Appendix D 

Dispersion Model Results 

for Coso Junction 

PM10 Planning Area
BLANK PAGE 
February 25, 2010 

Great Basin Unified APCD 

157 Short Street, Suite 6 

Bishop, CA 93514 

Attn: Mr. Duane M. Ono 

Re: Dispersion Modeling Results 

Coso Junction PM10 Nonattainment Area 

Dear Duane: 

Environ performed a dispersion modeling study to examine PM10 concentrations during high 

wind events along the southern boundary of the Owens Valley PM10 Planning Area. Dust source 

areas on Owens Lake were simulated using the methods described in the Owens Valley PM10

Planning Area 2003 and 2008 State Implementation Plan revisions (2003 and 2008 RSIPs). We 

understand the current simulations will be used to update the attainment demonstration for the 

Coso Junction PM10 SIP. Based on the sand flux and meteorological data collected during July 

2006 to June 2009, our simulations suggest PM10 concentrations from dust source areas on 

Owens Lake will not cause violations of the PM10 National Ambient Air Quality Standards 

(NAAQS) in the neighboring Coso Junction PM10 Nonattainment Area (NAA). The remainder of 

this letter describes the dispersion modeling techniques employed for the simulations, model 

performance, and presents the results of the analysis. 

Dispersion Modeling Techniques 

Dispersion model simulations were performed with the regulatory version 5.8 of the CALPUFF 

modeling system following the techniques of the Owens Lake Dust ID Program summarized in 

the 2003 and 2008 RSIPs. The data collected by the Owens Lake Dust ID Program include 

surface meteorological data, upper air meteorological soundings, source area delineations, and 

horizontal sand flux observations. Sand flux measurements are used as the basis for PM10

emission rates from windblown sources on Owens dry lakebed. In most respects the current 

modeling protocol followed the methods employed in the RSIP, which can be found in Board 

Order 080128-01, Attachment C, Section 6.0. Features of the current simulations are as follows: 

• The period for the simulations was July 2006 to June 2009 using the last three years of 

data available from the Owens Lake Dust ID Program. 

• The RSIP study domain was extended to the south to include the common boundary of 

the southern Owens Valley and northern Coso Junction PM10 NAAs. The revised 

modeling domain is depicted in Figure 1. The revised study domain is 36 km-by-67 km 

versus the RSIP domain of 34 km-by-48 km. The same vertical and horizontal mesh 

sizes are used in both modeling analyses. 

• Land use and terrain data were prepared for the current domain using the preprocessors 

that accompany the CALPUFF modeling system. The resulting terrain and land use fields 

are shown in Figure 1. 

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 2

• Data collected at two additional surface meteorological stations in the southern portions 

of the current domain were used to construct the wind fields for the simulations. Data 

from the Coso Junction (CoJu) and Coso Gate (CoGa) sites shown in Figure 1 were 

prepared using the same methods as described in the RSIP. 

• To assess attainment, PM10 concentration predictions were obtained at 90 receptors 

placed along the southern Owens Valley PM10 Planning Area boundary. The receptor 

interval shown in Figure 1 is 300-600 m. A receptor was also placed at the Coso Junction 

site where current and historical PM10 observations are/have been collected. 

• Area source PM10 emission fluxes were calculated using hourly Sensit sand motion data 

and seasonal proportionality constants (K-factors) for July 2006 to June 2009. The 

procedures used to derive the seasonal 75th percentile K-factors are described in the 

2003 and 2008 RSIPs. The K-factors used in the current simulations are shown in 

Table 1. 

• Twelve different area source configurations were available from the Owens Lake Dust ID 

Program based on source delineations for the three-year period. The periods for the area 

source configurations are listed in Table 1. As an example, Figure 2 shows the area 

source outlines used to simulate the period from February 17, 2009 to June 30, 2009. 

• No additional controls were assumed for the Owens Lake sources. Sources were 

characterized as observed during the simulation period without the effects of controls 

planned for many of these areas. 

• As in the 2003 and 2008 RSIP attainment demonstrations, the current simulations only 

include windblown emissions from sources on the lakebed and the Keeler Dunes. In 

order to account for background sources, model predictions were added to a background 

concentration of 20 μg/m3

. This background concentration was also used in both the 

2003 and 2008 RSIPs. 

