UTAH
 

PMIO Maintenance
 

Provisions for
 

Salt Lake County
 

Section IX.A.10
 

Adopted by the Air Quality Board
 

July 6, 2005
 
IX.A.IO.a 

IX.A.10.b 

IX.A.lO.c 

Adopted by tlte Air Quality Board July 6. 2005 

Table of Contents 

Introduction 1
 

(1) ThePM1oSIP 2
 

(2) Supplemental History of SIP Approval - PMIO 2
 

(3) Attainment of the PM 10 Standard and Reasonable Further Progress 2
 

Pre-requisites to Area Redesignation 3
 

(1) The Area Has Attained the PMIO NAAQS 4
 

(a) Ambient Air Quality Data (Monitoring) 4
 

(b) PM 10 Monitoring Network 7
 

(c) Modeling Element 9
 

(d) EPA Acknowledgement 10
 

(2) Fully Approved Attainment Plan for PMIO 10
 

(3) Improvements in Air Quality Due to Reductions in Emissions 10
 

(a) Improvement in Air Quality 10
 

(b) Reduction in Elllissions 18
 

(4) State has Met Requirements Under Section 110 and Part D 20
 

(5) Maintenance Plan for PMIO Areas 20
 

Maintenance Plan 21
 

(1) Demonstration of Maintenance - Modeling Analysis 21
 

(a) Meteorological data 22
 

(b) Emissions Data 24
 

(c) Modeling Results 24
 

(d) Annual Standard 27
 

(e) Magna 28
 

(2) Attainment Inventory 28
 

(3) Emissions Limitations 30
 

(4) Emission Reduction Credits 31
 

(5) Additional Controls for Future Years 31
 

(6) Mobile Source Budget for Purposes of Conformity 31
 

(a) Salt Lake County Mobile Source PMlO Emissions Budgets 32
 

(b) Net Effect to Maintenance Demonstration 33
 

(7) Nonattainment Requirements Applicable Pending Plan Approval 34
 

(8) Revise in Eight years 35
 

(9) Veritication of Continued Maintenance 35
 

(J 0) Contingency Measures 35
 

Section IX.A.I O. page i
 
_ __ _

Adopted by the Air Quality Board July 6,2005 

This Federal Register notice (66 FR 32752) and the milestone report from September 29, 1995 

have been included in the TSD. 

Furthermore, since these control measures are incorporated into the Utah SIP, the emission 

reductions that resulted are consistent with the notion of permanent and enforceable 

improvements in air quality. Taken together, the trends in ambient air quality illustrated in the 

preceding paragraph, along with the continued implementation of the nonattainment SIP for the 

Salt Lake County nonattainment area, provide a reliable indication that these improvements in air 

quality reflect the application of permanent steps to improve the air quality in the region, rather 

than just temporary economic or meteorological changes. 

(4) State has Met Requirements Under Section 110 and Part D 

eM 107(d)(3)(E)(v)· The State containing such area has met all requiremenrs applicable 10 the 

area under section 110 and part D. Section 110 of the CAA deals with the broad scope of state 

implementation plans and the capacity of the resIJe(:tive state agency to effectively administer 

such a plan. Sections I through VIII of Utah's SIP contain information relevant to these criteria. 

Part D deals specifically with plan requirements for nonattainment areas, and includes the 

requirements for a maintenance plan in Section 175A. 

Utah currently has an approved SIP that meets the requirements of section 110(aX2) of the 

Federal Clean Air Act. Many of these elements have been in place for several decades. In the 

March 9, 2001 approval of Utah's Ogden City Maintenance Plan for Carbon Monoxide, EPA 

stated: 

On August IS, 1984, we approved revisions to Utah's SIP as meeting the 

requirements of section 11O(a)(2) of the CAA (see 45 FR 32575). Although 

section 110 of the CAA was amended in 1990, most of the changes were not 

substantial. Thus, we have detennined that the SIP revisions approved in 1984 

continue to satisfy the requirements of section 110(a)(2). For further detail, see 

45 FR 32575 dated August 15. 1984 (Volume 49, No. 159) or 66 FR 14079 dated 

March 9, 2001 (Volume 66, No. 47.) 

Part D of the Clean Air Act addresses "Plan Requirements for Nonattainment Areas", One of the 

pre-conditions for a maintenance plan is a fully approved attainment plan for the area. This is 

also discussed in section IX.A.1O.b(2). 

For Salt Lake County, the Part D requirements for PMIQ were addressed in an attainment SIP 

approved by EPA on July 8,1994 (59 FR 35036). 

(5) Maintenance Plan for PM10 Areas 

As stated in the Act, an area may not request redesignation to attainment without first submitting, 

and then receiving EPA approval of, a maintenance plan. The plan is basically a quantitative 

showing that the area will continue to attain the NAAQS for an additional 10 years (from EPA 

approval), accompanied by sufficient assurance that the tenns of the numeric demonstration will 

be administered by the State and by the EPA in an oversight capacity. The maintenance plan is 

the central criterion for redesignation. It is contained in the following subsection. 

Section IX.A.IO, page 20 

---.. ..-..- .. ..... .. .. 
Adopted by the Air Quality Board July 6. 2005 

IX.A.I0.c Maintenance Plan
 

CM 107(d)(3)(E)(iv) . The Administrator hasJully approved a maintenance planJor the area as 

meeting the requirements ofsection 175A. An approved maintenance plan is one of several 

criteria necessary for area redesignation as outlined in CAA 107(d)(3)(E). The maintenance plan 

itself, as described in Section 175A of the CAA and further addressed in EPA guidance 

(Procedures for Processing Requests to Redesignate Areas to Attainment. John Calcagni to 

Regional Air Directors, September 4, 1992; or for the purpose of this docurrimt. simply 

"Calcagni"). has its own list of required elements. The following table is presented to summarize 

these requirements. Each will then be addressed in turn. 

