Discussion
Match each change in List I with its effect on ground level concentration in List II.
List I
A. Doubling wind speed
B. Doubling effective stack height
C. Halving mixing height
D. Doubling emission rate
List II
1. Roughly quarters the maximum
2. Halves the concentration
3. Doubles the concentration
4. Raises concentration, roughly doubling it in a box model
Select the correct match.
Answer: A
Correct answer: A-2, B-1, C-4, D-3
Each change is matched to its effect through the dependence in the plume equation. Doubling the wind speed (A) halves the concentration (2), since \( C \propto 1/u \). Doubling the effective stack height (B) roughly quarters the maximum (1), since \( C_{max} \propto 1/H^2 \).
Halving the mixing height (C) roughly doubles the concentration in a box model (4), because the same emission is confined to half the depth. Doubling the emission rate (D) doubles the concentration (3), the one strictly linear relation of the four - which is why the inverse-square height term is so much more powerful a control than proportional reductions in output.
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