C (x,y)=concentration at ground level at the point (x,y) µg/m³

x = horizontal distance downwind , m

y = horizontal distance from plume centre line, m

Q = emission rate of pollutants, µg/s

H = effective stack ht., m

u = average wind speed, m/s

= horizontal dispersion coefficient, m

= vertical dispersion coefficient, m

This equation is rarely used. Other than as a basis for more complex models because we it does not take into account "reflection " of pollutants from the ground.

THE MODEL WHICH IS NORMALLY USED IS:

C (x,y) = concentration at ground level at the point x,y µg/m³

x = horizontal distance downwind , m

y = horizontal distance from plume centre line, m

Q = emission rate of pollutants, µg/s

H = effective stack ht., m

u = average wind speed, m/s

= horizontal dispersion coefficient, m

= vertical dispersion coefficient, m

This model takes into account reflection from the ground in much the same way as Scorer approaches the subject (outlined above).

What basic things does the model predict?

Firstly the ground level concentration is proportional to source strength.
So we know how much source strength reduction needed to reach target.

Secondly as expected higher stacks produce lower ground level concentrations but the relationship is not linear.

Thirdly the downwind concentration appears, at first sight to be inversely proportional to wind speed but this applies only for a given EFFECTIVE chimney height. We should remember there is an effect of wind speed on plume rise where a higher wind speed generally gives lower .