Technical Support Document

for the Proposed Action on the South Coast 

2012 PM2.5 Plan and 2015 Supplement and Proposed 

Reclassification of the South Coast as Serious 

Nonattainment for the 2006 PM2.5 Standard

Air Division

U.S. EPA Region 9

September 2015
For further information on this technical support document, please contact:

Wienke Tax 

Office of Air Planning (AIR-2)

U.S. Environmental Protection Agency-Region 9

75 Hawthorne Street

San Francisco, California 94105

(415) 947-4192

Tax.wienke@epa.gov

Documents referenced in this technical support document may be found in the docket for this 

rulemaking, docket no. EPA-R09-OAR-2015-0204, which may be found at www.regulations.gov 

or at the address listed above.
Table of Contents

I. Background and SIP Submittals 5

A. History of PM2.5 NAAQS Implementation and PM2.5 Planning in the South Coast 5

B. PM2.5 Air Quality Data for the South Coast Air Basin 9

C. California SIP Submittals for the 2006 PM2.5 Standard in the South Coast 15

D. Public Notice and Hearing Requirements for and Completeness of SIP Submittals 16

II. Evaluation of the South Coast 2012 PM2.5 Plan and 2015 Supplement 21

A. Emissions Inventories 22

B. Air Quality Modeling 26

C. PM2.5 Precursors 51

D. Reasonably Available Control Measures/Reasonably Available Control Technology 

(RACM/RACT) 54

E. Major Stationary Source Control Requirements Under CAA Section 189(e) 63

F. Adopted Control Strategy 64

G. Demonstration of Impracticability 69

H. Reasonable Further Progress and Quantitative Milestones 72

I. Contingency Measures 76

J. Motor Vehicle Emissions Budgets 78

K. General Conformity Budgets 80

III. Proposed Reclassification as Serious Nonattainment and Serious Area SIP Requirements 84

A. Proposed Reclassification as Serious and Applicable Attainment Date 85

B. Clean Air Act Requirements for Serious PM2.5 Nonattainment Areas 86

C. Statutory Deadline for Submittal of a Serious Area Plan 87

D. Reclassification of Reservation Areas of Indian Country 91
Acronyms and Abbreviations

μ: micron (one millionth)

AB: California Assembly Bill

AERR: Air Emissions Report Rule, 40 CFR part 51, subpart A

ARB: California Air Resources Board (also CARB)

APCD: air pollution control district

AQMD: air quality management district

CARB: California Air Resources Board (also ARB)

CCR: California Code of Regulations

CERR: Consolidated Emissions Reporting Rule, 40 CFR part 51, subpart A

CFR: Code of Federal Regulations

CMAQ: Congestion Mitigation and Air Quality funds

CMAQ: Community Multiscale Air Quality [model]

CMB: chemical mass balance

CPM: condensable particulate matter

CRPAQS: California Regional Particulate Air Quality Study

District: South Coast Air Quality Management District

EC: elemental carbon

EPA: United States Environmental Protection Agency

FHWA: Federal Highway Administration

Fine particulate: PM2.5

FMVCP: Federal motor vehicle control program

FR: Federal Register

FRM: Federal Reference Method

FTA: Federal Transit Administration

HNO3: nitric acid

I/C: internal combustion

km: kilometer

m: meter

m3: cubic meter

mb: millibars

MFB: mean fractional bias

MFE: mean fractional error

MM5: a mesoscale model

MMPA: meteorological model performance analysis

MOZART: Model for Ozone And Related Chemical Tracers

MPO: metropolitan planning organization

MVEB: motor vehicle emissions budget

NAAQS: national ambient air quality standard

NH3: ammonia

NH4NO3: ammonium nitrate

NNSR: nonattainment new source review

NO2: nitrogen dioxide
Acronyms and Abbreviations

NOx: oxides of nitrogen

NSR: new source review

NYQ: not yet quantified

O3: ozone

OC: organic carbon

OH: hydroxyl radical

OTAQ: EPA’s Office of Transportation and Air Quality

PBL: planetary boundary layer

PM: particulate matter

PM10: particulate matter with a diameter of 10 μm or less, includes PM2.5

PM2.5: particulate matter with a diameter of 2.5 μm or less

PMC: coarse particulate matter

PMF: positive matrix factorization

RACM: reasonably available control measures

RACT: reasonably available control technology

RFP: reasonable further progress

RMD: Receptor Modeling Documentation

RMPA: Regional Modeling Performance Analysis

RRF: relative response factor

RTP: regional transportation plan

SANDWICH: Sulfate, adjusted nitrate, derived water, inferred carbonaceous material balance 

approach

SC: South Coast 

SCAQMD: South Coast Air Quality Management District

SIP: state implementation plan

SJV: San Joaquin Valley

SJVAPCD/SJVUAPCD: San Joaquin Valley (Unified) Air Pollution Control District

SMAT: Speciated Modeled Attainment Test

SO2: sulfur dioxide

SOA: secondary organic aerosol

STN: Speciation Trends Network

SOx: oxides of sulfur

TCM: transportation control measures

tpd: tons per day

TIP: transportation improvement program

TSD: technical support document

VMT: vehicle miles traveled

VOC: volatile organic compounds

WOE: weight of evidence

WRF: Weather Research and Forecasting Model
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Technical Support Document

for the Proposed Action on the South Coast 

2012 PM2.5 Plan and 2015 Supplement and Proposed 

Reclassification of the South Coast as Serious 

Nonattainment for the 2006 PM2.5 Standard

This document provides information and analysis supporting the EPA’s proposed

approval of the portions of the South Coast Air Quality Management District’s Final 2012 Air 

Quality Management Plan (December 2012) (“2012 PM2.5 Plan”) and Supplement to the 24-

Hour PM2.5 State Implementation Plan for the South Coast Air Basin, January 2015 (“2015 

Supplement”) that address attainment of the 2006 PM2.5 NAAQS and EPA’s proposed 

reclassification of the South Coast as Serious nonattainment for the 2006 PM2.5 standard. The 

2012 PM2.5 Plan and 2015 Supplement address the Clean Air Act’s requirements for attainment 

of the 2006 24-hour PM2.5 national ambient air quality standard in areas designated as 

nonattainment and classified as moderate. The South Coast is currently designated nonattainment 

and classified as moderate for the 2006 PM2.5 standard. See 79 FR 31566 (June 2, 2014) and 40 

CFR § 81.305.1

I. Background and SIP Submittals

A. History of PM2.5 NAAQS Implementation and PM2.5 Planning in the South 

Coast

On July 18, 1997, the EPA revised the primary and secondary national ambient air 

quality standards (“NAAQS” or “standards”) for particulate matter (PM) to add new annual and 

24-hour standards for PM2.5, particulate matter with a diameter of 2.5 microns or less.

