$4\mathrm{.}1$ A stack emitting $80$ g$/$s of NO has an effective stack height of

$100$ m$.$ The windspeed is $4$ m$/$s at $10$ m$,$ and it is a clear

summer day with the sun nearly overhead. Estimate the

ground$-$level NO concentration

$($a$)$ directly downwind at a distance of $2$ km$.$

$($b$)$ at the point downwind where NO is a maximum.

$($c$)$ at a point located $2$ km downwind and $0\mathrm{.}1$ km off the

downwind axis.