MEMORANDUM
MEMORANDUM To:
Ken Rairigh
From:
Till Stoeckenius
Date:
4/7/2005
Subject:
WY NO2 PSD modeling: Final modeling results for Task 1
This memo documents preliminary NO2 PSD increment modeling results for the Domain 1 (D1) near-field region centered on the Bridger-Fitzpatrick Class I Wilderness Area (see Figure 1). Annual average NO2 concentrations were predicted using both ISC and CalPuff. Both the shortterm (ST) and long-term (LT) versions of ISC were used. Emissions Emissions processing for sources in Sublette County was described in a previous memorandum.1 Aside from two WY power plant sources (as described below), emission sources used in this round of modeling were all located within Sublette County. Development of the modeling inventory was designed to provide a reasonable set of Sublette County 2002 emissions within the limited timeframe available for these tasks by keeping the emissions structure as closely aligned as possible with that used for the 1995 SWWYTAF project modeling.2 Sublette County NOx sources were grouped by type as specified by WY DEQ. Source groups and corresponding annual total emissions are shown in Table 1. Area source emission totals in this table represent totals of gridded emissions as they were input to the models.3 All NOx emissions data provided for use in this study were assumed to be total NOx reported as NO2 as is customary. For all modeling scenarios except CalPuff run with the RIVAD chemistry option, NOx emission rates were input directly into the models and predicted concentrations are labeled as NOx in the model outputs and in this report. For the CalPuff runs in which the RIVAD chemical mechanism was used, NOx emissions were speciated into NO and NO2 assuming a NO/NO2 molar ratio of 9:1 for all source categories. Both predicted NOx and NO2 are reported for these runs.
1
Stoeckenius, T., 2005. WY NO2 PSD modeling: Processing of emissions for 2002 for Sublette County. Memo to K. Rairigh, WY DEQ, 16 March. 2 Earth Tech, 2001. The Southwest Wyoming Regional CALPUFF Air Quality Modeling Study, Final Report. Earth Tech, Inc., Concord, NH, February. 3 In some cases these total gridded values differ slightly from county totals reported elsewhere due to details of the gridding procedure. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707 H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 2 Receptors Three sets of receptor networks were superimposed for use in all model runs: 1. Gridded receptor matrix covering D1 at 4 km resolution. 2. Receptors in the interior of the Bridger-Fitzpatrick Class I area at locations specified by the National Park Service (http://www2.nature.nps.gov/air/Maps/Receptors/). 3. Receptors at 2 km spacing along the boundary of the Bridger-Fitzpatrick Class I area as used in previous PSD increment modeling studies (Solvay/Simplot) and supplied for this project by WY DEQ. Receptor elevations for the last two networks were as specified by the NPS and WY DEQ, respectively. Elevations for the first network were determined from 1º DEM data via the interpolation method as implemented by the ISC Breeze software package. ISC Modeling Both the short-term (ISCST) and long-term (ISCLT) models were run in regulatory default mode with the reported NOx emissions as described above. Source parameters were identical to those used in CalPuff: point source stack parameters were supplied by WY DEQ, all area sources were assigned a release height of 10 m and an initial sigma-z of 25 m which is equal to one-half of the typical morning mixing height (Earth Tech, 1999)4. Predicted maximum annual average NOx concentrations by source group are summarized in Table 2. Note that the maximum is listed for each source group and all source groups combined regardless of location so the indicated maximum value for all source groups combined (column ALL) does not necessarily equal the sum of the individual maximum source contributions as the maxima generally occur in different locations for different source groups. Annual maxima predicted by ISCST are larger than those predicted by ISCLT by about 60 – 70% in the Class I area and 20 – 30% in the Class II area (all source groups combined). This difference is most likely due to the lack of a complex terrain treatment and the use of horizontal sector averaging in ISCLT. As expected, the Sublette County oil and gas field sources are responsible for the largest maximum value of any source group at Class II area receptors and the maximum from the JonahPindedale fields is nearly as large as that from all fields combined. Point sources also produce some relatively large impacts. Higher point (and area) source impacts may occur at Class II area locations close to some of the point (and area) sources in western Sublette County but the current receptor network does not cover that area (see Figure 1). Additional receptors in western Sublette County will be added as part of the Task 2 modeling effort. Within the Class I area, point sources produce larger maxima than the oil & gas sources, but even the maximum combined impact of all sources is estimated to be no more than 0.6 µg/m3; well below the NO2 4
Earth Tech, 1999. 1995 Air Emissions Within the Southwest Wyoming Regional Modeling Domain – Volume 1: CALPUFF Modeling Inventory. Earth Tech, Inc., Concord, MA and Air Sciences, Denver, CO, November. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707
H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 3 Class I increment of 2.5 µg/m . Similarly, the maximum impacts at Class II receptors are well below the NO2 increment for Class II areas of 25 µg/m3. 3
