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Evaluation of the Implementation of the
Coupled Ocean Atmosphere Response
Experiment (COARE) Algorithms into
AERMET for Marine Boundary Layer
Environments


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EPA-454/R-23-008
October 2023

Evaluation of the Implementation of the Coupled Ocean Atmosphere Response
Experiment (COARE) Algorithms into AERMET for Marine Boundary Layer Environments

U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, NC


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Preface

This document provides an evaluation of implementation of the Coupled Ocean-Atmosphere
Response Experiment (COARE) algorithms from the AERCOARE program into AERMET for
applications in marine boundary layer environments as part of the proposed updates to the 2023
revision of the Guideline on Air Quality Models. The purpose of the document is to provide
results indicating that the inclusion of COARE into AERMET gives equivalent results to
AERCOARE, and there were no coding errors in the implementation of COARE into
AERMET. Included in this document are descriptions of the inputs, comparison of
meteorological output from AERCOARE and AERMET, and comparison of AERMOD results
from AERCOARE and AERMET.

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Acknowledgements

This report was developed as part of the 2023 proposal of The Guideline on Air Quality Models,
Appendix W with input from the meteorological data workgroup comprised of staff from EPA's
Office of Air Quality Planning and Standards and Region 10. WRF a processing for the
evaluations were processed by General Dynamics Information Technology.

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Contents

1.0 Introduction

1

2.0 Methodology	2

2.1	Study Areas	2

2.1.1	Cameron, LA	3

2.1.2	Carpinteria, CA	7

2.1.3	Pismo Beach, CA	10

2.1.4	Ventura, CA	14

2.2	AERCOARE and AERMET configurations	16

2.2.1	Measured data	16

2.2.2	Prognostic data	19

2.3	Meteorological data evaluation	27

2.4	AERMOD evaluation	28

3.0 Results	29

3.1	Meteorological data comparisons	29

3.1.1	Measured data	29

3.1.2	Prognostic data	30

3.2	AERMOD results	33

3.2.1	Measured data	33

3.2.2	Prognostic data	35

4.0 Summary and Conclusions	37

5.0 References	39

iv


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Figures

Figure 1. Study areas for COARE to AERMET testing	3

Figure 2. Cameron, LA study area	4

Figure 3. Carpinteria, CA study area	7

Figure 4. Pismo Beach, CA study area	11

Figure 5. Ventura, CA study area	14

Figure 6. Cameron, LA WRF domains. The large outer box is the 12-km domain, the white box

is the 4-km domain, and the red box is the 1.33 km domain	20

Figure 7. Carpinteria, CA WRF domains. The large outer box is the 12-km domain, the white

box is the 4-km domain, and the red box is the 1.33 km domain	21

Figure 8. Pismo Beach, CA WRF domains. The large outer box is the 12-km domain, the white

box is the 4-km domain, and the red box is the 1.33 km domain	22

Figure 9. Ventura, CA WRF domains. The large outer box is the 12-km domain, the white box
is the 4-km domain, and the red box is the 1.33 km domain	23

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Tables

Table 1. Cameron measured meteorological data	5

Table 2. Cameron source and receptor data	6

Table 3. Carpinteria measured meteorological data	9

Table 4. Carpinteria source parameters data	10

Table 5. Pismo Beach measured meteorological data	12

Table 6. Pismo Beach release heights and receptor distances	13

Table 7. Ventura measured meteorological data	15

Table 8. Ventura receptor distances	16

Table 9. AERCOARE and AERMET-COARE configurations for measured data	19

Table 10. Time periods modeled for each location	24

Table 6. AERCOARE and AERMET-COARE configurations for prognostic data	26

Table 12. Meteorological variables for comparisons with tolerances	28

Table 13. Minimum and maximum AERMOD concentration ratios (AERMET/AERCORE) for

measured meteorological data	34

Table 14. AERMOD Robust Highest Concentration ratios (AERMET/AERCORE) for measured

meteorological data	35

Table 15. Minimum and maximum AERMOD concentration ratios (AERMET/AERCORE) for

prognostic meteorological data	36

Table 16. AERMOD Robust Highest Concentration ratios (AERMET/AERCORE) for
prognostic meteorological data	37

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1.0 Introduction

In recent years, applications of AERMOD (U.S. EPA, 2023a) in marine boundary layer
environments, i.e., overwater applications, have increased. Calculations of boundary layer
parameters for the marine boundary layer present special challenges as the marine boundary
layer can be very different from the boundary layer over land. For example, convective
conditions can occur in the overnight hours in the marine boundary layer while typically over
land, stable conditions occur at night. Also, surface roughness in the marine environment is a
function of wave height and wind speed and less static with time than surface roughness over
land.

While the Offshore and Coastal Dispersion Model (OCD) (DiCristofaro and Hanna, 1989) is the
preferred model for overwater applications, there are applications where the use of AERMOD is
applicable. These include applications that utilize features of AERMOD not included in OCD
(e.g., NO2 chemistry). Such use of AERMOD would require consultation with the Regional
Office and appropriate reviewing authority to ensure that platform downwash and shoreline
fumigation are adequately considered in the modeling demonstration.

For the reasons stated above, a standalone pre-processor to AERMOD, called AERCOARE
(U.S. EPA, 2012a) was developed to use the Coupled Ocean Atmosphere Response Experiment
(COARE) bulk-flux algorithms (Fairall et al., 2003) to bypass AERMET and calculate the
boundary layer parameters for input to AERMOD for the marine boundary layer. AERCOARE
can process either measurements from water-based sites such as buoys or prognostic data
processed via the Mesoscale Model Interface program (MMMIF) (Ramboll, 2023).
AERCOARE was developed in response of a need for overwater meteorology for an AERMOD
application in an Arctic Ice Free Environment (U.S. EPA, 201 la) and that the boundary layer
calculations in AERMET (U.S. EPA, 2023b) are more suited for land-based data.

To better facilitate the use of the COARE algorithms for AERMOD, EPA included the COARE
algorithms into AERMET version 23132 (U.S. EPA, 2023b) as part of the 2023 proposed
updates to the Guideline on Air Quality Models (U.S. EPA, 2023c), thus eliminating the need
for a standalone pre-processor and ensures the algorithms are updated as part of routine
AERMET updates.

