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ENVIRON

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C:\Documents and Settings\vbuyok\My Documents\308 SIP 2007-2008\Wyoming TSD\WRAP_PRP18bandPRP18cmv_Regional_Modeling_Analysis_081209_Chap. 5.doc

MEMORANDUM

To: Tom Moore and Lee Gribovicz, WRAP

From: Gerard Mansell

Date: 12 August 2009

Subject: 

Analysis of WRAP 2018 Preliminary Reasonable Progress Emissions Scenarios 

versions “b” and “cmv” in Regional CMAQ Air Quality Modeling and Projected 

Visibility Conditions

INTRODUCTION

Background

The Regional Haze Rule sets a 60-year timeline for states to improve visibility within mandatory 

federal Class I areas from Baseline (2000-04) levels to Natural Conditions by 2064. States are required 

to show that Reasonable Progress is expected to be made toward this goal over the course of 

intermediary planning periods. Reasonable Progress is defined by the EPA both in terms of what can 

be measured, attributed to sources, and projected using current scientific understanding, and, when 

reviewing controls for existing facilities, specific compliance-related statutory factors. EPA has 

prepared Guidance for Setting Reasonable Progress Goals Under the Regional Haze Program1, 

oriented toward control of traditional stationary point sources. To address the complex mix of 

anthropogenic and natural, controllable and uncontrollable sources affecting Class I areas in the 

WRAP region, the WRAP has developed an emissions projection methodology to address the technical 

requirements of determining Reasonable Progress for controllable anthropogenic sources. This 

methodology is based on existing EPA guidance and recommendations from WRAP forums and 

workgroups which includes the development and periodic revisions of regional emission inventory 

projections and using photochemical air quality grid modeling using the Community Multi-scale Air 

Quality modeling system (CMAQ).

The latest versions of the WRAP regional emission inventories, based on updates and revisions 

completed during Spring 2009 were incorporated into the CMAQ modeling system in order to estimate 

future year 2018 regional air quality and visibility. This regional emissions projection scenario for 

CMAQ modeling is called the 2018 Preliminary Reasonable Progress inventory “version b” (PRP18b). 

Additionally, an emission sensitivity simulation was performed to investigate the impacts of 2018 

projected emissions from Commercial Marine Vessels in the Eastern Pacific (PRP18cmv). 

 

1 EPA, 2007. Guidance for Setting Reasonable Progress Goals Under the Regional Haze Program. June 1, accessed 8/12/09 at: 

http://www.epa.gov/ttncaaa1/t1/memoranda/reasonable_progress_guid071307.pdf
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This technical Memorandum summarizes these regional air quality simulations and provides an 

analysis and evaluation of the results with respect to regional haze and visibility across the WRAP 

region. 

WRAP Emission Inventory Scenarios 

The most recent versions of the WRAP emission inventories for regional haze planning include:

2002 Base Case Version B -- The 2002 Base Case (Base02b) emission scenario was developed 

for use in the model performance evaluation, to determine whether the gridded air quality 

models performed was sufficiently well to justify continuing to use the model for planning 

purposes. The emissions configuration included actual point source, area sources, mobile 

sources from MOBILE6 with California mobile sources form EMFAC, biogenic emissions 

from the BEIS3 model, ammonia emissions and wind blown dust emissions were from models 

developed with WRAP funding, and actual wildfire, prescribed fires, and agricultural burning 

emissions for 2002 were used in this scenario. The model was extensively evaluated by 

comparing simulated concentrations of PM2.5 to ambient monitoring data for all available 

monitoring networks, and WRAP concluded that the model did perform sufficiently well to 

continue using the either the CMAQ or the CAMx models for planning purposes. The input 

data and model performance evaluation for this case are described in detail in Tonnesen et. al 

(2006).

2002 Planning Case Version D – The 2002 Planning (Plan02d) emission scenario represents a 

typical 2002 annual inventory of emissions from all source sectors derived from a number of 

sources, including state/county emission inventory submittals, permits, MOBILE6 modeling, or 

other modeled estimates based on activity levels. The planning inventories are used to provide 

representative baseline visibility conditions for comparisons and assessments of progress 

towards achieving natural visibility conditions in the future years. 

2018 Preliminary Reasonable Progress Version A – The Preliminary Reasonable Progress 

emission inventory for 2018 (PRP18a) incorporates growth and all known existing and/or 

planned emission controls and a preliminary estimate of SO2 reductions from BART controls

across the WRAP region. 

In spring of 2009, the WRAP developed two additional emission scenarios for air quality modeling, 

based on the PRP18a scenarios as follows:

2018 Preliminary Reasonable Progress Version B – The Preliminary Reasonable Progress 

emission inventory scenario for 2018 (PRP18b) is used to evaluate the regional haze air quality 

for future year 2018 conditions with all known and expected controls as of March 2009 and 

provide predicted 2018 future year air quality and visibility conditions in the Western Class I 

Areas for regional haze plans. The modeling results based on this emission inventory are used 

to gauge reasonable progress with respect to future year visibility. The PRP18b scenario was 

developed to incorporate the latest inventory updates completed during 2009, as described 

below.

2018 Preliminary Reasonable Progress, CMV Sensitivity – The Preliminary Reasonable 

Progress, CMV Sensitivity emissions inventory for 2018 (PRP18cmv) was developed to 

evaluate the sensitivity of regional air quality and visibility conditions to updated calendar year 
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2018 emissions for the Pacific Off-shore region. This emissions inventory scenario is identical 

to the PRP18b with the exception of the updated Pacific Off-shore emissions. 