2 The 

annual standards were set at a level of 15 micrograms per cubic meter (μ/m3), as determined by 

the 3-year average of annual mean PM2.5 concentrations. The 24-hour standards were set at a 

level of 65 μ/m3, as determined by the 3-year average of the 98th percentile of 24-hour 

concentrations.

In April 2005, we designated areas for the 1997 standards including designating the 

South Coast as nonattainment for both the annual and 24-hour PM2.5 standards. These 

 

1 The South Coast includes Orange County, the southwestern two-thirds of Los Angeles County, southwestern San 

Bernardino County, and western Riverside County (see 40 CFR 81.305.)

2 62 FR 38652 (July 18, 1997) and 40 CFR § 50.7. Prior to 1997, the EPA had addressed ambient particulate matter 

through other means, first by regulating “total suspended particles” and then, in 1987, by regulating PM10 

(particulate matter with a diameter of 10 microns or less). For more information on the particulate matter standards 

prior to 1997, see 78 FR 3086, 3090 (January 15, 2013). In addition to annual and 24-hour PM2.5 standards, the 

current suite of PM standards includes a 24-hour PM10 standard of 150 ug/m3that was originally set in 1987 

(52 FR 24663 (July 1, 1987)). The South Coast is designated as attainment for the PM10 NAAQS. 40 CFR 81.305.
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designations became effective on April 5, 2005.3In April 2007, the EPA issued an 

implementation rule to assist states with the development of SIP submissions to meet attainment 

planning requirements for the 1997 standards (the “2007 PM2.5 Implementation Rule”) (72 FR 

20583, (April 25, 2007)). The EPA premised the 2007 PM2.5 Implementation Rule on its prior 

interpretation of the Act as allowing for implementation of the PM2.5 standards solely pursuant to 

the general nonattainment area provisions of subpart 1, part D of title I of the CAA (“subpart 1”). 

Among other things, the 2007 PM2.5 Implementation Rule included nationally applicable 

presumptions regarding the need to evaluate and potentially control emissions of certain PM2.5

precursors.4

In November 2007, California submitted the South Coast 2007 AQMP to address the 

provisions of subpart 1 and the 2007 PM2.5 Implementation Rule for the 1997 PM2.5 standards.5

That plan included a demonstration that the South Coast would attain the 1997 PM2.5 standards 

by April 5, 2015, 10 years after the nonattainment designation and the latest attainment date 

allowed under subpart 1 (CAA section 172(b)). In November 2011, we approved all but one 

element of that plan.

6

On October 17, 2006, the EPA revised the 24-hour PM2.5 standard by lowering it to 35 

μg/m3(“2006 PM2.5 standard.”) and retained the annual standard at 15 μg/m3.

7 We designated 

South Coast as nonattainment for the 2006 24-hour standard effective December 14, 2009 (74 

FR 58688 (November 13, 2009)).8In March 2012, the EPA issued a guidance document to aid 

states in preparing SIPs to meet attainment plan requirements for the 2006 24-hour PM2.5

 

3 70 FR 944 (January 5, 2005). CAA section 107(d) generally requires the EPA to designate areas as either 

nonattainment or attainment no later than 3 years after the promulgation of a new standard. The delay in 

designations following the promulgation of the first PM2.5 standards in 1997 was a result of extended litigation on 

those standards and Congressional action. For further information, see 70 FR 944, 945.

4 Specifically, in 40 CFR 51.1002(c), the EPA provided, among other things, that a state was “not required to 

address VOC [and ammonia] as . . . PM2.5 attainment plan precursor[s] and to evaluate sources of VOC [and 

ammonia] emissions in the State for control measures,” unless the State or the EPA provided an appropriate 

technical demonstration showing that emissions from sources of these pollutants “significantly contribute” to PM2.5

concentrations in the nonattainment area (40 CFR 51.1002(c)(3), (4) and 72 FR 20586 at 20589-97 (April 25, 

2007)).

5 The 2007 AQMP addressing the PM2.5 NAAQS relied in part on the California Air Resources Board’s 2007 State 

Strategy (revised in 2011) for the additional mobile source measures needed to demonstrate attainment of the 1997 

PM2.5 standards in the South Coast. The State revised and updated the 2007 State Strategy in 2009 and both the 2007 

AQMP and the 2007 State Strategy in 2011. For more information on the 2007 State Strategy and 2007 AQMP, see

76 FR 41562, 41563-5 (July 14, 2011). In these rulemaking actions, we refer to the 2007 AQMP and 2007 State 

Strategy and their revisions collectively as the “South Coast 2007 AQMP.” 

6 76 FR 69928 (November 9, 2011). We disapproved the PM2.5 contingency measures provisions in the 2007 AQMP. 

In November 2011 and April 2013 the State submitted revised contingency measure which we approved in October 

2013 (78 FR 64402, October 29, 2013).

7 71 FR 61144 (October 17, 2006). On December 14, 2012, the EPA revised the annual PM2.5 standard by lowering 

the level of primary (health-based) annual PM2.5 standard to 12.0 μg/m3and changing its form. No changes were 

made to the 24-hour PM2.5 standards or the secondary (welfare-based) annual PM2.5 standards (78 FR 3086 (January 

15, 2013)). On January 15, 2015, the EPA published nonattainment area designations for the 2012 PM2.5 standard, 

including designation and classification of the South Coast Air Basin as moderate nonattainment for this NAAQS 

(80 FR 2206, 2215-16). Unless otherwise noted, all references to the “PM2.5 standard” in this action are to the 2006 

24-hour PM2.5 standard as codified in 40 CFR 50.13.