This report details the evaluation process to determine if the COARE algorithms in
AERCOARE were incorporated into AERMET (U.S. EPA, 2023b) correctly, i.e., no coding
errors. Results between AERCOARE and AERMET with COARE processing should be
equivalent or have very small differences (due to real type variables in AERCOARE vs. double
precision type variables in AERMET) when both processors are input with the same data. The
comparisons are made for both measured data processed in AERCOARE and AERMET and

1


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prognostic data processed in AERCOARE and AERMET. Both measured and prognostic data
are used to fully check the incorporation of COARE into AERMET and no attempt is made in
this document to compare the measured vs. prognostic data. For an evaluation of prognostic data
configurations in AERMET with COARE see U.S. EPA (2023d). The comparisons presented in
this report do not include the warm layer or cool skin options available for COARE. These
options have been included in AERMET but have not been evaluated as the data necessary for
these options are not available in the datasets used in this evaluation. Section 2 discusses the
methodology of the case studies. There are four case studies used to evaluate the incorporation
of COARE into AERMET: 1) Cameron, LA; 2) Carpinteria, CA, 3) Pismo Beach, CA, and 4)
Ventura, CA. This report includes comparisons of meteorological data output from
AERCOARE and AERMET and comparison of AERMOD results using AERCOARE and
AERMET meteorology. Section 2.0 describes the methodology of the evaluations, Section 3.0
discusses the results of the evaluations, and Section 4.0 is the summary and conclusion of the
evaluation.

2.0	Methodology

Following is the methodology of the evaluation of incorporating COARE into AERMET.

Section 2.1 describes the study areas, Section 2.2 describes the AERCOARE and AERMET
configurations, Section 2.3 describes the meteorological data evaluation and Section 2.4
describes the AERMOD evaluation.

2.1	Study Areas

Four case study areas were considered for evaluation (Figure 1) as noted in Section 1.0. Each
study area is detailed below and more information about each can be found in U.S. EPA
(2012b).

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Pismo Beach

¦ Carpinteria
¦

Ventura

Cameron

Figure 1. Study areas for COARE to AERMET testing.

2.1.1 Cameron. LA

The Cameron case study consisted of 26 tracer releases from field studies in July 1981 and
February 1982. Tracer was released from both a boat and a low-profile platform at a height of
13 m. Receptors were located in flat terrain near the shoreline with transport distances ranging
from 4 to 10 km (U.S. EPA, 2012b). Error! Reference source not found, shows the general
study area. The meteorological data for Cameron is shown in Table 1. Note, for all hours, the
station pressure was set to 1000 mb and wind direction was assumed to be 270° because
AERMOD would be run in screening mode. The data set contains both very stable and fairly
unstable conditions. There are several hours of stable lapse rates accompanied by unstable air-sea
temperature differences. For example, on February 15, 1982, hour 1700, the air-sea temperature
difference is -0.8 °C, while the virtual potential temperature lapse rate is 0.06 °C/m (extreme
stability "G" in OCD). Over 10 m, this virtual potential temperature lapse rate would result in at
least an air-sea temperature difference of +0.5 °C. The data was adjusted for the AERCOARE
evaluations by adjusting the air-sea temperature difference to be at least as stable as indicated by

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the virtual potential temperature lapse rate. The sea temperature was adjusted so the air-sea
temperature difference matched the measured potential temperature lapse rate (U.S. EPA, 2012b)

UTM East (km) Zone 15N, Datum. NAS-C

Figure 2. Cameron, LA study area

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Table 1. Cameron measured meteorological data.

Date

Hour
(LST)

Wind
ht
(m)

Wind

speed
(m/s)

Temperature/RH
height (m)

RH

(%)

Air
temperature
(°C)

Sea
temperature
(°C)

ae
(°)

Mixing
height
(m)

7/20/81

14

10

4.6

10

63

29.25

31.95

6.4

800

7/20/81

15

10

4.8

10

64

29.45

32.05

4.9

800

7/23/81

17

10

4.3

18

73

30.45

31.85

4.7

225

7/23/81

18

10

5.1

18

74

30.55

31.75

4.7

225

7/27/81

20

10

2.1

18

82

27.05

31.45

999

400

7/27/81

22

10

4.5

18

82

26.85

31.35

999

450

7/29/81

16

10

4.6

18

69

29.85

32.05

9.6

420

7/29/81

17

10

5

18

68

29.85

31.85

6.4

430

7/29/81

19

10

5

18

68

29.95

31.65

9.6

450

2/15/82

16

10

5.7

10

89

14.25

13.75

999

200

2/15/82

17

10

5.6

10

88

13.95

13.45

999

200

2/15/82

20

10

5.9

10

87

14.25

13.75

999

200

2/17/82

14

10

3.3

10

93

15.65

13.55

2.5

200

2/17/82

15

18

3.7

18

93

14.95

14.05

7.6

200

2/17/82

16

18

4.3

18

93

14.85

14.25

3.9

200

2/17/82

17

18

3.5

18

93

14.55

14.19

3.8

200

2/17/82

18

18

3.5

18

93

14.25

13.89

2.1

200

2/22/82

14

18

5.2

18

75

17.45

16.15

2.7

100

2/22/82

16

18

4.7

18

76

17.45

16.55

2.4

100

2/22/82

17

18

4.5

18

76

17.75

16.95

2.8

100

2/23/82

14

18

4.8

18

84

18.35

14.65

0.6

50

2/23/82

17

18

6.2

18

88

18.05

15.75

3.2

80

2/24/82

15

18

3.7

18

49

19.95

14.95

2.7

50

2/24/82

16

18

3.7

18

50

19.75

15.15

3.2

50

2/24/82

17

18

3.5

18

50

19.75

15.05

3.3

50

2/24/82

19

18

4.1

18

52

17.55

14.85

2.6

50

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Table 2 shows the Cameron source and receptor data for AERMOD. Release heights for
releases was 13.0 m. AERMOD was run in screening mode with westerly winds with the
source location at (0,0). Receptor coordinates are (X,0) where X is the downwind distance of
the peak observed concentration.

Table 2. Cameron source and receptor data.

Release
number

Date

Hour
(LST)

Building ht
(m)

Building width
(m)

Receptor distance
(m)

1

7/20/81

14

0.0

0.0

7180

2

7/20/81

15

0.0

0.0

7400

3

7/23/81

17

0.0

0.0

8930

4

7/23/81

18

0.0

0.0

8710

5

7/27/81

20

0.0

0.0

7020

6

7/27/81

22

0.0

0.0

7859

7

7/29/81

16

0.0

0.0

7820

8

7/29/81

17

0.0

0.0

9780

9

7/29/81

19

0.0

0.0

9950

10

2/15/82

16

7.0

20.0

4834

11

2/15/82

17

7.0

20.0

5762

12

2/15/82

20

7.0

20.0

4526

13

2/17/82

14

0.0

0.0

7000

14

2/17/82

15

0.0

0.0

6985

15

2/17/82

16

0.0

0.0

7400

16

2/17/82

17

0.0

0.0

7260

17

2/17/82

18

0.0

0.0

6950

18

2/22/82

14

0.0

0.0

7095

19

2/22/82

16

0.0

0.0

7070

20

2/22/82

17

0.0

0.0

6955

21

2/23/82

14

0.0

0.0

7769

22

2/23/82

17

0.0

0.0

7245

23

2/24/82

15

7.0

20.0

5669

24

2/24/82

16

7.0

20.0

5669

25

2/24/82

17

7.0

20.0

6023

26

2/24/82

19

7.0

20.0

4786

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2.1.2 Carpinteria. CA

The Carpinteria tracer study was conducted in September and October 1985. Studies were
conducted to examine offshore impacts caused by both interaction with complex terrain and
shoreline fumigation. The current analysis only evaluated the complex terrain data set as the
AERCOARE-AERMOD approach currently cannot simulate shoreline fumigation.

