3. An electric utility is planning to build a coal-fired generating plant in You
ID: 287071 • Letter: 3
Question
3. An electric utility is planning to build a coal-fired generating plant in Your Town, USA. During the winter, inversions often occur in the area due to radiation cooling. During a typical inversion, the air temperature found at 2000 m at the top of the inversion is 10C higher than that found at the surface. From the top of the inversion upwards, the atmosphere usually cools with a lapse rate of 7C km-1. The company plans to build a smoke stack which is 100 m high, and the gases will emerge from the smokestack at a temperature of 30C. Assume that the gases emerging from the smokestack cool at the dry adiabatic lapse rate (1C/100m). On a day when the surface temperature is 5C, will air pollution be a problem? Explain.
Explanation / Answer
The air pollution will be a problem on a day with 5°c surface temperature with not very turbulent winds at the surface.
The surface termperature inversions occur when air temperature increases with height from the ground level, which is the opposite of the normal phenomenon of decrease in the temperature as the height increases, or the temperature profile gets inverted. As a result of this, a layer of cool still air becomes trapped below warmer air.
The height at which the temperature increase from ground stops and temperature begins to decrease is called the inversion layer. At the inversion layer,the particulates and droplets (in the current example, the emission from the 100m smoke stack) will get concentrated in the cool layer, and gets isolated from the surrounding weather conditions. The movement of emissions will then be unpredictable, and can cause the particulate to spread anywhere, and can thicken the smog conditions (since winter fogs usually associated with the temperature inversions can fuse with smoke, causing smog conditions).
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