Attainment for the 24-hour PM10 NAAQS was assessed using the fourth highest daily prediction 

at the same receptor during the three-year simulation. 

Model Performance 

Environ conducted a model performance evaluation to assess the dispersion model techniques 

described above by comparing predictions to 24-hour PM10 observations during July 2006 

through June 2009. The methods employed followed the performance evaluation techniques 

included in the 2003 and 2008 RSIP attainment demonstrations. Features of the model 

performance evaluation are as follows: 

• The 24-hour statistics and plots are based on calendar day averages of hourly TEOM 

data. When hourly PM10 observations were missing both the observations and the 

corresponding model predictions were excluded from the daily averages. Only daily 

averages based on 18 or more hourly pairs were included in the analysis 

• The data pairs were filtered requiring the sum of the model prediction plus the 

observation must be greater than 150 μg/m3

. This symmetrical screen allows 

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 3

examination of both model under prediction and model over prediction while removing 

periods when both are less significant 

• Predictions and observations were compared for the ten monitoring sites of Dirty Socks, 

Keeler, Lone Pine, Olancha, Flat Rock, Shell Cut, Stanley, Lizard Tail, North Beach and 

Coso Junction. The locations of the PM10 monitoring sites are shown in Figure 1 

• The Coso Junction monitoring site is located just east of an unpaved parking lot and 

materials storage area. Windblown dust from this local source occasionally affects the 

monitor. Since this source of PM10 is not in the simulations, hours with westerly winds 

and PM10 concentrations above 50 μg/m3 were removed from the Coso Junction data 

set. Such hours were treated as missing for the purposes of calculating the 24-hour 

averages. 

• Quantile-quantile (Q-Q) plots were prepared to test the ability of the model predictions to 

represent the frequency distribution of the observations. Q-Q plots are simple ranked 

pairings of prediction and observed concentration, such that any quantile of the predicted 

concentration is plotted against the same ranking of the observed concentration 

• Log-log scatter diagrams were prepared to test the ability of the model to explain the 

temporal variability in the daily observations. When all sites are combined the scatter 

diagrams can also be used to infer whether the model can explain the spatial variability 

• Tabular statistics were also prepared comparing predicted versus observed: arithmetic 

mean, geometric mean, maximum, 98th percentile, and the number of concentrations 

greater than 150 μg/m3

• Both linear and geometric correlation coefficients were calculated to supplement the loglog scatter diagrams. Since the data are more log-normal than normally distributed the 

geometric correlation coefficient is a better measure of the model’s ability to explain the 

variability in the observations 

The results of the model performance evaluation are summarized in Table 2. The Q-Q plot in 

Figure 3 shows how well the model characterizes the frequency distribution of 24-hour PM10

concentrations at each of the ten sites. Figure 4 is Q-Q plot where the data are combined (e.g. 

unpaired in space). Figure 5 is a log-log scatter plot of 24-hour PM10 predictions versus 

observations. 

The model performance statistics suggest the model predictions as a whole are relatively 

unbiased. The predicted frequency distributions for each site are generally within a factor-of-two 

of the observed distribution. The predictions exhibit scatter and are not well correlated with the 

observations. 

Dispersion Model Results 

Table 3 summarizes the results for the CALPUFF simulations of Owens Lake dust events during 

July 2006 through June 2009, conservatively assuming no future controls would reduce 

emissions. Figure 6 shows predicted 24-hour design concentrations at the common NAA 

boundary. The 24-hour PM10 design concentration including background is 137 μg/m3

 predicted 

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 4

for January 5, 2007. Figure 7 shows a plot of the 24-hour concentrations predicted for the 

January 5, 2007 design day with the observations for the same day posted on the plot. The 

predicted PM10 concentration at the northern boundary of the Coso Junction PM10 NAA is under 

the 24-hour NAAQS of 150 μg/m3. 

The highest 24-hour PM10 concentrations at the southern boundary occur near the Owens Valley 

floor and along the western sides of the valley. These concentrations are much lower than 

predicted for receptors at the Owens Lake monitoring sites and along the Owens Lake historical 

shoreline. For example, the 24-hour design concentration at Dirty Socks during the July 2006 to 

June 2009 is 585 μg/m3

. The added distance to the southern boundary of the Owens Valley 

PM10 Planning Area and associated greater dilution of dust source plumes, produces much 

lower predictions than for receptors placed along the Owens Lake historical shoreline. 