Table IX.A.32 Requirements of a Maintenance Plan 

Addressed 

Cate20ry Requirement Reference in Section 

Maintenance Provide for maintenance of the relevant CAA: Sec IXAI0.c(1) 

demonstration NAAQS in the area for at least 10 years after 175A(a) 

redesignation. 

Revise in 8 The State must submit an additional revision to CAA: Sec IX.A.I0.c(8) 

Years the plan. 8 years after redesignation, showing 175A(b) 

an additional 10 years of maintenance. 

Continued The Clean Air Act requires continued CAA: Sec IX.A.1O.c(7) 

Implementation implementation of the nonattainment area 175A(c), 

of control strategy unless such measures are CAASec 

Nonattainment shown to be unnecessary for maintenance or 110(1), 

Area Control are replaced with measures that achieve Calcagni 

Strategy equivalent reductions. memo 

Contingency Areas seeking redesignation from CAA: Sec IX.A.lO.c( 10) 

Measures nonattainment to attainment are required to 175A(d) 

develop contingency measures that include 

State commitments to implement additional 

control measures in response to future 

violations of the NAAQS. . 

Verification of The maintenance plan must indicate how the Calcagni IX.A.1O.c(9) 

Continued State will track the progress of the maintenance memo 

Maintenance ] plan. 0_0 -

(1) Demonstration of Maintenance - Modeling Analysis 

CAA 175A(a) - Each State which submits a request under section l07(d) for redesignation of a 

nonattainment area as an area which has attained the NAAQS shall also submit a revision afthe 

applicable implementation plan to provide for maintenance ofthe NAAQS for at least J0 years 

after the redesignation. The plan shall contain such additional measures, if any. as may be 

required to ensure such maintenance. The maintenance demonstration is discussed in EPA 

guidance (Calcagni) as one of the core provisions that should be considered by states for 

inclusion in a maintenance plan. 

According to Calcagni, a State may generally demonstrate maintenance of the NAAQS by either 

showing that future emissions of a poHutant or its precursors will not exceed the level of the 

attainment inventory (discussed below) or by modeling to show that the future mix of sources and 

Section IX.A.lO, page 21 
Adopled by Ihe Air Quality Board July 6,2005 

emission rates will not cause a violation of the NAAQS. Utah has elected to make its 

demonstration based On air quality modeling. The guidance goes on to say that, in cases where a 

nonattainment SIP was based on air quality modeling, the maintenance plan should be based upon 

the same level of modeling used before. Furthennore, it says, such modeling should be consistent 

with current EPA modeling guidance. 

The existing PMIO nonattainment SlP demonstrations for both Salt Lake and Utah Counties were 

based on a statistical modeling approach called chemical mass balance (CMB). This is a receptor 

based model that does not directly factor meteorology or dispersion characteristics into its 

predictions. Furthermore, CMB is limited in its treatment of secondary aerosol formation, which 

has historically accounted for between 65% and 85% of the overall PM10 collected at the 

monitoring stations. While the success of these nonattainment SIPs is more or less an 

endorsement of the CMB modeling upon which they were founded, EPA felt that any subsequent 

demonstration of maintenance should rely instead on a model that is more comprehensive in its 

assumptions. 

In consultation with EPA Region VIII. DAQ decided to base the new Maintenance Plan upon a 

grid-based aerosol model called UAM-AERO. This model is an extension of the widely used 

photochemical model, the Urban Airshed Model (UAM) Version IV, which has been adapted to 

treat aerosol processes. DAQ established a UAM-AERO modeling domain that included each of 

Utah's three PMIO nonattainment areas. This single comprehensive modeling analysis serves as 

the basis for the maintenance demonstration for each area. 

The model was applied to address elevated 24-hour concentrations of PMIO along the Wasatch 

Front (WF). These develop during winter-time episodes of regional scale high pressure and 

associated valley temperature inversions. The inversions promote the accumulation of PMIO and 

PMIO precursor gases that lead to significant secondary aerosol formation. Before the 

nonattainment SlPs were implemented, these ambient values often exceeded the 24-hour health 

standard for PM10• 

In this analysis. DAQ has employed UAM-AERO to evaluate the airshed under worst case 

winter-time inversion conditions. In order to do so, the model considers two historical episodes: 

1) January 1-10,2001 and 2) February 1-8,2002. Episode selection was based on criteria that 

included meteorology, observed PMIO concentrations, and data availability. Further discussion 

concerning episode selection can be found in Section 2 of the modeling portion of the technical 

support document (TSD). 

Despite numerous severe inversion episodes during the past decade. PMlO concentrations have not 

been sufficient to cause a violation of the NAAQS. Consequently, the two selected episodes do 

not represent NAAQS violations, but do capture elevated PM 10 concentrations, worst-case 

meteorology. and current emission levels. Therefore, by modeling these episodes and projecting 

emissions into future years, the analysis should accurately reflect the ability of the nonattainment 

areas to maintain the PMIO NAAQs over the next 10 years. 

The DAQ modeling analysis requires two main inputs: meteorological data and emissions data. 

The applications of these inputs are discussed below. 

(a) Meteorological data 

Recent UDAQ meteorological modeling projects using advanced "state of the science" prognostic 

meteorological models have proven unsuccessful in simulating highly variable Wasatch Front 

meteorology during inversion conditiOnS. These problems led UDAQ to choose a diagnostic 

Section IX.A.lO. page 22 
Adopted by the Air Quality Board July 6, 2005 

meteorological model called the Diagnostic Wind Model (DWM) model for the January 200 1 and 

February 2002 episodes to avert many of the past modeling problems. The DWM assimilates 

actual observations of wind speed and direction to diagnose and construct a consistent wind field. 