8

 74 FR 58688 (November 13, 2009).
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NAAQS.9 The 2012 guidance was based, in large part, on the requirements in the 2007 PM2.5

Implementation Rule. 

California had three years from the December 14 , 2009 effective date of the South 

Coast’s designation as nonattainment for the 2006 PM2.5 NAAQS to submit a SIP for the South 

Coast that addressed the applicable requirements of the Act.10 On December 7, 2012, the District 

adopted the Final 2012 Air Quality Management Plan, and on January 25, 2013, CARB adopted 

the plan as an element of the California SIP and submitted it to EPA on February 13, 2013.11 On 

January 4, 2013, several weeks after the District’s adoption of the 2012 PM2.5 Plan, the U.S. 

Court of Appeals for the D.C. Circuit issued its decision in a challenge to EPA’s 2007 PM2.5

Implementation Rule. See NRDC v. EPA, (706 F.3d 428 (D.C. Cir. 2013). In NRDC, the court 

held that the EPA had erred in implementing the 1997 PM2.5 standards solely pursuant to the 

general implementation requirements of subpart 1, without also considering the requirements 

specific to particulate matter nonattainment areas in subpart 4, part D of title I of the CAA 

(“subpart 4”).12 The court reasoned that the plain meaning of the CAA requires implementation 

of the 1997 PM2.5 NAAQS under subpart 4 because PM2.5 particles fall within the statutory 

definition of PM10 and are thus subject to the same statutory requirements as PM10. The court 

remanded the 2007 PM2.5 Implementation Rule in its entirety, including the presumptions 

concerning VOC and ammonia in 40 CFR 51.1002, and instructed EPA “to repromulgate these 

rules pursuant to Subpart 4 consistent with this opinion.”

Consistent with the NRDC decision, on June 2, 2014 (79 FR 31566), the EPA published a 

final rule classifying all areas currently designated nonattainment for the 1997 and/or 2006 PM2.5 

standards as “Moderate” under subpart 4 and establishing a deadline of December 31, 2014 for 

states to submit any attainment-related and nonattainment new source review (NNSR) SIP 

elements required for these areas pursuant to subpart 4. The EPA provided its rationale for these 

actions in both the proposed and final classification/deadline rule. See 78 FR 69806, 69809 

(November 21, 2013) and 79 FR 31566, 31568 (June 2, 2014). 

On February 6, 2015, the District adopted the Supplement to the 24-Hour PM2.5 State 

Implementation Plan (SIP) for the South Coast Air Basin (“2015 Supplement”) as a revision to 

the 2012 PM2.5 Plan. The District adopted the 2015 Supplement to address subpart 4 

requirements for the 2006 PM2.5 standard to the extent that these requirements are not adequately 

addressed in the 2012 PM2.5 Plan. CARB submitted the 2015 Supplement to EPA on March 4, 

2015. The 2012 PM2.5 Plan and the 2015 Supplement are the subject of today’s proposal. The 

2015 Supplement includes information on the implementation of reasonably available control 

measures for ammonia sources in the South Coast and the District’s demonstration that the 2012 

PM2.5 Plan and 2015 Supplement satisfy the requirements of subpart 4. As a consequence of the 

 

9 Memorandum, dated March 2, 2012 (withdrawn June 6, 2013) from Stephen D. Page, Director, Office of Air 

Quality Planning and Standards, to EPA Regional Air Directors, Regions I-X re: “Implementation Guidance for the 

2006 24-Hour Fine Particle (PM2.5) National Ambient Air Quality Standards (NAAQS)” (“2012 Guidance”) 

Available at: http://epa.gov/ttn/naaqs/pm/pm25_guide.html. 

10 See CAA section 172(b) and 40 CFR § 51.1002(a).

11 This document will be referenced in this TSD and the Federal Register proposal as the “2012 PM2.5 Plan”, the 

“South Coast 2012 PM2.5 Plan”, or simply “the Plan”.

12 This NRDC decision also remanded the EPA’s 2008 final rule to implement the nonattainment New Source 

Review (NNSR) permitting requirements for the 1997 PM2.5 standards (73 FR 28231 (May 16, 2008)) which, like 

the 2007 PM2.5 Implementation Rule, was premised on the requirements of subpart 1. We are not addressing 

requirements for NNSR programs in this proposal. 
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NRDC decision, we are reviewing the South Coast 2012 PM2.5 Plan and the 2015 Supplement for 

compliance with the applicable requirements of both subpart 1 and subpart 4. 

The EPA provided its preliminary views on the CAA’s requirements for particulate 

matter plans under part D, title I of the Act in “State Implementation Plans; General Preamble for 

the Implementation of Title I of the Clean Air Act Amendments of 1990” (57 FR 13498, April 

16, 1992) (the “General Preamble”) and “State Implementation Plans for Serious PM–10 

Nonattainment Areas, and Attainment Date Waivers for PM–10 Nonattainment Areas Generally; 

Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act 

Amendments of 1990” (59 FR 41998, August 16, 1994) (the “Addendum”). The General 

Preamble at 13538 discusses the relationship between subpart 1 and subpart 4 SIP requirements, 

and notes that attainment plans for moderate nonattainment areas must meet the general 

provisions in subpart 1 to the extent that these provisions are not otherwise “subsumed by, or 

integrally related to, the more specific [subpart 4] requirements.” Some subpart 1 provisions 

have no subpart 4 equivalent (e.g., the emission inventories (CAA section 172(c)(3)) and 

contingency measures (CAA section 172(c)(9)) and for these provisions, subpart 1 continues to 

govern. Other provisions of subpart 1 are subsumed or superseded by more specific requirements 

in subpart 4 (e.g., certain provisions concerning attainment dates).

Additionally, in a proposed rule published March 23, 2015 (80 FR 15340), the EPA 

provided further interpretive guidance on the statutory SIP requirements that apply to areas 

designated nonattainment for the PM2.5 standards (hereafter “Proposed PM2.5 Implementation 

Rule”). We discuss these preliminary interpretations of the Act as appropriate in our evaluation 

of the 2012 PM2.5 plan and 2015 Supplement in section II of this TSD. 

