How do wind speed and atmospheric stability influence plume residence time near a receptor?

How do wind speed and atmospheric stability influence plume residence time near a receptor?

• A. Higher wind speed increases residence time.
• B. Higher wind speed reduces residence time; stable conditions reduce mixing, increasing residence time near the ground.
• C. Wind speed has no effect on residence time.
• D. Residence time is only affected by emission rate.

Answer: (B)

Residence time near a receptor is governed by how fast the plume is carried away (advection) and how much it mixes near the ground (turbulent dilution). When wind speed is high, the plume is swept past the receptor quickly, so it spends less time in the vicinity. Atmospheric stability controls mixing: stable conditions suppress vertical mixing, keeping pollutants closer to the ground and concentrated near the receptor for a longer period, which increases residence time. In contrast, unstable conditions enhance mixing and dilution, spreading the plume and reducing how long it remains near the receptor. So higher wind speeds shorten residence time, while stable (less mixing) conditions increase it near the ground.

Residence time near a receptor is governed by how fast the plume is carried away (advection) and how much it mixes near the ground (turbulent dilution). When wind speed is high, the plume is swept past the receptor quickly, so it spends less time in the vicinity. Atmospheric stability controls mixing: stable conditions suppress vertical mixing, keeping pollutants closer to the ground and concentrated near the receptor for a longer period, which increases residence time. In contrast, unstable conditions enhance mixing and dilution, spreading the plume and reducing how long it remains near the receptor. So higher wind speeds shorten residence time, while stable (less mixing) conditions increase it near the ground.