UDAQ embarked on a 4-phase modeling approach in order to develop the most realistic wind 

fields possible. Each phase of the 4-phase modeling approach utilized unique combinations of 

observed meteorological data for each analysis. Each of the 4 phases is described below: 

Phase 1 

The DWM model was run utilizing 60-100 surface observing stations, two radiosondes, and two 

SODARs per day. The surface station data was taken from the University of Utah MESOWEST 

database and included a wide variety of station types. Phase 1of modeling utilized only surface 

stations with an elevation of 5,500ft or lower. The National Weather Service Salt Lake City 

radiosonde data was used along with two DAQ SODAR units operated in Utah and Salt Lake 

valleys. It was thought that the multitude of available data would allow DWM to produce 

representative wind fields. 

UAM-AERO results showed modeled PMIO values that were only 40-50% of the observed values. 

Model output evaluation showed that PMIO was being advected out of the Salt Lake Valley (SLV) 

and the model domain to the SE. Afternoon up-valley NW winds moved PM10 into the mountains 

to the SE of the SLV. At night, winds became light and variable at most surface stations and asa 

result were unable to return the PM10 back to the SLV. Additionally, DAQ's hypothesized 

benefit of having a multitude of surface stations actually induced unrealistic vertical motions due 

to surface convergence of widely varying wind directions. 

Phase 2 

The failings of phase I encouraged DAQ to be more selective of the surface stations used in 

DWM. First, the Salt Lake Valley SODAR was discarded due to observations that were 

incongruent with the Utah Valley SODAR and the Salt Lake City radiosonde. Second, DAQ 

selected only the DAQ operated surface stations. These surface stations are situated in strategic 

locations across the Wasatch Front. 11 DAQ stations were used. The phase 2 hypothesis was 

that the more selective set of surface stations might produce a wind field with less convergence 

and resultant vertical motions. 

DAQ found that the phase 2 wind fierds produce periods of daytime 'N'W winds that advected 

pollutants out of the SLY. The noctumal and morning winds were light and variable and were 

unable to retum the pollutants to the SLY. Most of the observations within the SLY show a trend 

of daytime up-valley flow and nighttime weak variable flow. In reality, the daytime flown recirculates within the boundaries of the inversion but in UAM-AERO the continuous grid network 

cannot retain the flow within the open sided grid cells of the SLY. 

Phase 3 

Phase 2 results showed transport of PM10 out of the SLY. Model evaluation clearly showed a 

direct link with the observation wind direction and speeds. Phase 3 tested the possibility that a 

single station located in SLY might produce a wind field that has a more even distribution of 

wind direction and speeds. In other words. is there a station in SLY that is representative of the 

vaIley but where daytime winds and nighttime winds balance each other? If so, developing a 

wind field from a single station may reduce advection out of the SLV. 

Section IX.A.lO. page 23 
Adopted by the Air Quality Board July 6. 2005 

Three separate wind fields were developed in phase 3. These wind fields utilized the centrally 

located and well sited DAQ Hawthorne and West Valley monitors as wen as another well sited 

but southeasterly located DAQ Cottonwood station. The results of phase 3 modeling again 

showed advection out of the SLY and the domain. Stronger daytime NW winds compared to 

nighttime light and variable winds again forced the loss of PM10. 

Phase 4 

Phases 1-3 clearly demonstrated the inability of the DWM model to accurately represent the 

conceptual understanding of inversion conditions. The model deficiencies arise from the model 

grid-eell structure. The model grid cells are continuous and are unable to "trap" or contain air 

within an inversion layer. The real wind observations in the SLY do have advective properties 

that would allow the pollutants to move beyond the boundaries of the SLV under non-inversion 

conditions. However, under inversion conditions the advective properties of the real wind 

observations are negated by a forced recirculation of air within the inversion layer by the 

containing boundaries of the inversion. 

In phase 4, a purely idealized flow was created in the attempt to retain pollutants in the SLV. A 

bimodal wind direction field was created using an afternoon NW wind (330) and an evening, 

night, and morning SE wind (140). These directions correspond to daytime up-valley flow and 

nighttime down-valley flow. Wind speeds were chosen so that advection was limited to within 

the boundaries of the SLV. This wind field, while idealized, fits the conceptual understanding of 

inversion conditions. Phase 4 modeling retains PMIO within the SLY and DAM-AERO PMJO 

results show excellent agreement with the observations. 

(b) Emissions Data 

Area, point, and mobile emissions inventories were compiled for all sources within the modeling 

domain. Inventories included primary PMIO, sulfur dioxide (S02), oxides of nitrogen (NOx), 

carbon monoxide (CO), and volatile organic compounds (YOC). In addition, an ammonia (NH3) 

inventory was estimated for area and mobile sources. Estimates of biogenic emissions were not 

included in the analysis because the episodes occurred in January and February when biogenic 

emissions are negligible. Other seasonal adjustments were also made to the inventory 

(adjustments are described in the modeling portion of the TSD). Base-year and projection 

inventories are also described in more detail in the TSD. 

Emission inventories are processed and spatially placed in the modeling domain by the Sparse 

Matrix Operator Kernel Emission (SMOKE) modeling system. SMOKE was developed by EPA 

for integration into the Models-3 Air Quality Modeling System and has been used in many air 

quality studies. To ensure that the model represents actual emissions during each model episode 

day, SMOKE uses source specific Source Classification Codes to chemically speciale and 

temporally allocate emissions. In addition, SMOKE uses other emission characteristics, such as 

stack height. exit velocity, and plume temperature to place emissions in the correct vertical layer 

of DAM-AERO. Mobile and other area source emissions are treated as ground level emissions 

and input into the lowest model layer. 

(c) Modeling Results 

Projection year modeling was completed for the years 2005,2008,2011,2014,2015, and 2017. 

EPA's most current modeling guidance recommends that model predictions be used in a relative 

sense rather than an absolute sense. Applying the model this way is done by calculating a 

"relative reduction factor" (RRF) for grid cells that are co-located with a PM IO monitor. RRF 

Section IX.A.lO. page 24 
Adopted by the Air Quality Board July 6, 2005 

values were computed for each day of the base-case modeling years (January 2001 and February 

2002) and subsequently applied to the future year predictions. The technique for creating the 

individual RRF is described in section 7 of the modeling TSD. 