Spatial distributions of annual average NOx concentrations predicted by ISCST are shown in Figure 2 (for all sources) and Figure 3 (for the Jonah-Pinedale oil & gas sources). The spatial concentration patterns are very similar from year to year although the peak concentration magnitudes vary slightly (by ± 6 % for the all sources combined results). The peak impact area is associated with the concentration of oil & gas sources at the southeastern end of the JonahPinedale anticline. Concentration gradients run southeast to northwest roughly parallel to the Bridger-Fitzpatrick Class I area boundary – there is no significant intrusion of > 0.5 µg/m3 concentration isopleths into the Class I area. ISCST and ISCLT results for 2001 are compared in Figure 4. Both models produce very similar spatial patterns. CalPuff Modeling CalPuff was run using meteorological fields generated by applying the latest version of CalMet to the 1995 SWWYTAF modeling database (Earth Tech, 2001).2 CalPuff was run in four different configurations: 1. Inert (“no chemistry”) assuming no deposition. 2. Inert but with dry NOx deposition turned on. 3. With the MESOPUFF II chemical mechanism to model NOx to nitrate conversion. 4. With the RIVAD/ARM3 chemical mechanism to model NO to NO2 and NOx to nitrate conversion. Scenarios 2, 3 and 4 were run with dry deposition turned on. Source inputs and receptor configurations for the CalPuff runs were identical to those used in ISC. Maximum annual average NOx concentrations (along with NO2 from the RIVAD chemistry run) predicted at the Class I and Class II receptors are summarized in Table 3. Note that the maximum is listed for each source group and all source groups combined regardless of location so the indicated maximum value for all source groups combined (column ALL) does not necessarily equal the sum of the individual maximum source contributions as the maxima generally occur in different locations for different source groups. Maximum annual average NOx concentrations within the Class II area predicted by CalPuff under the no chemistry and no deposition run are 55 to 70 % greater with those predicted by ISCLT and 21 to 38 % greater than those predicted by ISCST. Percentage differences are larger at the Class I receptors where peak concentrations are much lower. The relative impacts of each source group are roughly similar to those seen in the ISC results. Annual average NOx concentration impacts predicted by CalPuff for all sources and the Jonah-Pinedale oil & gas sources under the no chemistry and no chemistry with dry deposition runs are shown in Figure 5. Concentration patterns in all cases are similar to those obtained from the ISC results. Introducing dry deposition into the model results in a modest 4 % decrease in the peak Class II all sources impact. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707 H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 4 Use of the MESOPUFF II chemical mechanism in CalPuff lowers the predicted Class II peak NOx concentration by 13% relative to the dry deposition only run. Use of the RIVAD chemical mechanism results in NOx predictions that fall in between those from the dry deposition only run and the MESOPUFF II run. Class II area peak NO2 concentrations for all sources combined predicted with the RIVAD mechanism are 20% lower than the corresponding NOx prediction using MESOPUFF II but Class I area predicted peak NO2 concentrations are slightly larger than corresponding predicted by NOx using MESOPUFF II. At the location of maximum Class II area impact from the Jonah-Pinedale fields, the RIVAD predicted NO2/NOx ratio is 0.70. At the location of the maximum Class I area impact, the NO2/NOx ratio is 0.95. These ratios are consistent with our expectations regarding near source (i.e., Class II) and more distant (Class I) NO2/NOx ratios. Annual average NOx concentrations predicted using the MESOPUFF II chemistry and NO2 concentrations predicted using the RIVAD mechanism are shown in Figure 6. The overall concentration patterns are the same as in the no-chemistry results. Annual average NOx concentrations presented above do not include impacts from two large power plants (Bridger and Naughton) located in southwestern Wyoming but outside of Sublette County. A no-chemistry run was performed with CalPuff for these two sources; results are presented in Table 4. The maximum impact of the Bridger plant on the Class I area, while small, is on par with the maximum impact from all Sublette County sources, the maximum impact from Naughton is about half as much. As shown in Figure 7, the Bridger plant peak impact on the Class I area is at the southeast end of the wilderness area. A more detailed view of the concentration gradient in and near the Class I area (Figure 8) shows that, even with the Bridger and Naughton plant impacts included, the peak NOx impact within the Class I area is at the point on the border of the area that is closest to the Jonah-Pinedale field and not near the area of peak impact from the Bridger plant. The northwest – southeast orientation of the concentration gradient shown in Figure 8 runs roughly parallel to the contour of the terrain. We hypothesize that this results from high concentration events (which contribute most heavily to the annual average) occurring under stagnant, light wind conditions possibly in conjunction with low-level or ground-based temperature inversions that keep low lying source emissions from reaching into the higher elevations. Source contributions to the Class I area annual average concentrations at locations of peak impacts from all sources, Sublette County sources only, Jonah-Pinedale oil & gas sources, and the Bridger power plant are shown in Figure 9. These results confirm the separation between the Bridger power plant impacts and impacts from Sublette County sources. These results also show that, while none of the concentrations are large relative to the Class I area NO2 increment of 2.5 µg/m3, source contributions from the Jonah-Pinedale oil & gas fields (based on the 2002 inventory used for the present analysis) are a small fraction of the total impact from all Sublette County sources.