As part of this proposal, the EPA is proposing to determine that the South Coast cannot 

practicably attain the 2006 PM2.5 standard by the Moderate area attainment date of December 31, 

2015, and to reclassify the area including reservation areas of Indian Country and any other area 

of Indian Country within it where the EPA or a tribe has demonstrated that the tribe has 

jurisdiction, from Moderate to Serious nonattainment under subpart 4. Should EPA finalize this 

proposal to reclassify the South Coast area as a Serious area, the State will be required to adopt 

and submit a new plan addressing the Serious area requirements in subparts 1 and 4 of part D, 

title 1 of the Act. We discuss these Serious area requirements in more detail in Section III below.
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B. PM2.5 Air Quality Data for the South Coast Air Basin

The South Coast PM2.5 nonattainment area is located in the southern part of California. It 

comprises portions of Los Angeles County, all of Orange County, and the urbanized portions of 

San Bernardino and Riverside Counties. It is home to almost 18 million people and is one of the 

nation’s leading area for goods movement. See Figure IB-1 for a map of the South Coast 

nonattainment area and the major sources of air pollution in the nonattainment area. The local 

air district with primary responsibility for developing a plan to attain the PM2.5 NAAQS in this 

area is the South Coast Air Quality Management District (“SCAQMD” or “District”). For a 

complete description of the PM2.5 nonattainment area, please refer to 40 CFR part 81.305.

1. PM2.5 Levels in the South Coast

Ambient PM2.5 levels in the South Coast have declined considerably in the past 15 years 

to levels just above the 2006 PM2.5 NAAQS. For the 2011-2013 period, the 24-hour PM2.5 design 

value for the area, based on monitored readings at the Mira Loma monitor, is 36 ug/m3.

13,14

Figure IB-2 is a map of the current monitoring system in the South Coast.

Since comprehensive monitoring began for PM2.5 in the South Coast in the late 1990s, the 

area has seen a significant decline in ambient levels. All data have been certified by SCAQMD 

for the 2012-2014 period. Data for all sites meets quarterly 75% completeness but four sites 

have at least one quarter with completeness less than 75% in the 2012-2014 period: Burbank, 

Pasadena, Ontario Fire Station, and San Bernardino.

 

13 AQS Design Value Report, AMP 480, September 28, 2015. “Design value” means the calculated concentration 

according to the applicable appendix of 40 CFR part 50 for the highest site in an attainment or nonattainment area 

(40 CFR 58.1).

14 Some data in the 2nd, 3rd and 4th quarter of 2014 may have been impacted by a temporary lab closure and other 

issues at SCAQMD and are currently under review. Therefore, the 2012-2014 design value may be subject to 

change.
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Figure IB-2 -

Figure IB-1. South Coast Nonattainment Area and Location of Major Sources of Air 

Pollution
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Figure IB-2 – Ambient PM2.5 Monitoring Locations In the South Coast Air Basin 
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2. Chemical Composition of PM2.5 in the South Coast

PM2.5 in the air is a complex mixture of components. Common components include: 

nitrate (NO3); sulfate (SO4); ammonium; elemental carbon; a great variety of organic 

compounds; and inorganic material (including metals, dust, sea salt, and other trace elements) 

generally referred to as “crustal” material, although it may contain material from other sources. 

“Primary” particles are emitted directly into the air as a solid or liquid particle (e.g., elemental 

carbon from diesel engines or fire activities, or condensable organic particles from gasoline 

engines). “Secondary” particles (e.g., nitrate and sulfate) form in the atmosphere as a result of 

chemical reactions between precursor pollutants such as NOx, SO2, VOC, and ammonia. The 

South Coast 2012 PM2.5 Plan includes an updated ammonia inventory. Understanding the 

compounds that impact an area’s PM2.5 problem is necessary in order to develop control 

strategies that are effective for attaining the 1997 PM2.5 NAAQS. 

PM2.5 in the South Coast Air Basin is overwhelmingly formed as a secondary pollutant. 

(South Coast 2007 AQMP, page ES-9). Therefore, the South Coast 2007 AQMP relies on 

reducing precursors to PM2.5 and some directly-emitted PM2.5 rather than fugitive dust. In 

general, the organic carbon (OC) mass accounts for approximately 30 percent of the total mass at 

each station. Ammonium, sulfate and nitrates account for an approximate 45 percent of the total 

mass at each monitoring location. The Rubidoux and Fontana monitors are the most heavily 

impacted by nitrates. Sulfate is highest in the near coastal or ports of Los Angeles/Long Beach 

areas, particularly Wilmington and Long Beach. Elemental carbon (EC) and metals 

measurements were highest at Wilmington, accounting for almost 24 percent of the mass when 

combined. All sites observed measurable concentrations of sodium and chloride ions reflecting 

the influence of the marine air as it is transported inland. Figure IB-3 shows the annual 

distribution of PM2.5 species in the South Coast PM2.5 nonattainment area.

Figure IB-3: MATES-III 2005 Annual Distribution of PM2.5 Species (μg/m3)15

 

15 South Coast 2007 AQMP, Appendix V, p. V-2-4.
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More recent data collected for the Multiple Air Toxics Exposure Study IV (MATES IV)

is presented below. To characterize the ambient level of pollutants in the South Coast Air Basin, 

PM2.5, PM10 and Total Suspended Particles (TSP) samples were collected once every six days at 

10 monitoring stations from July, 2012 to June, 2013. 

Figure IB-4 below illustrates the chemical closure of PM2.5. Overall, OM is the most 

dominant category, contributing an average of 44.2 ± 1.0% to the reconstructed mass. The levels 

of OM are relatively higher in sites that are further from the coast, namely Pico Rivera (annual 

avg. = 6.53 μg/m3), Burbank (annual avg. = 6.73 μg/m3), Inland Valley San Bernardino (annual 

avg. = 6.77 μg/m3) and Rubidoux (annual avg. = 6.47 μg/m3), although their contributions to the 

reconstruction mass are similar with other sites. The group of inorganic ions (36.0 ± 1.5%) is 

another major source category, with 16.0, 11.2 and 8.7% attributable to nitrate, sulfate and 

ammonia, respectively. EC accounts for an average of 8.6% of the reconstructed mass, and 

higher fractions are found at Pico Rivera (9.5%) and West Long Beach (9.3%). In general, the 

standard deviations of the site-wide annual average contribution of EC, OM and inorganic ions 

are less than 10% of their corresponding averages, highlighting the relatively low spatial 

variation of the three major source categories in this Basin. Approximately 5.9% of the 

reconstructed mass is attributed to crustal materials, with higher fractions at West Long Beach

(8.1%) and Inland Valley San Bernardino (7.8%). Sea salt accounts for 5.3% of the reconstructed 

mass. Higher fractions are observed at West Long Beach (6.8%) and North Long Beach (7.2%), 

while the inland stations of Inland Valley San Bernardino and Rubidoux record lower fractions at 

3.6% and 3.7%, respectively.

