What does the equation tplume = E/(pi σy σz u) represent in plume dispersion terms?

What does the equation tplume = E/(pi σy σz u) represent in plume dispersion terms?

• A. The maximum (ensemble) average concentration for a continuous passive plume from a point source at a given downwind distance
• B. The instantaneous ground-level concentration
• C. The emission rate
• D. The plume's vertical spread

Answer: (A)

The main idea here is the centerline, ensemble-averaged concentration for a steady, continuous point source in a Gaussian dispersion field. In the Gaussian plume model, the plume spreads in the horizontal crosswind direction and vertically with standard deviations σy and σz, and the concentration falls off as you move away from the plume centerline. The emission rate E sets how much pollutant is released, while the wind speed u and the spreads σy and σz determine how dilute the plume becomes downwind. The largest concentration along a given downwind distance occurs right on the plume’s centerline (where you’re not off to the sides), and evaluating the standard Gaussian solution there yields the form with E in the numerator and σy, σz and u in the denominator, giving the maximum ensemble-averaged concentration. So this expression represents the maximum concentration along the centerline for a continuous passive plume from a point source at that distance, rather than an instantaneous value, the emission rate by itself, or the vertical spread alone.

The main idea here is the centerline, ensemble-averaged concentration for a steady, continuous point source in a Gaussian dispersion field. In the Gaussian plume model, the plume spreads in the horizontal crosswind direction and vertically with standard deviations σy and σz, and the concentration falls off as you move away from the plume centerline. The emission rate E sets how much pollutant is released, while the wind speed u and the spreads σy and σz determine how dilute the plume becomes downwind. The largest concentration along a given downwind distance occurs right on the plume’s centerline (where you’re not off to the sides), and evaluating the standard Gaussian solution there yields the form with E in the numerator and σy, σz and u in the denominator, giving the maximum ensemble-averaged concentration. So this expression represents the maximum concentration along the centerline for a continuous passive plume from a point source at that distance, rather than an instantaneous value, the emission rate by itself, or the vertical spread alone.