Results demonstrated that modeled PM10 concentrations are highest in 2005. From there they 

decline until reaching a minimum value in 2011 or 2014, and then increase again through 2017. 

No PM10 values greater than 150 uglm3 were modeled for any ambient air using either episode. 

Ambient air means anywhere that would be accessible to the general public. There were two grid 

cells which showed predicted concentrations in excess of 150 uglm3

, but they are both located on 

the property of Kennecott Utah Copper Corp. The general public does not have access to this 

area, and so these grid-cells do not represent ambient air. Results of the modeling analysis are 

presented below for each of Utah's three PMIO nonattainment areas. 

Figure IX.A.32. Highest Predicted 24-hr Concentration 

Salt Lake County 

150 

- '"' -5, 140 

..,.,..­ -24-hr Standard

{ - 130 __Peak Cell 

.. -­ -Ir- N. Salt Lake 

-

c: 120 ___ Hawthome 

c ___ Cottonwood 0 

0 110 ___ Magna 0

.... 

:& 

Q, 100 

-­ ---­ -­ 90 

2005 2008 2011 2014 2017 

Projection Year 

Figure lX.A.32 above illustrates the trend of predicted concentrations at the monitoring stations 

and the highest modeled grid cells in the Salt Lake County PMlO nonattainment area and the 

entire domain. The peak cell is near the Cottonwood monitor. These data reflect the modeled 

PMlO concentrations after application of the RRF. 

.-.
 

-.
 

Section IX.A.lO, page 25 
Adopted by the Air Quality Board July 6.2005 

(-­

Figure IX.A.33. Highest Predicted 24-hr Concentration
 

Utah County
 

t 

155 

150 

145 

::l

C 140 

0 

.... 

-------- /" ... 

..... 

---... /' -

2005 2008 2011 2014 2017 

Projection Vear 

:= -24-hr Standard

.. 

c 

135 l!! -.-Undon 

8 130 -.-N. Pro\() c 

S 125 

0

... 

::E 120

A. 

115
 

110
 

Figure IX.A.33 above illustrates the trend of predicted concentrations at the highest modeled 

grid-cells in the Utah County PMIO nonattainment area. The highest grid cell is located near the 

Lindon monitor. The data reflects the modeled PMIO concentrations after application of the RRF. 

The model predicts a significant margin of "safety" with respect to the health standard throughout 

the projection years. 

Section IX.A.lO, page 26 
Adopted by the Air Quality Board July 6. 2005 

Figure IX.A.34. Highest Predicted 24·hr Concentration 

Ogden City 

155 ,-------------------., 

150 +-------------------+ 

E145 +-------------------~
 

"it!
 

::I. 140 +----------------~------__l
 c 

o 

1-24-hr Standard I

r:: +--------------------1 I Ogden 

O 

o

..I - 125 +---------------------1 

120 +-------------------,""'..,.'------!

.. --" 

115 -!-==:::~~=====~====::----_1

110 +----.....,.----..,....-----,r-------r----' 

2005 2008 2011 2014 2017 

Projection Veer 

Figure IX.A.34 above illustrates the trend of predicted concentrations at the highest modeled grid 

cells in the Ogden City PMIO nonattainment area. The monitor is located in this highest grid cell. 

The data reflects the modeled PMIO concentrations after application of the RRF. The model 

predicts a significant margin of "safety" with respect to the health standard throughout the 

projection years. 

(d) Annual Standard 

As presented above, the modeled demonstration of maintenance was designed to address the 24­

hour standard for PM10 during the winter conditions that drive secondary aerosol formation. This 

scenario has historically led to elevated concentrations of PM10 along the Wasatch Front. 

The attainment demonstrations in the 1991 PMIO SIP were also designed to address the 24-hour 

standard, based on EPA guidance which states that "The SIP related emission limits should be 

based on the NAAQS (annual or 24-hour) which result in the most stringent control 

requirements" (see Subsection IX.A.9). As stated (by EPA or in that version of the SIP), it was 

assumed that "the application of many of the control strategies that are being implemented to 

reduce the 24-hour PMIO concentrations will also result in a reduction of the annual PMIO 

concentmtions even though they are designed to reduce wintertime 24-hr concentrations." Due to 

the disparity in concentrations observed during the remainder of the year, "the winter season is 

the period that has the greatest impact on the annual average (see Table IX.A.24), and controlling 

PMIO concentrations during the winter will have the greatest impact on the annual average." -. 

As discussed in the section concerning improvements in air quality, the downward trend in the 

annual arithmetic mean concentrations is reflective of these control strategies, many of which 

Section IXA. 10, page 27 
Adopted by the Air Quality Board July 6. 2005 

were directed at the wintertime 24-hour concentrations. This corroborates the assumption made 

in the 1991 SIP. 

This maintenance plan will continue to rely upon that assumption. Since the control strategies 

required by the 1991 SIP were sufficient to achieve compliance with the 24-hour standard, the 

maintenance plan requires no new control strategies for continued compliance. Since the controls 

required by the 1991 SIP were deemed sufficient to ensure compliance with the annual standard, 

no further controls will be necessary to achieve continued compliance with that standard either. 

Thus, the modeled demonstration of attainment for the 24-hour PMIO standard provides adequate 

assurance that the annual PMIO standard will be protected as well. 

(e) Magna 

The violations of the PM10 standard in Magna were caused primarily by the blowing oftailings 

from the Kennecott tailings pond under certain meteorological conditions while the plant was 

shut down. 

While this scenario was never explicitly modeled in the 1991 SIP. it was addressed by requiring 

reasonably available control methods (RACM), which took the form of a comprehensive fugitive 

dust plan. The terms of this dust plan have been incorporated into the SIP at Section IX Part H. 

(2) Attainment Inventory 1'­

The attainment inventory is discussed in EPA guidance (Calcagni) as another one of the core 

provisions that should be considered by states for inclusion in a maintenance plan. 

