AERMOD/BLP Development and Testing

i

EPA-454/P-15-004

July 2015

AERMOD/BLP Development and Testing

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Air Quality Assessment Division

Air Quality Modeling Group

Research Triangle Park, North Carolina
ii

Preface

This document provides the modification and evaluation procedures used to incorporate the 

Buoyant Line and Point Source (BLP) model into AERMOD.
iii

Acknowledgements

The incorporation of BLP into AERMOD was performed by Jim Paumier of AMEC 

Foster/Wheeler Environment & Infrastructure Inc., Part 4, Task Order No. EP-G15-D-00208, 

contract No. GS-35F-0851R with Chris Owen as Part 4 Task Order Project Officer.
iv

Contents

Preface............................................................................................................................................. ii

Acknowledgements........................................................................................................................iii

Figures............................................................................................................................................. v

Tables............................................................................................................................................. vi

1. Introduction................................................................................................................................. 1

2. Source Code Modifications......................................................................................................... 1

3. Testing......................................................................................................................................... 2

3.1 Initial Tests............................................................................................................................ 2

3.2 Further Testing of AERMOD ............................................................................................. 17

4. Differences between AERMOD/BLP and BLP........................................................................ 24

5. Additional Changes to AERMOD/BLP.................................................................................... 24

5.1 Background Concentration.................................................................................................. 24

5.2 Event Processing ................................................................................................................. 24

5.3 BLP Source Group .............................................................................................................. 24

6. Recommendations..................................................................................................................... 24

APPENDIX................................................................................................................................... 26

1. AERMOD Keywords for Buoyant Line Sources.................................................................. 26
v

Figures

Figure 1. Buoyant Line Source and Receptor Locations............................................................... 3
vi

Tables

Table 1. Beginning and Ending Coordinates of the Buoyant Lines ............................................... 2

Table 2. Bouyant Line Source Average Parameters....................................................................... 2

Table 3. Top 50 1-hour Concentration Estimates (μg/m3): 1-day Scenario ................................... 4

Table 4. Top 50 3-hour Concentration Estimates (μg/m3): 1-day Scenario ................................... 5

Table 5. Top 50 24-hour Concentration Estimates (μg/m3

): 1-day Scenario ................................. 6

Table 6. Top 50 1-hour Concentration Estimates (μg/m3

): 4-day Scenario ................................... 7

Table 7. Top 50 3-hour Concentration Estimates (μg/m3): 4-day Scenario ................................... 8

Table 8. Top 50 24-hour Concentration Estimates (μg/m3): 4-day Scenario ................................. 9

Table 9. Top 50 1-hour Concentration Estimates (μg/m3): 1-month Scenario............................. 10

Table 10. Top 50 3-hour Concentration Estimates (μg/m3

): 1-month Scenario........................... 11

Table 11. Top 50 24-hour Concentration Estimates (μg/m3): 1-month Scenario......................... 12

Table 12. Top 50 1-hour Concentration Estimates (μg/m3): 1-year Scenario .............................. 13

Table 13. Top 50 3-hour Concentration Estimates (μg/m3

): 1-year Scenario .............................. 15

Table 14. Top 50 24-hour Concentration Estimates (μg/m3

): 1-year Scenario ............................ 16

Table 15. Additional Tests - 1-year Scenarios.............................................................................. 17

Table 16. Top 5 Concentration Estimates (μg/m3

), Test A (Gridded Network)........................... 18

Table 17. Top 5 Concentration Estimates (μg/m3

), Test B (Includes Two Point Sources).......... 18

Table 18. Concentration Estimates (μg/m3

), Test C.................................................................... 18

Table 19. Concentration Estimates (μg/m3

), Test C..................................................................... 19

Table 20. Concentration Estimates (μg/m3

) for Test D ............................................................... 19

Table 21. Concentration Estimates (μg/m3) for Test E................................................................ 20

Table 22. Concentration Estimates (μg/m3) for Test F (24-hr PM-2.5)....................................... 21

Table 23. Concentration Estimates (μg/m3) for Test G (1-hr SO2).............................................. 22

Table 24. Concentration Estimates (μg/m3) for Test H -.............................................................. 23

Table 25. Concentration Estimates (μg/m3

) for Test I - ............................................................... 23

Table 26. Concentration Estimates (μg/m3) for Test J -............................................................... 23
1

1. Introduction

The AERMOD dispersion model was modified to incorporate the buoyant line algorithms of the 

Buoyant Line and Point source (BLP) dispersion model. For purposes of this discussion, we will 

refer to this draft of AERMOD as AERMOD/BLP.

2. Source Code Modifications

The buoyant line algorithms in BLP (version 99176) were first incorporated into AERMOD 

version 14134 and later into version 15181. For this phase of development, the buoyant line 

algorithms were ported unchanged from BLP to AERMOD. To keep the routines easily 

identifiable in AERMOD/BLP, "BL_" was added to the beginning of the subroutine and function 

names. Within those subroutines and functions, variable names were added as needed or 

changed to match the AERMOD variable names, such as the reference height wind speed. BLP 

was written decades ago and used GOTO statements and other obsolescent structures to control 

conditional programming. Those structures were replaced with IF..THEN..ELSE..ENDIF and 

SELECT..CASE structures. Other parts of the original BLP code were updated to reflect more 

recent versions of the Fortran language such as named DO loop structures, double precision, and 

allocatable arrays. Some of the GOTO statements were retained since deconstructing those 

structures would require a much greater effort. A new module, buoyant_line, was added to 

centralize the global variables associated with BLP. Variables and constants in the module and 

routines were defined as double precision.

