Calculate the mass concentration in mg/m³ on the centerline of the plume at this x location and at ground level.
a. 37.2 mg/m³ and 25.8 mg/m³
b. 25.8 mg/m³ and 37.2 mg/m³
c. 30.0 mg/m³ and 30.0 mg/m³
d. 22.0 mg/m³ and 42.0 mg/m³