Figure IB-4: MATES-IV Annual Average (July 2012 –June 2013) Chemical Composition 

and Gravimetric Mass Concentrations in PM2.5 Species (μg/m3)16

 

16 Multiple Air Toxics Exposure Study IV (MATES IV), Final Report, May 2015, SCAQMD. Appendix X, The 

Spatial and Temporal Trends of PM2.5, PM10, and TSP Components in the South Coast Air Basin. 
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The Multiple Air Toxics Exposure Study IV (MATES IV) is a monitoring and evaluation 

study conducted in the South Coast Air Basin. The study is a follow up to previous air toxics 

studies in the Basin (MATES II, MATES III) and is part of the SCAQMD Governing Board 

Environmental Justice Initiative. The measurements for MATES IV spanned July 1, 2012, to 

June 30, 2013. The measurements for the previous study, MATES III, spanned April 2004 to 

March 2006. A network of 10 fixed sites was used to monitor toxic air contaminants once every 

six days for one year. The locations of the sites for MATES IV were generally the same as in the 

MATES III study to allow for comparisons over time. The one exception is the West Long 

Beach site, which was about 0.8 mile northwest of the location used in MATES III. 
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C. California SIP Submittals for the 2006 PM2.5 NAAQS in the South Coast

We are proposing to act on the two submittals that California has made to address 

applicable CAA planning requirements for the 2006 PM2.5 NAAQS in the South Coast.

1. SCAQMD, Final 2012 Air Quality Management Plan (December 7, 2012)

CARB submitted the 2012 PM2.5 Plan as a SIP revision on February 13, 2013. See letter,

dated February 13, 2013, James N. Goldstene, Executive Officer, California Air Resources

Board, to Jared Blumenfeld, Regional Administrator, EPA Region 9, with enclosures. The Plan 

was adopted on December 7, 2012 by the South Coast Air Quality Management District 

(SCAQMD or District) and on January 25, 2013 by CARB. See SCAQMD Governing Board 

Resolution 12-19 “A Resolution of the South Coast Air Quality Management District (AQMD or 

District) Governing Board Certifying the Final Program Environmental Impact Report for the 

2012 Air Quality Management Plan (AQMP), adopting the Draft Final 2012 AQMP, to be 

referred to after adoption as the Final 2012 AQMP, and to be submitted into the California State 

Implementation Plan,” December 7, 2012 and CARB Resolution 13-3, “South Coast Air Basin 

2012 PM2.5 and Ozone State Implementation Plans,” January 25, 2013. This document will be 

referenced in this TSD and the Federal Register proposal as the “2012 PM2.5 Plan”, the “South 

Coast 2012 PM2.5 Plan,” or simply “the Plan.”

2. SCAQMD, Draft Supplement to the 24-Hour PM2.5 State Implementation Plan for the South 

Coast Air Basin, January 2015

CARB submitted the 2015 Supplement as a SIP revision on March 4, 2015. See letter,

dated March 4, 2015, Richard D. Corey, Executive Officer, California Air Resources Board, to 

Jared Blumenfeld, Regional Administrator, EPA Region 9, with enclosures. The 2015 

Supplement was adopted on February 6, 2015 by the South Coast Air Quality Management 

District (SCAQMD or District) and on February 19, 2015 by CARB. See SCAQMD Governing 

Board Resolution 15-3 “A Resolution of the South Coast Air Quality Management District 

(SCAQMD) Governing Board approving the Supplement to the 24-Hour PM2.5 State 

Implementation Plan (SIP) for the South Coast Air Basin, and Submittal into the SIP,” February 

6, 2015 and CARB Resolution 15-2, “Minor Revision to the South Coast Air Basin 2012 PM2.5

State Implementation Plan” February 19, 2015. This document will be referenced in this TSD 

and the Federal Register proposal as the “2015 Supplement” or “Supplement.”
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D. Public Notice and Hearing Requirements for and Completeness of SIP 

Submittals

1. Public Notice and Hearing Requirements for SIP Submittals

CAA sections 110(a)(1) and (2) and 110(l) require each state to provide reasonable public 

notice and opportunity for public hearing prior to the adoption and submittal of a SIP or SIP 

revision. To meet this requirement, every SIP submittal must include evidence that adequate 

public notice was given and that an opportunity to request a public hearing was provided 

consistent with the EPA’s implementing regulations in 40 CFR § 51.102.

Both the District and CARB satisfied applicable statutory and regulatory requirements for 

reasonable public notice and hearing prior to adoption and submittal of the 2012 PM2.5 Plan and 

2015 Supplement. The District conducted public workshops, provided public comment periods, 

and held a public hearing prior to the adoption of the Plan on December 7, 2012. See SCAQMD 

Governing Board Resolution, page 3. CARB also provided the required public notice and 

opportunity for public comment prior to its January 25, 2013 public hearing on the Plan. See

Notice of Pubic Meeting to Consider Approval of the South Coast Air Basin 2012 PM2.5 and 

Ozone State Implementation Plans, December 21, 2012.

For the 2015 Supplement, the District made the Supplement available for public review 

and comment on December 19, 2014, more than 30 days in advance of the February 6, 2015 

Board hearing. See SCAQMD Governing Board Resolution 15-3, page 2. CARB also provided 

the required public notice and opportunity for public comment prior to its February 19, 2015 

public hearing on the Supplement. See Notice of Public Meeting to Consider a Minor Revision to 

the South Coast 2012 PM2.5 State Implementation Plan,” February 9, 2015.

The SIP submittals include proof of publication of notices for these public hearings. We 

find, therefore, that the 2012 PM2.5 Plan and 2015 Supplement meet the procedural requirements 

for public notice and hearing in CAA sections 110(a) and 110(l).

