Lecture 27 - Ohio Northern University

Report
Ohio Northern University
CE 3231 - Introduction to Environmental Engineering and Science
Introduction
Chemistry, Microbiology & Material Balance
Water & Air Pollution
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.
Env Risk Management
Readings for This Class:
5.5-5.6
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
°C
km
Γsaturated = 6
°C
km
or
5.4
in tropopause
°F
1,000 ft
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
æ -y 2 ö
æ -H 2 ö
C ( x, y) =
exp ç 2 ÷ exp çç 2 ÷÷
p uH s ys z
è 2s z ø
è 2s y ø
Q
Gaussian Plume Modeling
æ -y 2 ö
æ -H 2 ö
C ( x, y) =
exp ç 2 ÷ exp çç 2 ÷÷
p uH s ys z
è 2s z ø
è 2s y ø
Q
where:
C (x,y) = downwind conc. at ground level(z=0), g/m3
Q = emission rate of pollutants, g/s
sy, sz = plume standard deviation, m
uH = wind speed, m/s
x,y, and z = distance, m
H = stack height
How will the model change for ground-level
along the plume?
æ -y 2 ö
æ -H 2 ö
C ( x, y) =
exp ç 2 ÷ exp çç 2 ÷÷
p uH s ys z
è 2s z ø
è 2s y ø
Q
Simplified Plume Modeling
(Downwind Ground-Level Concentration)
æ -H 2 ö
C ( x, 0) =
exp ç 2 ÷
p uHs ys z
è 2s z ø
Q
Gaussian Plume Modeling
æ -H 2 ö
C ( x, 0) =
exp ç 2 ÷
p uHs ys z
è 2s z ø
Q
where:
C (x,0) = downwind conc. at ground level (z=0, y=0), g/m3
Q = emission rate of pollutants, g/s
sy, sz = plume standard deviation, m
uH = wind speed, m/s
x,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
æ -H 2 ö
C ( x, 0) =
exp ç 2 ÷
p uHs ys z
è 2s z ø
Q
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 groundlevel concentration of SO2 4 km directly downwind.
Gaussian Plume Modeling
æ -H 2 ö
C ( x, 0) =
exp ç 2 ÷
p uHs ys z
è 2s z ø
Q
Q = 6.5x108 mg SO2 /sec
H = 300 m.
U = 2.5 m/s @ 10 m
X= 4 km
Atmospheric 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)
æH ö
uH = ua ç ÷
è za ø
p
p
0.25
æH ö
æ 300 ö
uH = ua ç ÷ = 2.5ç
÷ = 5.85m / s
è 10 ø
è za ø
Finding sy , sz
D – neutral @ 4 km
sy = 250 m and sz = 80 m
Gaussian Plume Modeling
æ -H 2 ö
C ( x, 0) =
exp ç 2 ÷
p uHs ys z
è 2s z ø
Q
Q = 6.5x108 mg SO2 /sec
H = 300 m.
U = 2.5 m/s @ 10 m
X= 4 km
Atmospheric condition = D
uH = 5.85 m/s
sy = 250 m
sz = 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.
æ -300 2 ö
650g / s
C ( x, 0) =
exp ç
2÷
p 5.85(250)(80)
è 2(80) ø
C ( x, 0) =1.56ug / m3

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