Urban ecology in temperate climates. Greenhouse gas emissions include those of carbon dioxide and methane from the combustion of fossil fuels to supply energy needed by vast urban metropolises. Other greenhouse gases include water vapor, and nitrous oxide. Increases in greenhouse gases due to urban transport, construction, industry and other demands have been correlated strongly with increase in temperature. Sources of methane are agricultural dairy cows and landfills. Processes related to urban areas result in the emission of numerous pollutants, which change corresponding nutrient cycles of carbon, sulfur, nitrogen, and other elements. Ecosystems in and around the urban center are especially influenced
Sulfur hexafluoride circuit breaker Sulfur hexafluoride circuit breaker Sulfur hexafluoride circuit breakers protect electrical power stations and distribution systems by interrupting electric currents, when tripped by a protective relay. Instead of oil, air, or a vacuum, a sulfur hexafluoride circuit breaker uses sulfur hexafluoride (SF) gas to cool and quench the arc on opening a circuit. Advantages over other media include lower operating noise and no emission of hot gases, and relatively low maintenance. Developed in the 1950s and onward, SF circuit breakers are widely used in electrical grids at transmission voltages up to 800 kV, as generator circuit breakers, and in distribution systems