What is the typical difference between centerline concentration and receptor concentration at off-center positions?

What is the typical difference between centerline concentration and receptor concentration at off-center positions?

• A. Centerline is maximum along y=0
• B. Off-center receptors are higher
• C. They are equal for all conditions
• D. Centerline is zero

Answer: (A)

In a Gaussian plume, the concentration field is highest directly downwind along the centerline, where crosswind distance is zero (y = 0). The crosswind profile is Gaussian and symmetric about this centerline, so the concentration falls off as you move away from it, roughly following exp(-y^2/(2 σ_y^2)). That means receptors off-center (y ≠ 0) see lower concentrations than those on the centerline. The centerline concentration is not zero and is, in fact, the maximum for a given downwind distance.

In a Gaussian plume, the concentration field is highest directly downwind along the centerline, where crosswind distance is zero (y = 0). The crosswind profile is Gaussian and symmetric about this centerline, so the concentration falls off as you move away from it, roughly following exp(-y^2/(2 σ_y^2)). That means receptors off-center (y ≠ 0) see lower concentrations than those on the centerline. The centerline concentration is not zero and is, in fact, the maximum for a given downwind distance.