Given: Q = 100 g/s, H = 50 m, u = 10 m/s, class D stability in a rural area. The ground-level concentration along the centerline at a downwind distance of 500 m from a stack (i.e., x = 500, y = 0, z = 0) is ______ g/m³. The general dispersion model is (Use Figure 4-6 and Figure 4-7 if needed; 1 g = 10⁶ g):