270 271 272 273 274
UTM East (km) Zone 11N, Datum: NAS-C

100

Snow/Ice

-90

"85 Tundra
-80

"'5 Barren
-70

-65 Wetland
60

-55 Water
-50

-45 Forest
40

35 Range
-30

-25 Agriculture
-20

-15 Llrban/Built-Up
10

Land Use

sampler Locations:
X - Complex Terrain
X - Fumigation
Tracer Releases:

~	- Complex Terrain

~	— Fumigation

shows the land use and terrain for the Carpinteria field study. The shoreline receptors are located
on a 20 m to 30 m high bluff within 0.8 km to 1.5 km of the offshore tethersonde release. Two
tracers were released with heights varying from 18 m to 61 m. The tethersonde was well above
the anchor boat and downwash was not considered in the simulations.

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¦too

Snow/Ice

-90

"85 Tundra
-80

" 75 Barren
.-70
"65 Wetland

-60

-55 Water
J-SO
-45 Forest
-40

• 35 Range
-30

-25 Agnculture
-20

. 15 Urban/Buill-Up
-10
land Use

Sampler Locations:
X - Complex Terrain
X - Fumigation

Tracer Releases:
A - Complex Terrain
A - Fumigation

268 269 270 271 272 273 274 275 276
UTM East (km) Zone 11N. Datum: NAS-C

Figure 3. Carpinteria, CA study area.

Table 3 displays the meteorological data used in the current simulations and previous evaluations
of OCD and CALPUFF. The winds were very light for most of the releases, especially
considering the wind measurement heights were from 30 m to 49 m. Note that the air
temperature and relative humidity measuring height was 9 m for all hours, station pressure was
1,000 mb for all hours, and the mixing height was 500 m for all hours. The combined influences
of low wind speeds and the air-sea temperature differences in Table 3 result in cases with
unstable to very stable stratifications. Unlike the Cameron data set, the
virtual potential temperature lapse rates do not contradict the gradient inferred from the air
temperature difference measurements. One suspect aspect of the data is the constant mixed layer
height of 500 m for the entire data set. In cases where plumes are not trapped under a strong
inversion, CALPUFF and OCD are less sensitive to the mixing height than AERMOD. Thus,
uncertainty in the boundary layer height in this experiment may not have been important to the
original investigators.

Table 4 lists the source release parameters used for the AERCOARE simulations of the
Carpinteria data set. Unlike the other databases, actual wind directions, source locations and
receptor sites were used in the analysis to consider the effects of terrain elevation on the model
predictions. Receptor elevations and scale heights for AERMOD were calculated with AERMAP

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(Version 11103) (EPA, 201 lb) using 1/3 arc-second terrain data from the National Elevation
Data (NED) set. The peak predicted concentration was compared to the peak measured
concentration for each release.

Table 3. Carpinteria measured meteorological data.

Date

Hour

(LST)

Wind ht

(m)

Wind
speed
(m/s)

Wind
direction

(°)

RH

(%)

Air
temperature

(°C)

Sea
temperature

(°C)

oe(°)

9/19/85

9

30

1.3

259.7

78.8

16.3

17.4

26.8

9/19/85

10

30

1.3

235.4

79

16.8

17.6

28.4

9/19/85

11

30

2.6

214.1

80.1

17

17.7

24.4

9/19/85

12

30

3.1

252.9

80.1

17.1

17.8

32.9

9/22/85

9

30

1

220.8

70.6

17.4

16.9

32.1

9/22/85

10

30

1.2

251.1

81

17

16.7

17.4

9/22/85

11

30

2.4

253.8

92.1

16.4

15.4

8

9/22/85

11

30

2.4

230

92.1

16.4

15.4

8

9/22/85

12

30

2.8

248.4

91.1

16.3

15.2

17.4

9


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9/22/85

12

30

2.8

237.7

91.1

16.3

15.2

17.4

9/25/85

10

24

1

163.8

60.3

21.2

18.4

41.7

9/25/85

11

46

1.6

163.8

69.9

21

18.7

9.9

9/25/85

12

46

1

165.6

90.3

20.9

18.8

26.1

9/25/85

13

46

1

175

90.4

21.4

18.7

18.4

9/26/85

12

49

3.8

262

83.5

18.7

19.4

10.9

9/26/85

13

49

4

262.2

81

18.8

19.8

11.8

9/28/85

10

24

5.4

155.8

85.1

18.1

18.7

8.9

9/28/85

10

24

5.4

155.8

85.1

18.1

18.7

8.9

9/28/85

11

24

3.2

174.7

84.1

18

18.8

10.9

9/28/85

11

24

3.2

177

84.1

18

18.8

10.9

9/28/85

13

24

1.5

234.5

82.5

18.3

18.9

10.9

9/28/85

13

24

1.5

229.5

82.5

18.3

18.9

10.9

9/28/85

14

24

2.1

215

81.7

18.5

18.8

11.8

9/28/85

14

24

2.1

215

81.7

18.5

18.8

11.8

9/29/85

11

30

3.4

243.7

86

18.2

18.5

18.4

9/29/85

12

30

3.1

238.9

87.8

18.1

18.5

5

9/29/85

12

30

3.1

232.7

87.8

18.1

18.5

5

10/1/85

9

61

2

215.5

92.1

16.5

17.4

19.2

10/3/85

10

61

1

164.6

89

26.3

24.2

12.8

10/3/85

11

61

1.8

215.5

95.9

24.8

21.4

32.9

10/4/85

12

76

1.7

216.9

70.3

21.6

18.3

14.7

10/4/85

9

76

2.6

231.2

71.9

21.7

18.4

11.8

10/4/85

10

76

1.7

186.4

76.4

21.3

18

13.7

10/5/85

11

91

1.3

171.3

66.8

20.9

20.2

28.4

10/5/85

11

91

1.5

208.2

64.8

21.3

20.6

19.2

10/5/85

12

91

1

195.2

62.7

21.5

20.8

28.4

Table 4. Carpinteria source parameters data.

