Plume Dispersion Estimate Calculator

Work out plume dispersion estimate instantly with clear inputs, formula shown and shareable results.

About Plume Dispersion Estimate Calculator

The Gaussian plume model gives ground level concentration as Q / (pi u sigma_y sigma_z) times an exponential term for the stack height. Dispersion coefficients grow with distance and depend on atmospheric stability — the values here approximate neutral Pasquill class D conditions.

Formula

Gaussian plume

C = Q / (pi u sigma_y sigma_z) x exp(-H^2 / (2 sigma_z^2))

Worked example

With the default values below, Plume Dispersion Estimate Calculator returns Ground Level Concentration of 251.0356. Change any input above and every figure here is recalculated in your browser.

Inputs used

Emission Rateminimum 0 g/s: 25 g/s
Wind Speed At Stack Heightminimum 0 m/s: 5 m/s
Effective Stack Heightminimum 0 m: 45 m
Downwind Distanceminimum 0 m: 500 m

Results

Ground Level Concentration: 251.0356
Horizontal Dispersion Coefficient: 39.036
Vertical Dispersion Coefficient: 22.678
Indicative Maximum Concentration: 67.6576

Step by step

1Values used
2Gaussian plume
3Ground Level Concentration= 251.0356
4Horizontal Dispersion Coefficient= 39.036
5Vertical Dispersion Coefficient= 22.678
6Indicative Maximum Concentration= 67.6576

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Dispersion modelling for regulatory purposes requires approved models, site-specific meteorology and terrain data. This is a screening estimate only.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Dispersion modelling for regulatory purposes requires approved models, site-specific meteorology and terrain data. This is a screening estimate only.

Frequently Asked Questions

Which stability class gives the worst concentrations?

Very stable conditions produce high concentrations far downwind, while unstable conditions can cause short-lived high ground level values from looping plumes. Screening must test a range of classes.

What is effective stack height?

Physical height plus plume rise from buoyancy and momentum, which can add tens of metres for a hot high-velocity plume. It is the height that actually governs dispersion.