2. Completeness Determinations on SIP Submittals

CAA section 110(k)(1)(B) requires the EPA to determine whether a SIP submittal is 

complete within 60 days of receipt. This section also provides that any plan that we have not 

affirmatively determined to be complete or incomplete will become complete by operation of 

law six months after the date of submittal. A completeness review allows us to determine if the 

submittal includes all the necessary items and information we need to evaluate and act on it for 

substantive compliance with applicable requirements.

We make completeness determinations using criteria we have established in 

40 CFR part 51, Appendix V. These criteria fall into two categories: administrative information 

and technical support information. The administrative information provides documentation that 

the state has followed basic administrative procedures during the SIP adoption process and thus 

we have a legally-adopted SIP revision before us. The technical support information provides us 

the information we need to determine the impact of the proposed revision on attainment and 

maintenance of the air quality standards.

We notify a state of our completeness determination by letter unless the submittal became 

complete by operation of law. A finding of completeness does not approve the submittal as part 
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of the SIP nor does it indicate that the submittal is approvable. It does start the 12-month clock 

we have to act on the SIP submittal under CAA section 110(k)(2).

CARB’s February 13, 2013 submittal of the 2012 PM2.5 Plan became complete by 

operation of law on August 13, 2013. The 2015 Supplement became complete by operation of 

law on September 4, 2015 . See Table I-1 below.
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Table I-1. Completeness Evaluation for the South Coast 2012 PM2.5 Plan and the 2015 Supplement

Administrative Materials (per Appendix V, Section 2.1)

(a) Submittal letter from Governor/designee Y 2012 PM2.5 Plan: Letter, James N. Goldstene, Executive Officer, California Air Resources 

Board, to Jared Blumenfeld, Regional Administrator, EPA Region 9, February 13, 2013. 

2015 Supplement: Letter, Richard Corey, Executive Officer, California Air Resources Board, 

to Jared Blumenfeld, Regional Administrator, EPA Region 9, March 4, 2015.

CARB is the governor’s designee for the purposes of SIP submittals.

(b) Evidence of adoption Y 2012 PM2.5 Plan: SCAQMD Governing Board Resolution 12-19 “A Resolution of the South 

Coast Air Quality Management District (AQMD or District) Governing Board Certifying the 

Final Program Environmental Impact Report for the 2012 Air Quality Management Plan

(AQMP), adopting the Draft Final 2012 AQMP, to be referred to after adoption as the Final 

2012 AQMP, and to be submitted into the California State Implementation Plan.,” December 

7, 2012

CARB Resolution 13-3, South Coast PM2.5 and Ozone State Implementation Plans, January 

25, 2013.

2015 Supplement: SCAQMD Governing Board Resolution 15-3, “A Resolution of the South 

Coast Air Quality Management District (AQMD or District) Governing Board approving the 

Supplement to the 24-hour PM2.5 State Implementation Plan (SIP) for the South Coast Air 

Basin and Submittal into the SIP,” February 6, 2015.

CARB Resolution 15-2: “Minor Revision to the South Coast Air Basin 2012 PM2.5 State 

Implementation Plan” February 19, 2015.

(c) State/District legal authority to adopt Y District: California H&SC 40600(b)

CARB: California H&SC 41650(a)

(d1) Copy of actual rule/plan Y 2012 PM2.5 Plan: SCAQMD, 2012 PM2.5 Plan (main volume plus 10 Appendices), adopted 

December 7, 2012 and CARB “Staff Report on Proposed Revisions to the PM2.5 and Ozone 

State Implementation Plans for the South Coast Air Basin,” Release Date: January 11, 2013.

2015 Supplement: “Draft Supplement to the 24-Hour PM2.5 State Implementation Plan for 

the South Coast Air Basin,” January 2015.

(d2) Rule changes indicated by underline/crossoutN/A No previous version of this SIP has been adopted or submitted. 

(e) Proof that action met procedural requirements Y See items (f) and (g) below.
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Table I-1. Completeness Evaluation for the South Coast 2012 PM2.5 Plan and the 2015 Supplement

(f) Copy of public notice Y 2012 PM2.5 Plan: District: Proofs of Publication of SCAQMD’s notices of public hearing, 

dated July 27, 2012, October 4, 2012, and November 7, 2012.

CARB: Notice of Public Meeting to Consider Approval of the South Coast Air Basin 2012 

PM2.5 and Ozone State Implementation Plans,” December 21, 2012. 

2015 Supplement: District: Proofs of Publication of SCAQMD’s notices of public hearing, 

dated December 19, 2014.

CARB: Notice of Public Meeting to Consider a Minor Revision to the South Coast 2012 

PM2.5 State Implementation Plan,” February 9, 2015.

(g) Certification that hearing fulfilled public 

notice

Y 2012 PM2.5 Plan: See SCAQMD Governing Board Resolution 12-19 “A Resolution of the 

South Coast Air Quality Management District (AQMD or District) Governing Board 

Certifying the Final Program Environmental Impact Report for the 2012 Air Quality 

Management Plan (AQMP), adopting the Draft Final 2012 AQMP, to be referred to after

adoption as the Final 2012 AQMP, and to be submitted into the California State 

Implementation Plan.,” December 20, 2012, p. 4.

CARB Resolution 13-3, South Coast Air Basin 2012 PM2.5 and Ozone State Implementation 

Plans, January 24, 2013, p. 6.

2015 Supplement:

(h) Public comments & agency response Y 2012 PM2.5 Plan: South Coast 2012 PM2.5 Plan, Response to Comments and copies of written 

comments received by CARB on the South Coast 2012 PM2.5 Plan.

2015 Supplement: Minutes from SCAQMD Board Meeting on February 6, 2015, included in 

SIP submittal package from CARB to EPA, dated March 4, 2015.