The PRP18b emission scenario was developed based on updates to the PRP18a emissions inventories 

completed during calendar year 2009. These updates include the following:

Update of California 2018 on-road and non-road emission inventories (PDF)

Update of 2018 locomotive emissions (PDF)

Update of WRAP 2018 stationary point source emissions (PDF)

Update of WRAP 2018 area source emissions (PDF)

Mexico 2018 projections (PDF)

2

A discussion of the development of the PRP18b and PRP18cmv inventories in presented in the next 

section, as well as a summary of final emissions used in CMAQ modeling efforts.

EMISSION INVENTORIES

The development of the PRP18b and PRP18cmv emission scenarios, SMOKE processing and emission 

summaries and discussion are provided in this section.

Emission Scenario Development 

A summary of the various inventory versions, by source sector and geographic region, used in the 

development of the PRP18b and PRP18cmv scenarios are provided below. 

PRP18b

The PRP18b emission scenario was based on previous emission inventories with specific updates as 

noted above. The following source sectors and inventory versions were unchanged from the PRP18a 

scenario:

From Base02a

o BEIS3 biogenic emissions (includes soil NO)

o Windblown fugitive PM dust emissions – all components from WRAP WB Dust model

o WRAP NH3 from WRAP NH3 model

o Ontario, Canada point fires

From Plan02a

o WRAP baseline wildfires

o WRAP baseline wildland fire use

o Offshore commercial shipping: no change (see Plan02a) 

From Base18a:

o WRAP (except California) non-road mobile (annual and seasonal)

From Base18b:

o CENRAP on-road mobile

o WRAP baseline prescribed fires (natural and anthropogenic)

o WRAP baseline agricultural fires

o WRAP baseline non-federal rangeland fires 

 

2 ERG, 2009. Mexico 2018 Emissions Projections for Point, Area, On-Road Motor Vehicle and Nonroad Mobile Sources. 

Technical Memorandum prepared for Lee Gribovicz and Tom Moore, WRAP. April 27.
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From PRP18a:

o Non-WRAP stationary area

o Non-WRAP stationary point 

o Non-WRAP mobile sources (on-road & off-road)

o WRAP Oil & Gas

o Fugitive dust 

o CENRAP & VISTAS point fires 

o Offshore Area, Gulf of Mexico

o Gridded Offshore Shipping (Gulf of Mexico and Atlantic: Corbet/ENVIRON inventory)

o Canada - 2020 inventory

o Mexico – Road dust extracted from Phase II area inventory and had transport factors 

applied.

The following emission updates were included in simulation PRP18b:

Stationary Area 

o WRAP: Updated 2018 inventory

o Mexico: Phase III inventory and updates to gridding data

Non-road Mobile

o WRAP: Updated 2018 inventory for California

o Mexico: Phase III inventory and updates to gridding data (annual)

On-road Mobile

o WRAP: Updated 2018 inventory for California

o Mexico: Phase III inventory and updates to gridding data

Fugitive Dust 

o WRAP: Extracted from Updated 2018 stationary area source inventory 

o Mexico: Extracted from Phase III inventory

Stationary Point

o WRAP: Updated 2018 inventory

o VISTAS: Updated 2018 Best & Final inventory

o Mexico: Phase III inventory

PRP18cmv

The PRP18_cmv emission scenario was based on the PRP18b scenario with the only change being the 

replacement of the Pacific Offshore inventory with the updated 2018 CMV inventory for the Eastern 

Pacific, and some corrections to units and chemical speciation for VOC emissions, as discussed below.

The emissions estimates for each of the sectors and regions described above were modeled using the 

SMOKE emissions modeling system to generate CMAQ model-ready emissions data for air quality 

modeling. A discussion of the results of the SMOKE modeling for the PP18b and PRP18cmv 

scenarios is provided below.

Emission Inventory Summary and Discussion

PRP18b

The objective of emissions simulation PRP18b was to incorporate emissions inventory updates 

completed during 2009 by WRAP contractors to create a new future year, annual 36-km grid resolution 
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emissions dataset for air quality modeling. Updated 2018 PRP inventories (for selected source 

categories – see above) for the WRAP states were obtained and processed through SMOKE. The 

RMC also obtained updated 2018 inventories for the VISTAS states, year 2020 inventories for Canada 

and new 2018 national inventories for Mexico (Phase III). These updated inventory data were 

incorporated into the existing emissions data from the PRP18a emissions scenario to develop the 

PRP18b emissions. 

The RMC received new data for the WRAP states and tribes that included 2018 PRP inventories for 

the stationary area, stationary point, on-road mobile, and non-road mobile sectors. Fugitive dust PM 

emissions sources were extracted from the stationary area inventory using the list of sources consistent 

with simulation PRP18a (originally developed during Base18b modeling). The changes to the WRAP 

stationary area inventory impacted only some of the states in the region. The states impacted by this

inventory update included California, Idaho, Nevada, South Dakota, and Washington. The WRAP 

stationary point inventory update impacted all 13 states and some of the Tribes. The on-road mobile 

updates only impacted California and the non-road mobile updates impacted all of the states in the 

WRAP region. The rest of the inventory sectors in the WRAP region remained unchanged in 

simulation PRP18b relative to PRP18a. 

Updated 2018 stationary point inventory emissions data for the VISTAS RPO were also included in 

simulation PRP18b. The 2018 best & final inventory from the VISTAS RPO was used as a 

replacement to the 2018 point inventory used in simulation PRP18a. No other changes were made to 

any of the other U.S. inventories outside of the WRAP and VISTAS regions in simulation PRP18b. In 

addition to the WRAP and VISTAS updates, new 2018 Mexican inventories in simulation PRP18b.

