Air Pollution Dispersion Model

Pollutant Type

SO₂

NO₂

PM₁₀

PM₂.₅

O₃

Custom

Emission Source Parameters

Emission Rate

g/s

Stack Height

Stack Diameter

Exit Velocity

m/s

Exit Temperature

°C

Ambient Temperature

°C

Meteorological Conditions

Wind Speed

m/s

Wind Direction

° (from North)

Atmospheric Stability Class

A (Very Unstable)

B (Unstable)

C (Slightly Unstable)

D (Neutral)

E (Slightly Stable)

F (Stable)

Mixing Height

Receptor Location

Downwind Distance

Receptor Height

Crosswind Distance

Terrain Roughness

m (z₀)

Calculating...

Pollution Dispersion Results

42.5 μg/m³

Ground-Level Concentration

1,250 m

Maximum Impact Distance

58.7 μg/m³

Maximum Concentration

Moderate

Air Quality Impact

Pollution Concentration Map

Low Concentration

Moderate

High

Very High

Dispersion Parameters

Parameter	Value	Units	Description
Effective Stack Height	68.3	m	Stack height + plume rise
Plume Rise	18.3	m	Additional height due to buoyancy/momentum
σy (Horizontal Dispersion)	124.5	m	Standard deviation of horizontal distribution
σz (Vertical Dispersion)	78.2	m	Standard deviation of vertical distribution
Maximum Concentration Distance	850	m	Distance where maximum concentration occurs
Critical Wind Speed	4.2	m/s	Wind speed producing maximum concentration

Important Note: This tool is for educational and preliminary assessment purposes only. The results are based on simplified models and should not be used for regulatory compliance, official environmental impact assessments, or critical decision-making. For accurate pollution dispersion analysis, please use certified professional software and consult with environmental engineering experts.

Air Pollution Dispersion Fundamentals

Air pollution dispersion modeling is the mathematical simulation of how air pollutants disperse in the atmosphere. It is used to predict pollutant concentrations at specific locations based on emission sources and meteorological conditions.

Key Application: Dispersion models are essential for environmental impact assessments, regulatory compliance, emergency planning, and air quality management.

Gaussian Plume Model

The Gaussian plume model is the most commonly used air pollution dispersion model. It assumes that pollutants spread in a Gaussian (normal) distribution in both the horizontal and vertical directions.

The basic Gaussian plume equation for ground-level concentrations is:

C = [Q / (2πuσyσz)] × exp[-0.5(y/σy)²] × exp[-0.5(H/σz)²]

Where:

C = Ground-level concentration (g/m³)
Q = Emission rate (g/s)
u = Wind speed (m/s)
σy, σz = Horizontal and vertical dispersion coefficients (m)
y = Crosswind distance from plume centerline (m)
H = Effective stack height (stack height + plume rise) (m)

Air Quality Standards

Pollutant	Averaging Time	Standard	Units
PM₂.₅	24-hour	35	μg/m³
PM₂.₅	Annual	12	μg/m³
PM₁₀	24-hour	150	μg/m³
O₃	8-hour	70	ppb
NO₂	1-hour	100	ppb
SO₂	1-hour	75	ppb
CO	8-hour	9	ppm

Atmospheric Stability Classes

Atmospheric stability significantly affects pollutant dispersion. The Pasquill-Gifford stability classes are commonly used:

Class	Description	Conditions	Dispersion
A	Extremely Unstable	Strong solar radiation, light winds	Rapid vertical mixing
B	Moderately Unstable	Moderate solar radiation	Good vertical mixing
C	Slightly Unstable	Slight solar radiation	Moderate vertical mixing
D	Neutral	Overcast or strong winds	Neutral conditions
E	Slightly Stable	Thin overcast, light winds	Limited vertical mixing
F	Moderately Stable	Clear night, light winds	Poor vertical mixing

Plume Rise Calculations

Plume rise is the additional height gained by a plume due to its momentum and buoyancy. Common plume rise formulas include:

Formula	Application	Equation
Briggs	General purpose	Δh = 1.6 F^1/3 u^-1 x^2/3
Holland	Simple estimation	Δh = (vs d / u) (1.5 + 2.68×10^-3 P ΔT d / T)
Concave	Buoyant plumes	Δh = 3.0 (F / u)^3/5 x^2/5

Model Limitations

While Gaussian models are widely used, they have several limitations:

Assumes steady-state conditions (constant emissions and meteorology)
Limited accuracy for complex terrain or building wakes
Does not account for chemical transformations of pollutants
Simplified treatment of atmospheric turbulence
May not accurately represent calm wind conditions

Model Selection: For complex situations (complex terrain, coastal areas, reactive pollutants), more sophisticated models like CALPUFF, AERMOD, or CFD models may be more appropriate.