Release
number

Date

Hour
(LST)

Release
type

Release
ht (m)

UTM
East
(m)

UTM
North (m)

1

9/19/85

9

SF6

30.5

270,343

3,806,910

2

9/19/85

10

SF6

30.5

270,343

3,806,910

3

9/19/85

11

SF6

30.5

270,343

3,806,910

4

9/19/85

12

SF6

30.5

270,343

3,806,910

5

9/22/85

9

SF6

18.3

270,133

3,806,520

6

9/22/85

10

SF6

18.3

270,133

3,806,520

7

9/22/85

11

SF6

18.3

270,133

3,806,520

8

9/22/85

11

Freon

36.6

270,133

3,806,520

9

9/22/85

12

SF6

18.3

270,133

3,806,520

10


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10

9/22/85

12

Freon

36.6

270,133

3,806,520

11

9/25/85

10

SF6

24.4

271,024

3,806,660

12

9/25/85

11

SF6

24.4

271,024

3,806,660

13

9/25/85

12

SF6

24.4

271,024

3,806,660

14

9/25/85

13

SF6

24.4

271,024

3,806,660

15

9/26/85

12

Freon

24.4

269,524

3,807,330

16

9/26/85

13

Freon

24.4

269,524

3,807,330

17

9/28/85

10

SF6

24.4

271,289

3,806,340

18

9/28/85

10

Freon

42.7

271,289

3,806,340

19

9/28/85

11

SF6

24.4

271,289

3,806,340

20

9/28/85

11

Freon

42.7

271,289

3,806,340

21

9/28/85

13

SF6

24.4

270,133

3,806,520

22

9/28/85

13

Freon

39.6

270,133

3,806,520

23

9/28/85

14

SF6

24.4

270,133

3,806,520

24

9/28/85

14

Freon

39.6

270,133

3,806,520

25

9/29/85

11

SF6

30.5

270,133

3,806,520

26

9/29/85

12

SF6

30.5

270,133

3,806,520

27

9/29/85

12

Freon

61

270,133

3,806,520

2.1.3 Pismo Beach. CA

The Pismo Beach experiment was conducted during December 1981 and June 1982. A depiction
of land use, release point locations and receptor sites are shown in Figure 4 based on U.S. EPA
(2012b). Tracer was released from a boat mast height of 13.1 m to 13.6 m above the water. Peak
concentrations occurred near the shoreline at sampling distances from 6 km to 8 km away. The
Pismo Beach evaluation database consists of 31 samples.

11


-------
CO
<
z

Q


-------
Table 5. Pismo Beach measured meteorological data.

Date

Hour
(LST)

Wind
speed
(m/s)

RH (%)

Air
temperature

(°C)

Sea
temperature

(°C)


-------
with the highest observed concentration, a constant westerly wind was assumed, and predictions
were obtained at a single receptor located the correct distance east of the release point.

Table 6. Pismo Beach release heights and receptor distances.

Release
number

Date

Hour
(LST)

Release
ht (m)

Receptor
distance

(m)

1

12/8/81

15

13.1

6730

2

12/8/81

16

13.1

6506

3

12/11/81

14

13.1

6422

4

12/11/81

15

13.1

6509

5

12/11/81

17

13.1

6619

6

12/11/81

19

13.1

7316

7

12/13/81

14

13.1

6516

8

12/13/81

15

13.1

6372

9

12/13/81

17

13.1

6870

10

12/14/81

13

13.1

6378

11

12/14/81

15

13.1

6378

12

12/14/81

17

13.1

6526

13

12/15/81

13

13.1

6944

14

12/15/81

14

13.1

6697

15

12/15/81

19

13.1

8312

16

6/21/82

15

13.6

6532

17

6/21/82

16

13.6

6589

18

6/21/82

17

13.6

6748

19

6/21/82

18

13.6

6532

20

6/22/82

15

13.6

6125

21

6/22/82

16

13.6

6214

22

6/22/82

19

13.6

6054

23

6/24/82

13

13.6

6244

24

6/24/82

15

13.6

6244

25

6/25/82

12

13.6

6406

26

6/25/82

13

13.6

6377

27

6/25/82

15

13.6

6406

28

6/25/82

16

13.6

6435

29

6/25/82

17

13.6

6455

30

6/27/82

16

13.6

6630

31

6/27/82

18

13.6

6579

14


-------
2.1.4 Ventura. CA

The Ventura experiment was conducted during September 1980 and January 1981. Land use,
release point locations and receptor sites are shown in Figure 5 based on the files from the
CALPUFF evaluation archives. The tracer was released from a boat mast height of 8.1 m above
the water. Peak concentrations occurred along the closet arc of receptors in Figure 5 at sampling
distances from 7 km to 11 km away. The Ventura evaluation database consists of 17 samples.

VENTURA, CA

379ft-

3796-

0	3794-
(0
<
z

1	3702-
W
o

5 3790-

3788-

3786-

3784-

3782-

3780-

-

Hi



/ 1







m





/





'H

|

4

*

n

©

u

u
—

y













y.

'li	



—or

X

















X

<



X

X'









A

M.

A







X



x>

X .

xx

















X
X





*

















L x

X





X

y x















>

<
X





X























X

X



















































284 286 288 290 292 294 296 298 300 302 304
UTM East (km) Zone 11N, Datum NAS-C

Figure 5. Ventura, CA study area.



r 100



-95

Snow/Ice



-90





-85

Tundra



-80





-75

Barren



70





-65

Wetland



-60





-55

Water



-50





-45

Forest



-40





-35

Range



-30





-25

Agnculture



-20





-15

Urban'Built-Up



- 10



Land Use

X Sampler Locations
~ Tracer Releases

The Ventura meteorological data used in the current analysis are shown in Table 7. Note for all
hours the station pressure was 1000 mb, wind measurement height was 20.5 m, air
temperature/relative humidity measurement height was 7.0 m, and wind direction was 270°
because AERMOD was run in screening mode. The OCD and CALPUFF model evaluation data
set stabilities ranged from moderately unstable to slightly stable. As with the Pismo Beach data,
there are several hours of stable lapse rates accompanied by unstable air-sea temperature
differences. For example, on September 29, 1980, hour 1400, the air-sea temperature difference
is -0.8 °C, while the virtual potential temperature lapse rate is 0.03 °C/m. These contradictory

15


-------
data were resolved using the same methodology as in the Pismo Beach and Cameron datasets
and the revised estimates are highlighted in gray in Table 7.

Table 7. Ventura measured meteorological data.

Date

Hour
(LST)

Wind
speed
(m/s)

RH (%)

Air
temperature

(°C)

Sea
temperature

(°C)

°e (°)

Mixing
height
(m)

9/24/80

16

4.1

72

15.15

17.25

8

400

9/24/80

18

6.2

78

14.85

16.85

6.5

400

9/24/80

19

6.9

77

14.85

16.95

6

400

9/27/80

14

6.3

80

14.85

16.75

4.7

400

9/27/80

19

6.1

80

15.85

16.85

3.6

400

9/28/80

18

3.1

80

16.85

16.85

4.4

250

9/29/80

14

3.3

76

15.55

15.44

5

100

9/29/80

16

5.1

76

16.15

16.04

3.9

100

9/29/80

18

5.2

76

16.05

15.94

5.2

50

1/6/81

16

4

60

17.15

15.55

21.5

50

1/6/81

17

5.1

58

17.45

15.75

13.1

50

1/6/81

18

4.9

60

17.25

15.45

9.4

50

1/9/81

15

4.7

87

14.45

15.35

3.4

100

1/9/81

16

4.6

85

14.85

15.35

4.8

100

1/9/81

18

4.9

87

15.05

15.35

3.1

100

1/13/81

15

5.8

65

16.95

15.55

11.6

50

1/13/81

17

4.2

84

15.85

15.45

8.5

50

Table 8 shows the source and receptor characteristics used in the Ventura tracer simulations. The
boat releases assumed a release height of 8.1 m, building height of 7 m and a width (and length)
of 20 m. Downwind receptor distances were varied to match the downwind distances of the
measurement site with the highest observed concentration for each period.