The Mexico inventories in simulation PRP18b were updated with the Phase III 2018 inventory 

produced by ERG, Inc. The Phase III 2018 Mexico inventory replaced the 1999 Mexican inventories 

used in simulation PRP18a. The Phase III inventories cover the entire country for all emissions sectors. 

As the 2018 Phase III Mexican inventory did not contain road dust estimates, the same Mexican road

dust inventory used in all previous modeling runs were used in the PRP18b scenario. The inventory 

sources for Canada, as well as the domain-wide biogenic emissions did not change in simulation 

PRP18b.

Overall the WRAP emissions on an annual basis (annual totals for all WRAP states) decreased for all 

inventory pollutants, with the exception of CO, for simulation PRP18b relative to simulation PRP18a. 

The largest reductions for the PM pollutants came from the non-road mobile and fugitive 

dust/stationary area sectors. Increases in PM emissions from the on-road mobile and stationary point 

sectors slightly offset the PM emissions reductions in PRP18b. The NOx emissions reductions in 

simulation PRP18b relative to PRP18a were driven by the stationary point sector, with smaller 

reductions from non-road mobile and stationary area. The only sector that exhibited NOx increases in 

comparing these two simulations was the on-road mobile sector. The SO2 reductions in simulation 

PRP18b relative to PRP18a were driven primarily by the stationary point sector with smaller 

reductions in the stationary area and non-road mobile sectors. There was a small offsetting increase in 

SO2 emissions from the on-road mobile sector. Simulation PRP18b included only reductions in NH3

emissions relative to simulation PRP18a and these were the result of changes primarily in the on-road 

mobile sector. Smaller NH3 reductions occurred in the stationary point, non-road mobile, and 

stationary area sectors. The stationary area sector contributed the only VOC reduction, which was 

offset by smaller increases in VOC emissions from the on-road mobile, non-road mobile, and 

stationary point sectors. A relatively large increase in CO emissions from non-road mobile sources was 

offset by smaller decreases in the stationary area, stationary point, and on-road mobile sectors.
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Relative to simulation Plan02c, the PRP18b WRAP emissions decreased for PM2.5, NOx, SO2, NH3 and 

CO and increased for PMC, PM10, and VOC. The PM2.5 reductions were driven by the on-road mobile, 

non-road mobile, and stationary area sectors and offset by increases in the stationary point, road dust 

and fugitive dust sectors. The largest increase in PM2.5 is from the fugitive dust sector and reflects the 

expanded list of dust sources that were applied after simulation Plan02c. The NOx emissions decreased 

as a result of the on-road mobile, non-road mobile, and stationary point sectors. These decreases were 

offset slightly by NOx increases in the stationary area and oil and gas sectors. The SO2 reductions were 

driven by stationary point, on-road mobile, and non-road mobile sectors. A large CO reduction in the 

on-road mobile sector was offset by increases in the stationary area, stationary point, non-road mobile, 

and oil and gas sectors. PMC and PM10 increased in simulation PRP18b relative to Plan02c primarily 

because of the fugitive dust and road dust sectors. The only major offset to these increases were 

reductions in PMC and PM10 emissions from stationary area sources. Decreases in NH3 emissions were 

driven by the on-road mobile sector. Large increases in VOC emissions from the oil and gas and 

stationary area sectors were offset by smaller decreases in the on-road and non-road mobile sectors.

PRP18cmv

The objective of emissions simulation PRP18_CMV was to incorporate emissions inventory updates 

and corrections completed during 2009 by WRAP contractors to create a new future year Pacific 

Ocean commercial shipping inventory. The changes to commercial marine vessels (CMV) in 

simulation PRP18b_cmv included the addition of a new 2018 inventory for the Pacific Ocean and the 

correction of units conversion and chemical speciation errors that were present in the previous CMV 

inventories. The 2018 inventory represents projected activities and emissions factors for CMV sources 

in the Eastern Pacific Ocean for the year 2018. By not accounting for the metric ton units of the CMV 

inventory and assuming that it was provided in short ton units, these emissions were underestimated in 

earlier RMC simulations by about 10%. This error was corrected in simulation PRP18_cmv. An error 

in the VOC speciation of the CMV emissions was also corrected which resulted in a net decrease of the 

overall VOC emissions in simulation PRP18_cmv. 

With the only difference between simulations PRP18_cmv and PRP18b occurring in the Pacific 

shipping emissions, the inventory summaries and emissions plots reflect only differences in this sector. 

There are no emissions differences over land between these two simulations. The emissions changes in 

the CMV sector are the result of the inventory update and the corrections to the unit conversion and 

speciation errors. The overall results of these changes were that all inventory pollutants except VOC 

increased in the 2018 Pacific CMV inventory relative to the 2002 inventory. The VOC decrease in the 

PRP18_cmv emissions resulted from correcting an over prediction of formaldehyde emissions in the 

2002 inventory.

Annual anthropogenic emissions for the WRAP states, by source sector are summarized in Tables 1-3

below which present the Plan02d, PRP18a, PRP18b, respectively, in tons/year. Table 4 summarizes 

the difference in annual Pacific Offshore CMV emissions between the PRP18b and PRP18_cmv 

emission scenarios. Emission summaries are also displayed graphically in Figures 1-7, for NOx, VOC, 

CO, SO2, PM10, PM2.5 and NH3.

