Map: ground-level concentration. Strip below: vertical cross-section along the wind axis through the selected factory (click one; it shows how stack height and stability set where the plume reaches the ground). C = Q / (pi u sigma_y sigma_z) exp(-y^2/2 sigma_y^2) exp(-H^2/2 sigma_z^2); urban Briggs (1973) curves. Q_eff = Q (1 - r)(1 - eta [filter on]). WHO 2021 24-h PM2.5 guideline = 15 ug/m3.