Technical Support (per Appendix V, Section 2.2)

(a) Regulated pollutants identified Y 2012 PM2.5 Plan: Chapters 4 and 5 and Appendix V, and 

2015 Supplement: Attachments D and E

(b) Affected sources & attainment status 

identified

Y 2012 PM2.5 Plan: Chapter 1

2015 Supplement: Main body of Supplement

(c) Rule/plan emissions impact Y 2012 PM2.5 Plan: Chapters 4, 5 and Appendix III

2015 Supplement: Attachments A and F
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Table I-1. Completeness Evaluation for the South Coast 2012 PM2.5 Plan and the 2015 Supplement

(d) Attainment, PSD & other required 

demonstration

Y 2012 PM2.5 Plan, Chapter 5 and Appendix V, and Supplement, Attachment A

2015 Supplement: Attachments A and D

(e) Modeling support as appropriate Y 2012 PM2.5 Plan: Chapter 5 and Appendix V

2015 Supplement: Attachment A

(f) Reliance on continuous emission reductions Y 2012 PM2.5 Plan: Chapter 4 and Appendix III

2015 Supplement: Attachment F

(g) Evidence of limits & other needed 

requirements 

Y 2012 PM2.5 Plan: Chapter 4 and Appendices IV-A, VI, IV-C

2015 Supplement: Attachment D

(i) Justification for deviation from EPA policy N/A

OVERALL COMPLETENESS Submittals are complete per 40 CFR part 51, Appendix V
II. Evaluation of the South Coast 2012 PM2.5 Plan and 2015 

Supplement
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A. Emissions Inventories

1. Requirements for Emissions Inventories

In addition to the requirements of subpart 4, SIPs for Moderate PM2.5 nonattainment areas 

must also meet the general provisions applicable to all nonattainment areas in subpart 1 of part 

D, to the extent that these provisions are not superseded by more specific requirements in subpart 

4. Among these subpart 1 provisions is the requirement in CAA section 172(c)(3) that a state

submit a SIP revision that includes a “comprehensive, accurate, current inventory of actual 

emissions from all sources of the relevant pollutant or pollutants in [the] area...” 

By requiring an accounting of actual emissions from all sources of the relevant pollutants 

in the area, CAA section 172(c)(3) provides for the “base year” inventory to include all 

emissions that contribute to the formation of a particular NAAQS pollutant. For the 2006 24-

hour PM2.5 NAAQS, this would include primary PM2.5 (also referred to as direct PM2.5) as well 

as the main chemical precursors to the formation of secondary PM2.5: NOx, SO2, volatile organic 

compounds (VOC), and ammonia (NH3). Primary PM2.5 includes condensable and filterable 

particulate matter (40 CFR § 51.50 “Particulate Matter”).

The EPA has issued the “Emissions Inventory Guidance for Implementation of Ozone 

and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze 

Regulations,” EPA–454/R–05–001, November 2005 (EI Guidance)17 to assist States in 

developing the required inventories.

The emissions inventory required under section 172(c)(3) is a SIP provision that must be 

approved by the EPA under CAA section 110(k) and is therefore subject to public hearing 

requirements pursuant to sections 110(a)(1),(a)(2), and (l).

18 A state should include in its SIP 

submittal documentation explaining how the emissions data were calculated (EI Guidance, p. 

37). In estimating mobile source emissions, a state should use the latest emissions models and 

planning assumptions available at the time the SIP is developed (EI Guidance, p. 16). California

is required to use EMFAC2011 to estimate tailpipe and brake and tire wear emissions of PM2.5, 

NOx, SO2, and VOC from on-road mobile sources (78 FR 14533 (March 6, 2013)). States are 

required to use the EPA’s AP–42 road dust method for calculating re-entrained road dust 

emissions from paved roads (76 FR 6328 (February 4, 2011)).

In addition to the base year inventory submitted to meet the requirements of CAA section 

172(c)(3), the state should also submit future “baseline inventories” for the projected attainment 

year and each reasonable further progress (RFP) milestone year, and any other year of 

significance for meeting applicable CAA requirements (EI Guidance, p. 7). By “baseline 

inventories” (also referred to as “projected baseline inventories”), we mean projected emissions 

 

17

 Available at www.epa.gov/ttn/chief/eidocs/eiguid/index.html) or in the docket for this proposed rule. We note that 

this guidance was developed to address requirements for the initial implementation of the 1997 ozone and PM2.5

NAAQS and therefore, certain elements (e.g., the selection of 2002 as the inventory base year) are no longer 

relevant.

18 See Memorandum dated September 29, 1992, John Calcagni, Director, Air Quality Management Division, Office 

of Air Quality Planning and Standards, EPA and William Laxton, Director, Technical Support Division, Office of 

Air Quality Planning and Standards, EPA, to Air Division Directors, Region I-X, “Public Hearing Requirements for 

1990 Base-Year Emissions Inventories for Ozone and Carbon Monoxide Nonattainment Areas.”
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inventories for future years that account for, among other things, the ongoing effects of economic 

growth and adopted emissions control requirements. The SIP submission should include 

documentation explaining how the emissions projections were calculated.

2. Emissions Inventories in the 2012 PM2.5 Plan and 2015 Supplement

The annual average planning inventories for direct PM2.5 and all PM2.5 precursors (NOx, 

SOx, VOC, and ammonia) for the South Coast PM2.5 nonattainment area together with 

documentation for the inventories are found in Chapter 3 and Appendix III of the South Coast

2012 PM2.5 Plan and in Attachment A to the 2015 Supplement.

19 Additional inventory 

documentation, specific to the air quality modeling, is in Appendix V. Annual average

inventories are provided for the 2008 base year and for future years 2014 and the PM2.5

attainment year of 2015. (Additional years such as 2017, 2019, 2023 and 2030 are also provided, 

but these inventories are largely for purposes of ozone attainment.). Baseline inventories reflect 

all control measures adopted by the District prior to June 2012 and by CARB prior to August 

2011. Growth factors used to project these baseline inventories are derived mainly from data 

obtained from the Southern California Association of Governments (SCAG), the metropolitan 

planning organization (MPO) for the Los Angeles area (2012 PM2.5 Plan, page 3-1).

Each inventory includes emissions from point, area, on-road, and non-road sources. 

Stationary sources include point and area sources. Point sources in the South Coast air basin that 

emit 4 tons per year or more of VOC, NOx, SOx or PM report annual emissions to the District. 

