Air Quality & Emissions Workbench

Interactive workspace initializes in your browser. Engineering method, assumptions, validation, and references are available below.

Engineering reference

Air Quality & Emissions: theory, method, and sources

This environmental & energy engineering workspace publishes 9 governing equations, 5 stated assumptions, 1 documented boundary, and 2 sources so the numbers it returns can be checked rather than taken on trust.

Calculations run locallyCalculation & source methodology

How this tool works

Nine modules cover stack emission rates, control device efficiency, Gaussian plume dispersion, box-model urban concentrations, particle settling, and indoor air ventilation.

Both the outdoor dispersion models and the indoor mass balance report concentrations in the same units, so a source can be traced from the stack to a receptor and to indoor exposure in one place.

Calculators and topics covered

air quality
emissions
dispersion
ventilation
stack emissions
Gaussian plume
particle settling
indoor air quality
ACH

Core equations

\text{emission rate:}\quad E = C \times Q

\text{control efficiency:}\quad \eta = \frac{C_{in} - C_{\mathrm{out}}}{C_{in}} \times 100 \%

\text{stack flow:}\quad Q = A \cdot v\; \text{with}\; \text{density}\; \text{correction}\; to\; \text{standard}\; \text{conditions}

\text{Gaussian plume centreline:}\quad C = \frac{Q}{\pi \; u\; \sigma _{y}\; \sigma _{z}} \cdot \exp \left(\frac{- H^{2}}{2 \sigma _{z}^{2}}\right)

\text{box model:}\quad C = C_{bg} \frac{+ E}{u \cdot \mathrm{W} \cdot H_{\mathrm{mix}}}

\text{Stokes settling velocity:}\quad v_{s} = \frac{\left(\rho _{p} - \rho _{a}\right) gd^{2}}{18 \mu }

\text{air changes per hour:}\quad \mathrm{ACH} = \frac{3600 Q}{V}

\text{indoor steady state:}\quad C = \frac{S + Q \cdot C_{\mathrm{out}}}{Q + kV}

\text{ventilation mass removal:}\quad \dot{M} = Q \left(C_{in} - C_{\mathrm{out}}\right)

Method and assumptions

Assumptions

The Gaussian plume model assumes steady wind, flat terrain, and a continuous source; dispersion coefficients are user-supplied for the chosen stability class.
The box model assumes complete instantaneous mixing to the mixing height with no chemical reaction.
Stokes settling is valid only for small particles at low Reynolds number, and neglects slip correction, coagulation, and turbulence.
Indoor calculations assume a single well-mixed zone and a first-order decay or removal rate.
Plume rise, downwash, deposition, and secondary pollutant formation are not modelled.

Limitations and design boundaries

Educational screening calculations only. Regulatory emissions, dispersion, indoor-air, and control-device analyses require approved methods, representative measurements, current standards, uncertainty evaluation, and qualified review.

Sources and references

Primary sources are preferred for ratings, standards, manufacturer data, and externally defined constants.

Source policy

Cooper and Alley, Air Pollution Control: A Design Approach
Wark et al., Air Pollution: Its Origin and Control