The spatial distribution of the difference in total (all source sectors) annual emissions between the 

PRP18a and PRP18b scenarios are displayed in Figure 8, in tons/year. The spatial distribution of the 

change in emissions between PRP18_cmv and PRP18b is displayed in Figure 9, in tons/year.
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Table 1. Plan02d WRAP total annual emissions by sector (tons/yr)

Sector CO NOX VOC NH3 SO2 PM10 PM2_5 PMC

Fires 8928013 202217 436714 45263 53856 726518 627618 119796

Area 1268874 259990 1331075 24519 85117 213825 190665 23197

Point 533870 897910 260247 780738 780738 147818 60424 105346

Non Road 3917820 1005930 535025 734 67286 74322 69424 4898

Onroad 12186508 1632549 1028968 55668 30253 50453 38902 11551

Biogenic 2624814 286996 18197340 0 0 0 0 0

WOG 46846 118573 439330 0 1182 0 0 0

Road Dust 0 0 0 0 0 581980 63358 518630

Fugitive 

Dust 0 0 0 0 0 915642 146387 769256

Wind-Blown 

Dust 0 0 0 0 0 1962165 431676 1530489

Offshore 

Platforms 0 0 0 0 0 0 0 0

Offshore 

Shipping 40868 524797 367468 149 280561 36352 35220 1132

Ag 

Ammonia 0 0 0 817256 0 0 0 0

Total 29547611 4928961 22596168 1724327 1298993 4709074 1663673 3084295

Table 2. PRP18a WRAP total annual emissions by sector

Sector CO NOX VOC NH3 SO2 PM10 PM2_5 PMC

Fires 8928013 202217 436714 45263 53856 726518 627618 119796

Area 1446307 320345 1860528 25430 110772 240738 211012 29765

Point 752028 895549 299700 14031 535055 190862 58607 132255

Non Road 4367813 594397 328247 1409 4074 43367 39320 4047

Onroad 5708505 519090 400626 71408 5933 36368 23618 12749

Biogenic 2624814 286996 18197340 0 0 0 0 0

WOG 68260 191728 749979 0 89 0 0 0

Road Dust 0 0 0 0 0 689599 72821 616779

Fugitive Dust 0 0 0 0 0 1123032 166125 956919

Wind-Blown 

Dust 0 0 0 0 0 1962165 431676 1530489

Offshore 

Platforms 0 0 0 0 0 0 0 0

Offshore 

Shipping 40868 524797 367468 149 280561 36352 35220 1132

Ag Ammonia 0 0 0 817256 0 0 0 0

Total 23936606 3535119 22640603 974946 990341 5049001 1666017 3403931

Table 3. PRP18b WRAP total annual emissions by sector (tons/yr)

Sector CO NOX VOC NH3 SO2 PM10 PM2_5 PMC

Fires 8928013 202217 436714 45263 53856 726518 627618 119796

Area 1386853 290874 1830236 25387 108274 233469 205202 28306

Point 714163 811324 300509 11564 512467 196677 59046 147229

Non Road 4520104 557423 332659 922 3186 35095 31673 3442

Onroad 5706430 533287 410149 43339 6116 38603 25509 13094

Biogenic 2624814 286996 18197340 0 0 0 0 0

WOG 68260 191728 749979 0 89 0 0 0

Road Dust 0 0 0 0 0 689599 72821 616779
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Fugitive Dust 0 0 0 0 0 1099367 166474 932901

Wind-Blown 

Dust 0 0 0 0 0 1962165 431676 1530489

Offshore 

Platforms 0 0 0 0 0 0 0 0

Offshore 

Shipping 40868 524797 367468 149 280561 36352 35220 1132

Table 4. 2018 – 2002 Pacific commercial marine shipping emissions difference (tons/yr)

Sector CO NOX VOC NH3 SO2 PM10 PM2_5 PMC

Pacific 

Shipping 38657 380360 -330155 107 247607 99836 98354 1481

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of NOX 

Sector

scenario

Figure 1. Anthropogenic NOx emissions for the WRAP states, by source sector (tons/year) 

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

2000000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of VOC 

Sector

scenario

Figure 2. Anthropogenic VOC emissions for the WRAP states, by source sector (tons/year)
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0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of CO 

Sector

scenario

Figure 3. Anthropogenic CO emissions for the WRAP states, by source sector (tons/year)

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of SO2 

Sector

scenario

Figure 4. Anthropogenic SO2 emissions for the WRAP states, by source sector (tons/year)
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0

500000

1000000

1500000

2000000

2500000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of PM10 

Sector

scenario

Figure 5. Anthropogenic PM10 emissions for the WRAP states, by source sector (tons/year)

0

100000

200000

300000

400000

500000

600000

700000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of PM2_5 

Sector

scenario

Figure 6. Anthropogenic PM2.5 emissions for the WRAP states, by source sector (tons/year)
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0

100000

200000

300000

400000

500000

600000

700000

800000

900000

Ag

Ammonia

Area Fires Fugitive

Dust

Non Road Offshore

Platforms

Offshore

Shipping

Onroad Point Road Dust WindBlown

Dust

WOG

p02c p02d prp18a prp18b prp18cmv

Sum of NH3 

Sector

scenario

Figure 7. Anthropogenic NH3 emissions for the WRAP states, by source sector (tons/year)
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Figure 8. Annual difference in emissions between PRP18a and PRP18b – All source sectors 

(tons/year)
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Figure 9. Annual difference in emissions between PRP18_cmv and PRP18b – All source sectors 

(tons/year)

CMAQ MODELING RESULTS

The PRP18b and PRP18_cmv emission scenarios were used in annual regional CMAQ modeling to 

estimate the 2018 future year air quality and regional visibility across the WRAP region. A discussion 

of the results of these simulations is provided below. 