According to Calcagni, the stated purpose of the attainment inventory is to establish the level of 

emissions during the time periods associated with monitoring data showing attainment. 

In cases such as this, where a maintenance demonstration is founded on a modeling analysis, the 

attainment inventory is necessary to validate the model with respect to the ambient measurements 

that were made at the air monitoring locations during the commensurate period in time. For this 

analysis, base-year attainment inventories were compiled for 2001 and 2002. 

Continued attainment is then demonstrated by running an air quality model, which considers 

factors related to meteorology, topography. and certain stack characteristics as well as the 

emissions of an air contaminant. After evaluating all of these factors. the model predicts 

concentrations of the air contaminant that are then compared to the health standard. 

This implies that the analysis will require additional projection year inventories. Calcagni speaks 

to this as well, noting that the projection inventory should consider future growth. including 

population and industry. should be consistent with the base-year attainment inventory. and should 

document data inputs and assumptions. Any assumptions concerning emission rates must reflect 

permanent, enforceable measures. 

Utah has compiled both attainment and projection inventories for use in a quantitative modeling 

demonstration. The emissions contained in the inventories include sources located within a 

regional area called a modeling domain. The modeling domain encompasses all three areas 

within the state that were designated as nonattainment areas for PM10: Salt Lake County, Utah 

County, and Ogden City, as well as a bordering region see Figure IX.A.23. 

Section IX.A.W. page 28 
Adopted by the Air Quality Board July 6, 2005 

There are three general categories of sources included in these inventories: industrial point 

sources, smaller area sources, and mobile sources. 

For each of these source categories, the pollutants that were inventoried included: particulate 

matter with an aerodynamic diameter often microns or less (PM10), sulfur dioxide (502), oxides 

of nitrogen (NOx), carbon monoxide (CO), and volatile organic compounds (VOC). S02 and 

NOx are specifically defined as PM10 precursors, that is, compounds that, after being emitted to 

the atmosphere, undergo chemical or physical change to become PMtO• Any PMIO that is created 

in this way is referred to as secondary aerosol. The UAM-AERO model also considers ammonia, 

CO and VOC to be contributing factors in the formation of secondary aerosol. 

The unit of measure for point and area sources is the traditional tons per year, but the UAM· 

AERO model includes a pre-processor that converts these emission rates to hourly increments 

throughout each day for each episode. Mobile source emissions are reported in terms of tons per 

day, and are also pre-processed by the model. 

The basis for the point source and area inventories, for both the base-year attainment inventories 

as well as all future-year projection inventories, was the 2001 inventory of actual emissions that 

had already been compiled by the Division of Air Quality. 

Area sources, as well as the smaller point sources, were projected forward from 2001, using 

population and economic forecasts from the Governor's Office of Planning and Budget. 

The larger point sources - those whose emissions could exceed 100 tons per year (tpy) of PM10, 

200 tpy NOx, or 250 tpy S02 - were projected somewhat differently. These sources were 

evaluated at their maximum emission rates, based on existing regulatory conditions of operation 

and construction. Furthermore, they were evaluated on their capability to emit on a short-term 

basis. As such, the projected emissions from these large sources reflect enforceable emission 

limits that are pertinent to the protection of public health with respect to a 24-hour standard for 

PM10. Point source projections also include any current emission reduction credits (banked 

emissions). 

Mobile source emissions were calculated for each year using MOBILE6.1/6.2 in conjunction with 

the appropriate estimates for vehicle miles traveled (VMT). VMT estimates for the urban 

counties were based on a travel demand model that is only run periodically for specific projection 

years. VMT for intervening years were estimated by interpolation. 

Since this SIP subsection takes the form of a maintenance plan, it must demonstrate that the area 

will continue to attain the PM JO NAAQS throughout a period of ten years from the date of EPA 

approval. It is also necessary to "spot check" this ten-year interval. Hence, projection inventories 

were prepared for the following years: 2005,2008,2011,2014, and 2017 (the ten-year mark from 

anticipated EPA approval). 2015 was also projected as p<;lssible planning year for the purpose of 

future transportation confonnity analyses. 

The following table is provided to sununarize these inventories. As described, they represent 

point, area, and mobile sources in the modeling domain. They include PMIO, S02' NOx, CO and 

VOC, and they span from the base-years (2001 and 2002) through the projection years of 2005, 

2008,2011,2014, and 2017. 

-


Section IXAlO, page 29 
Adopted by the Air Quality Board July 6, 2005 

,­

Table IX.A.33	 Emission Inventories for the Modeling Domain. Actual Emissions for 

2001-2002; Emission Projections for 2005-2017 

Input 

.cQ 2001 I 2002 I 2005 I 2008 I 2011 I 2014 I 2015 I 2017 I 

Point (TonslYear) • 30,850.43 25,237.47 63,184.04 64,254.04 65,401.66 66,512.50 66,882.78 67,590.87 

Area (TonslYear) 184,125.74 186,748.59 195,132.88 203,263.30 211,525,98 219,584.84 222,202.47 227,463.10 

On-Road (TonsJOay) •• 1,801.72 1,935.13 2,327.33 1,987.96 1,896.95 1,832.70 1,808.67 1,824.95 

2001 I 2002 I 2005 I 2008 I 2011 I 2014 I 2015 I 2017 I 

Point (TonslYear) • 17,263.27 15.606.80 37,618.03 37,947.67 38,290.32 38,614.84 38,722.94 38,918.61 

Area (TonSlYear) 31,822.89 31,665.83 31,555.39 31,043.87 30,622.93 30,660.63 30,756.97 31,044.91 

On·Road (Tons/Day)" 160.57 161.19 181.55 145.70 117.38 90.91 84.96 82.75 

2001 2002 2005 2008 2011 2014 2015 2017 fM1Jl	 I I I I I I I I 

Point (TonsIYear) • 7,418.19 6,818.33 14,438.83 14,612.90 14,n9.78 14,938.94 14,991.99 15,077.57 

