Exam 19: Air Pollution

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Beijing has the worst air quality in the world. The primary causes of the air pollution problems are a rapidly-increasing population and the resulting increases in automobile exhaust, dust from construction sites, and coal-powered electricity production. In preparation for the 2008 summer Olympics, Beijing took significant steps to decrease its air pollution. Efforts included increasing public transportation, improving power plants and switching to low-sulfur coal, and improving automobile emission standards.
Air pollution in Mexico City is primarily caused by automobile exhaust from older vehicles (gasoline in Mexico also contains many contaminants), dried fecal matter from sewage, and leaks from liquefied petroleum gas lines. In addition to its large population, Mexico City's air pollution problems are related to its topographical setting. Mexico City is located in a bowl-shaped valley ringed on three sides by mountains, making temperature inversions fairly common during the late fall and early winter months. To improve Mexico City's air quality, steps have been taken to introduce cleaner vehicles, cleaner gasoline, driving restrictions, and emissions testing. Moreover, Mexico's national oil company has upgraded its refineries, and increased imports of cleaner fuel from the United States.

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Ozone is found in both the stratosphere (10-45 km above earth's surface) and the troposphere (atmosphere closest to Earth). Ozone in the stratosphere, which occurs as a result of oxygen reacting with ultraviolet radiation, prevents much of the damaging solar UV radiation from penetrating to the Earth's surface. Unfortunately, ozone in the stratosphere is threatened by man's use of chemicals like CFCs, which break down the ozone into oxygen. Ozone in the troposphere is a human-made secondary pollutant. Ozone in the troposphere causes health problems and stresses plants. Ozone in the troposphere does not ever find its way to the stratosphere to fix the declining composition there. Thus, reducing ozone in the stratosphere and increasing ozone in the troposphere are both air quality concerns, though for different reasons.