PRP18b

To evaluate seasonal differences in the comparison of PRP18b to PRP18a, plots of monthly average 

changes in concentrations for each of the PM species were prepared and evaluated. Although displays

for all 12 months are available on the RMC webpage (link), we present summary results here for the 

months of January and July. These months were selected because the largest variation in model results 

is typically between the winter and summer months. Figures 10 through 14 show the monthly average 

model concentrations of the PM species for the PRP18b case relative to the PRP18a case. There were 

significant reductions in predicted nitrate concentrations in winter in the San Francisco Bay Area and 

Southern California with slight increases in the Central Valley of California as well as in the eastern 

portion of the WRAP regions and in central Washington State. Additionally, a large increase in nitrate 

is seen in the El Paso area of western Texas. In the summer months, small reductions are seen in the 

urban areas of California. Particulate sulfate concentrations are reduced slightly in winter in Southern 

California and along the western coast of the Mexican mainland and in the Seattle area during the 

summer months. Large increases in sulfate concentrations from the PRP18b case relative to the 

PRP18a case are seen in southern and eastern New Mexico and throughout northern Mexico extending 

into eastern and central Texas during both summer and winter months. Concentrations of OC and EC 

are predicted to increase for PRP18b relative to PRP18a, in the Seattle area with small reductions in 

eastern Washington State in both January and July. Reductions in predicted EC concentrations are also 

seen in the urban areas of California for both the winter and summer seasons. Increases in both OC 

and EC are seen throughout Mexico. 
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Figure 10. Difference in predicted particulate nitrate concentrations: PRP18b – PRP18a. Left –

January; right - July

Figure 11. Difference in predicted particulate sulfate concentrations: PRP18b – PRP18a. Left –

January; right - July
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Figure 12. Difference in predicted elemental carbon concentrations: PRP18b – PRP18a. Left –

January; right - July

Figure 13. Difference in predicted organic carbon concentrations: PRP18b – PRP18a. Left – January; 

right - July
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Figure 14. Difference in predicted PM2.5 concentrations: PRP18b – PRP18a. Left – January; right -

July

To evaluate seasonal differences in the comparison of PRP18b to Plan02d, plots of monthly average 

changes in concentrations for each of the PM species were prepared and evaluated. We present 

summary results here for the months of January and July; displays for all 12 months are available on 

the RMC webpage (link). Figures 15 through 22 show the monthly average model concentrations of 

ozone and PM species for the PRP18b case relative to the Plan02d case. There were small reductions 

in sulfate in PRP18b in the winter months and larger reductions in nitrate, ammonium and elemental 

carbon throughout large regions in the WRAP states. Figure 18 shows that there were small reductions 

in ozone of about 1 to 3 ppb though much of the WRAP domain, excluding some major urban areas 

were low ozone levels increased because of reduced NOx emissions and reduced titration of ozone by 

NO. 

Figure 15 shows the changes in sulfate for January and July. The largest change was caused by 

updates to the Mexican SOx emissions inventory, with large reductions in sulfate in the Baja California 

area and large increases in sulfate in northern Mexico and southern Texas. Overall, there was a mixed 

response in sulfate concentration in the WRAP states in January, and there was a reduction in sulfate in 

the WRAP states in July. 

Figure 16 shows the change in nitrate for January and July. There were reductions in nitrate in most of 

the WRAP region throughout the year, due largely to large reductions in NOx emissions in the PRP18b 

mobile source inventory. The PRP18b point inventory had reductions in NOx emissions in some areas 

and increases in other areas, and Figure 16 shows small increases for PRP18b compared to Plan02d 

nitrate in parts of Nevada and Arizona in January. The reductions in nitrate in PRP18b were largest in 

the winter months because nitrate concentrations are much larger in the winter than in the summer 

months.

Figure 17 shows that there were mostly reductions in ammonium concentrations in PRP18b compared 

to Plan02d, consistent with the large reductions in nitrate. There were some areas, mostly in Mexico 
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and Texas, where ammonium increased in PRP18b because of the increases in sulfate in PRP18b 

compared to Plan02d.

Figure 18 shows the change in ozone in PRP18b compared to Plan02d for January and July. During 

January, PRP18b had higher ozone concentration in urban influenced areas because of the reduced 

NOx emissions in PRP18b. During winter months, high NOx concentrations mostly act to titrate 

ozone, so reductions in NOx causes increases in ozone in winter months. However, the ozone 

concentrations are usually low during the winter and exceedances of the ozone NAAQS are rare. 

During July, the PRP18b NOx reductions cause significant reductions of ozone in the WRAP region 

with the largest reductions, up to 8 ppb for the monthly average, occurring in California’s central 

valley.

Figure 19 shows the change in elemental carbon (EC) in PRP18b compared to Plan02d for January and 

July. EC concentrations were reduced in the WRAP region throughout the year in PRP18b, in part due 

to reductions in mobile source emissions. Reductions were larger in the winter months, as much a 2 

ug/m3 in December compared with smaller reductions of up to 1 ug/m3 in July, because of less vertical 

mixing in the winter months. Figure 20 shows changes in organic carbon (OC) in PRP18b compared 

to Plan02d for January and July. There were mostly reductions in OC in PROP18b compared to 

Plan02d, with the exception of increases in OC in both the Seattle and Phoenix areas in PRP18b.

Figure 21 shows the change in total PM2.5 in PRP18b compared to Plan02d for January and July. 