Area (TonaIYear) 16,314.20 16,231.96 16,347.93 16,595.09 16,974.18 17.365.87 17,484.59 17,692.48 

On-Road (Ton8lDay)·· 51.30 52.33 71.02 75.85 81.18 90.00 104.84 105.38 

SQx 2001 I 2002 I 2005 I 2008 I 2011 1 2014 I 2015 I 2017 I 

Point (TonaIYear) • 8,884.91 6,048.77 35,494.35 35,550.44 35,607.07 35,659.65 35,6n.17 35,703.41 

Area (TonslYear) 2,134.56 2,149.09 2,219.34 2,294.93 2,370.11 2,441.92 2,465.20 2,510.63 

On·Road (TonslOay) .. 5.32 5.46 7.29 7.43 8.04 8.63 8.83 8.83 

2001 I 2002 I 2005 I 2008 I 2011 I 2014 2015 I 2017 I I

Point (TonslYear) • 5,309.57 5,183.67 8,034.87 8,206.38 8,379.58 8,545.44 8,600.73 8,696.39 

Area (TonsIYear) 150,738.67 150,585.37 151,664.80 153,339.12 156.232.05 159,330.42 160,290.66 162,032.65 

On-Road (TonslDay) •• 89.16 89.44 88.80 71.74 60.37 51.39 49.96 49.n 

• Point source totals for 2001 & 2002 include slight variations between specific episode days.
 

The numbers reported In this table reflect the highest number for each pollutant.
 

Banked emissions are Included In all projection year inventories (2005 forward).
 

•• On-Road source totals for every year include slight variations between specific episode days. 

The numbers reported in this table reflect the episode day on which the NOx and the PM10 were the highest. 

More detail concerning any element of the inventory can be found at the appropriate section of 

the Technical Support Document (TSD). More detail about the general construction of the 

inventory may be found in the Inventory Preparation Plan at Section 1.a of the TSD. Discussion 

concerning any adjustments that were made to the inventoried emissions prior to use in the UAMAERO model may be found in the modeling section of the TSD. . 

(3) Emissions Limitations 

As discussed above, there was a distinction made in the modeling of projected emissions for the 

point source category. The larger sources within the modeling domain were modeled at their 

maximum allowable emissions. as determined on a 24-hour basis. 

A subset of these "large" sources was subsequently identified for the purpose of establishing 

emission limitations as part of the Utah SIP. This subset includes any large source located within 

any of the three current nonattainment areas for PM1o: Salt Lake County, Utah County, or Ogden 

Section IXA.lD, page 30 
Adopted by the Air Quality Board July 6. 2005 

City. A source was also included in the subset if it was currently regulated for PMIQ under 

section IX, Part H of the Utah SIP. There were several sources in Davis County that were close 

enough to the border so as to have originally been included in the original PMIO SIP. 

As discussed before, the emission limits for these sources had already been reflected in the 

projected emissions inventories used in the modeling analysis. Many of these limits appear in 

State issued Approval Orders or Title V Operating Permits. Such regulatory documents typically 

include many emission limits and operating restrictions. Only those limits that are truly 

significant from an airshed management perspective have been incorporated specifically into the 

SIP. 

These limits are incorporated in the Utah SIP at Section IX. Part H (formerly Sections 1 and 2 of 

Appendix A to Section IX, Part A), and as such remain federally enforceable. 

These conditions demonstrate maintenance through 2017 see subsections IX.A.lO.c.( 1) and (2). 

(4) Emission Reduction Credits 

Existing Emission Reduction Credits on file with the Utah Division of Air Quality were included 

in the modeled demonstration of maintenance outlined in Subsection IX.A.IO.c( 1). Concerning 

the subsequent banking of any emission reduction credits for PMIQ, or precursors thereto, the 

emission levels contained in the modeled demonstration of maintenance outlined in Subsection 

IX.A.lO.c(l). or incorporated into the Utah SIP at Section IX, Part H (formerly Appendix A to 

Section IX, Part A,) should serve to establish a baseline for the emission rates relied upon by this 

maintenance plan. These emission reduction credits, whether pre-existing or established 

subsequent to the approval of this SIP revision. are alJowed to the extent that they are established 

by actual, verifiable. and enforceable reductions in emissions. 

(5) Additional Controls for Future Years 

Since the emission limitations discussed in subsection IX.A.1O.c.(3) remain federally enforceable 

and, as demonstrated in IX.A.lO.c( I) above, are sufficient to ensure continued attainment of the 

PM10 NAAQS, there is no need to require any additional control measures to maintain the PMIO 

NAAQS. 

(6) Mobile Source Budget for Purposes of Conformity 

The transportation conformity provisions of section l76(c)(Z)(A) of the Clean Air Act (CAA) 

require regional transportation plans and programs to show that" ...emissions expected from 

implementation of plans and programs are consistent with estimates of emissions from motor 

vehicles and necessary emissions reductions contained in the applicable implementation plan ... " 

EPA's transportation confonnity regulation (40 CFR 93.118, last amended at 69 FR 40072, July 

1,2004) also requires that motor vehicle emission budgets must be established for the last year of 

the maintenance plan, and may be established for any years deemed appropriate. If the 

maintenance plan does not establish motor vehicle emissions budgets for any years other than the 

last year of the maintenance plan, the conformity regulation requires that a "demonstration of 

consistency with the motor vehicle emissions budgets must be accompanied by a qualitative - finding that there are not factors which would cause or contribute lO a new violation or exacerbate 

an existing violation in the years before the last year of the maintenance plan." The normal 

Section IX.A.IO, page 31 
Adopted by the Air Quality Board July 6, 2005 

{,­

interagency consultation process required by the regulation shall determine what must be 

considered in order to make such a finding. 

Road dust projections were estimated using the EPA PART5 particulate emissions model. 