BLP version 99176 is very limited in the number of sources (up to 10 lines in a single buoyant 

line source and 51 point sources) and receptors (up to 100) that can be processed in a single 

model run. As part of the porting process, array size limitations imposed by BLP were changed 

to allocatable arrays in AERMOD/BLP. 

Additional keywords and parameters were added to process buoyant lines. These additions can 

be found in the appendix attached to this memo.

The following files were modified in the process of incorporating BLP into AERMOD:

aermod.f, calc1.f, soset.f, reset.f, setup.f, modules.f, metext.f, and evcalc.f (minimal changes; not 

all necessary changes were made for event processing). For testing AERMOD/BLP, 64-bit 

executables were generated.
2

3. Testing

3.1 Initial Tests

Modifications to BLP version 99176were required to compare concentration estimates between 

BLP and AERMOD/BLP. These included reading and processing command line arguments 

(complying with the Intel Fortran requirements) and increasing the number of receptors. Since 

BLP was originally limited to 100 receptors, the BLP code was modified to allow up to 1000 

receptors. 

During the initial development and debugging process, one-day and four-day meteorological data 

sets were used to evaluate whether or not BLP and AERMOD/BLP were giving the same results. 

A buoyant line source consisting of three lines parallel to each other was defined, with the lines 

oriented northwest-to-southeast at a 45-degree angle as shown in Figure 1. The endpoints of the 

three lines that make up the line source are in Table 1.

Table 1. Beginning and Ending Coordinates of the Buoyant Lines

Source ID Xbegin Ybegin Xend Yend

BLINE1 300 800 900 200

BLINE2 300 1000 900 400

BLINE3 300 1200 900 600

BLP requires the average value for several parameters in its calculations. These values are 

defined in the BLP User's Manual. The average parameters associated with the buoyant line 

source used in this testing are taken from one of the example cases packaged with BLP version 

99176 and are presented in Table 2.

Table 2. Bouyant Line Source Average Parameters

Bldg Length 

(m)

Bldg Hgt

(m)

Bldg Width

(m)

Line Width

(m)

Bldg Separation

(m)

Buoyancy Param.

(m4/s3)

848.0 20.0 100.0 2.0 37.5 300.0

The release height for the lines was 20.0 meters (m) and the elevation for the lines was 0.0 m.

A 31-by-31 discrete receptor grid, with the origin at (0,0), and 50-meter node spacing was 

defined for the analyses, for a total of 961 receptors. The receptors are shown in Figure 1 as 

light grey dots.
3

For these initial tests, each buoyant line was modeled with an emission rate of 1.0 

grams/second/square meter (g/s/m2). The averaging times modeled were 1-, 3-, and 24-hr. Some 

test scenarios were modeled with 8-hr averaging periods, but the results are not reported here. 

Flat terrain was assumed for all model runs.

Figure 1. Buoyant Line Source and Receptor Locations

To run the AERMOD meteorology (or as near as possible) in BLP, which requires 

PCRAMMET-like format, AERMOD/BLP was modified to output the necessary parameters for 

BLP to read. The parameters are: wind speed (meters/second, m/s), flow vector (although it is 

referred to as wind direction in the BLP manuals) (degrees), ambient temperature (kelvin), 

Pasquill-Gifford (P-G) stability class, and rural and urban mixing heights (m). The wind 

direction, an input to AERMOD, was converted to flow vector for BLP. Since the P-G stability 

class is not an input to AERMOD, the subroutine LTOPG found in AERMOD was used to 

generate and output the appropriate stability class for the hour. The rural and urban mixing 

heights were set to the same value and are the larger of the convective and mechanical mixing 

heights that are input to AERMOD. For the one-day and four-day periods, all meteorological 

parameters were present (i.e., no missing data).
4

The results from BLP and AERMOD/BLP were compared and significant differences were noted 

with the one- and four-day runs. The code was reviewed and a few bugs were corrected, but 

differences remained. The difference was traced to the use of double precision in 

AERMOD/BLP (real variables are declared double precision). BLP was recompiled with the

real-size:64 option (the default is real-size:32) and the results from both models (AERMOD/BLP 

and BLP) for the two short meteorological data sets were nearly identical. Table 1 shows the top 

50 1-hour concentration impacts for the one-day scenario with the discrete receptor grid. Table 2 

shows the 3-hour impacts, and Table 3 shows the 24-hour impacts. The 'NaN' in Table 3 for 

BLP indicates 'not a number'; the cause of this is unclear or why it would appear in the top 50.

Table 3. Top 50 1-hour Concentration Estimates (μg/m3

): 1-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

1493.2

843.5

517.9

211.7

193.0

175.2

108.1

 97.9

 97.5

 96.6

 95.0

 94.1

 91.7

 91.0

 90.3

 90.3

 90.0

 89.8

 89.6

 89.1

 88.4

 88.3

 88.2

 88.1

 87.9

1345.38

843.51

517.93

211.68

181.35

175.19

108.07

 97.87

 97.50

 96.57

 95.03

 93.87

 91.72

 91.02

 90.85

 90.31

 90.31

 89.98

 89.07

 88.42

 88.31

 88.18

 88.14

 87.94

 87.68

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

87.7

87.4

87.0

86.9

86.4

86.2

86.1

85.9

85.5

85.3

85.2

84.7

84.5

84.4

84.2

83.8

83.6

83.1

83.0

82.2

82.2

81.7

81.3

81.3

81.1

87.39

87.01

86.94

86.40

86.20

86.10

85.90

85.45

85.31

85.18

84.70

84.48

84.41

84.21

83.78

83.62

83.14

83.03

82.24

82.15

81.66

81.34

81.30

81.14

81.07
5

Table 4. Top 50 3-hour Concentration Estimates (μg/m3): 1-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

