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1、Lesson 14Air pollutionAir pollution is the human introduction into the atmosphere of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment. Air pollution causes deaths and respiratory disease. Air
2、pollution is often identified with major stationary sources, but the greatest source of emissions is mobile sources, mainly automobiles. Gases such as car bon dioxide, which contribute to global warming, have recently gained recognition as pollutants by climate scientists, while they also recognize
3、that carbon dioxide is essential for plant life through photosynthesis.The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to
4、the Earths ecosystemsAn air pollutant i s known as a substance in the air that can cause harm to humans and the environment. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made.Pollutants can be classified as primary or secondary.
5、 Usually, primary pollutants are directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories.Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants r
6、eact or interact. An important example of a secondary pol lutant is ground 1 evel ozone one of the many secondary pollutants that make up photochemical smog.Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.M
7、ajor primary pollutants produced by human activity include: Sulfur oxides (SOx) especially sulfur dioxide, a chemical compound with the formula S02. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates s
8、ulfur dioxide. Further oxidation of SO2, usual 1y in the presence of a catalyst such as NO2, forms H2SO1, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources. Nitrogen oxides (NOx) especially nitrogen dioxide are emitted
9、fromhigh temperature combustion. Can be seen as the brown haze dome above or plume downwind of cities. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. N02 is one of the mos
10、t prominent air pollutants. Carbon monoxide 一 is a colorless, odorless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide. Carbon dioxide (CO2), a greenhouse gas emitted fo
11、rm combustion. Volatile organic compounds VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH1) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hyd
12、rocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and
13、 may 1 ead to leukemia through prolonged exposure.1 , 3-butadiene is another dangerous compound which is often associated with industrial uses. Particulate matter Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles ofsolid or 1iquid suspended in a
14、 gas. Tn contrast, aerosol refersto particles and the gas together, can be man made or natural. Some originating from volcanoes, dust fires, living vegetation, and seaSources of particulate matter particulates occur naturally, storms, forest and grassland spray. Human activities, suchas the burning
15、of fossi1 fuels in vehicles, power plants andvarious industrial processes al so generate significant amounts ofaerosols. Averaged over the globe, anthropogenic aerosolsthosemade by human activitiescurrently account for about 10 percentof the total amount of aerosols in our atmosphere. Increased leve
16、ls of fine particles in the air are 1 inked to heal th hazards such as heart disease, altered lung function and lung cancer. Toxic metals, such as lead, cadmium and copper. Chlorofluorocarbons (CFCs), harmful to the ozone layer emittedfrom products currently banned from use. Ammonia (NII3), emi tted from agricul tural processes. Ammonia is a compound with the formula NH3. It is normally encountered as a gaswith a chara