However, prior to applying these emission estimates in an attainment demonstration using the 

UAM-AERO model, the road dust inventory was discounted by 75% as part of the attainment 

modeling method to more accurately reflect the conventional understanding of the relationship of 

modeled road dust emissions and actual fugitive dust measurements recorded by the State air 

quality monitoring network. The mobile source budgets set forth in this Plan for direct PMIO 

(including road dust) are based on the unmodified estimates from the PART5 model, and as such, 

no discount adjustments should be applied as part of the regional emissions analysis for future 

conformity determinations. 

For transportation plan analysis years after the last year of the maintenance plan (in this case 

2017), a conformity detennination must show that emissions are less than or equal to the 

maintenance plan's motor vehicle emissions budget(s) for the last year of the implementation 

plan. 

Mobile sources are not significant contributors of S02' This SIP does not establish a motor 

vehicle emissions budget for S02' 

(a) Salt Lake Couoty Mobile Source PM10 Emissions Budgets 

In this maintenance plan, the State is establishing transportation confonnity motor vehicle 

emission budgets (MVEB) for 2015 and 2017. 

(i) Direct PM10 Emissions Budget 

As presented in the Technical Support Document (SMOKE Formats for Urban Counties), 

estimated on-road mobile source emissions for Salt Lake County, in 2015 and 2017, of direct 

sources of PMIO (road dust, brake wear, tire wear, and exhaust particles) were 48.86 tons per 

winter weekday. The maintenance demonstration in Subsection IX.A.lO.c.(I) estimates a 

maximum PMIO concentration of 147.7 uglm3 in 2017 within the Salt Lake County portion of the 

modeling domain. This value is 2.3 ug/m3 below the NAAQS of 150 uglm3

• 

EPA's confonnity regulation (40 CPR 93.124) also allows the implementation plan to quantify 

explicitly the amount by which motor vehicle emissions could be higher while still demonstrating 

compliance with the maintenance requirement. The implementation plan can then allocate some 

or all of this additional "safety margin" to the emissions budgets for transportation confonnity 

purposes. In this case, the safety margin equates to 2.3 ug/m3

. 

Using the same emission projections for point and area and non-road mobile sources. the UAMAERO model was re-run using 52.00 tons of PMlO per winter weekday for mobile sources (and 

35.00 tons/winter weekday of NOx). The revised maintenance demonstration for 2015 and 2017 

still shows maintenance of the PMIO standard. It estimates a maximum PMIO concentration of 

148.5 ug/m3 in 2017 within the Salt Lake County portion ofthe modeling domain. This value is 

1.5 ug/m3 below the NAAQ Standard of 150 ug/m3

• This maintenance plan allocates 0.8 ug/m3 of 

the safety margin to the transportation MVEB. and thereby sets the direct PM 10 MVEB for 2015 

and 2017 at 52.00 tons/winter weekday. 

In terms of emissions, the safety margin can be described as follows: Using 52.00 tons per day of 

PM\o and 35.00 tons per day of NOx when modeling mobile source emissions in 2015 and 2017, 

Section IX.A.! O. page 32 
Adopted by the Air Quality Board July 6. 2005 

the highest predicted concentration ofPM1o was 148.5lLglcubic meter within the Salt Lake 

County portion of the modeling domain. This shows that the safety margin is at least 3.14 tons 

per day of PM,o (52.00 tons per day minus 48.86 tons per day) and 0.04 tons per day of NOx 

(35.00 tons per day minus 34.96 tons per day). This maintenance plan allocates a portion of the 

safety margin to the mobile source budgets. 

Mobile sources are not significant contributors of direct S04 exhaust particulates. This SIP does 

not establish a separate MVEB for S04' 

(ii) NOx Emissions Budget 

NOx emissions indirectly contribute to PMIO concentrations through secondary chemical 

reactions and for this reason are sometimes referred to as indirect or secondary PMIO• As 

presented in the TSD (SMOKE Fonnats for Urban Counties), estimated on-road mobile source 

NOx emissions in 2015 and 2017 were 34.96 tons per winter weekday. The maintenance 

demonstration in Subsection IX.A.lO.c(l} estimates a maximum PMIO concentration of 147.7 

uglm3 in 2017 within the Salt Lake County portion of the modeling domain. This value is 2.3 

uglm3 below the NAAQS of 150 uglm3. 

EPA's conformity regulation (40 CPR 93.124) also allows the implementation plan to quantify 

explicitly the amount by which motor vehicle emissions could be higher while still demonstrating 

compliance with the maintenance requirement. The implementation plan can then allocate some 

or all of this additional "safety margin" to the emissions bUd§ets for transportation conformity 

purposes. In this case, the safety margin equates to 2.3 uglm . 

Using the same emission projections for point and area and non-road mobile sources, the UAM­ - AERO model was re-run using 35.00 tons ofNOx per winter weekday for mobile sources (and 

52.00 tons/winter weekday of PMJO). The revised maintenance demonstration for 2015 and 2017 

still shows maintenance of the PM10 standard. It estimates a maximum PMIO concentration of 

148.5 uglm3 in 2017 within the Salt Lake County portion ofthe modeling domain. This value is 

1.5 uglm3 below the NAAQS of 150 uglm3

• This maintenance plan allocates 0.8 uglm3 of the 

safety margin to the transportation MVEB, and thereby sets the NOx MVEB for 2015 and 2017 at 

35.00 tons/winter weekday. 

In terms of emissions. the safety margin can be described as follows: Using 52.00 tons per day of 

PM10 and 35.00 tons per day of NOx when modeling mobile source emissions in 2015 and 2017, 

the highest predicted concentration of PM10 was 148.5 JLglcubic meter within the Salt Lake 

County portion of the modeling domain. This shows that the safety margin is at least 3.14 tons 

per day of PMIO (52.00 tons per day minus 48.86 tons per day) and 0.04 tons per day of NOx 

(35.00 tons per day minus 34.96 tons per day). This maintenance plan allocates a portion of the 

safety margin to the mobile source budgets. 