The dust sources on the Owens lakebed were simulated as ground level area sources located 

inside the historical shoreline. The CALPUFF modeling system assumes passive, non-buoyant 

ground based sources remain ground based as they travel downwind and concentrations within 

individual dust plumes always decrease with downwind distance. Stagnation and re-circulation of 

dust source plumes that might result in pockets of higher concentrations at fixed downwind 

receptor locations generally do not occur concurrently with the regional high wind events that are 

necessary to produce emissions on the lakebed. When only emissions from lakebed sources 

are considered, attainment of the PM10 NAAQS at the northern boundary of the Coso Junction 

PM10 NAA is sufficient to demonstrate attainment within the entire NAA. 

Finally, the current analysis used estimates of windblown emissions during July 2006 through 

June 2009. Environ did not account for controls currently planned on many of these source 

areas that will be implemented in the future. If such planned controls were considered, predicted 

concentrations would be much lower than suggested by the current simulations. 

If the District has any questions regarding the simulations presented in this letter, please do not 

hesitate to contact Environ. 

Sincerely, 

Environ 

Ken Richmond 

Senior Air Quality Scientist 

Attachments: Tables and Figures 

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 5

Table 1 – Source Configurations and Seasonal K-Factors 

Seasonal 75th Percentile K-factors 

(x10-5) by General Source Area 

Source 

Setup Period 

Keeler 

Dunes North Central South 

7/1/2006 11/30/2006 1.7 4.4 6.9 1.9 1 

12/1/2006 12/31/2006 2.3 3.9 12.0 13.8 

2 1/1/2007 1/31/2007 2.3 3.9 12.0 13.8 

2/1/007 4/30/2007 2.3 3.9 12.0 13.8 3 5/1/2007 6/30/2007 2.5 1.5 6.9 1.9 

4 7/1/2007 11/30/2007 2.5 1.5 6.9 1.9 

5 12/1/2007 1/4/2008 2.6 3.9 17.5 4.7 

6 1/5/2008 1/24/2008 2.6 3.9 17.5 4.7 

7 1/25/2008 2/12/2008 2.6 3.9 17.5 4.7 

8 2/13/2008 2/21/2008 2.6 3.9 17.5 4.7 

9 2/22/2008 4/13/2008 2.6 3.9 17.5 4.7 

4/14/2008 4/30/2008 2.6 3.9 17.5 4.7 

5/1/2008 5/1/2008 2.6 1.5 17.5 4.7 

5/2/2008 5/22/2008 4.6 1.5 17.5 4.7 10 

5/23/2008 6/30/2008 4.6 1.5 6.9 1.9 

7/1/2008 11/30/2008 4.6 1.5 6.9 1.9 11 12/1/2008 2/16/2009 3.4 15.4 19.0 10.3 

2/17/2009 3/31/2009 3.4 15.4 19.0 10.3 

12 4/1/2009 4/30/2009 3.4 15.4 7.9 2.6 

5/1/2009 6/30/2009 3.4 1.5 7.9 2.6 

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 6

Table 2 – Summary of Model Performance 

24-hour PM10 Samples from July 2006 to June 2009 

10 Sites 1

Parameter Observed Predicted 2

No. O+P>150 μg/m3 3

245 

Mean (μg/m3) 207 204 

Geometric Mean(μg/m3) 150 134 

Maximum (μg/m3) 2101 1952 

Days > 150 μg/m3114 115 

98th Percentile 744 683 

Linear Correlation Coef. 0.559 

Geometric Correlation Coef. 0.146 

1. The 10 sites are Dirty Socks, Keeler, Shell Cut, Olancha, Flat Rock, 

Lone Pine, Stanley, Lizard Tail, North Beach and Coso Junction

2. Predictions based on seasonal 75th percentile K-factors

3. Statistics based on the number of 24-hour samples where the 

Prediction (P) plus the Observation (O) is greater than 150 μg/m3. 

Twenty-four hour averages calculated from hourly samples for days 

with at least 18 samples.

