Conference on the Environment- GUERRA presentation Nov 19, 2014
CALPUFF versus AERMOD comparison
1. A Comparison of AERMOD and CALPUFF Models for
Regulatory Dispersion Modelling in the Alberta Oil
Sands Region
Garrett Hoeksema, M.Sc., Air Quality Scientist
Koray Önder, P.Eng., Senior Air Quality Engineer
Greg Unrau, M.Sc., Air Quality Meteorologist
3. Background
Air Quality modelling
To get ground-level concentrations based on what is being input into
the atmosphere from emissions sources
Many different models to choose from in order to obtain the ground-level
concentrations
AERMOD, CALPUFF, SCREEN3
Air quality models are sensitive to:
Input Meteorological Data
Model Switches
The purpose of this study is:
1. Effect of different model switches or different meteorology on
individual models
2. Compare predictions from different models
3
4. Background – Air Dispersion Modelling
AERMOD
Steady-state plume dispersion model designed to predict near field
CALPUFF
Lagrangian Gaussian puff dispersion model for both near and far
field applications
Both AERMOD and CALPUFF have been approved for regulatory
modelling in Alberta, including near field
CALPUFF has historically been used in the oil sands region
It can handle regional emissions and predict potential acid input
Experience shows that for certain pollutants and for distances less than
10 km, results can vary considerably between the two models
4
5. Methods
CALPUFF and AERMOD runs were performed for various types of
emission sources
Steam Generator (30 m)
Glycol Heater (9 m)
Incinerator (100 m)
Flare (90 m)
Area
Modelling was performed for SO2
Unit emission rate of 1 g/s used
The point source was placed in a valley to observe how each model
handles terrain features
Stack characteristics were chosen based on those typical for the type of
source found in the oil sands industry
5
6. Methods
CALPUFF model runs
Two CALPUFF runs were completed utilizing two different model
settings for each run
1. U.S. EPA default model settings were used
2. Alternate model settings were used (based on BC and Ontario
modelling guidelines)
Parameter CALPUFF Run 1 CALPUFF Run 2
MDISP 3 – PG coefficients 2 – internally
(rural) and MP calculated coefficients
coefficients (urban)
MPDF 0 – does not use PDF 1 – uses PDF for
for dispersion dispersion
6
7. Methods
AERMOD model runs
Three AERMOD runs were completed based on different
meteorological data
Meteorological AERMOD Run 1 AERMOD Run 2 AERMOD Run 3
data
Upper Air Data MM5 MM5 MM5
meteorological meteorological meteorological
data data data
Surface Air Data MM5 Fort McMurray and Fort McMurray and
meteorological Mannix Tower low Mannix tower all
data level only (20 m) levels (20 m, 45 m,
75 m)
7
8. Results
Source Averaging Period CALPUFF CALPUFF AERMOD AERMOD AERMOD
Run 1 Run 2 Run 1 Run 2 Run 3
Steam 1-hr 1st highest [µg/m³] 13.0 11.9 12.6 15.0 17.5
Generator
1-hr 9th highest [µg/m³] 4.7 4.3 9.4 11.7 11.0
Stack
height = Distance -direction 1.7 km 0.2 km 1.6 km 1.5 km 1.5 km
30 m NNE NE ENE E E
24-hr 1st highest [µg/m³] 1.6 2.4 2.7 2.7 2.4
Annual [µg/m³] 0.06 0.13 0.15 0.16 0.10
Glycol 1-hr 1st highest [µg/m³] 62.7 47.8 58.0 60.8 124.9
Heater
1-hr 9th highest [µg/m³] 27.1 35.0 49.4 36.9 44.2
Stack
height = Distance -direction 1.5 km 0.1 km 0.1 km 1.8 km 0.9 km
9m NNE NNW NNW S ENE
24-hr 1st highest [µg/m³] 10.8 25.8 28.3 19.9 8.5
Annual [µg/m³] 0.61 2.72 3.16 1.33 0.38
8
9. Results
Source Averaging Period CALPUFF CALPUFF AERMOD AERMOD AERMOD
Run 1 Run 2 Run 1 Run 2 Run 3
Incinerator 1-hr 1st highest [µg/m³] 3.41 4.63 0.87 1.05 1.88
Stack
1-hr 9th highest [µg/m³] 0.87 1.13 0.52 0.64 0.92
height =
100 m Distance -direction 1.6 km 1.5 km 0.7 km 10.0 km 0.5 km
NNW N NW E WNW
24-hr 1st highest [µg/m³] 0.22 0.33 0.23 0.21 0.19
Annual [µg/m³] 0.011 0.022 0.012 0.020 0.013
Flare 1-hr 1st highest [µg/m³] 1.85 2.70 0.62 0.66 1.04
Stack
1-hr 9th highest [µg/m³] 0.54 0.71 0.41 0.66 0.51
height =
90 m Distance -direction 2.0 km 2.1 km 0.8 km 3.6 km 2.5 km
N NNE ENE WSW NW
24-hr 1st highest [µg/m³] 0.18 0.19 0.19 0.15 0.11
Annual [µg/m³] 0.007 0.010 0.008 0.011 0.007
9
10. Results
Source Averaging Period CALPUFF CALPUFF AERMOD AERMOD AERMOD
Run 1 Run 2 Run 1 Run 2 Run 3
Area 1-hr 1st highest [µg/m³] 168.9 130.3 96.0 186.3 189.7
1-hr 9th highest [µg/m³] 147.4 114.0 92.4 162.8 172.9
Distance -direction 0.3 km 0.3 km 0.7 km 0.7 km 0.7 km
ENE ENE NW NW NW
24-hr 1st highest [µg/m³] 68.6 61.0 66.7 81.2 92.8
Annual [µg/m³] 16.7 14.1 13.3 27.9 34.8
10
11. Results
CALPUFF concentrations are higher
in close proximity to the source
Comparing the two CALPUFF runs
Run 1 results in a higher
distribution of the pollutant
AERMOD transports the pollutant
farther away from the source
Comparing the three AERMOD runs
Including surface data results in
distribution over a larger spatial
area
11
12. Summary
CALPUFF and AERMOD are both approved models for use in
regulatory applications in Alberta
Considerably variable concentrations occur, depending on the model
used and the inputs into the model
Both models are very sensitive to model inputs and source parameters,
meteorological data and model switches
AERMOD distributes the pollutant further away from the point source
AERMOD is not an option for the large regional area and large number
of sources of the oil sands
Could be used for individual sources
CALPUFF keeps the pollution within the valley and close to the point
sour
CALPUFF should continue to be used for large-scale regional modelling
Alternate switches are more appropriate for near field applications
12