Wind profiles and stack plume patterns
- 1. Wind profiles and stack plume patterns •The dispersion of emitted gases from the source of their production is known as plume. •The source is known as stack (chimney). •The behavior of a plume emitted from any stack depends on localized air stability. •The geometric forms of stack plumes are the function of the vertical temperature and wind profiles or vice versa. •The behavior and dispersion of a plume entirely depend on the environmental lapse rate influencing the plume behavior are the diurnal(seasonal) variations in the atmospheric stability and the long term variations which occur with change in seasons.
- 2. Six types of plume behavior • Fanning plumes • Looping plumes • Coning plumes • Fumigating plumes • Lofting plumes • Trapping plume
- 3. Fanning plume requires stable air and slow vertical movement of the emission. It is common after calm clear nights. The temperature inversion limits the rise of the plume into the upper atmosphere. Creates a higher concentration of polluted air at lower levels. It exists for several hours. It is a type of plume emitted under these extreme inversion conditions. The plume under those conditions will spread horizontally, but little it at all vertically. therefore the prediction of ground level concentration is difficult here. Fanning plume
- 4. Looping plume requires windy conditions which cause the plume can swirl up and down. It is common in the afternoon. Moderate and strong winds are formed on sunny days creating unstable conditions. It is a type of plume which has a wavy character. It occurs in a highly unstable atmosphere because of rapid mixing. The high degree of turbulence helps in dispersing the plume rapidly but high concentrations may occur close to the stack if the plume touches the ground. It exists for several hours. Looping plume
- 5. Cone shaped plume. This take place in a near neutral atmosphere, when the wind velocity is greater than 32 km/hr. However the plume reaches the ground at greater distances than with looping. it requires moderate winds and overcast days. It is wider than it is deep, and is elliptical in shape. Coning plume exists for several hours. Coning plume
- 6. Fumigating plume is short-lived (fraction of an hour), but reaches the earth’s surface. It occurs when the conditions more from stable to unstable. A fanning plume develops overnight under stable conditions but as the day heats up, unstable air is produced. the unstable air caused the plume to move up and down and it can cause localized pollution. It becomes looping or coning plumes as the air conditions stabilize. Fumigating plume
- 7. When plume is above the inversion layer it becomes a lofting plume. Normal wind direction and speed will disperse the plume into the atmosphere without effect from ground warming or cooling. Lofting occurs when there is a strong lapse rate above a surface inversion. Under this condition diffusion does not penetrate the inversion layer under these conditions, emission will not reach surface. Lofting plume
- 8. Trapping plumes Inversion layer exist above and below stack. So the plume neither goes up or down. Plume gets trapped between the inversion layers. So it is called trapping plume. This plume is not ideal for dispersion of pollutants as it cant go above a certain height.