Problem $7\mathrm{.}36($modified$),$ Masters and Ela, Introduction to Environmental Engineering and Science, $3$rd Ed$.$:

A stack emitting $75\frac{g}{s}$ of NO has an effective stack height of $50m.$ The windspeed is $3\mathrm{.}5\frac{m}{s}$ at $10m,$ and it is a clear summer day with a few broken clouds. Assuming smooth terrain, estimate the ground$-$level NO concentration:

a$.$ directly downwind at a distance of $2\mathrm{.}0km.$

b$.$ at a point located $2\mathrm{.}0km$ downwind and $0\mathrm{.}5km$ off the downwind axis.