498.0

281.3

203.0

93.3

89.6

71.5

55.2

54.4

54.0

53.3

52.6

51.3

51.1

50.9

46.2

45.5

44.3

43.0

42.8

42.2

40.2

40.1

39.8

39.8

39.5

448.63

281.34

199.91

 75.40

 75.33

 71.53

 54.35

 53.97

 52.64

 51.33

 51.31

 50.93

 46.15

 45.53

 45.01

 44.31

 43.21

 42.97

 42.82

 42.20

 40.52

 40.22

 40.07

 39.79

 39.52

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

39.4

39.0

37.6

37.6

37.3

37.2

37.0

36.4

36.3

36.3

35.4

35.1

35.0

33.7

33.6

33.2

33.0

33.0

32.7

32.2

31.9

31.8

31.7

31.2

31.2

39.41

39.01

38.06

37.59

37.26

37.20

37.18

37.04

36.30

36.30

35.75

35.05

33.66

33.56

33.00

32.98

32.71

32.71

32.17

32.16

31.75

31.59

31.50

31.24

31.23
6

Table 5. Top 50 24-hour Concentration Estimates (μg/m3): 1-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

110.0

54.5

26.9

21.7

20.5

19.6

18.0

17.0

15.7

14.1

13.8

12.8

12.7

12.7

12.3

12.3

11.9

11.7

11.7

11.7

11.6

11.4

11.3

11.1

11.1

102.23

 52.89

 25.14

 22.32

 20.76

 20.64

 18.60

 17.07

 16.66

 15.79

 14.87

 14.53

 13.51

 13.20

 13.19

 12.81

 12.59

 12.59

 12.56

 12.40

 11.96

 11.95

 11.80

 11.73

 11.61

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

11.1

11.1

11.1

10.9

10.6

10.6

10.5

10.2

10.2

10.2

10.2

10.1

10.1

10.1

10.0

10.0

10.0

9.9

9.9

9.8

NaN

9.8

9.7

9.7

9.6

11.58

11.49

11.38

11.38

11.28

11.27

11.23

11.19

11.14

11.00

10.97

10.96

10.91

10.68

10.67

10.60

10.59

10.58

10.49

10.42

10.40

10.30

10.18

10.16

10.02
7

For the 4-day scenario with the discrete receptor network, Table 4 shows the top 50 1-hour 

concentration impacts for the one-day scenario with a discrete receptor grid. Table 5 shows the 

3-hour impacts, and Table 6 shows the 24-hour impacts. 

Table 6. Top 50 1-hour Concentration Estimates (μg/m3): 4-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

1493.2

843.5

517.9

265.5

244.3

211.7

206.5

193.0

191.2

189.2

188.7

184.3

180.2

178.8

178.4

176.2

175.2

171.5

170.5

169.9

168.3

167.8

166.3

163.9

163.5

1345.38

843.51

517.93

265.46

226.88

211.68

191.17

189.72

189.16

188.66

184.32

181.35

180.25

178.78

178.39

176.16

175.19

171.54

170.48

169.94

168.32

167.82

166.27

163.86

163.47

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

157.9

157.6

156.0

155.5

154.8

154.6

154.2

152.7

150.7

149.1

148.7

146.7

146.5

145.8

145.2

142.0

141.9

140.3

138.1

137.7

135.5

135.2

134.6

133.8

133.8

157.92

157.55

156.02

155.47

154.76

154.63

154.19

152.70

150.71

149.13

148.66

146.67

146.53

145.80

145.19

142.44

141.87

140.26

138.07

137.66

135.50

135.17

134.64

133.81

133.76
8

Table 7. Top 50 3-hour Concentration Estimates (μg/m3): 4-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

498.0

281.3

202.5

145.9

145.4

129.2

100.1

97.7

97.2

95.1

91.9

89.4

88.8

88.2

80.3

78.8

77.5

77.3

77.2

75.4

75.1

75.0

73.8

73.8

73.5

448.63

281.34

199.91

145.88

145.43

129.17

100.05

97.69

91.92

89.95

89.37

88.21

80.40

79.88

78.80

77.46

77.28

77.18

76.10

75.40

75.33

75.03

73.83

73.75

73.52

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

72.2

71.5

69.4

68.8

68.2

68.0

67.0

66.6

63.7

63.3

63.1

63.1

62.8

62.5

62.3

62.2

62.1

62.0

62.0

61.9

61.7

61.5

61.4

61.1

61.1

 72.23

 71.53

 69.39

 68.81

 68.18

 67.02

 66.63

 64.45

 63.72

 63.26

 63.09

 63.05

 62.78

 62.50

 62.32

 62.17

 62.13

 62.04

 62.01

 61.86

 61.73

 61.51

 61.39

 61.14

 61.07
9

Table 8. Top 50 24-hour Concentration Estimates (μg/m3): 4-day Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

109.6

52.9

38.6

33.0

32.9

32.6

31.6

30.6

30.3

30.2

29.8

29.4

29.4

28.5

28.1

28.0

28.0

27.9

27.7

27.7

27.7

26.7

26.7

26.1

26.0

102.23

52.89

38.60

32.99

32.87

32.63

31.39

30.60

30.40

30.30

30.16

29.65

29.48

29.37

28.19

28.10

27.92

27.88

27.82

27.77

27.68

26.95

26.06

26.01

25.83

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

25.8

25.3

25.2

25.2

24.9

24.7

24.6

24.5

24.5

24.3

23.8

23.4

23.1

23.0

22.7

22.7

22.4

22.4

22.4

22.3

22.1

22.0

21.9

21.7

21.7

25.34

25.32

25.14

25.00

24.92

24.83

24.62

24.61

24.50

24.26

23.87

23.60

23.09

23.04

22.73

22.66

22.56

22.43

22.32

22.28

22.05

22.03

22.00

21.70

21.68
10

A 1-month scenario (January) was run using meteorological data processed for the Lovett 

evaluation. To get AERMOD to accept the data, the version number in the header of the .SFC 

file was changed to 14134. For the discrete receptor network, Table 7 shows the top 50 1-hour 

concentration impacts for the one-day scenario with a discrete receptor grid. Table 8 shows the 

3-hour impacts, and Table 9 shows the 24-hour impacts. For the 1-hour estimates, differences 

are apparent immediately after the highest value, but are more in line with each other further 

down.