(b) Net ElTed to Maintenance Demonstration 

Using the procedure described above. some of the safety margin indicated earlier in Subsection 

IX.A.IO.c(6) has been allocated to the mobile vehicle emissions budgets. The results of this 

modification are presented below. 

-


Section IX.A.IO, page 33 
Adopted by the Air Quality Board July 6, 2005 

(i)	 Inventory: The emissions inventory was adjusted by adding the following 

sums to the on road mobile source emissions totals for the entire modeling domain: 

in 2015: 4.04 ton/day PMIO and 0.19 ton/day NOx 

in 2017: 5.41 ton/day PMIO and 2.49 ton/day NOx 

(ii)	 Modeling: 

The effect on the modeling results throughout the domain is sununarized in the following 

table (which shows predicted concentrations in ug/m3

). It demonstrates that with the 

allocation of the safety margin, the NAAQS is still maintained through 2017 in all areas. 

Table IX.A.34 Modeling of Attainment, 2005 - 2017, Including the Portion of the Safety 

Margin Allocated to Motor Vehicles 

2001 Base Year E Isode 2005 2008 2011 2014 2015 

Cottonwood	 91.45 89.13 88.57 89.92 93.40 

Hawthome	 124.17 121.71 119.76 120.84 125.60 

0·­ Magna	 81.33 80.32 80.11 80.52 

N. Salt Lake	 144.05 143.07 142.96 144.37 

Ogden	 113.19 113.04 113.75 116.62 121.75~f'l"ii.a11 133.2<1iiWl 

Lindon	 78.82 81.00 82.97 84.79 90.16 90.3~ 91.9~ 92.1~ N. Provo	 62.04 62.22 63.50 65.11 69.68 69.8 71.4 71.6 

Plus safety 

Marain 

80.44 81.91 

147.27t;'~1:-~'···

2002 Base Vear Episode 2005 2008 2011 2014 2015 2017 

Cottonwood 132.83 125.45 121.54 121.08 124.04 125.2~

Hawthorne 136.60 127.78 122.80 122.03 125.35 126.61 

Magna 93.92 94.03 95.34 96.73 96.00 98.47 

N. Salt Lake 148.77 139.92 134.87 133.19 136.01 137.27 

Peak Cell (near Cottonwood) 149.97 140.36 134.92 133.85 137.43 138.75 

2015 2017 

125.3e 126.56 

126.13 127.98 

96.60 99.07 

137.41 138.66 

139.0B 140.39 

Ogden	 117.70 116.09 116.02 117.59 121.20 122.121 126.6~ 127.511 

Lindon	 131.09 126.27 124.12 123.87 127.71·· 

N. Provo	 122.46 118.22 116.74 117.34 121.60 

(7) Nonattainment Requirements Applicable Pending Plan Approval 

CAA 175A(c) - Until such plan revision is approved and an area is redesignated as attainment. 

the requirements ofeM Part D, Plan Requirements/or Nonattainment Areas, shall remain in 

force and effect. The Clean Air Act requires the continued implementation of the nonattainment 

Section lX.A.lO, page 34 
Adopted by the Air Quality Board July 6,2005 

area control strategy unless such measures are shown to be unnecessary for maintenance or are 

replaced with measures that achieve equivalent reductions. Utah will continue to implement the 

emissions limitations and measures from the PMJO SIP. 

(8)	 Revise in Eight Years 

CAA 175A(b) • Eight years after redesignation. the State must submit an additional plan revision 

which shows maintenance ofthe applicable NMQSfor an additional 10 years. Utah agrees to 

fulfill this obligation at the appropriate point in time. 

(9)	 Verification of Continued Maintenance 

Implicit in the requirements outlined above is the need for the State to determine whether the area 

is in fact maintaining the standard it has achieved. There are two complementary ways to 

measure this: 1) by monitoring the ambient air for PMJ(lt and 2) by inventorying emissions of 

PM10 and its precursors from various sources. 

The State will continue to maintain an ambient monitoring network for PMlO in accordance with 

40 CFR Part 58 and the Utah SIP. The State anticipates that the EPA will continue to review the 

ambient monitoring network for PMJO each year, and any necessary modifications to the network 

wiJI be implemented. 

The State will also continue to collect actual emissions inventory data from all sources of PMIO, 

S02' and NOx in excess of 25 tons (in aggregate) per year, as required by R307-150. 

(10) Contingency Measures 

eM 175A(d) - Each maintenance plan shall contain contingency measures to assure that the 

State will promptly correct any violation ofthe standard which occurs after the redesignation of 

the area to attainment. Such provisions shall include a requirement that the State will implement 

all control measures which were contained in the SIP prior to redesignation. Utah has· 

implemented all measures contained in the plan, and will continue to do so even after 

redesignation. This revision need only address such contingency measures as may be necessary 

to mitigate any future violation of the standard. 

This Contingency Plan for Salt Lake County supercedes Subsection IX.A.8, Contingency 

Measures, which is part of the original PM IO SIP. 

The State will rely upon ambient PMIO monitoring to determine whether a violation has occurred. 

Upon monitoring a violation of the PM10 NAAQS, the State will take the following actions. 

•	 The State will identify the source(s) ofPM1o causing the violation, and report the 

situation to EPA Region VIII within four months. 

•	 The State will identify a means of corrective action within six months. The maintenance 

plan contingency measures to be considered and selected will be chosen from the 

following list or any other emission control measures deemed appropriate based on a 

	 Section IX.A.lO, page 35 
Adopted by the Air Quality Board JuLy 6, 2005 

consideration of cost-effectiveness, emission reduction potential, economic and social 

considerations, or other factors that the State deems appropriate: 

Re-evaluate the thresholds at which a red or yellow burn day is triggered, as 

established in R307-302; 

Further controls on stationary sources; 

The State will require implementation of such corrective action no later than one year after the 

violation was confmned. 

Section IX.A.lO, page 36