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Temperature Inversion Basics
Under most circumstances, the temperature of the atmosphere decreases with height, meaning it gets colder the higher you go. However, a temperature inversion occurs when the atmosphere actually becomes warmer as altitude increases. This typically occurs within a defined layer of the atmosphere. Temperature inversions, when they occur, have a major impact on air pollution and air quality. There are two types of inversions--permanent and surface--each corresponding to a different impact.
Permanent Inversions
Permanent temperature inversions occur high above the surface of the planet. In regard to air pollution, the most important of these is the stratosphere. This atmospheric layer stretches from an average of seven miles to 31 miles above the earth's surface. The stratosphere sits atop the troposphere, the lowest layer of the atmosphere and home to the majority of all weather. The stratosphere̵7;s temperature inversion impacts global, long-term air pollution.
Surface Inversions
Surface temperature inversions occur directly above the earth̵7;s surface, in the lower troposphere. They're frequently triggered by rapid surface cooling, caused by the release of radiant energy overnight. These inversions are also frequent during the winter months, when nights are long and the sun, low on the horizon, heats the atmosphere more than the planet̵7;s surface. Surface inversions impact local, short-term air pollution.
Atmospheric Effects
Temperature inversions affect air pollution because they change the dynamics of air movement. Warm air rises in the atmosphere because it's less dense and, therefore, more buoyant than the cooler air above it. This tendency to rise is what creates the vertical development found in thunderstorms. However, a temperature inversion prevents this vertical movement, also known as convection. Stated differently, inversions function like an atmospheric lid or blanket. This smothering effect traps air pollutants and allows their concentrations to increase.
Air Pollution Effects
Surface inversions are responsible for producing smog, trapping the pollutants produced by vehicles, fires and industrial activities. Furthermore, the hydrocarbons and nitrogen oxides present in these trapped pollutants are converted into harmful ozone by sunlight, which results in reduced air quality. The stratosphere̵7;s inversion traps pollutants within the stable layer, something that typically occurs when greenhouse gases are injected high into the atmosphere by volcanic eruptions. Without the vertical mixing provided by convection, these gases remain suspended within the inversion layer - resulted in a long-term impact on the global climate.