Table 9. Top 50 1-hour Concentration Estimates (μg/m3): 1-month Scenario

Rank BLP AERMOD AERMOD

(UREF=50)

Rank BLP AERMOD AERMOD

(UREF=50)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

1208.3

841.6

787.3

763.2

755.3

676.9

674.6

654.5

604.5

548.5

545.8

521.7

508.1

500.0

499.9

497.1

494.1

494.1

485.1

484.7

475.8

475.1

471.7

465.5

461.5

1208.26

1098.06

1038.66

841.62

787.32

763.23

755.30

676.90

674.59

654.49

604.45

548.53

545.84

521.73

499.99

499.93

497.10

494.11

494.07

471.74

461.54

454.19

454.09

453.48

451.39

1208.26

1098.06

1038.66

841.62

787.32

763.23

755.30

676.90

674.59

654.49

604.45

548.53

545.84

521.73

508.09

499.99

499.93

497.10

494.11

494.07

485.13

484.74

475.76

475.14

471.74

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

454.2

454.1

453.5

451.4

451.0

447.5

447.4

445.0

443.0

441.7

432.8

429.4

425.4

421.4

419.0

411.4

410.7

407.2

404.8

403.9

403.0

401.0

400.6

399.2

399.0

447.49

447.39

443.00

429.36

425.40

421.43

418.98

411.38

404.82

403.88

402.95

400.58

399.16

399.02

398.14

397.58

397.13

386.52

384.66

383.36

383.24

378.09

374.51

371.74

371.59

465.48

461.54

454.19

454.09

453.48

451.39

450.96

447.49

447.39

444.99

443.00

441.69

432.77

429.36

425.40

421.43

418.98

411.38

410.67

407.23

404.82

403.88

402.95

401.00

400.58
11

Table 10. Top 50 3-hour Concentration Estimates (μg/m3): 1-month Scenario

Rank BLP AERMOD AERMOD

(UREF=50)

Rank BLP AERMOD AERMOD

(UREF=50

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

440.4

420.8

402.8

390.3

378.3

370.5

350.1

331.4

327.1

326.7

323.3

280.4

275.0

247.8

237.4

234.2

233.6

229.0

219.6

218.8

217.9

213.0

199.0

196.1

195.9

440.37

420.79

402.75

390.34

378.27

370.46

367.97

366.02

350.14

331.44

327.06

326.73

323.27

280.36

275.02

247.83

237.36

234.17

229.00

219.57

218.82

217.91

212.95

196.06

195.88

440.37

420.79

402.75

390.34

378.27

370.46

367.97

366.02

350.14

331.44

327.06

326.73

323.27

280.36

275.02

247.83

237.36

234.17

233.61

229.00

219.57

218.82

217.91

212.95

199.03

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

195.8

194.9

193.4

192.8

192.8

191.1

189.9

189.9

188.5

186.7

186.0

184.2

183.7

183.3

180.3

179.9

179.6

179.2

178.0

177.5

174.0

171.4

171.2

171.0

170.3

195.75

194.91

193.38

192.80

192.77

191.09

189.92

188.48

186.66

185.98

184.15

183.70

183.34

180.25

179.92

179.24

178.04

177.52

174.03

171.62

171.37

170.34

170.33

169.57

168.73

196.06

195.88

195.75

194.91

193.38

192.80

192.77

191.09

189.92

189.90

188.48

186.66

185.98

184.15

183.70

183.34

180.25

179.92

179.56

179.24

178.04

177.52

174.03

171.37

171.22
12

Table 11. Top 50 24-hour Concentration Estimates (μg/m3): 1-month Scenario

Rank BLP AERMOD AERMOD

(UREF=50)

Rank BLP AERMOD AERMOD

(UREF=50

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

84.7

79.9

76.3

73.6

70.8

70.5

70.1

68.9

68.3

67.2

67.1

66.4

65.9

65.9

65.8

65.8

64.7

64.7

64.2

63.7

63.6

63.2

62.9

62.9

62.5

84.53

76.75

72.75

70.79

63.65

61.60

61.02

61.02

60.73

60.60

60.39

59.07

58.64

58.53

58.12

57.45

57.44

56.31

56.13

55.63

55.03

54.95

54.56

54.05

53.26

84.67

79.74

76.30

73.63

70.90

70.81

70.54

70.08

68.93

68.33

68.01

67.19

66.39

65.92

65.86

65.78

65.75

64.71

64.68

64.18

63.65

63.54

63.16

62.94

62.48

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

62.3

61.9

61.7

61.6

61.5

61.3

61.3

61.2

60.9

60.8

60.3

60.1

60.0

59.9

58.9

58.7

58.3

57.0

56.9

56.7

56.7

56.5

56.4

56.3

56.1

52.66

52.62

52.62

52.56

52.26

52.25

52.14

51.53

51.49

51.48

51.30

50.99

50.91

50.60

50.39

50.30

50.24

50.22

50.16

50.01

49.90

49.54

49.25

49.20

48.42

62.36

62.33

61.86

61.70

61.64

61.34

61.29

61.15

60.91

60.76

60.25

60.14

60.06

59.97

59.91

58.91

58.71

58.64

58.31

57.04

56.86

56.67

56.66

56.47

56.41

It is important to note that the reference measurement height for winds in the Lovett-based 

meteorology can vary from 10 m to 50m and even as high as 100 m, whereas the 'measurement 

height' in BLP is a user-defined static value. For these tests it was set at 50 m. To eliminate this 

height as a source of possible differences, the reference height in AERMOD/BLP (UREFHT) 

was set to 50 m for all hours. As seen in Table 11, it makes some difference, ranging from 1-2% 

to as much as 15%.