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Page 5 Table 1. Model input NOx emissions by source group. Source Group Emissions (TPY) 1. Point sources: Sublette County sources 3,395 with potential to emit > 10 TPY 2. Area sources 2.1 Agricultural equipment 161 2.2 Recreational marine and 58 recreational vehicles 2.3 Other (urban area sources in 58 cities of Pinedale, Marbleton, and Big Piney) 3. Oil & Gas field sources (heaters and flaring) 3.1 Jonah field and Pinedale field 569 3.2 All other fields in Sublette 951 County 4. On-Road mobile 453
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Page 6 Table 2. Maximum NOx impacts predicted by a) ISCLT and b) ISCST. Source groups are: Jonah-Pinedale fields(GASJP), all gas&oil fields (GAS), point sources (PTS), on-road (MOBILE), recreational marine and recreational equipment (RECMAR), urban area sources (CITY), agricultural equipment (AG); Other Area = RECMAR+CITY+AG. a) ISCLT Max NOx ug/m3 ALL
GASJP
GAS
PTS
MOBILE
RECMAR
CITY
AG
Other Area
1999 Class I
0.28
0.05
0.08
0.13
0.05
0.01
0.01
0.02
0.05
Class II
3.58
2.24
2.31
1.35
0.46
0.36
1.04
0.10
1.16
2000 Class I
0.36
0.06
0.10
0.18
0.07
0.02
0.01
0.03
0.06
Class II
3.66
2.43
2.52
1.75
0.50
0.40
1.06
0.10
1.19
2001 Class I
0.32
0.05
0.09
0.15
0.06
0.02
0.01
0.03
0.06
Class II
3.80
2.46
2.54
1.44
0.52
0.39
1.09
0.11
1.23
2002 Class I
0.32
0.06
0.09
0.14
0.07
0.02
0.02
0.03
0.06
Class II
3.66
2.37
2.45
1.50
0.49
0.39
1.08
0.10
1.22
2003 Class I
0.33
0.05
0.09
0.15
0.06
0.01
0.01
0.03
0.05
Class II
3.91
2.39
2.46
1.51
0.51
0.41
1.10
0.11
1.23
b) ISCST Max NOx ug/m3
ALL
GASJP
GAS
PTS
MOBILE
RECMAR
CITY
AG
Other Area
1999 Class I
0.43
0.08
0.12
0.23
0.07
0.02
0.02
0.03
0.06
Class II
4.41
2.55
2.64
1.85
0.46
0.41
1.15
0.12
1.29
2000 Class I
0.57
0.11
0.18
0.27
0.09
0.03
0.02
0.04
0.09
Class II
4.75
2.83
2.97
2.37
0.51
0.45
1.18
0.13
1.36
2001 Class I
0.55
0.11
0.18
0.24
0.09
0.03
0.02
0.04
0.09
Class II
4.91
2.97
3.09
2.00
0.56
0.46
1.24
0.15
1.41
2002 Class I
0.51
0.09
0.15
0.23
0.09
0.03
0.02
0.04
0.09
Class II
4.60
2.81
2.95
1.97
0.51
0.45
1.22
0.14
1.41
2003 Class I
0.53
0.10
0.16
0.26
0.09
0.02
0.02
0.04
0.08
Class II
5.04
2.81
2.93
2.15
0.54
0.47
1.24
0.14
1.41
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Page 7 Table 3. Summary of maximum annual average NO2 concentrations by source group predicted by the CalPuff model for a) no chemistry run, b) no chemistry but with dry deposition, c) MESOPUFF II chemical mechanism, d) RIVAD chemical mechanism – NOx predictions, e) RIVAD chemical mechanism – NO2 predictions. Source groups are as in Table 2. a) No Chemistry CALPUFF NOx Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.30 6.09
0.04 4.27
0.08 4.43
0.13 1.74
0.05 0.96
Other Area
0.08 1.53
b) Dry Deposition CALPUFF NOx Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.27 5.87
0.04 4.12
0.07 4.26
0.12 1.70
0.04 0.93
Other Area
0.07 1.49
c) MESOPUFF II Chemistry CALPUFF NOx MESOPUFF II, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
Other Area
GASJP
0.16 5.12
0.02 3.69
0.04 3.78
0.07 1.49
0.02 0.78
0.05 1.39
d) RIVAD Chemistry (NOx) CALPUFF NOx RIVAD, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.23 5.54
0.03 3.91
0.05 4.03
0.10 1.62
0.03 0.86
Other Area
0.06 1.45
e) RIVAD Chemistry (NO2) CALPUFF NO2 RIVAD, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.21 4.10
0.03 2.75
0.05 2.87
0.10 1.28
0.03 0.50
Other Area
0.05 0.78
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Page 8 Table 4. Maximum annual average NO2 impacts at the Domain 1 Class I and Class II receptors predicted under the no-chemistry scenario by CalPuff from all Sublette County sources and two power plants (PP) in southwestern Wyoming. CALPUFF NOx
Sublette Co. Sources
Class I Class II
0.30 6.09
Bridger PP
0.27 0.54
Naughton PP
0.13 0.27
ALL
0.51 6.40
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Page 9
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D1x SW Corner: 167.0, -30.0
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NX,NY: 41 x 34 -150
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Figure 1. Near-field domain 1 (D1) modeling receptor domain (indicated by grid of + symbols) in southwestern WY with receptors at 4 km grid resolution (+), receptors along the border of and inside the Bridger-Fitzpatrick Wilderness (O), and Sublette County point sources (◊). Box enclosing D1x domain indicates extent of 4 km model computational grid used for tracking puffs.
