If the total airborne mass is doubled, the concentration at a fixed downwind distance is:

If the total airborne mass is doubled, the concentration at a fixed downwind distance is:

• A. Doubled
• B. Halved
• C. Quadrupled
• D. Unchanged

Answer: (A)

Concentration at a fixed downwind location scales with the emission rate. If you double the total airborne mass released, you increase the amount of material entering the plume per unit time while keeping wind speed, atmospheric stability, and the dispersion pattern the same. Under these conditions, the dilution factors don’t change, so the concentration at that point doubles. The other options would imply either less mass somehow producing more concentration, a nonlinear change, or no effect from the emission rate, which isn’t the case for a steady plume under the usual dispersion assumptions.

Concentration at a fixed downwind location scales with the emission rate. If you double the total airborne mass released, you increase the amount of material entering the plume per unit time while keeping wind speed, atmospheric stability, and the dispersion pattern the same. Under these conditions, the dilution factors don’t change, so the concentration at that point doubles. The other options would imply either less mass somehow producing more concentration, a nonlinear change, or no effect from the emission rate, which isn’t the case for a steady plume under the usual dispersion assumptions.