Once most of the 'bugs' had been worked out using the short meteorological data sets, testing was 

extended to using a full year of meteorological data. The Lovett evaluation database profile and 

surface files were used: LOVETT.PFL and LOVETT.SFC. As with the one- and four-day cases, 

AERMOD/BLP was run to output the year of meteorological data for BLP.

BLP requires a complete period of meteorological record but AERMOD will skip the hour if 

critical parameters are missing. There were approximately 250 hours skipped in the output 

meteorological file generated by AERMOD/BLP for the year of meteorological data. Periods 
13

ranged from one hour to several consecutive hours. The resulting output file for BLP was edited 

manually to fill those hours. Interpolation, persistence, and professional judgment were used to 

fill the parameters, depending on the variable and, in part, on the length of the missing data 

period.

A single case was developed to test AERMOD/BLP initially and identify any further bugs with 

the three lines and receptors shown in the figure above. Tables 12-14 show the top 50 1-hr, 3-

hr, and 24-hr impacts, respectively.

Table 12. Top 50 1-hour Concentration Estimates (μg/m3): 1-year Scenario

Rank BLP AERMOD BLP

(realsize:32)

Rank BLP AERMOD BLP

(realsize:32)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

2528.8

2525.6

2364.9

2220.2

1825.4

1821.3

1602.4

1501.9

1488.1

1332.6

1330.8

1291.5

1208.3

1171.8

1167.5

1153.9

1133.0

1131.1

1082.2

1079.9

1078.1

1066.2

1046.9

1013.9

1013.0

146052.19

 2528.82

 2525.60

 2434.01

 2364.93

 2220.21

 2208.78

 1825.36

 1821.31

 1761.65

 1602.43

 1548.45

 1501.89

 1488.07

 1332.55

 1330.77

 1291.44

 1208.26

 1171.84

 1167.48

 1153.89

 1132.99

 1131.08

 1098.06

 1079.88

146002.9

 6802.1

 3010.3

 3006.0

 2713.6

 2517.8

 2472.9

 2434.0

 2208.8

 1827.7

 1825.4

 1821.3

 1761.6

 1626.7

 1548.4

 1501.9

 1488.1

 1332.6

 1330.8

 1291.4

 1282.3

 1275.1

 1264.0

 1242.3

 1240.1

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

966.4

940.5

919.8

895.3

793.3

766.7

751.6

730.2

718.8

696.3

691.3

674.2

671.0

668.4

663.0

662.8

660.9

660.1

650.8

650.1

648.0

644.3

637.3

637.3

636.4

1078.10

1071.29

1066.18

1065.83

1054.35

1046.85

1038.66

1013.93

1012.96

966.38

940.46

939.13

919.75

895.25

874.41

841.62

831.39

793.28

791.68

790.26

787.32

766.66

763.23

761.52

755.30

1208.3

1185.6

1183.6

1174.5

1149.7

1113.7

1112.6

1098.1

1071.3

1066.2

1065.8

1054.3

1038.7

1012.2

999.8

999.8

982.7

966.3

819.5

 1.3

 NaN

919.8

874.4

847.5

838.8

With the full year of data the 1-hour concentration estimates were found to be vastly different: 

146,052 μg/m3 for AERMOD/BLP and 2,528 μg/m3 for BLP. The remaining impacts were two 

orders of magnitude smaller, with the concentration estimates between AERMOD/BLP and BLP 
14

somewhat similar, although there are ranks where the AERMOD/BLP is 30-40 percent (%) 

greater than BLP. The large hourly value also affects the maximum 3-hour and 24-hour results.

AERMOD/BLP also was run with the wind reference height set a constant 50 meters (as is the 

case in BLP). There is little difference between the two AERMOD/BLP model runs, with most 

differences 2% or less. These results are not shown here.

On further investigation, the highest AERMOD/BLP impact was at receptor at x=450, y=1050. 

That receptor is on one of the lines (#3, the uppermost line in Figure 1) and the wind direction 

associated with the date of the highest value is 315° or long the line. This may partly explain the 

extreme value (a receptor right on the line). However, several other receptors appear to fall 

directly on the lines and there are nearly 40 cases where the winds direction is 315° as well, yet 

the impacts are much smaller. Why this single hour stands out has not been investigated.