16


-------
Table 8. Ventura receptor distances.

Release
number

Date

Hour (LST)

Receptor distance (m)

1

9/24/80

16

9291

2

9/24/80

18

9211

3

9/24/80

19

10799

4

9/27/80

14

9123

5

9/27/80

19

9123

6

9/28/80

18

9145

7

9/29/80

14

8085

8

9/29/80

16

7854

9

9/29/80

18

7854

10

1/6/81

16

7463

11

1/6/81

17

7416

12

1/6/81

18

7463

13

1/9/81

15

7956

14

1/9/81

16

7749

15

1/9/81

18

7704

16

1/13/81

15

7705

17

1/13/81

17

6914

2.2 AERCOARE and AERMET configurations

2.2.1 Measured data

For the case studies, AERCOARE and AERMET were run with the following the
configurations and case study/configuration combinations are shown in Table 9 for measured
data. An 'X' in the cell for a scenario and location indicates that scenario was run for the case
location.

• Scenario 1:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
25 m if less than 25 m.

17


-------
o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

•	Scenario la:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
1 m if less than 1 m.

o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

•	Scenario lb:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
5 m if less than 5 m.

o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

•	Scenario lc:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
15 m if less than 15 m.

o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

18


-------
• Scenario 2:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
25 m if less than 25 m.

o Do not use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

•	Scenario 3:

o Reset absolute value of Monin-Obukhov length to 1 m if absolute value of
Monin-Obukhov length is less than 1 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective and mechanical mixing heights;

Reset mechanical mixing height to 1 m if less than 1 m.

o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs;

•	Scenario 4:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective and mechanical mixing heights;

Reset mechanical mixing height to 1 m if less than 1 m.

o Use measured go (standard deviation of wind direction) to calculate ov in
AERMOD runs

19


-------
Table 9. AERCOARE and AERMET-COARE configurations for measured data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura

1

X

X

X

X

la



X

X



lb



X

X



lc



X

X



2

X

X

X

X

3

X

X

X

X

4

X

X

X

X

2.2.2 Prognostic data
2.2.2.1 WRF simulations

WRF version 4.4.2 was applied over multiple near-shore locations in Louisiana and California.
The time periods modeled for each location are indicated in Table 10 below. These simulations
were conducted using nested domains of 12-km, 4-km, and 1.33-km and utilizing a 354ayer
vertical resolution. These WRF domains encompass the entire dispersion modeling domain and
are shown for each location in Figure 6 through Figure 9. The ERA-Interim 6-hourly reanalysis
dataset was used for initialization. All WRF simulations utilized the physics options outlined
below:

•	Microphysics: Thompson

•	Planetary Boundary Layer: UW

20


-------
•	Cumulus: Kain-Fritsch

•	Radiation: RRTMG

•	Land Surface Model: NOAH

•	Surface Layer: Eta

An effort was made to select model options and domains similar to work conducted during the
development of AERCOARE (U.S. EPA, 2015). That report outlines extensive model
performance evaluation and is the basis for the options selected here.

WRF Domain - Cameron

36° N

34°N

32°N

3Q°N

28°N

26DN

100°W 98°W	96°W	94°W	92°W	90°W	88SW	86UW

Figure 6. Cameron, LA WRF domains. The large outer box is the 12-km domain, the white box
is the 4-km domain, and the red box is the 1.33 km domain.

21


-------
WRF Domain - Carpinteria

Figure 7. Carpinteria, CA WRF domains. The large outer box is the 12-km domain, the white
box is the 4-km domain, and the red box is the 1.33 km domain.

22


-------
WRF Domain - Pismo

Figure 8. Pismo Beach, CA WRF domains. The large outer box is the 12-krn domain, the white
box is the 4-km domain, and the red box is the 1.33 km domain.

23


-------
WRF Domain - Ventura

Figure 9. Ventura, CA WRF domains. The large outer box is the 12-km domain, the white box
is the 4-km domain, and the red box is the 1.33 km domain.

24


-------
Table 10. Time periods modeled for each location.

Location

Period

Cameron, LA

Period 1: 7/15/1981 - 7/31/1981
Period 2: 2/10/1982 - 2/25/1982

Carpinteria, CA

Period 1: 9/15/1985 -- 9/30/1985

Pismo Beach, CA

Period 1: 12/5/1981 - 12/20/1981
Period 2: 6/15/1982-6/30/1982

Ventura, CA

Period 1: 9/15/1980-9/30/1980
Period 2: 1/1/1981 - 1/15/1981

2.2.2.2 MMIF output

Once WRF simulations were completed, the 1.3 km WRF output was processed in MMIF to
generate data formatted for input to AERCOARE. Locations for extraction were based on the
release point locations shown in Figure 2 through

VENTURA. CA

379ft-

3796-

<

I
~

i 3790-

0

s

1	3788-

3766-

3784-

3782-

3780-







1



,i«V<

few









/





|§

Wj

4

IS

if

Or

O



fr

¦S

y













x-



' v—

_	fsr

X

















X

X



¦ X

x-









~
*

A







X

5



XX

X .

*x

















X

X
X





*x
*

















X
X





&

X

















>

<
X





X























X

X



















































284 286 288 290 292 294 296 298 300 302 304
UTM East (km) Zone 11N, Datum NAS-C



r 100



-95

Snow/Ice



-90





-86

Tundra



-80





-75

Barren



70





-65

Wetland



-60





-55

Water



-50





-45

Forest



-40





-35 Range



-30





-25 Agnculture



-20





-15

Urban'Built-Up



-10



Land Use

X Sampler Locations
~ Tracer Releases

25


-------
Figure 5. These same files were processed in AERCOARE and AERMET with the COARE
processing. Winds were output for 10 m and temperature and relative humidity at 2 m. In
addition to winds, temperature, and relative humidity, sea surface temperature, pressure,
downward solar radiation, downward longwave radiation, precipitation, total sky cover, mixing
height, vertical potential temperature gradient above the PBL, and depth of sea surface
temperature measurement. See the MMIF user's guide (Ramboll, 2023) for AERCOARE
formatted output.

