Correct Answer - Option 1 : Looping
Concept-
Lapse rate refers to the rate of change of temperature or pressure with height. In the atmosphere, this rate of change of temperature with altitude is called as Environmental Lapse Rate (ELR) and corresponds to 6.5°C/km.
If a dry air parcel is considered instead of environment, a linear relationship exists between temperature and altitude for rising or sinking air parcel, which is known as Dry Adiabatic Lapse Rate (DALR) and is equal to 9.8°C/km.
Looping plume:
It takes place when the atmosphere is very unstable, wind speed is greater than 10 m/s, has super-adiabatic lapse rate and is accompanied with solar heating.
When Environmental Lapse Rate (ELR) > > Dry Adiabatic Lapse Rate (DALR) then looping plume occurs.
Looping plume has a wavy character and occurs in super – adiabatic environment; which produces highly unstable atmosphere, because of rapid mixing.
During the high degree of turbulence, the dispersion of plume would be rapid, yet higher concentrations near the ground may occur due to turbulence, before the dispersion is finally completed.
Coning plume-
It results when the vertical air temperature gradient occurs between dry adiabatic and isothermal, the air being slightly unstable with some horizontal and vertical mixing occurring. Coning is most likely to occur during cloudy or windy periods.
Fanning plume:
They spread out horizontally but do not mix vertically. Fanning plumes take place when inversion condition exists in atmosphere, that is, the air temperature increases with altitude. The plume rarely reaches the grounds level unless the inversion is broken by surface heating or a topographical barrier such as a hill. At night, with light winds and clear skies, fanning plumes are quite common
Neutral plume:
Neutral plume is the upward vertical rise of the plume from the stack, which occurs when the environmental lapse rate is equal to or very near to the adiabatic lapse rate. The upward lifting of the plume will continue till it reaches an air of density similar to that of the plume itself.
Coning plume:
The neutral plume tends to cone, when the wind velocity is greater than 32 km/hr, and when cloud cover blocks the solar radiation by day and terrestrial radiation by night.
Coning plume also occurs under sub – adiabatic conditions (i.e. when environmental lapse rate is less than the adiabatic lapse rate).
From the above example it can be concluded that the resultant decibel level when two sources make noise of equal decibels will increase by 3 decibels.
