaspray from the oceans, which can wash out particulatesand other water-soluble pollutants from air that flowsfrom land onto the oceans.A third factor is winds, which can help sweep pollutantsaway, dilute them by mixing them with cleanerair, and bring in fresh air. However, these pollutantsare blown somewhere else or are deposited from thesky onto surface waters, soil, and buildings. There isno away.Four other factors can increase outdoor air pollution.One is urban buildings, which can slow wind speedand reduce dilution and removal of pollutants. Anotheris hills and mountains. They can reduce the flow ofair in valleys below them, allowing pollutant levels tobuild up at ground level. In addition, high temperaturesfound in most urban areas promote the chemical reactionsleading to photochemical smog formation.A fourth factor is called the grasshopper effect basedon atmospheric distillation, which transfers volatile airpollutants from tropical and temperate areas to theearth’s poles. It occurs when volatile compoundshttp://biology.brookscole.com/miller14441