In dispersion modeling, sigma_y and sigma_z describe the plume's:

In dispersion modeling, sigma_y and sigma_z describe the plume's:

• A. Vertical spread
• B. Lateral (crosswind) dispersion
• C. Temperature change
• D. Chemical reactivity

Answer: (B)

The main idea here is that sigma_y and sigma_z are dispersion parameters in the Gaussian plume model that describe how the pollutant plume spreads away from its centerline as it moves with the wind. They determine how quickly concentration falls off with distance in two directions: across the wind (crosswind) and vertically. In the math, concentration depends on exp(-y^2/(2 sigma_y^2)) and exp(-z^2/(2 sigma_z^2)), so larger sigmas mean a wider plume. The best match among the options is lateral (crosswind) dispersion, because sigma_y specifically governs spread perpendicular to the wind direction. (Note: sigma_z governs vertical dispersion, but the overall concept described by these sigmas is the plume’s spread, of which crosswind dispersion is the characteristic dimension highlighted in the choice.) Temperature change and chemical reactivity are not what these dispersion parameters describe.

The main idea here is that sigma_y and sigma_z are dispersion parameters in the Gaussian plume model that describe how the pollutant plume spreads away from its centerline as it moves with the wind. They determine how quickly concentration falls off with distance in two directions: across the wind (crosswind) and vertically. In the math, concentration depends on exp(-y^2/(2 sigma_y^2)) and exp(-z^2/(2 sigma_z^2)), so larger sigmas mean a wider plume.

The best match among the options is lateral (crosswind) dispersion, because sigma_y specifically governs spread perpendicular to the wind direction. (Note: sigma_z governs vertical dispersion, but the overall concept described by these sigmas is the plume’s spread, of which crosswind dispersion is the characteristic dimension highlighted in the choice.)

Temperature change and chemical reactivity are not what these dispersion parameters describe.