$2-$ A stack emitting $75\frac{g}{s}$ of NO has an effective stack height of $110$ m $.$ The wind speed is $4\frac{m}{s},$ and it is a clear summer day with the sun nearly overhead. Estimate the ground$-$level NO concentration:

a$)$ directly $($i$.$e$.,$ centerline$)$ downwind at a distance of $2\mathrm{.}5$ km $.$

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

c$)$ at the point downwind where NO is maximum.