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Page 10 100
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ISCST 2000 Annual Average NOx [ug/m^3] Max = 4.75 ug/m^3
ISCST 1999 Annual Average NOx [ug/m^3] Max = 4.41 ug/m^3
1999
2000
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ISCST 2002 Annual Average NOx [ug/m^3] Max = 4.60 ug/m^3
ISCST 2001 Annual Average NOx [ug/m^3] Max = 4.91 ug/m^3
2001
2002
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ISCST 2003 Annual Average NOx [ug/m^3] Max = 5.04 ug/m^3
2003 Figure 2. Annual average NOx predictions from ISCST for all sources.
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Page 11
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ISCST 1999 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.55 ug/m^3
ISCST 2000 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.83 ug/m^3
1999
2000
100
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ISCST 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.97 ug/m^3
ISCST 2002 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.81 ug/m^3
2001
2002
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ISCST 2003 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.81 ug/m^3
2003 Figure 3. Annual Average NOx predicted by ISCST for Jonah and Pinedale Gas Sources.
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ISCLT 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.46 ug/m^3
ISCLT 2001 Annual Average NOx [ug/m^3] Max = 3.80 ug/m^3
100
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ISCST 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.97 ug/m^3
ISCST 2001 Annual Average NOx [ug/m^3] Max = 4.91 ug/m^3
Figure 4. ISCLT (top row) and ISCST (bottom row) annual average NOx for all sources (left column) and Jonah-Pinedale (right column) for 2001.
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Page 13
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Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources) Max = 6.09 ug/m^3
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Calpuff 1995 Annual Average NOx No Chemistry Run (Only Jonah Pinedale Sources) Max = 4.27 ug/m^3 100
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Calpuff 1995 Annual Average NOx No Chemistry Run with Deposition (All Sources) Max = 5.87 ug/m^3
Calpuff 1995 Annual Average NOx No Chemistry Run with Deposition (Only Jonah Pinedale Sources) Max = 4.12 ug/m^3
Figure 5. Annual average NOx concentrations predicted by CalPuff for all Sublette County sources (left column) and Jonah-Pinedale oil & gas field sources only (right column). Top row: no chemistry. Bottom row: no chemistry but with dry deposition turned on.
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Page 14
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Calpuff 1995 Annual Average NOx MESOPUFF II Chemistry (All Sources) Max = 5.12 ug/m^3
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Calpuff 1995 Annual Average NOx MESOPUFF II Chemistry (Only Jonah Pinedale Sources) Max = 3.69 ug/m^3
100
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80
5
80
4.5 4
60
4.5 4
60
3.5 3
40
3.5 3
40
2.5 2
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Calpuff 1995 Annual Average NO2 RIVAD/ARM3 Chemistry (All Sources) Max = 4.10 ug/m^3
-20
0.5 0
-20
-160
-140
-120
-100
-80
-60
-40
-20
Calpuff 1995 Annual Average NO2 RIVAD/ARM3 Chemistry (Jonah Pinedale Sources) Max = 2.75 ug/m^3
Figure 6. Annual average NOx predicted using MESOPUFF II chemistry (top row) and NO2 concentrations predicted using RIVAD chemistry (bottom row): impact of all Sublette county sources combined (left column), impact of Jonah-Pinedale oil & gas field sources only (right column).
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Page 15
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0.45
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0.4
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0.35
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Calpuff 1995 Annual Average NOx No Chemistry Run Bridger Plant Only Max = 0.5434 ug/m^3
Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources. with 2 SWWY Power Plant) Max = 6.40 ug/m^3 100
0.5
80
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Calpuff 1995 Annual Average NOx No Chemistry Run Naughton Plant Only Max = 0.2690 ug/m^3
Figure 7. Annual average NOx concentrations predicted by CalPuff for all sources (top left), Bridger power plant only (top right) and Naughton power plant only (bottom left). Note different color scale used to represent power plant impacts.
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Page 16
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Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources. with 2 SWWY Power Plant) Max = 6.40 ug/m^3 Figure 8. Annual average NOx concentrations from all sources in Sublette County and the Bridger and Naughton power plants with contour scale altered to show concentration gradient within and near the Bridger-Fitzpatrick Class I area.
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Page 17
Source Contributions at Locations of Maximum Class I Area Impacts 0.35
Annual Avg. NOx (ug/m3)
0.30
0.25
All Source Max
0.20
All Sublett Max Jonah-Pinedale Max 0.15
Bridger Max
0.10
0.05
0.00 Points
All O&G
JonahPinedale
Location All Src Max All Sublett Max Jonah-Pinedale Max Bridger Max
On-Road Other Area All Mobile Sublette Co.
All Sources 0.51 0.50 0.51 0.50
Sublette Co. 0.27 0.30 0.27 0.12
Bridger
JonahPinedale 0.04 0.04 0.04 0.02
Naughton
Bridger 0.11 0.08 0.11 0.27
Figure 9. Source contributions (µg/m3) to annual average NOx at locations of maximum impacts in the Bridger-Fitzpatrick Class I area from all sources combined, all sources in Sublette Co., Jonah – Pinedale oil & gas sources, and the Bridger power plant.