Why this single hour at one receptor yielded such a large impact while similar receptors (i.e., on 

a line) and wind directions did not has not been investigated in detail. However, BLP was 

recompiled with real-case:32 (32-bit precision) and, unexpectedly, the 32-bit version of BLP 

yielded an estimate of the same magnitude as AERMOD/BLP (Table 12). The remaining BLP 

maximum values are all greater than the corresponding AERMOD/BLP values to the 44th

maximum value. The 45th (1.3) and 46th (NaN) values cannot be explained at this time, and is 

similar to the NaN seen in Table 5. Nor is it clear why the 47th-50th values are about the same 

magnitude as the 44th value. This issue may require further exploration, although since it is an 

issue with BLP, it may not be important for AERMOD/BLP.
15

Table 13. Top 50 3-hour Concentration Estimates (μg/m3): 1-year Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

917.8

848.8

763.7

652.8

614.4

545.4

543.1

507.0

472.2

455.0

440.4

435.5

434.8

427.5

425.2

400.9

389.9

384.6

380.1

369.3

369.0

362.8

352.6

350.4

342.6

48710.30

 917.78

 849.38

 815.06

 807.64

 781.35

 763.73

 652.83

 632.31

 614.38

 578.72

 543.10

 507.04

 504.81

 472.22

 454.98

 440.37

 440.29

 435.54

 434.75

 425.18

 420.79

 402.75

 400.92

 390.61

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

340.7

315.2

313.9

289.9

282.1

281.3

280.4

266.3

264.2

264.2

252.6

251.8

248.5

245.1

243.4

242.6

236.6

235.5

231.6

229.9

227.1

222.7

222.4

217.0

216.2

390.34

389.85

384.60

380.06

378.27

372.41

370.46

369.49

369.30

368.99

367.97

366.02

362.82

357.25

355.91

350.39

350.14

347.01

342.61

340.66

334.85

333.33

331.44

328.37

327.06
16

Table 14. Top 50 24-hour Concentration Estimates (μg/m3): 1-year Scenario

Rank BLP AERMOD Rank BLP AERMOD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

138.7

131.0

126.2

103.6

101.3

100.8

93.3

90.8

90.1

88.6

88.3

83.2

82.9

82.3

79.1

78.2

76.6

74.9

74.4

74.4

74.3

71.6

71.4

70.9

69.7

6094.37

142.76

131.84*

131.19

129.66

125.95

122.70

121.06

119.73

109.95*

109.74

106.66

104.74

103.60*

 98.31

 97.62

 95.75

 95.56

 93.79

 93.34

 92.73

 89.54

 89.09

 88.60

 86.93

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

69.5

69.3

64.7

64.2

63.2

63.2

63.1

62.3

61.5

61.3

61.2

59.8

59.1

58.4

56.3

56.3

55.7

54.1

53.9

53.5

52.2

52.2

51.9

51.8

51.6

84.53

84.14

83.88

82.44

82.14

80.33

80.10

78.89

78.86

78.22*

78.06

77.90

77.52

77.27

76.75

76.68

76.45

75.68

74.64

74.14

73.92

73.78

73.54

72.90

72.75

* missing data processing

At this juncture, it is important to note that the original BLP model removes receptors that are 

within the rectangle defined by the maximum extents that enclose the multiple lines that define a 

buoyant line source (the three lines in this case). In Figure 1 this would result in about 275 

receptors being removed. To be able to compare AERMOD/BLP to BLP, that part of the BLP 

code (only about 3 lines) was commented out, otherwise it would be impossible to compare and 

debug AERMOD/BLP with BLP. This removal of receptors likely would result in the 

elimination of the large AERMOD/BLP impact since it is exactly on the line. Recall that it is up 

to the user to eliminate receptors inside a facility boundary in AERMOD; as such, the receptors 

within the rectangle defined by the buoyant line source would likely be removed during this 

process and this large discrepancy never an issue.
17

3.2 Further Testing of AERMOD

Several additional one-year test cases were created. The buoyant line source always consisted of 

three lines. In those test cases that indicate two point sources, the sources were located slightly 

south of the center of the buoyant line source. These additional cases are described here.

Table 15. Additional Tests - 1-year Scenarios

Test Scenario

A Buoyant line source and gridded receptor network

B Buoyant line source and two point sources

C Buoyant line source, using an hourly emissions file: two scenarios - hourly emissions for a 

single line and hourly emissions for all three lines

D Buoyant line source and two point sources, using HROFDY emission factors for the lines

E Buoyant line source and two point sources, using three different emission factors for each of 

the lines (SEASON, HROFDY, MONTH)

F Buoyant line source and two point sources modeling 24-hr PM2.5 and using MAXDCONT 

G Buoyant line source and two point sources modeling 1-hr SO2 and using MAXDCONT

H Buoyant line source and two point sources with the lines oriented ENE to WSW

I Buoyant line source and two point sources with the lines oriented vertically

J Buoyant line source and two point sources with the lines oriented horizontally

Since most of the testing was to exercise AERMOD options, and similar options are not 

available in BLP, model-to-model comparisons are not possible, except for Tests A and B. For a 

few of the tests, variations on input parameters were modeled to see if the results were as 

expected. For example, the emission rate in the hourly emission file was doubled or tripled to 

see if the resulting impacts doubled or tripled. All results appear to be in line with what is 

expected.

With the exception of the highest value, the remaining impacts in Tables 16 and 17 are 

comparable between AERMOD/BLP and BLP for all three averaging periods.
18

Table 16. Top 5 Concentration Estimates (μg/m3), Test A (Gridded Network)

1-hour 3-hour 24-hour

Rank BLP AERMOD BLP AERMOD BLP AERMOD

1

2

3

4

5

3010.3

3006.0

2713.6

2517.8

1827.7

146052.19

 2528.82

 2525.60

 2434.01

 2364.93

1083.3

1010.3

865.8

652.8

619.4

48710.30

 917.78

 849.38

 815.06

 807.64

157.2

154.2

148.7

105.2

103.6

6094.37

142.76

131.84

131.19

129.66

Table 17. Top 5 Concentration Estimates (μg/m3), Test B (Includes Two Point Sources)

1-hour 3-hour 24-hour

Rank BLP AERMOD BLP AERMOD BLP AERMOD

1

2

3

4

5

2528.8

2525.6

2364.9

2220.2

1825.4

146052.19

 2528.82

 2525.60

 2434.01

 2364.93

917.8

848.8

763.7

652.8

614.4

48710.30

 917.78

 849.39

 815.06

 807.67

138.7

131.0

126.2

103.6

101.3

6094.38

142.81

132.32

131.27

129.76

The remaining tests were only performed with AERMOD/BLP since BLP does not have all the 

processing options that AERMOD employs. Tables 18-25 correspond to Test C-J. The 

maximum 5 values are shown for the 1-hour, 3-hour, and 24-hour impacts. For the annual 

average, the high-first-high through high-fifth-high are shown. 

