Chapter 17 Air resources The atmosphere layer is very thin compared to the size of the Earth.

17.1 The Earth’s atmosphere is a mixture of gases. Our atmosphere is a result of actions of both heat and gravity (a) Atmosphere with gravity but no solar heat: molecules lie on the earth’s surface (a) Atmosphere with solar heat but no gravity : molecules escape into outer space (a) Atmosphere with solar heat and gravity : molecules reach high altitudes but are prevented from escaping into outer space Fig 17.1 our atmosphere is a result of the actions of both solar heat and gravity

Atmosphere is divided into layers. Fig 17.2 the two lowest atmospheric layers-troposphere and stratosphere

17.2 Human activities have increased air pollution Volcano Fig 17.3 the cloud of sulfur dioxide generated by the June 15,1991, eruption of Mount Pinatubo reached India in four days. (the black strips are where satellite data are missing.) by July 27, the sulfur dioxide cloud had traveled around the globe

Aerosol ( 烟、雾、气凝胶 ) and particulates facilitate chemical reactions involving pollutants Aerosol Fig 17.4 (a) micrograph of aerosols in the atmosphere. (b) an aerosol is the site of many chemical reactions involving pollutants. Water surrounding the solid particle attracts airborne molecules that them readily react in aqueous solution before being released back into the atmosphere

Removal of Aerosol and particulates Fig 17.5 during scrubbing of industrial gaseous effluents, a fine mist of water captures and removes solid particles that have diameters as small as millimeter.

Fig 17.6 (a) particulates in industrial gaseous effluents become negatively charged by an electrode and are attracted to the positively charged wall of the electrostatic precipitator. Once it touches the wall, a particulate loses its charge and falls into a collection bin. (b) smokestacks with and without electrostatic precipitators Without electrostatic precipitator With electrostatic precipitator To collection bin electrode particles voltage(+)(-) Gas and suspende d particles Gas

There are two kinds of smog: Industrial and photochemical Industrial smog: sulfur dioxide and sulfuric acid Photochemical smog: nitrogen oxides, ozone and hydrocarbons from internal combustion engine. Catalytic converters reduce automobile emissions Fig 17.8 the average daily concentration of nitrogen monoxide, nitrogen dioxide, and ozone in Los Angeles *ppm = parts per million nightsunrisenoonsunsetnight NO,NO 2,O 3 (ppm)

17.3 Stratospheric ozone protects the Earth from UV radiation O 3 + UV O 3 + heat Fig false-color image of ozone levels over the Northern Hemisphere, recorded by NASA’s total- ozone mapping spectrometer (TOMS). Blue and purple areas are areas of ozone depletion; red and green areas are areas of higher-than-normal ozone levels.

17.4 Air pollution may result in global warming Fig glass acts as a one-way valve, letting visible light in and preventing infrared energy from exiting. Fig the greenhouse effect in the earth’s atmosphere. Visible light from the sun is absorbed by the ground, which then emits infrared radiation. Carbon dioxide, water vapor, and other greenhouse gases in the atmosphere absorb and re- emit heat that would otherwise be radiated from the earth into space Long-wavelength infrared radiation is not transmitted out through the glass and is trapped inside Short-wavelength visible light from the sun is transmitted through the glass

Atmospheric carbon dioxide is a greenhouse gas Increased emission from carbon dioxide is mainly from burning of fossil fuel and deforestation. The potential effects of global warming are uncertain levels of atmospheric carbon dioxide and global temperatures appear to be closely related to each other