Table 3 – Summary of Maximum PM10 Predictions 

July 2006 to June 2009 

Statistic Period 

PM10

(μg/m3) 

Max 24-hour 3q06-2q09 225.5 

2

nd 24-hour 3q06-2q09 164.2 

3

rd 24-hour 3q06-2q09 150.5 

4

th 24-hour 3q06-2q09 136.6 1

1. The design concentration is the 4th highest 24-hour prediction in 

the three-year simulation at the same location

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 7

400 405 410 415 420 425 430

UTM East-West (km)

3990

3995

4000

4005

4010

4015

4020

4025

4030

4035

4040

4045

4050

4055

UTM North-South (km)

Keel

Lone

Sock

Olan

Atow

Delt

Flat

Scut

Cott

Mill

CoJu CoGa

Btow

Stan

Lizt

Figure 1. Dispersion Modeling Domain

Monitoring Stations Shown on 1-km Mesh Size Land Use and Terrain 

Terrain Contours in Meters, USGS Land Use

10

20

30

40

50

60

70

80

90

100

USGS

Land Use

NAA Boundary

Mixed urban

Agriculture

Range

Forest

Water

Wetland

Salt Flat/Sand/Barren

Snow

Tundra/Bare

Met. Site

TEOM

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 8

400 405 410 415 420 425 430

UTM East-West (km)

3990

3995

4000

4005

4010

4015

4020

4025

4030

4035

4040

4045

4050

4055

U

T

M

North-South (km)

Figure 2. Owens Lake Source Areas and Sensits

February 17, 2009 to June 30, 2009

Sand Flux Site

Source Area (2/17 - 6/30/09)

Appendix D
Dispersion Modeling Results 

Coso Junction PM10 Nonattainment Area 

Figure 3. Q-Q Plot, by Site, P+O>150

7/1/2006 - 6/30/09, 24-hour Averages, 75% filled with RSIP Default K-factors

10

100

1000

10000

10 100 1000 

TEOM PM10 (ug/m3)

Pred PM10 (ug/m3)

dsoxscutkeelolanflatlonestanliztnorbcoju_f
Dispersion Modeling Results 

Coso Junction PM10 Nonattainment Area 

Figure 4. All Sites Q-Q Plot

7/1/2006 - 6/30/2009, 24-hour Averages, 75% filled with RSIP Default K-factors

10

100

1000

10000

10 100 1000 

TEOM PM10 (ug/m3)

Pred PM10 (ug/m3)
Dispersion Modeling Results 

Coso Junction PM10 Nonattainment Area 

Figure 5. Scatter Diagram by Site, P+O>150

7/1/2006 - 6/30/2009, 24-hour Averages, 75% filled with RSIP Default K-factors

10

100

1000

10000

1 10 100 1000 

TEOM PM10 (ug/m3)

Pred PM10 (ug/m3)

dsoxscutkeelolanflatlonestanliztnorbcoju_f
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 12

400 405 410 415 420 425 430

UTM East-West (km)

3990

3995

4000

4005

4010

4015

4020

4025

4030

4035

4040

4045

4050

4055

UTM North-South (km)

Keel

Lone

Sock

Olan

Atow

Delt

Flat

Scut

Cott

Mill

CoJu CoGa

Btow

Stan

Lizt

39

46

61 116115 80

116

7983 86

9387

8379 66

67

65

59

57

56

56 47

Figure 6. Predicted 4th Highest 24-hour PM10 (μg/m3)

Receptors at Southern Limit of Owens Valley PM10 Planning Area

July 2006 to June 2009, Every 4th Prediction Plotted

Hi-4th Highest = 136.6 μg/m3

CoJu 4th Hi = 57.8 μg/m3

Appendix D
Dispersion Modeling Results February 25, 2010 

Coso Junction PM10 Nonattainment Area Page 13

400 405 410 415 420 425 430

UTM East - West (km)

3990

3995

4000

4005

4010

4015

4020

4025

4030

4035

4040

4045

4050

4055

U

T

M

North - South (k

m)

367

148

19

240

117

47 40

86

Figure 7. Predicted 24-hour PM10 (μg/m3) on Jan 05, 2007

Background of 20 μg/m3

20.001

50

100

150

200

500

1000

Hi-4th Highest = 136.6 μg/m3

PM10 (μg/m3)

Observed

PM10 (μg/m3)

Appendix D