$18\mathrm{.}7$ The power plant in Problem $18\mathrm{.}6$ uses coal with a $14\%$ by weight ash content,

half of which is fly ash $($entrained in the off$-$gas$).$ If the ash particles $($which we assume

to be uniform!$)$ have a diameter of $15m$ and a density of $1\mathrm{.}5\frac{g}{c}{m}^3,$ calculate the ash

deposition rate along the plume center line $($a$)5$ km downwind on a bright sunny day

and $($b$)10$ km downwind on a night when the weather is overcast. Use the minimum

compatible wind speeds.