PM2.5 represents the sum of the changes in the speciated PM results shown in Figure 15 through 20. 

The largest reductions in PM2.5 were in January in California, as large as 6 ug/m3, because of large 

reductions there in nitrate, ammonium and EC from the updated mobile source inventory in PRP18b. 

The magnitude of the reductions in PM2.5 for PRP18b were smaller in the summer months in 

California, but reduction extended over a much larger area, including the mountain states, because of 

reductions in sulfate, ammonium and EC in those areas for the PRP18b simulation. Figure 22 shows 

the change in total coarse matter (CM) in PRP18b compared to Plan02d for January and July. There 

were mostly increases in CM associated with urban areas in PRP18b, with the exception of Clark 

County, NV, were there were large reductions in CM. 
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Figure 15. Difference in monthly average sulfate concentrations for the PRP18b compared to the Plan02d 

CMAQ simulations for January (left) and July (right).

Figure 16. Difference in monthly average nitrate concentrations for the PRP18b compared to the Plan02d 

CMAQ simulations for January (left) and July (right).
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Figure 17. Difference in monthly average ammonium (NH4) concentrations for the PRP18b compared to the 

Plan02d CMAQ simulations for January (left) and July (right).

Figure 18. Difference in monthly average ozone (O3) concentrations for the PRP18b compared to the 

Plan02d CMAQ simulations for January (left) and July (right).

.
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Figure 19. Difference in monthly average elemental carbon (EC) concentration for the PRP18b compared to 

the Plan02d CMAQ simulations for January (left) and July (right).

Figure 20. Difference in monthly average organic carbon (OC) concentrations for the PRP18b compared to 

the Plan02d CMAQ simulations for January (left) and July (right).
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Figure 21. Difference in monthly average total PM2.5 concentrations for the PRP18b compared to the 

Plan02d CMAQ simulations for January (left) and July (right).

Figure 22. Difference in monthly average total Coarse PM (PMC) concentrations for the PRP18b 

compared to the Plan02d CMAQ simulations for January (left) and July (right).
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PRP18_cmv

To evaluate seasonal differences in the comparison of PRP18cmv to PRP18b, we prepared plots of 

monthly average changes in concentrations for ozone and each of the PM species. Plots for all 12 

months are available on the RMC webpage (link) but we present summary results here for the months 

of January and July as the largest variation in model results is typically between the winter and 

summer months. Figures 23 through 29 display the monthly average model concentrations of ozone 

and PM species for the PRP18cmv case relative to the PRP18b case. As expected, Figure 23 shows 

that the largest effect of the updated shipping emissions was an increase in SOx emissions offshore and 

an increase in sulfate concentration over the eastern Pacific. The increased sulfate extended over 

some coastal areas, including Washington, Oregon, northern CA and Baja California. There were 

significant reductions in sulfate in the Los Angeles area because SOx emission were reduced in the LA 

port and increased offshore. The pattern of sulfate reduction was similar throughout the year with 

larger sulfate changes in the summer months. 

Figure 24 shows no change in nitrate concentrations, except for the Los Angeles area, where nitrate 

increased during all months for the PRP18cmv case. The increase in nitrate is a direct result of the 

reduced sulfate concentrations in the Los Angeles area in PRP18cmv. The lower sulfate concentrations 

result in greater availability of gas phase ammonia and increased formation of ammonium nitrate in the 

Los Angeles area. 

Figure 25 shows that the changes in ammonium aerosol are consistent with the sulfate and nitrate 

results. Increased sulfate in coastal Washington, Oregon and Baja California in the PRP18cmv case 

resulted in higher ammonium concentrations in those areas, especially in the winter months. The 

PRP18cmv case had lower ammonium concentrations in the Los Angeles area because of the reduction 

in ammonium sulfate. 

Figure 26 shows small increases in ozone concentrations during July in the PRP18cmv case, from 1 to 

5 ppb, over the eastern Pacific as a result of the increased shipping activity in those areas.

Figure 27 shows reductions in elemental carbon (EC) for the PRP18cmv case in the Los Angeles and 

San Francisco areas because of reduced shipping emissions in the ports in those cities. The monthly 

average reduction in EC was approximately 0.2 ug/m3, for both January and July, in the port areas. 

Essentially no change was predicted for OC concentrations as illustrated in Figure 28.

Figure 29 shows the change in monthly average PM2.5 for the PRP18cmv case for January and July. 

Changes in sulfate were the largest component of the changes in PM2.5, and the plots for PM2.5 are 

similar to the sulfate results in Figure 23. Note that the scale is different in the two plots. 
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Figure 23. Difference in monthly average sulfate concentrations for the PRP18cmv compared to the PRP18b 

CMAQ simulations for January (left) and July (right).

Figure 24. Difference in monthly average nitrate concentrations for the PRP18cmv compared to the PRP18b 

CMAQ simulations for January (left) and July (right).
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Figure 25. Difference in monthly average ammonium (NH4) concentrations for the PRP18cmv compared to 

the PRP18b CMAQ simulations for January (left) and July (right).

Figure 26. Difference in monthly average ozone (O3) concentrations for the PRP18cmv compared to the 

PRP18b CMAQ simulations for January (left) and July (right).
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Figure 27. Difference in monthly average elemental carbon (EC) concentration for the PRP18cmv compared 

to the PRP18b CMAQ simulations for January (left) and July (right).

Figure 28. Difference in monthly average elemental carbon (OC) concentrations for the PRP18cmv 

compared to the PRP18b CMAQ simulations for January (left) and July (right).
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Figure 29. Difference in monthly average total PM2.5 concentrations for the PRP18cmv compared to the 

PRP18b CMAQ simulations for January (left) and July (right).