Table 18 represents hourly emissions for all three of the buoyant lines, whereas Table 19 show 

the results when Line 3 is the only contributor to the estimates (lines 1 and 2 are not included in 

the hourly emission file and the emission rate is set to 0.0 g/s in the control file). The only effect 

is seen mostly for the annual averaging period and somewhat in the 24-hr averaging period.

Table 18. Concentration Estimates (μg/m3), Test C

(Hourly Emissions File with All Three Lines Contributing)

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

146052.19

 2528.82

 2525.60

 2434.01

 2364.93

48710.30

 917.78

 849.38

 815.06

 807.64

6094.37

142.76

131.84

131.19

129.66

47.58

27.84

26.99

24.88

22.45
19

Table 19. Concentration Estimates (μg/m3), Test C 

(Hourly Emissions File with Only Line 3 Contributing)

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

146052.19

 2528.82

 2525.60

 2434.01

 2364.93

48710.30

 917.78

 848.13

 815.06

 800.67

6094.37

131.83

130.61

130.43

129.34

42.39

15.47

15.24

14.42

13.50

Table 20 shows the impacts when the HROFDY keyword is used to control the emissions. The 

following factors were used. 

EMISFACT BLINE1 HROFDY 5*0.0 0.0 18*0.0

EMISFACT BLINE2 HROFDY 5*0.0 0.0 18*0.0

EMISFACT BLINE3 HROFDY 5*0.0 0.5 18*0.0

The only contributor to the concentration estimates is BLINE3 and only for 0600. This hour 

corresponds to the hour when the extremely large impacts were seen on October 3. Since the 

emission factor is 0.5, the resulting hourly rate should be half of the largest value seen in the 

tables above. This is in fact the case: 146052/2 = 73026. One would expect slight differences in 

the 3-hour and 24-hour values since there are no contributions from the other hours to these 

averaging periods.

Table 20. Concentration Estimates (μg/m3

) for Test D

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

73026.09

 523.42

 468.59

 465.44

 465.26

24342.03

 297.76

 294.39

 294.32

 292.62

3042.76

 72.29

 72.22

 71.55

 71.44

9.41

5.26

5.16

5.08

5.00

Table 21 shows the impacts when the three different emission factor keywords are used to 

control the emissions. The following factors were used. In this scenario, the SEASON emission 

factor was used for line 3 (BLINE3) and was set to 0.0 for the fall (October-December). The 

highest impacts seen in the tables above (e.g., Table 18) are the result of the extreme 

concentration estimate on October 3 at 0600. With the emission factor set to 0.0, this hour's 

impact does not factor in to the results in Table 21.

 EMISFACT BLINE3 SEASON 1.0 1.0 1.0 0.0 

 EMISFACT BLINE2 HROFDY 5*0.0 1.0 18*0.0 

 EMISFACT BLINE1 MONTH 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
20

Table 21. Concentration Estimates (μg/m3) for Test E

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

2528.82

2525.60

2434.01

2220.21

1761.65

917.78

848.14

815.06

763.73

632.31

3042.76

 72.29

 72.22

 71.55

 71.44

9.41

5.26

5.16

5.08

5.00

Table 22 shows the results for the 24-hr PM-2.5 impacts with the three buoyant lines and the two 

point sources modeled and the MAXDCONT output option specified for source groups ALL, 

STACKS (both stacks), and BLINES (three lines). The emission rate was 1.0 g/s/m2 for all three 

lines, i.e. no emission factors were applied.
21

Table 22. Concentration Estimates (μg/m3) for Test F (24-hr PM-2.5)

Group Rank Average 

Concentration

Contribution

ALL

Contribution

STACKS

Contribution

BLINES

ALL 1

2

3

4

5

6

7

8

9

10

6094.38

126.54

110.07

104.95

103.66

 98.67

 97.67

 93.06

 90.05

 87.16

6094.38

126.54

0.01

0.58

6094.37

125.95

STACKS 1

2

3

4

5

6

7

8

9

10

 72.29

 72.22

 71.55

 71.43

 71.06

 70.69

 70.64

 70.47

 69.51

 69.51

79.67

79.85

72.29

72.22

7.37

7.63

LINES 1

2

3

4

5

6

7

8

9

10

6094.37

125.95

109.74

104.74

103.60

 98.31

 97.62

 92.73

 89.54

 86.93

6094.38

126.54

0.01

0.58

6094.37

125.95
22

Table 23 shows the results for the 1-hr SO2 impacts with the three buoyant lines and the two 

point sources modeled. The MAXDCONT output option was specified for source groups ALL, 

STACKS, and BLINES. The emission rate was 1.0 g/s/m2 for all three lines, i.e. no emission 

factors were applied. 