2.2.2.3 AERCOARE and AERMET-COARE configurations

The prognostic data used for comparisons do not contain turbulence data so Scenarios 1, la-lc
are analogous to the scenarios in Section 2.2.1 except without turbulence. Scenarios 2 and 3 are
analogous to Scenarios 3 and 4 respectively in Section 2.2.1 except without turbulence. The
following scenarios were run for the prognostic data and are shown in Table 11. An 'X' in the
cell for a scenario and location indicates that scenario was run for the case location.

•	Scenario 1:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
25 m if less than 25 m.

•	Scenario la:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
1 m if less than 1 m.

•	Scenario lb:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

26


-------
o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
5 m if less than 5 m.

•	Scenario lc:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective mixing height and calculate

mechanical mixing height without smoothing; Reset mechanical mixing height to
15 m if less than 15 m.

•	Scenario 2:

o Reset absolute value of Monin-Obukhov length to 1 m if absolute value of
Monin-Obukhov length is less than 1 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective and mechanical mixing heights;

Reset mechanical mixing height to 1 m if less than 1 m.

Scenario 3:

o Reset absolute value of Monin-Obukhov length to 5 m if absolute value of
Monin-Obukhov length is less than 5 m. Retain original sign (+ or -) of Monin-
Obukhov length

o Use observed mixing height for convective and mechanical mixing heights;
Reset mechanical mixing height to 1 m if less than 1 m.

Table 11. AERCOARE and AERMET-COARE configurations for prognostic data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura

1

X

X

X

X

la



X

X



27


-------
lb



X

X



lc



X

X



2

X

X

X

X

3

X

X

X

X

To ensure a fair comparison between AERCOARE and AERMET so that differences were due
to possible coding errors in AERMET, AERCOARE was modified with the following changes:

* The mechanical mixing height equation, 2300u*3 2 was changed to 2400u*3 2. Prior to
2013, both AERCOARE and AERMET used the same equation with the 2300
coefficient. With AERMET 13350, the coefficient was changed to 2400 to match the
original formula in Venkatram (1980). AERCOARE, created in 2012, has not been
updated since 2012 and does not include the change. The coefficient in AERCOARE
was changed to match AERMET.

The output formats for the surface and profile file output from AERCOARE to
AERMOD were modified to match those of AERMET.

For the comparisons using prognostic data, both AERCOARE and AERMET were run with a
wind speed threshold of 0.3 m/s. This is because AERCOARE does not reset winds below 21/2
x Gvmin where avmin=0.2 m/s to 21/2 x avmin as AERMET does. This threshold does not follow
the recommendation in the Guidance on the Use of the Mesoscale Model Interface Program
(MMIF) for AERMOD Applications (U.S. EPA, 2023e) which states that the threshold speed
input to AERMET should be 0 m/s. To allow a fair comparison between AERCOARE and
AERMET to ensure the code in AERMET was implemented properly, the threshold was set to
0.3 m/s in both programs.

2.3 Meteorological data evaluation

The meteorological data evaluation or comparison between AERCOARE and AERMET
generally follows the methodology used for comparing AERMET 22112 and AERMET 21112
in Appendix F of the AERMET User's Guide (U.S. EPA, 2023b). Hourly comparisons were
made for all surface variables and profile variables with a tolerance to account for rounding

28


-------
differences since AERMET 22112 uses double precision vs. real for variable while
AERCOARE uses real variables.

Table 12 lists the variables and tolerances.

29


-------
Table 12. Meteorological variables for comparisons with tolerances.

Variable

Tolerance

Sensible heat flux

0.2 W/m2

Surface friction velocity

0.002 m/s

Convective velocity scale

0.002 m/s

0 lapse rate above mixing height

0.002 K/m

Convective mixing height

1 m

Mechanical Mixing height

1 m

Monin-Obukhov length

0.2 m

Surface roughness

0m

Bowen ratio

0

Albedo

0

Reference wind speed

0 m/s

Reference wind direction

0°

Reference wind height

0m

Reference temperature

0.2 K

Reference temperature height

0m

Precipitation code

0

Precipitation

0 mm/hr

Relative humidity

1 %

Station pressure

2 mb

Cloud cover

0 tenths

Wind flag

Character: character strings compared

Profile height

0m

Profile top indicator

Not checked

Profile wind speed

0 m/s

Profile wind direction

0°

Profile temperature

0°C

Profile oe

0°

Profile o„

0 m/s

2.4 AERMOD evaluation

Except for Carpinteria, all AERMOD runs were run in screening mode, i.e., the receptor was
assumed to be on the plume centerline and the AERMOD SCREEN model option used. For
those screening mode cases using measured data, the wind direction was set to 270°, or westerly
winds. Carpinteria AERMOD runs reflected actual source-receptor distances and orientation.

30


-------
All AERMOD runs were with version 22112. AERMOD output based on AERCOARE and
AERMET with COARE were compared in time and space. Ratios of concentrations were
calculated for each hour and receptor. Additionally, test statistics called Robust Highest
Concentrations (RHC) (U.S. EPA, 1992) were calculated and compared as well for each study
area. The RHC is calculated as:

RHC = X(JV) + [X - X(JV)] x In [^±]	(1)

Where X(N) is the Nth largest value, X is the average of N-l values, and N is the number of
values exceeding the threshold value, in this case 10.

3.0	Results

3.1	Meteorological data comparisons

3.1.1 Measured data

•	Cameron (all scenarios)

o 13 hours where Bowen ratio from AERCOARE was -1.0 and Bowen ratio from
AERMET was 0.01. this is due to AERMET setting any Bowen ratio to 0.01
regardless of sign. Note Bowen ratio is not used by AERMOD.

o Two hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

•	Carpinteria (all cases)

o 13 hours where Bowen ratio from AERCOARE was -1.0 and Bowen ratio from
AERMET was 0.01. this is due to AERMET setting any Bowen ratio to 0.01
regardless of sign. Note Bowen ratio is not used by AERMOD.

•	Pismo Beach (all cases)

o 25 hours where Bowen ratio from AERCOARE was -1.0 and Bowen ratio from
AERMET was 0.01. this is due to AERMET setting any Bowen ratio to 0.01
regardless of sign. Note Bowen ratio is not used by AERMOD.

o Two hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

31


-------
o 1 hour where Monin-Obukhov length differed by 4 m.

• Ventura (all cases)

o 9 hours where Bowen ratio from AERCOARE was -1.0 and Bowen ratio from
AERMET was 0.01. this is due to AERMET setting any Bowen ratio to 0.01
regardless of sign. Note Bowen ratio is not used by AERMOD.

3.1.2 Prognostic data

Prognostic data evaluation covered all grid cells that were processed for each study area.
Multiple grid cells may have covered the same dates so reported totals are across all grid cell
and date combinations.