VISIBILITY PROJECTIONS 

The impacts of the PRP18b and PRP18_cmv model simulations on the predicted visibility at Class I 

Areas were evaluated with respect to the rate of progress in achieving the goals of the Regional Haze 

Rule. As seen in Figures 10 and 11, compared to the PRP18a case, relatively minor decreases in the 

predicted nitrate and sulfate concentrations throughout most of the WRAP region are realized for the 

PRP18b case and therefore only minimal impacts on visibility are expected with the exception of the 

increased sulfate concentrations in southern Arizona and New Mexico, as well as the Central Valley of 

California. 

Visibility Impacts Due to the PRP18b Scenario

A review of the 2018 visibility conditions at several Class I Areas throughout New Mexico was 

conducted to evaluate these impacts. The evaluations presented herein are based on various tools 

available on the WRAP Technical Support System (TSS) website. Figures 30 through 34 display 

potential emission source sectors and regions impacting the visibility on the 20% worst visibility days 

at GUMO, SACR, WHIT, GICL and CHIR IMPROVE monitor locations. These displays indicate that 

for the PRP18b scenario, large potential increased impacts from point and area source SOx and NOx 

emissions from Mexico in comparison with the PRP18a scenario likely contribute to visibility 

degradation at these Class I Areas. 
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Figure 30. Potential emission sources and regions impacting visibility at GUMO for the 

PRP18a scenario (top) and the PRP18b scenario (bottom) 

Figure 31. Potential emission sources and regions impacting visibility at SACR for the PRP18a 

scenario (top) and the PRP18b scenario (bottom) 
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Figure 32. Potential emission sources and regions impacting visibility at WHIT for the PRP18a 

scenario (top) and the PRP18b scenario (bottom) 

Figure 33. Potential emission sources and regions impacting visibility at GICL for the PRP18a 

scenario (top) and the PRP18b scenario (bottom) 
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Figure 34. Potential emission sources and regions impacting visibility at CHIR for the PRP18a 

scenario (top) and the PRP18b scenario (bottom) 

A review of the point and area source emission inventories for Mexico comparing the PRP18a and 

PRP18b scenarios show considerable changes from 18a to 18b for these source sectors primarily in the 

states of Chihuahua and Coahuila. The development of the 2018 projected emission inventories for 

Mexico, as used in the PRP18b scenario, is described in ERG, 20093. Figures 35 and 36 display the 

total state-level point and area source NOx and SO2 emissions for Mexico, respectively for both 

PRP18a and PRP18b. Relative to PRP18a, the stationary source SO2 and NOx emissions in 

Chihuahua and Coahuila states are almost double in the PRP18b scenario. Note that the state of Nuevo 

Leon also shows considerable increases in emission from these source sectors, although their impacts 

on Class I Area in the WRAP region are likely not as important, impacting regions in eastern Texas 

more than in the Western States. Figures 37 and 38 display municipality-level point source SO2 

emissions in Chihuahua and Coahuila states, respectively. Although a large decrease in SO2 point 

source emissions is seen in the municipality of Delicias in Chihuahua state, the increase in SO2 

emissions in the city of Chihuahua likely has more impact on the WRAP region as it is located closer 

to the US-Mexico border. However, Figure 38 shows a more than doubling of SO2 point source 

emissions from Nava municipality in Coahuila state and is probably the more likely source impacting 

visibility throughout New Mexico. 

 

3 ERG, 2009. Mexico 2018 Emissions Projections for Point, Area, On-Road Motor Vehicle and Nonroad Mobile Sources. 

Technical Memorandum prepared for Lee Gribovicz and Tom Moore, WRAP. April 27.
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Mexico NOx Emissions (Point + Area Source)

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000 Aguascalientes Baja California

Baja California Sur Chihuahua Coahuila Durango Guanajuato Hidalgo Jalisco Nayarit Nuevo Leon Queretaro Quintana Roo San Luis Potosi Sinaloa Sonora Tamaulipas Veracruz Yucatan Zacatecas NOx (tpy)

prp18a prp18b

Figure 35. State-level stationary source NOx emissions for Mexico for scenarios PRP18a and 

PRP18b

Mexico SOx Emissions (Point + Area Source)

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000 Aguascalientes Baja California

Baja California Sur Chihuahua Coahuila Durango Guanajuato Hidalgo Jalisco Nayarit Nuevo Leon Queretaro Quintana Roo San Luis Potosi Sinaloa Sonora Tamaulipas Veracruz Yucatan Zacatecas SOx (tpy)

prp18a prp18b

Figure 36. State-level stationary source SOx emissions for Mexico for scenarios PRP18a and 

PRP18b
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Chihuahua Point Source SO2 Emisisons

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000 DELICIAS JUAREZ CHIHUAHUA MORIS SAUCILLO CAMARGO SANTA BARBARA HIDALGO DEL PARRAL CUAUHTEMOC tpy

Prp18a Prp18b

Figure 37. Municipality-level point source SO2 emissions for Chihuahua, Mexico for scenarios 

PRP18a and PRP18b

Coahuila Point Source SO2 Emissions

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000 NAVA MONCLOVA TORREON SAN JUAN DE SABINAS RAMOS ARIZPE MUZQUIZ SALTILLO OCAMPO CUATROCIENEGAS CASTAOS PIEDRAS NEGRAS FRANCISCO I MADERO FRONTERA SABINAS ABASOLO ACUNA ALLENDE ARTEAGA CANDELA ESCOBEDO FRANCISCO I. MADERO tpy

Prp18a Prp18b

Figure 38. Municipality-level point source SO2 emissions for Coahuila, Mexico for scenarios 

PRP18a and PRP18b

The 2018 predicted visibility resulting from the PRP18a and PRP18b scenarios were reviewed for 

several sites in New Mexico which are impacted by these emission changes in the Mexico inventories. 

