CE 3231 - Introduction to Environmental Engineering and Science

Readings for This Class:

5.5-5.6

Ohio Northern University

IntroductionChemistry, Microbiology & Material

BalanceWater & Air Pollution Env Risk Management

Atmospheric Dispersion (Modeling)The atmosphere is a complex and dynamic system. Under certain conditions, the atmosphere can trap pollution at the Earth surface and lead to adverse health effects. Understanding near surface atmospheric conditions and their effect on pollution dispersion is the point of this lecture.

Lecture 27

Atmospheric Dispersion (Modeling)(Air Quality II)

Introduction to Air Quality

Air Quality II

Topics Covered Include: Adiabatic Lapse Rate

Atmospheric Stability

Inversions

Plume Shapes and Dynamics

Gaussian Plume Modeling

Simplified Model to Predict Downwind Ground Level

Pollution

Adiabatic Lapse Rate

• Temperature drops as you increase in altitude

Γdry = 9.76 or 5.4

Γsaturated = 6 in tropopause

Atmospheric Stability

• Stable Air– Air mass remains at set altitude– Problematic for pollution

• Unstable Air– Air mass changes altitude– Favors mixing and pollution dispersion

Temperature Inversions

– Stable atmosphere– Nocturnal cooling– Earth cools rapidly, traps colder air on bottom– Pollution can get trapped near surface– Daytime sunlight radiates ground and breaks

inversion

http://www.metoffice.gov.uk/education/secondary/students/smog.html

Plumes and Adiabatic Lapse Rates

Plumes and Adiabatic Lapse Rates

Plumes and Adiabatic Lapse Rates

Gaussian Plume Modeling

Gaussian Plume Modeling

Gaussian Plume Modeling

where:

C (x,y) = downwind conc. at ground level(z=0), g/m3

Q = emission rate of pollutants, g/ssy, sz = plume standard deviation, muH = wind speed, m/sx,y, and z = distance, mH = stack height

How will the model change for ground-level along the plume?

Simplified Plume Modeling (Downwind Ground-Level Concentration)

Gaussian Plume Modeling

where:

C (x,0) = downwind conc. at ground level (z=0, y=0), g/m3

Q = emission rate of pollutants, g/ssy, sz = plume standard deviation, muH = wind speed, m/sx,y, z and H = distance, m

Dispersion Constants

A – very unstable; B – moderately unstable; C- slightly unstable, D – neutral, E – slightly stable; F – stable

Gaussian Plume Modeling

A new power plant releases SO2 at a legally allowable rate of 6.5x108 mg SO2 /sec. The stack has an effective height of 300 m. An anemometer on a 10 m pole measures 2.5 m/s of wind, and it is a cloudy summer day. Predict the ground-level concentration of SO2 4 km directly downwind.

Gaussian Plume Modeling

Q = 6.5x108 mg SO2 /sec H = 300 m. U = 2.5 m/s @ 10 mX= 4 kmAtmospheric condition = ?uH = ?sy , sz = ?

Finding the Atmospheric Condition

Atmospheric Condition

A – very unstable, sunny day with wind speed < 3 m/s

B – moderately unstable, sunny day clear night with winds between 3 – 5 m/s

C- slightly unstable, sunny day with winds > 5 m/s

D – neutral cloudy or overcast day; cloudy night winds > 3 m/s; clear night winds > 5 m/s

E – slightly stable cloudy or overcast night winds < 3 m/s

F – stable clear night winds < 5 m/s

Finding uH

Atmospheric Condition (p value)

A – (0.15) B – (0.15)C- (0.2)D – (0.25) E – (0.4) F – (0.6)

Finding sy , sz

D – neutral @ 4 km sy = 250 m and sz = 80 m

Gaussian Plume Modeling

Q = 6.5x108 mg SO2 /sec H = 300 m. U = 2.5 m/s @ 10 mX= 4 kmAtmospheric condition = DuH = 5.85 m/ssy = 250 msz = 80 m

Gaussian Plume Modeling

A new power plant releases SO2 at a legally allowable rate of 6.5x108 mg SO2 /sec. The stack has an effective height of 300 m. An anemometer on a 10-mile pole measures 2.5 m/s of wind, and it is a cloudy summer day. Predict the ground-level concentration of SO2 4 km directly downwind.