Which of the following is NOT listed as affecting the dispersal of agents?

• A. Humidity
• B. Windspeed
• C. Pollutants
• D. Precipitation

Answer: (D)

Dispersal of agents in the air is shaped by how environmental conditions affect transport, residence time, and particle behavior. Humidity changes how droplets evaporate and whether the material stays as a small, long‑lasting aerosol or as a larger droplet that settles more quickly. Windspeed directly drives the transport of the plume and influences dilution and travel distance. Pollutants can modify atmospheric stability and turbulence and can interact with particles, altering dispersion and deposition rates. Precipitation mainly removes airborne material from the air through wet deposition, reducing spread rather than promoting it, so it isn’t listed as a dispersal factor.