Note that, in addition to the results at the IMPROVE sites presented below, corresponding results for 

all other sites can be reviewed on the TSS. The sites presented here are those with the largest predicted 
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impacts on visibility, although others may also show some slight degradation in visibility conditions. 

Figure 35 through 40 present the 2018 projected visibility conditions on the 20% worst visibility days

for several Class I Areas in the Southwest in terms of the Glide Slope showing progress towards 

achieving the Regional Haze Rule goals. As seen in these figures, for most of the sites evaluated 

visibility degradations are relatively small, on the order of 0.2 to 0.6 dV, with the largest change 

occurring for the GUMO monitor, and are generally the result of increased sulfate extinction 

associated with the increased SO2 emissions in Northern Mexico. 

Figure 35. Visibility Glide Slope for GUMO for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 
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Figure 36. Visibility Glide Slope for GUMO for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 

Figure 37. Visibility Glide Slope for SACR for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 
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Figure 38. Visibility Glide Slope for WHIT for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 

Figure 39. Visibility Glide Slope for GICL for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 
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Figure 40. Visibility Glide Slope for BOAP for the PRP18a scenario (top) and the PRP18b 

scenario (bottom) 

Visibility Impacts Due to the PRP18_cmv Scenario

A review of Figures 23 through 29 indicate the impacts of the PRP18_cmv scenario on predicted 

visibility affect primarily only the coastal regions of Washington, Oregon and California, as well as 

large regions of Baja California, as expected. In general the predicted changes in the particulate matter 

species affecting regional visibility are increases relative to the PRP18a scenario, with the exception of 

the urban areas in Southern California for which decreases are predicted with this emission scenario. 

As with the PRP18b scenario, several Class I Areas were evaluated to determine the specific impacts 

due to the inclusion of updated calendar year 2018 CMV emission in the Eastern Pacific. Figures 41 

through 43 display the visibility Glide Slopes for selected sites along the coast of Washington State. 

Figure 41 displays the predicted visibility, as deciview and particle extinction, for Mount Rainier 

(MORA). Displayed are the Glide Slopes of the PRP18a, PRP18b and PRP18_CMV scenarios. At this

site, visibility is seen to be degraded from PP18a to PRP18b and further degraded based on the 

PRP18_CMV scenarios. By contrast, visibility at the North Cascades (NOCA) and Olympic NP 

(OLYM) sites (Figures 42 and 43) is seen to improve slightly from PRP18a to PRP18b, and then 

slightly deteriorate with the PRP18_CMV case. In all these cases, changes in visibility are driven by 

associated changes in the sulfate and OC extinction. Similar results are seen in other Class I Areas 

throughout Washington and the State of Oregon, although to a somewhat lesser degrees as the area are 

further inland from the coast.
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Figure 41. Visibility Glide Slopes for MORA for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom) 
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Figure 42. Visibility Glide Slopes for OLYM for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom)
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Figure 43. Visibility Glide Slopes for NOCA for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom)

Visibility results for Class I Areas along the California coast were also evaluated with respect to the 

changes in the PRP18a, PRP18b and PRP18_cmv emission scenarios. Figure 44 displays these results 

for Redwoods NP on the Northern California coast. At this site, although the total deciview is 

basically unchanged between the OPROP18a and PRP18b scenarios, sulfate extinction increases 

slightly, offset by a decrease in the nitrate extinction. In the PRP18_cmv scenario, the visibility, as 

measured by deciview is degraded considerably compared to both the PRP18a and PRP18b cases, 

driven by increases in both the sulfate and nitrate extinction. Results for Pinnacles NM and Ventana 

Wilderness (PINN), in Central California are displayed in Figure 45. At this site, visibility 

improvements are realized with the PRP18b scenario over the PRP18a scenario with visibility 
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degradations seen in the PRP18_cmv scenario, although the total deciview is still slightly lower than 

for the PRP18a scenario. 

Figure 44. Visibility Glide Slopes for REDW for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom)
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Figure 45. Visibility Glide Slopes for PINN for the PRP18a scenario (top), the PRP18b scenario 

(middle) and the PRP18_cmv scenario (bottom)

In contrast to Class I Areas along the northern coast of the Western US, a number of sites in Southern 

California exhibit visibility improvements under the PRP18_cmv scenario. Figure 46 displays the 

visibility projections for the San Gabriel and Cucamonga Wilderness areas (SAGA). Visibility 

improvements at this sight are seen from PRP18a to PRP18b and again for PRP18_cmv, driven 

primarily by reductions in the nitrate extinction. Figure 47 displays similar results for Agua Tibia 

(AGTI). In this case, visibility improvements are driven by significant decreases in the sulfate 

extinction related to emissions reductions at the ports along the Southern California coast.

While only a select number of Class I Areas were reviewed and evaluated for this Technical 

Memorandum, the results for all Class I Areas across the WRAP region, for all emission scenarios can 

be found on the WRAP TSS.
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Figure 46. Visibility Glide Slopes for SAGA for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom)
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Figure 47. Visibility Glide Slopes for SAGA for the PRP18a scenario (top), the PRP18b 

scenario (middle) and the PRP18_cmv scenario (bottom)