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Ken Rairigh
From:
Till Stoeckenius
Date:
4/7/2005
Subject:
WY NO2 PSD modeling: Final modeling results for Task 1
This memo documents preliminary NO2 PSD increment modeling results for the Domain 1 (D1) near-field region centered on the Bridger-Fitzpatrick Class I Wilderness Area (see Figure 1). Annual average NO2 concentrations were predicted using both ISC and CalPuff. Both the shortterm (ST) and long-term (LT) versions of ISC were used. Emissions Emissions processing for sources in Sublette County was described in a previous memorandum.1 Aside from two WY power plant sources (as described below), emission sources used in this round of modeling were all located within Sublette County. Development of the modeling inventory was designed to provide a reasonable set of Sublette County 2002 emissions within the limited timeframe available for these tasks by keeping the emissions structure as closely aligned as possible with that used for the 1995 SWWYTAF project modeling.2 Sublette County NOx sources were grouped by type as specified by WY DEQ. Source groups and corresponding annual total emissions are shown in Table 1. Area source emission totals in this table represent totals of gridded emissions as they were input to the models.3 All NOx emissions data provided for use in this study were assumed to be total NOx reported as NO2 as is customary. For all modeling scenarios except CalPuff run with the RIVAD chemistry option, NOx emission rates were input directly into the models and predicted concentrations are labeled as NOx in the model outputs and in this report. For the CalPuff runs in which the RIVAD chemical mechanism was used, NOx emissions were speciated into NO and NO2 assuming a NO/NO2 molar ratio of 9:1 for all source categories. Both predicted NOx and NO2 are reported for these runs.
1
Stoeckenius, T., 2005. WY NO2 PSD modeling: Processing of emissions for 2002 for Sublette County. Memo to K. Rairigh, WY DEQ, 16 March. 2 Earth Tech, 2001. The Southwest Wyoming Regional CALPUFF Air Quality Modeling Study, Final Report. Earth Tech, Inc., Concord, NH, February. 3 In some cases these total gridded values differ slightly from county totals reported elsewhere due to details of the gridding procedure. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707 H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 2 Receptors Three sets of receptor networks were superimposed for use in all model runs: 1. Gridded receptor matrix covering D1 at 4 km resolution. 2. Receptors in the interior of the Bridger-Fitzpatrick Class I area at locations specified by the National Park Service (http://www2.nature.nps.gov/air/Maps/Receptors/). 3. Receptors at 2 km spacing along the boundary of the Bridger-Fitzpatrick Class I area as used in previous PSD increment modeling studies (Solvay/Simplot) and supplied for this project by WY DEQ. Receptor elevations for the last two networks were as specified by the NPS and WY DEQ, respectively. Elevations for the first network were determined from 1º DEM data via the interpolation method as implemented by the ISC Breeze software package. ISC Modeling Both the short-term (ISCST) and long-term (ISCLT) models were run in regulatory default mode with the reported NOx emissions as described above. Source parameters were identical to those used in CalPuff: point source stack parameters were supplied by WY DEQ, all area sources were assigned a release height of 10 m and an initial sigma-z of 25 m which is equal to one-half of the typical morning mixing height (Earth Tech, 1999)4. Predicted maximum annual average NOx concentrations by source group are summarized in Table 2. Note that the maximum is listed for each source group and all source groups combined regardless of location so the indicated maximum value for all source groups combined (column ALL) does not necessarily equal the sum of the individual maximum source contributions as the maxima generally occur in different locations for different source groups. Annual maxima predicted by ISCST are larger than those predicted by ISCLT by about 60 – 70% in the Class I area and 20 – 30% in the Class II area (all source groups combined). This difference is most likely due to the lack of a complex terrain treatment and the use of horizontal sector averaging in ISCLT. As expected, the Sublette County oil and gas field sources are responsible for the largest maximum value of any source group at Class II area receptors and the maximum from the JonahPindedale fields is nearly as large as that from all fields combined. Point sources also produce some relatively large impacts. Higher point (and area) source impacts may occur at Class II area locations close to some of the point (and area) sources in western Sublette County but the current receptor network does not cover that area (see Figure 1). Additional receptors in western Sublette County will be added as part of the Task 2 modeling effort. Within the Class I area, point sources produce larger maxima than the oil & gas sources, but even the maximum combined impact of all sources is estimated to be no more than 0.6 µg/m3; well below the NO2 4
Earth Tech, 1999. 1995 Air Emissions Within the Southwest Wyoming Regional Modeling Domain – Volume 1: CALPUFF Modeling Inventory. Earth Tech, Inc., Concord, MA and Air Sciences, Denver, CO, November. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707
H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 3 Class I increment of 2.5 µg/m . Similarly, the maximum impacts at Class II receptors are well below the NO2 increment for Class II areas of 25 µg/m3. 3