• Cameron (all cases)

o A total of 1,656 hours evaluated for each case. Values reported below are
for each case, not cumulative across all cases.

o 1 hour of missing albedo, Bowen ratio, surface roughness, u*, w*, surface
heat flux, Monin-Obukhov length, mixing heights, and potential
temperature lapse rate for AECOARE and non-missing for AERMET for
July 31, 1981 hour 9. This is a calm hour and AERCOARE skips
processing while AERMET continues processing. Will not impact
AERMOD results since hour is calm.

o 334 hours where Bowen ratio from AERCOARE was -1.0 and Bowen
ratio from AERMET was 0.01. this is due to AERMET setting any
Bowen ratio to 0.01 regardless of sign. Note Bowen ratio is not used by
AERMOD.

o 14 hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

o 30 hours where Monin-Obukhov length differed with a range of -28.6 m
to -0.2 m. Only 6 hours differed more than 1 m.

o 1 hour in profile where winds for AERCOARE were calm and winds
were set to missing for AERMET. These were hours below the threshold
of 0.3 m/s and AERMET sets the wind to missing for the profile.
AERCOARE sets these hours to calm. Will not impact AERMOD results
since hour is calm or missing and both are treated the same in AERMOD.

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o 481 hours where potential temperature lapse rate is 0.01 for AERCOARE
and less than 0.01 for AERMET. AERCOARE values reset to 0.01 if
below 0.005 or greater than 0.1. AERMET values are based on the input
lapse rate value from MMIF and not reset.

o 9 hours where potential temperature lapse rate is 0.01 for AERCOARE
and 0 for AERMET.

• Carpinteria (all cases)

o A total of 1,224 hours evaluated for each case. Values reported below are
for each case, not cumulative across all cases.

o 37 hours of missing albedo, Bowen ratio, surface roughness, u*, w*,
surface heat flux, Monin-Obukhov length, mixing heights, and potential
temperature lapse rate for AECOARE and non-missing for AERMET.
These are calm hours and AERCOARE skips processing while AERMET
continues processing. Will not impact AERMOD results since hour is
calm.

o 544 hours where Bowen ratio from AERCOARE was -1.0 and Bowen
ratio from AERMET was 0.01. this is due to AERMET setting any
Bowen ratio to 0.01 regardless of sign. Note Bowen ratio is not used by
AERMOD.

o 2 hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

o 49 hours where Monin-Obukhov length differed with a range of -17.7 m
to -0.2 m. 19 hours differed more than 1 m.

o 37 hours in profile where winds for AERCOARE were calm and winds
were set to missing for AERMET. These were hours below the threshold
of 0.3 m/s and AERMET sets the wind to missing for the profile.
AERCOARE sets these hours to calm. Will not impact AERMOD results
since hour is calm or missing and both are treated the same in AERMOD.

o 58 hours where potential temperature lapse rate is 0.01 for AERCOARE
and less than 0.01 for AERMET. AERCOARE values reset to 0.01 if
below 0.005 or greater than 0.1. AERMET values are based on the input
lapse rate value from MMIF and not reset.

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•	Pismo Beach (all cases)

o A total of 2,856 hours evaluated for each case. Values reported below are
for each case, not cumulative across all cases.

o 3 hours of missing albedo, Bowen ratio, surface roughness, u*, w*,
surface heat flux, Monin-Obukhov length, mixing heights, and potential
temperature lapse rate for AECOARE and non-missing for AERMET.
These are calm hours and AERCOARE skips processing while AERMET
continues processing. Will not impact AERMOD results since hour is
calm.

o 523 hours where Bowen ratio from AERCOARE was -1.0 and Bowen
ratio from AERMET was 0.01. This is due to AERMET setting any
Bowen ratio to 0.01 regardless of sign. Note Bowen ratio is not used by
AERMOD.

o 7 hours where Bowen ratio from AERCOAR was 1.0 and Bowen ratio
from AERMET is 0.01. This is due to AERMET setting any Bowen ratio
to 0.01 regardless of sign. Note Bowen ratio is not used by AERMOD.

o 38 hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

o 40 hours where Monin-Obukhov length differed with a range of -2.4 m to
-0.2 m. 7 hours differed more than 1 m.

o 3 hours in profile where winds for AERCOARE were calm and winds
were set to missing for AERMET. These were hours below the threshold
of 0.3 m/s and AERMET sets the wind to missing for the profile.
AERCOARE sets these hours to calm. Will not impact AERMOD results
since hour is calm or missing and both are treated the same in AERMOD.

o 276 hours where potential temperature lapse rate is 0.01 for AERCOARE
and less than 0.01 for AERMET. AERCOARE values reset to 0.01 if
below 0.005 or greater than 0.1. AERMET values are based on the input
lapse rate value from MMIF and not reset.

o 1 hour of wind direction of 0 in AERCOARE and 360 in AERMET.

Wind speed for the hour was 4.92 m/s.

•	Ventura (all cases)

o A total of 1,200 hours evaluated for each case. Values reported below are
for each case, not cumulative across all cases.

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o 5 hours of missing albedo, Bowen ratio, surface roughness, u*, w*,
surface heat flux, Monin-Obukhov length, mixing heights, and potential
temperature lapse rate for AECOARE and non-missing for AERMET.
These are calm hours and AERCOARE skips processing while AERMET
continues processing. Will not impact AERMOD results since hour is
calm.

o 807 hours where Bowen ratio from AERCOARE was -1.0 and Bowen
ratio from AERMET was 0.01. this is due to AERMET setting any
Bowen ratio to 0.01 regardless of sign. Note Bowen ratio is not used by
AERMOD.

o 8 hours where Bowen ratio differed by 0.01 between AERCOARE and
AERMET.

o 51 hours where Monin-Obukhov length differed with a range of -8.6 m to
-0.2 m. 13 hours differed more than 1 m.

o 4 hours in profile where winds for AERCOARE were calm and winds
were set to missing for AERMET. These were hours below the threshold
of 0.3 m/s and AERMET sets the wind to missing for the profile.
AERCOARE sets these hours to calm. Will not impact AERMOD results
since hour is calm or missing and both are treated the same in AERMOD.

o 10 hours where potential temperature lapse rate is 0.01 for AERCOARE
and less than 0.01 for AERMET. AERCOARE values reset to 0.01 if
below 0.005 or greater than 0.1. AERMET values are based on the input
lapse rate value from MMIF and not reset.

o 2 hours where potential temperature lapse rate is non-missing for
AERCOARE and missing for AERMET. These are two of the calm
hours.

3.2 AERMOD results

3.2.1 Measured data

Table 13 lists the range of ratios of AERMOD results paired in time and space for each
scenario. Ratios are AERMOD using AERMET/AERMOD using AERCOARE. Table 14 lists
the Robust Highest Concentration (RHC) ratio (AERMET/AERCOARE) for each scenario.
Differences for Carpinteria are due to slight differences in air temperatures (approximately 0.1
degrees) and differences for Pismo Beach are due to slight differences in Monin-Obukhov
length. RHC values are based on N=10.

