Work out air emission stack height instantly with clear inputs, formula shown and shareable results.
Stack height is set by the most demanding of several criteria: at least 2.5 times the height of nearby buildings to escape their wake cavity, an empirical relationship based on sulphur dioxide emission rate, and whatever dispersion modelling shows is needed to meet ground level concentration limits.
Good practice height
Height = 2.5 x nearby building height
Empirical SO2 height
Height (m) = 14 x (SO2 emission in kg/h)^0.3
Stack height determination for permitting requires dispersion modelling to an approved methodology and regulator agreement. Empirical formulae are screening tools only.
Below that, the plume is drawn into the turbulent wake behind the building and brought rapidly to ground level, causing high local concentrations. Escaping the cavity is the first requirement of any stack design.
It reduces local ground level concentration but increases the area affected and does not reduce total emissions. Regulators generally require abatement first and treat height as a residual dispersion measure.