Spatial distributions of annual average NOx concentrations predicted by ISCST are shown in Figure 2 (for all sources) and Figure 3 (for the Jonah-Pinedale oil & gas sources). The spatial concentration patterns are very similar from year to year although the peak concentration magnitudes vary slightly (by ± 6 % for the all sources combined results). The peak impact area is associated with the concentration of oil & gas sources at the southeastern end of the JonahPinedale anticline. Concentration gradients run southeast to northwest roughly parallel to the Bridger-Fitzpatrick Class I area boundary – there is no significant intrusion of > 0.5 µg/m3 concentration isopleths into the Class I area. ISCST and ISCLT results for 2001 are compared in Figure 4. Both models produce very similar spatial patterns. CalPuff Modeling CalPuff was run using meteorological fields generated by applying the latest version of CalMet to the 1995 SWWYTAF modeling database (Earth Tech, 2001).2 CalPuff was run in four different configurations: 1. Inert (“no chemistry”) assuming no deposition. 2. Inert but with dry NOx deposition turned on. 3. With the MESOPUFF II chemical mechanism to model NOx to nitrate conversion. 4. With the RIVAD/ARM3 chemical mechanism to model NO to NO2 and NOx to nitrate conversion. Scenarios 2, 3 and 4 were run with dry deposition turned on. Source inputs and receptor configurations for the CalPuff runs were identical to those used in ISC. Maximum annual average NOx concentrations (along with NO2 from the RIVAD chemistry run) predicted at the Class I and Class II receptors are summarized in Table 3. Note that the maximum is listed for each source group and all source groups combined regardless of location so the indicated maximum value for all source groups combined (column ALL) does not necessarily equal the sum of the individual maximum source contributions as the maxima generally occur in different locations for different source groups. Maximum annual average NOx concentrations within the Class II area predicted by CalPuff under the no chemistry and no deposition run are 55 to 70 % greater with those predicted by ISCLT and 21 to 38 % greater than those predicted by ISCST. Percentage differences are larger at the Class I receptors where peak concentrations are much lower. The relative impacts of each source group are roughly similar to those seen in the ISC results. Annual average NOx concentration impacts predicted by CalPuff for all sources and the Jonah-Pinedale oil & gas sources under the no chemistry and no chemistry with dry deposition runs are shown in Figure 5. Concentration patterns in all cases are similar to those obtained from the ISC results. Introducing dry deposition into the model results in a modest 4 % decrease in the peak Class II all sources impact. Golden Gate Plaza $ 101 Rowland Way $ Novato, California 94945-5010 USA Tel: (415) 899-0700 $ Fax: (415) 899-0707 H:\WYDEQ PSD\AQ_Modeling\Reports\Task1memo_a1.doc
Page 4 Use of the MESOPUFF II chemical mechanism in CalPuff lowers the predicted Class II peak NOx concentration by 13% relative to the dry deposition only run. Use of the RIVAD chemical mechanism results in NOx predictions that fall in between those from the dry deposition only run and the MESOPUFF II run. Class II area peak NO2 concentrations for all sources combined predicted with the RIVAD mechanism are 20% lower than the corresponding NOx prediction using MESOPUFF II but Class I area predicted peak NO2 concentrations are slightly larger than corresponding predicted by NOx using MESOPUFF II. At the location of maximum Class II area impact from the Jonah-Pinedale fields, the RIVAD predicted NO2/NOx ratio is 0.70. At the location of the maximum Class I area impact, the NO2/NOx ratio is 0.95. These ratios are consistent with our expectations regarding near source (i.e., Class II) and more distant (Class I) NO2/NOx ratios. Annual average NOx concentrations predicted using the MESOPUFF II chemistry and NO2 concentrations predicted using the RIVAD mechanism are shown in Figure 6. The overall concentration patterns are the same as in the no-chemistry results. Annual average NOx concentrations presented above do not include impacts from two large power plants (Bridger and Naughton) located in southwestern Wyoming but outside of Sublette County. A no-chemistry run was performed with CalPuff for these two sources; results are presented in Table 4. The maximum impact of the Bridger plant on the Class I area, while small, is on par with the maximum impact from all Sublette County sources, the maximum impact from Naughton is about half as much. As shown in Figure 7, the Bridger plant peak impact on the Class I area is at the southeast end of the wilderness area. A more detailed view of the concentration gradient in and near the Class I area (Figure 8) shows that, even with the Bridger and Naughton plant impacts included, the peak NOx impact within the Class I area is at the point on the border of the area that is closest to the Jonah-Pinedale field and not near the area of peak impact from the Bridger plant. The northwest – southeast orientation of the concentration gradient shown in Figure 8 runs roughly parallel to the contour of the terrain. We hypothesize that this results from high concentration events (which contribute most heavily to the annual average) occurring under stagnant, light wind conditions possibly in conjunction with low-level or ground-based temperature inversions that keep low lying source emissions from reaching into the higher elevations. Source contributions to the Class I area annual average concentrations at locations of peak impacts from all sources, Sublette County sources only, Jonah-Pinedale oil & gas sources, and the Bridger power plant are shown in Figure 9. These results confirm the separation between the Bridger power plant impacts and impacts from Sublette County sources. These results also show that, while none of the concentrations are large relative to the Class I area NO2 increment of 2.5 µg/m3, source contributions from the Jonah-Pinedale oil & gas fields (based on the 2002 inventory used for the present analysis) are a small fraction of the total impact from all Sublette County sources.
