Background on: -origin of air quality regulations -Gaussian models -AERMOD -Case study for an Aluminum Manufacturing Facilty

1. Sergio Guerra, PhD | GHD
A&WMA’s 112th Annual Conference & Exhibition
Quebec City, Canada
June 26, 2019
Case Studies in Air Dispersion
Modeling for Young Professionals

2. Why do we regulate the air?
• In December 1930, 63 people died in Belgium's Meuse Valley during
a five-day fog; most of the deaths occurring on the fourth and fifth
days.
• In October 1948, a thick cloud of air pollution formed above the
industrial town of Donora, Pennsylvania. The cloud which lingered
for five days, killed 20 people and caused sickness in 6,000 of the
town's 14,000 people.
• In 1952, over 3,000 people died in what became known as London's
"Killer Fog." The smog was so thick that buses could not run without
guides walking ahead of them carrying lanterns.

3. Why do we regulate the air?

4. Dispersion Modeling
• A series of equations that mathematically describe pollutant
behavior in the atmosphere
• Can be simple or complex depending on the assumptions and
mathematical equations used
• Is a tool used in air permitting to ensure that the air quality will not
be compromised
• Based on best available science
• Performance is evaluated for specific scenarios
• Like any other numerical tool it has its limitations

5. What are the Reasons to Model?
• Regulatory purposes
• Design purposes
• Health
• Ecology

6. AERMOD
“A steady-state plume model that incorporates air dispersion based on
planetary boundary layer turbulence structure and scaling concepts,
including treatment of both surface and elevated sources, and both
simple and complex terrain.” SCRAM web site:
www.epa.gov/scram001/dispersion_prefrec.htm

7. Gaussian Distribution
⋅
















−=
2
2
1
exp
y
y
Value
σ1.0
0.5

8. Plume Rise Example Result
INPUTS
Hb = 40 m
Hs = 90 m
Ve = 5 m/s
Ts = 430K
Ta = 279K
d = 2.1 m
Neutral stability

9. Horizontal and Vertical Dispersion
x
y
z
σz
hs+hr
σy /σz vary with:
- Downwind distance
- Surface roughness
- Ambient turbulence levels
- Atmospheric stability
- Urban or rural
- Building downwash

10. Inputs
BPIPBuilding Geometry
Meteorological Data
Terrain Data
AERMET
AERMAP
Operating ParametersOperating Parameters
AERMOD

11. Source Types
Point source
Volume source
Area source
Line source
Open pit

12. Case Study: Aluminum Manufacturing Facility
• Existing melting furnace exists with a baghouse: BH1
• Adding 2 new melting furnaces: MELT1 and MELT2
• Evaluating PM2.5 24-hr standard
• NAAQS is 35 ug/m3
YP Panel on Dispersion Modeling
Emission Unit PM2.5 Emission Rate
BH1 0.7 lb/hr
MELT1 1.5 lb/hr
MELT2 1.5 lb/hr

13. Cases Evaluated
Case Description
1 Base case
2 MELT1 and MELT2 routed to BG with 95% control efficiency
3 MELT1 and MELT2 w/o BH and Relocated to North Building
4 Same as #3 but with restricted access road
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14. Definition of Ambient Air
“that portion of the atmosphere, external to buildings, to which the
general public has access.” 40 CFR § 50.1(e)
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15. Base Case
Max Rec is 35.9 ug/m3
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16. Add new Bag Houses to MELT1 and MELT2
Max Rec is 4.6 ug/m3
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17. Relocate MELT1 and MELT2 (no Baghouse)
Max Rec is 21.3 ug/m3
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18. Relocate MELT1 and MELT2 and add guard shack
Max Rec is 17.5 ug/m3
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19. Results
Modeled
Conc (ug/m3)
Background
(ug/m3)
Total
(ug/m3)
Percent of
24-hr NAAQS
Case 1 35.9
17
52.9 151%
Case 2 4.6 21.6 62%
Case 3 21.3 38.3 109%
Case 4 17.5 34.5 99%
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20. Sergio A. Guerra, PhD
sergio.guerra@ghd.com
Office: 720 974 0935
Questions
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21. www.ghd.com
YP Panel on Dispersion Modeling