Table 23. Concentration Estimates (μg/m3) for Test G (1-hr SO2)

Group Rank Average 

Concentration

Contribution

ALL

Contribution

STACKS

Contribution

BLINES

ALL 1

2

3

4

5

6

7

8

9

10

146052.19

 1825.36

 1488.07

 1171.84

 841.63

 831.39

 790.26

 787.33

 763.23

 761.52

146052.19

1825.36

0.00

0.00

146052.19

1825.36

STACKS 1

2

3

4

5

6

7

8

9

10

 471.12

 466.96

 464.74

 459.90

 456.18

 446.70

 437.29

 436.62

 427.32

 413.75

475.09

469.95

471.12

466.96

3.97

2.98

LINES 1

2

3

4

5

6

7

8

9

10

146052.19

 1825.36

 1488.07

 1171.84

 841.62

 831.39

 790.26

 787.32

 763.23

 761.52

146052.19

1825.36

0.00

0.00

146052.19

1825.36

The next three tests demonstrate the impacts resulting from different orientations of the buoyant 

line source: rotated 90 degrees, vertical, and horizontal. In these tests, the receptor and the 

buoyant line that caused the extremely large impact seen in the tables above do not coincide, thus 

the smaller impacts. The purpose of these tests is to show consistency between the results, i.e. 

there is no apparent anomalous behavior.
23

Table 24 shows the impacts when the buoyant lines are oriented from the WSW to the ENE, i.e. 

rotated 90 degrees from the orientation shown in Figure 1. 

Table 24. Concentration Estimates (μg/m3) for Test H -

Buoyant Lines Oriented ENE to WSW

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

468.59

465.44

465.26

459.41

452.37

297.76

294.39

294.32

292.62

288.80

73.06

72.85

72.62

72.41

71.67

20.67

19.33

18.47

17.83

17.38

Table 24 shows the impacts when the buoyant lines are oriented from the WSW to the ENE, i.e. 

rotated 90 degrees from the orientation shown in Figure 1. 

Table 25. Concentration Estimates (μg/m3

) for Test I -

Buoyant Lines Vertically

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

608.86

608.85

566.36

566.36

566.36

325.94

314.33

314.33

314.33

304.85

89.16

87.73

85.22

81.96

78.68

30.85

28.59

26.04

23.81

20.50

Table 24 shows the impacts when the buoyant lines are oriented from the WSW to the ENE, i.e. 

rotated 90 degrees from the orientation shown in Figure 1. 

Table 26. Concentration Estimates (μg/m3) for Test J -

Buoyant Lines Horizontally

Rank 1-hour 3-hour 24-hour Annual

1

2

3

4

5

469.16

465.80

465.70

459.92

452.98

297.88

294.54

294.52

292.72

288.97

81.28

81.05

80.44

80.31

79.98

25.27

25.09

24.64

24.39

24.26
24

4. Differences between AERMOD/BLP and BLP

Some differences between the two models (AERMOD/BLP and BLP) are to be expected due in 

part, to:

1) The AERMOD/BLP meteorology has a variable reference height as developed by 

AERMET. However, in BLP the measurement height (ZMEAS in the METIN namelist) 

is a constant 50 meters. Some tests were run to see if this made a difference. Although it 

changed the AERMOD/BLP results, the changes were not significant.

2) Filling of missing meteorological data for BLP. 

3) Use of a compiler option to enforce double precision versus explicit declaration in the 

code - the effect of this option may contribute to differences.

Further testing may yield insights of other reasons differences are seen between AERMOD/BLP 

and BLP.

5. Additional Changes to AERMOD/BLP

5.1 Background Concentration

Investigation of the use of the background keyword was initiated. The results were not as 

expected, but there was no opportunity to determine why the results were not as expected. 

5.2 Event Processing

A couple lines of code were added in the file evcalc.f for event processing but did not go any 

further. The buoyant_line module was added as was code to save the ambient temperature (note 

that when processing point sources, AERMOD changes the value of the ambient temperature 

stored in the variable TA), and a comment about the P-G stability class.

5.3 BLP Source Group

The BLPGROUP keyword was not added since it would not provide any additional capabilities 

at this stage of incorporating a single buoyant line source (composed of multiple lines). This

keyword will be useful as a future enhancement to allow more than one buoyant line source to be 

processed in a single model run.

6. Recommendations
25

A primary recommendation for AERMOD/BLP is to develop the meteorology and source 

information associated with the 1979 SF6 tracer study at the Reynolds Metals Patterson Plant. 

Since all the relevant data are hardcopy (paper), time will be needed to enter the data 

electronically.
26

APPENDIX

1. AERMOD Keywords for Buoyant Line Sources

One LOCATION record for each line that comprises the buoyant line source.

SO LOCATION sourceID BUOYLINE Xb Yb Xe Ye (Zs)

Xb, Yb = coordinate of the beginning of the line source (m)

Xe, Ye = coordinate of the end of the line source (m)

Zs = line elevation (m) - optional; defaults to 0.0 if omitted

One SRCPARAM record for each line that comprises the buoyant line source.

SO SRCPARAM sourceID blemis relhgt

Blemis = emission rate (g/s/m2

)

Relhgt = release height (m)

The BLPINPUT keyword defines the average values for the buoyant line (as a whole and not as 

the individual lines that comprise the buoyant line source). The order shown is the same as the 

input in BLP (in the namelist RISE), with the variable name used in BLP shown in parentheses. 

This keyword can only appear once.

SO BLPINPUT blavgblen blavgbhgt blavgbwid blavglwid blavgbsep blavgfprm

blavgblen (L) = average building length (m)

blavgbhgt (HB) = average building height (m)

blavgbwid (WB) = average building width (m)

blavglwid (WM) = average line source width (m) (of the individual lines)

blavgbsep (DX) = average building separation (m) (between the individual lines)

blavgfprm (FPRIME) = average buoyancy parameter (m4

/s3)

United States

Environmental Protection

Agency

Office of Air Quality Planning and Standards

Air Quality Assessment Division

Research Triangle Park, NC

Publication No. EPA-454/P-15-004

July 2015