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Page 5 Table 1. Model input NOx emissions by source group. Source Group Emissions (TPY) 1. Point sources: Sublette County sources 3,395 with potential to emit > 10 TPY 2. Area sources 2.1 Agricultural equipment 161 2.2 Recreational marine and 58 recreational vehicles 2.3 Other (urban area sources in 58 cities of Pinedale, Marbleton, and Big Piney) 3. Oil & Gas field sources (heaters and flaring) 3.1 Jonah field and Pinedale field 569 3.2 All other fields in Sublette 951 County 4. On-Road mobile 453
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Page 6 Table 2. Maximum NOx impacts predicted by a) ISCLT and b) ISCST. Source groups are: Jonah-Pinedale fields(GASJP), all gas&oil fields (GAS), point sources (PTS), on-road (MOBILE), recreational marine and recreational equipment (RECMAR), urban area sources (CITY), agricultural equipment (AG); Other Area = RECMAR+CITY+AG. a) ISCLT Max NOx ug/m3 ALL
GASJP
GAS
PTS
MOBILE
RECMAR
CITY
AG
Other Area
1999 Class I
0.28
0.05
0.08
0.13
0.05
0.01
0.01
0.02
0.05
Class II
3.58
2.24
2.31
1.35
0.46
0.36
1.04
0.10
1.16
2000 Class I
0.36
0.06
0.10
0.18
0.07
0.02
0.01
0.03
0.06
Class II
3.66
2.43
2.52
1.75
0.50
0.40
1.06
0.10
1.19
2001 Class I
0.32
0.05
0.09
0.15
0.06
0.02
0.01
0.03
0.06
Class II
3.80
2.46
2.54
1.44
0.52
0.39
1.09
0.11
1.23
2002 Class I
0.32
0.06
0.09
0.14
0.07
0.02
0.02
0.03
0.06
Class II
3.66
2.37
2.45
1.50
0.49
0.39
1.08
0.10
1.22
2003 Class I
0.33
0.05
0.09
0.15
0.06
0.01
0.01
0.03
0.05
Class II
3.91
2.39
2.46
1.51
0.51
0.41
1.10
0.11
1.23
b) ISCST Max NOx ug/m3
ALL
GASJP
GAS
PTS
MOBILE
RECMAR
CITY
AG
Other Area
1999 Class I
0.43
0.08
0.12
0.23
0.07
0.02
0.02
0.03
0.06
Class II
4.41
2.55
2.64
1.85
0.46
0.41
1.15
0.12
1.29
2000 Class I
0.57
0.11
0.18
0.27
0.09
0.03
0.02
0.04
0.09
Class II
4.75
2.83
2.97
2.37
0.51
0.45
1.18
0.13
1.36
2001 Class I
0.55
0.11
0.18
0.24
0.09
0.03
0.02
0.04
0.09
Class II
4.91
2.97
3.09
2.00
0.56
0.46
1.24
0.15
1.41
2002 Class I
0.51
0.09
0.15
0.23
0.09
0.03
0.02
0.04
0.09
Class II
4.60
2.81
2.95
1.97
0.51
0.45
1.22
0.14
1.41
2003 Class I
0.53
0.10
0.16
0.26
0.09
0.02
0.02
0.04
0.08
Class II
5.04
2.81
2.93
2.15
0.54
0.47
1.24
0.14
1.41
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Page 7 Table 3. Summary of maximum annual average NO2 concentrations by source group predicted by the CalPuff model for a) no chemistry run, b) no chemistry but with dry deposition, c) MESOPUFF II chemical mechanism, d) RIVAD chemical mechanism – NOx predictions, e) RIVAD chemical mechanism – NO2 predictions. Source groups are as in Table 2. a) No Chemistry CALPUFF NOx Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.30 6.09
0.04 4.27
0.08 4.43
0.13 1.74
0.05 0.96
Other Area
0.08 1.53
b) Dry Deposition CALPUFF NOx Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.27 5.87
0.04 4.12
0.07 4.26
0.12 1.70
0.04 0.93
Other Area
0.07 1.49
c) MESOPUFF II Chemistry CALPUFF NOx MESOPUFF II, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
Other Area
GASJP
0.16 5.12
0.02 3.69
0.04 3.78
0.07 1.49
0.02 0.78
0.05 1.39
d) RIVAD Chemistry (NOx) CALPUFF NOx RIVAD, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.23 5.54
0.03 3.91
0.05 4.03
0.10 1.62
0.03 0.86
Other Area
0.06 1.45
e) RIVAD Chemistry (NO2) CALPUFF NO2 RIVAD, Dry Deposition Class I Class II
ALL
GAS
PTS
MOBILE
GASJP
0.21 4.10
0.03 2.75
0.05 2.87
0.10 1.28
0.03 0.50
Other Area
0.05 0.78
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Page 8 Table 4. Maximum annual average NO2 impacts at the Domain 1 Class I and Class II receptors predicted under the no-chemistry scenario by CalPuff from all Sublette County sources and two power plants (PP) in southwestern Wyoming. CALPUFF NOx
Sublette Co. Sources
Class I Class II
0.30 6.09
Bridger PP
0.27 0.54
Naughton PP
0.13 0.27
ALL
0.51 6.40
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Page 9
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0
D1x SW Corner: 167.0, -30.0
100
NX,NY: 41 x 34 -150
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Figure 1. Near-field domain 1 (D1) modeling receptor domain (indicated by grid of + symbols) in southwestern WY with receptors at 4 km grid resolution (+), receptors along the border of and inside the Bridger-Fitzpatrick Wilderness (O), and Sublette County point sources (◊). Box enclosing D1x domain indicates extent of 4 km model computational grid used for tracking puffs.