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Table 13. Minimum and maximum AERMOD concentration ratios (AERMET/AERCORE) for
measured meteorological data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura Beach

1

1

0.996-1.0001

0.999-1.0001

1

la

NA

0.9953-1.00008

0.999-1.0001

NA

lb

NA

0.9953-1.002

0.999-1.0001

NA

lc

NA

0.9953-1.00007

0.999-1.0001

NA

2

1

0.996-1.0001

1.0-1.0008

1

3

1

0.9975-1.00004

0.9999-1.0001

1

4

1

0.9982-1.00003

0.9999-1.0001

1

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Table 14. AERMOD Robust Highest Concentration ratios (AERMET/AERCORE) for measured
meteorological data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura Beach

1

1

1.00005

1

1

la

NA

1.00004

1

NA

lb

NA

1.00007

1

NA

lc

NA

1.00006

1

NA

2

1

1.00005

0.999

1

3

1

1.00001

1

1

4

1

1

1

1

3.2.2 Prognostic data
Table 15 and

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Table 16 are analogous to Table 13 and Table 14 respectively for prognostic data.

Table 15. Minimum and maximum AERMOD concentration ratios (AERMET/AERCORE) for
prognostic meteorological data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura Beach

1

1.00-1.0002

0.9999-1.000009

1.0-1.00003

1.0-1.00003

la

NA

0.9999-1.000009

1.0-1.00003

NA

lb

NA

0.9999-1.000009

1.0-1.00003

NA

lc

NA

0.9999-1.000009

1.0-1.00003

NA

2

1.00-1.0002

0.9999-1.000009

1.0-1.00003

1.0-1.00002

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3

1.00-1.0002

0.9999-1.000009

1.0-1.00003

1.0-1.00002

Table 16. AERMOD Robust Highest Concentration ratios (AERMET/AERCORE) for
prognostic meteorological data.

Scenario

Cameron

Carpinteria

Pismo Beach

Ventura Beach

2

1.00004

1

1

1

la

NA

1

1

NA

lb

NA

1

1

NA

lc

NA

1

1

NA

2

1.00002

1

1

1

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3

1.00002

1

1

1

4.0 Summary and Conclusions

COARE algorithms were incorporated into AERMET version 23132 to allow processing of
measured or prognostic meteorological data to calculate representative boundary layer
parameters for the marine boundary layer environment. Four case studies were used to assess
the accuracy of the code incorporation into AERMET by comparing meteorological outputs
from AERCOARE and AERMET as well as AERMOD outputs from both AERCOARE and
AERMET. The results of the evaluations of meteorological data and AERMOD concentrations
indicated that there were no coding errors when the COARE algorithms were incorporated into
AERMET for the default configuration of COARE (no warm layer or cool skin options
selected). Differences were due to the transition from real variables in AERCOARE to double
precision in AERMET.

Given the equivalency between AERCOARE and AERMET with COARE, the original
conclusions of the AERCOARE-AERMOD approach in U.S. EPA (2012b) are still valid with
the AERMET-COARE approach:

•	The AERCOARE-AERMOD modeling approach was not biased towards underestimates
at the high-end of the concentration frequency distribution.

•	The AERCOARE-AERMOD approach performed better using the observed o@
measurements.

•	AERCOARE-MOD predictions were sensitive to the mixing height. An estimate of the
mechanical mixing height based on the friction velocity, as in AERMET, was a better
alternative than using the observed mixing height from the field studies.

•	The AERCOARE-AERMOD approach was sensitive to assumptions during low wind
speed conditions and restricting the Monin-Obukhov length such that the absolute value
of L > 5 seemed to improve performance by limiting the occurrence of extremely
unstable or stable conditions.

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5.0 References

DiCristofaro, D.C. and S.R. Hanna, 1989. OCD: The Offshore and Coastal Dispersion Model,
Version 4. Volume I: User's Guide, and Volume II: Appendices. Sigma Research
Corporation, Westford, MA. (NTIS Nos. PB 93-144384 and PB 93-144392).

Fairall, C.W., E.F. Bradley, J.E. Hare, A.A. Grachev, and J.B. Edson, 2003: "Bulk

Parameterization of Air-Sea Fluxes: Updates and Verification for the COARE
Algorithm." J. Climate, 16, 571-591.

Ramboll, 2023: The Mesoscale Model Interface Program (MMIF) Version 4.1 User's Manual.

U.S. EPA, 1992: Protocol for Determining the Best Performing Model, EPA-454/R-92-025.
U.S. Environmental Protection Agency, Research Triangle Park, NC.

U. S. EPA, 2011a: Model Clearinghouse Review AERMOD-COARE as an Alternative Model in
an Arctic Ice Free Environment. George Bridgers Memorandum dated May 6, 2011,
Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina,
27711.

https://gaftp.epa.gov/Air/aqmg/SCRAM/mchisrs/R1444 Bridgers 6 May 11 AMERO
D-COARE.pdf

U.S. EPA, 201 lb: User's Guide for the AERMOD Terrain Preprocessor (AERMAP). EPA-
454/B-03-003. U.S. Environmental Protection Agency, Research Triangle Park, North
Carolina.

U.S. EPA, 2012a: User's Manual AERCO ARE Version 1.0. EPA-910/R-12-008. U.S. EPA,
Region 10, Seattle, WA.

U.S. EPA, 2012b: Evaluation of the Combined AERCO ARE AERMOD Modeling Approach for
Offshore Sources. EPA-910/R-12-007. U.S. EPA, Region 10, Seattle, WA.

U.S. EPA, 2015: Combined WRF MMIF AERCO ARE AERMOD Overwater Modeling Approach
for Offshore Emission Sources: Volume 3 - Analysis of AERMOD Performance Using
Weather Research and Forecasting Model Predicted Meteorology and Measured
Meteorology in the Arctic. EPA-910/R-15-001c. U.S. EPA, Region 10, Seattle, WA.

U.S. EPA, 2023a: User's Guide for the AMS EPA Regulatory Model (AERMOD). EPA-454/B-
23-008. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina.

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U. S. EPA, 2023b: User's Guide for the AERMOD Meteorological Preprocessor (AERMET).
EPA-454/B-23-005. U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina.

U.S. EPA, 2023c: Guideline on Air Quality Models. 40 CFR Part 51 Appendix W.

U.S. EPA, 2023 d: Evaluation of Prognostic Meteorological Data in AERMOD Overwater
Applications. EPA-454/R-23-010. U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina.

U. S. EPA, 2023 e: Guidance on the Use of the Mesoscale Model Interface Program (MMIF) for
AERMOD Applications. EPA-454/B-23-006. U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina.

Venketram, A., 1980. "Estimating the Monin-Obukhov Length in the Stable Boundary Layer for
Dispersion Calculations." Bound. Layer Meteor., 19, 481-485.

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United States	Office of Air Quality Planning and Standards	Publication No. EPA-454/R-23-008

Environmental Protection	Air Quality Assessment Division	October 2023

Agency	Research Triangle Park, NC


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