Atmospheric Dispersion of Pollutants - Part 2 Flashcards
What is on the horizontal and vertical axes of stability diagrams?
Horizontal axis - Temperature (oC)
Vertical axis - Height (m)
What is the gradient of the lines for stability diagrams?
dz/dT
What happens if dT/dz is more negative?
dz/dT is less negative and the gradient of the lines is lower
What is the meaning of an unstable behaviour of a plume?
dT/dz is below the adiabatic lapse rate
What does this mean for the gradients of the line of the unstable behaviour?
The gradient of the atmospheric conditions is less than that of the dry and wet adiabatic lapse rates
What happens if a packet of gas is displaced upwards in unstable behaviour?
The temperature decreases but not so much as the surroundings. In its new surroundings, it will be warmer and less dense than the ambient air so it will continue to rise.
What happens if a packet of gas is displaced downwards in unstable behaviour?
The temperature will rise but not so much as that of the surrounding air. It will be cooler and more dense than surrounding air and so will continue to sink.
What does it mean by the unstable situation?
Random eddies will reverse the direction of movement from time to time and as a result mixing will be rapid. This is usually what we want.
What is the meaning of stable behaviour of a plume?
dT/dz is less negative than the adiabatic lapse rate
What does this mean for the gradients of the lines of stable behaviour?
The gradient of wet and dry adiabatic lapse rates is less than that for atmospheric conditions. The gradient for the atmospheric pressure can also be positive.
What happens if a packet of gas is displaced upwards in stable behaviour?
The temperature will fall more than the surrounding air. It will be colder and more dense than the latter. Its rise will be decelerated and eventually buoyancy forces will return it to the original altitude.
What happens if a packet of gas is displaced downwards in stable behaviour?
If the packet of gas is displaced downwards then the temperature will rise more than the surrounding air. It will be warmer and more buoyant and will return to its original height.
What does it mean in the stable situation?
The gas will stay at the same height and disperses only slowly. Usually undesirable.
What is the meaning of neutral behaviour for plume behaviour?
dT/dz is close to the adiabatic lapse rate
What does this mean for the gradients of the line of neutral behaviour?
The line for the atmospheric conditions is between the gradients for wet and dry adiabatic lapse rates