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ISCST 2000 Annual Average NOx [ug/m^3] Max = 4.75 ug/m^3
ISCST 1999 Annual Average NOx [ug/m^3] Max = 4.41 ug/m^3
1999
2000
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ISCST 2002 Annual Average NOx [ug/m^3] Max = 4.60 ug/m^3
ISCST 2001 Annual Average NOx [ug/m^3] Max = 4.91 ug/m^3
2001
2002
100
5
80
4.5 4
60
3.5 3
40
2.5 2
20
1.5 1
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ISCST 2003 Annual Average NOx [ug/m^3] Max = 5.04 ug/m^3
2003 Figure 2. Annual average NOx predictions from ISCST for all sources.
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Page 11
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60
4.5 4
60
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ISCST 1999 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.55 ug/m^3
ISCST 2000 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.83 ug/m^3
1999
2000
100
100
5
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5
80
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60
4.5 4
60
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ISCST 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.97 ug/m^3
ISCST 2002 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.81 ug/m^3
2001
2002
100
5
80
4.5 4
60
3.5 3
40
2.5 2
20
1.5 1
0
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ISCST 2003 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.81 ug/m^3
2003 Figure 3. Annual Average NOx predicted by ISCST for Jonah and Pinedale Gas Sources.
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ISCLT 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.46 ug/m^3
ISCLT 2001 Annual Average NOx [ug/m^3] Max = 3.80 ug/m^3
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ISCST 2001 Annual Average NOx [ug/m^3] from Jonah and Pinedale Gas Max = 2.97 ug/m^3
ISCST 2001 Annual Average NOx [ug/m^3] Max = 4.91 ug/m^3
Figure 4. ISCLT (top row) and ISCST (bottom row) annual average NOx for all sources (left column) and Jonah-Pinedale (right column) for 2001.
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Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources) Max = 6.09 ug/m^3
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Calpuff 1995 Annual Average NOx No Chemistry Run (Only Jonah Pinedale Sources) Max = 4.27 ug/m^3 100
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Calpuff 1995 Annual Average NOx No Chemistry Run with Deposition (All Sources) Max = 5.87 ug/m^3
Calpuff 1995 Annual Average NOx No Chemistry Run with Deposition (Only Jonah Pinedale Sources) Max = 4.12 ug/m^3
Figure 5. Annual average NOx concentrations predicted by CalPuff for all Sublette County sources (left column) and Jonah-Pinedale oil & gas field sources only (right column). Top row: no chemistry. Bottom row: no chemistry but with dry deposition turned on.
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Calpuff 1995 Annual Average NOx MESOPUFF II Chemistry (All Sources) Max = 5.12 ug/m^3
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Calpuff 1995 Annual Average NOx MESOPUFF II Chemistry (Only Jonah Pinedale Sources) Max = 3.69 ug/m^3
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Calpuff 1995 Annual Average NO2 RIVAD/ARM3 Chemistry (All Sources) Max = 4.10 ug/m^3
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Calpuff 1995 Annual Average NO2 RIVAD/ARM3 Chemistry (Jonah Pinedale Sources) Max = 2.75 ug/m^3
Figure 6. Annual average NOx predicted using MESOPUFF II chemistry (top row) and NO2 concentrations predicted using RIVAD chemistry (bottom row): impact of all Sublette county sources combined (left column), impact of Jonah-Pinedale oil & gas field sources only (right column).
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Calpuff 1995 Annual Average NOx No Chemistry Run Bridger Plant Only Max = 0.5434 ug/m^3
Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources. with 2 SWWY Power Plant) Max = 6.40 ug/m^3 100
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Calpuff 1995 Annual Average NOx No Chemistry Run Naughton Plant Only Max = 0.2690 ug/m^3
Figure 7. Annual average NOx concentrations predicted by CalPuff for all sources (top left), Bridger power plant only (top right) and Naughton power plant only (bottom left). Note different color scale used to represent power plant impacts.
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Calpuff 1995 Annual Average NOx No Chemistry Run (All Sources. with 2 SWWY Power Plant) Max = 6.40 ug/m^3 Figure 8. Annual average NOx concentrations from all sources in Sublette County and the Bridger and Naughton power plants with contour scale altered to show concentration gradient within and near the Bridger-Fitzpatrick Class I area.
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Source Contributions at Locations of Maximum Class I Area Impacts 0.35
Annual Avg. NOx (ug/m3)
0.30
0.25
All Source Max
0.20
All Sublett Max Jonah-Pinedale Max 0.15
Bridger Max
0.10
0.05
0.00 Points
All O&G
JonahPinedale
Location All Src Max All Sublett Max Jonah-Pinedale Max Bridger Max
On-Road Other Area All Mobile Sublette Co.
All Sources 0.51 0.50 0.51 0.50
Sublette Co. 0.27 0.30 0.27 0.12
Bridger
JonahPinedale 0.04 0.04 0.04 0.02
Naughton
Bridger 0.11 0.08 0.11 0.27
Figure 9. Source contributions (µg/m3) to annual average NOx at locations of maximum impacts in the Bridger-Fitzpatrick Class I area from all sources combined, all sources in Sublette Co., Jonah – Pinedale oil & gas sources, and the Bridger power plant.
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