CE 3231 - Introduction to Environmental Engineering and Science Readings for This Class: 5.5-5.6 Ohio Northern University Introducti on Chemistry, Microbiology & Material Balance Water & 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.
Transcript
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
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.
