Calc 1: Blowing up Emerald Forest
At some point after a clash between Alpha and a goon, Emerald Forest gets its shit fucked so let's calc that.
Emerald Forest is about 10 km^2 in area, leaving us with a radius of 1.58113883008419 km.
((1.58113883008419/0.28)^3)/2 = 90.03387106437851 kilotons, Town level+
Calc 2: Blowing up Emerald City
Emerald City is approximately 1980 km^2, giving us a radius of 22.24859546128699 km.
(((22.24859546128699/0.28)^3)/2)/1000 = 250.8439949284133 megatons, Mountain level
So yeah, there you go.