$4\mathrm{.}1$ A $40$ percent$-$efficient $(1000$ MW$),$ coal$-$fired power plant emits

SO$2$ at the legally allowable rate of $0\mathrm{.}6$ lb per million Btu of heat

into the plant. The stack has an effective height of $300$ m$.$ An

anemometer on a $10-$m pole measures $2\mathrm{.}5$ m$/$s of wind, and it is

a cloudy summer day. Predict the ground$-$level concentration of

SO$24$ km directly downwind.