Point source emissions for the 2008 base year emissions inventory were based on emissions 

reported from the SCAQMD’s Annual Emissions Reporting Program. Area sources include 

smaller emissions sources distributed across the nonattainment area. CARB and the District 

estimate emissions for about 400 area source categories using activity information and emission 

factors. Activity data may come from national survey data or reports (e.g., from the DOE Energy 

Information Administration) or local sources such as the Southern California Gas company, paint 

suppliers, and District databases. Emission factors can be based on a number of sources 

including source tests, compliance reports, and EPA’s AP-42.20

Emissions inventories are constantly being revised and improved. Between the 

finalization of the South Coast 2007 AQMP and the development of the 2012 PM2.5 Plan , the 

District added new area source categories such as liquefied petroleum gas (LPG) transmission 

losses, storage tank and pipeline cleaning and degassing, and architectural colorants to the 

inventories in the 2012 PM2.5 Plan. Emissions estimates for other source categories such as 

commercial and industrial internal combustion engines, landfills, composting waste, metalcoating operations, and livestock waste were adjusted based on new information available to the 

District. See 2012 PM2.5 Plan, pages 3-3 and 3-4, and Appendix III. Mobile Sources include on-

 

19 Additional information, including a detailed breakdown of source categories, can be found on CARB’s website at 

http://www.arb.ca.gov/ei/emissiondata.htm.

20 AP-42 is EPA’s Compilation of Air Pollutant Emission Factors, and has been published since 1972 as the primary 

compilation of EPA's emission factor information. It contains emission factors and process information for more 

than 200 air pollution source categories. A source category is a specific industry sector or group of similar emitting 

sources. The emission factors have been developed and compiled from source test data, material balance studies, and 

engineering estimates.
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road and off-road (also called nonroad) sources. The on-road mobile inventories use 

EMFAC2011 for estimating motor vehicle emissions (2012 PM2.5 Plan, p. 3-1).

21

 

Since EMFAC2011 was released in 2011, CARB has adopted additional regulations to 

control air pollution from mobile sources. For the 2012 PM2.5 Plan, the State adjusted 

EMFAC2011 emissions estimates for the advanced clean cars program, reformulated gasoline

rules, and the Smog Check program to reflect this new information (2012 PM2.5 Plan, p. 3-5). Reentrained paved road dust emissions were calculated using EPA’s AP-42 road dust methodology 

(2012 PM2.5 Plan, Appendix III, p. III-1-13 and 2015 Supplement, Attachment B). SCAG, the 

MPO for the Los Angeles area, provided transportation activity data from the adopted 2012 

Regional Transportation Plan (RTP). CARB’s EMFAC2011 was updated to reflect the most 

recent vehicle population, activity, and emissions data from the California Department of Motor 

Vehicles as well as rules adopted since EMFAC2007 including on-road diesel fleet rules, clean 

car standards, the low carbon fuel standard, and CARB’s Truck and Bus Rule. 

Off-road emissions such as construction, mining, gardening and agricultural equipment 

emissions were calculated using CARB’s 2011 In-Use Off-road Fleet Inventory Model. The offroad equipment population was adjusted due to the 2007-2009 recession, and equipment hours of 

use were adjusted based on reported activity. Equipment load factors were updated using a 2009 

academic study and information provided by engine manufacturers. External adjustments were 

made to CARB’s off-road emissions estimates for locomotives, large-spark ignition engines, and 

nonagricultural internal combustion engines. CARB also calculated emissions from ocean-going 

vessels, commercial harbor craft, locomotives, and cargo handling equipment. Locomotive 

emissions reflect EPA regulations effective in 2008 and adjustments due to reduced economic 

activity. The District estimated aircraft emissions. Future emissions forecasts are based largely 

on growth forecasts (demographic and economic information) from SCAG. See 2012 PM2.5 Plan, 

Appendix III, p. III-1-16 through II-1-23 and III-2-5.

A summary of the Plan’s 2008 base year inventory and the 2014 projected inventory is 

provided in Table A-1 below. For a more detailed discussion of the inventories, see the 2012 

PM2.5 Plan, Appendix III.

3. Evaluation and Proposed Action

The emissions inventories in the 2012 PM2.5 Plan were made available to the public for 

comment and were subject to public hearing at both the District and State levels. See SCAQMD 

Governing Board Resolution 12-19, p. 3 and CARB Resolution 13-3, p. 4.

The inventories in the South Coast PM2.5 SIP are based on the most current and accurate 

information available to the State and District at the time the Plan and its inventories were being

developed in 2011 and 2012, including the latest EPA-approved version of California’s mobile 

source emissions model, EMFAC2011 and the EPA’s most recent AP-42 methodology for paved 

road dust. The inventories comprehensively address all source categories in the South Coast and

were developed consistent with EPA’s inventory guidance. For these reasons, we are proposing 

to approve the 2008 base year emissions inventory in the 2012 PM2.5 Plan as meeting the 

requirements of CAA section 172(c)(3). We also propose to find that the baseline inventories in 

 

21 EMFAC2011 was approved for use in SIPs and conformity on March 6, 2013 (see 78 FR 14533).
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the Plan provide an adequate basis for the reasonably available control measure (RACM), 

reasonable further progress (RFP) and attainment demonstrations in the 2012 PM2.5 Plan.

Table A-1. Summary of Emissions for the South Coast PM2.5 Nonattainment Area

(annual average in tons per day)

2008 2014

Direct PM2.5

Stationary and Area Sources 48 50

On-Road Mobile Sources 19 12

Off-Road Mobile Sources 13 8

Total 80 70

Nitrogen Oxides

Stationary and Area Sources 92 77

On-Road Mobile Sources 462 272

Off-Road Mobile Sources 204 157

Total 758 506

Sulfur Dioxide

Stationary and Area Sources 14 12

On-Road Mobile Sources 2 2

Off-Road Mobile Sources 38 4

Total 54 18

Volatile Organic Compounds

Stationary and Area Sources 257 234

On-Road Mobile Sources 209 117

Off-Road Mobile Sources 127 100

Total 593 451

Ammonia

Stationary and Area Sources 88.7 85.6

On-Road Mobile Sources 19.9 16.5

Off-Road Mobile Sources 0.1 0.1

Total 108.9 102.1

Source: South Coast 2012 PM2.5 Plan, Chapter 3, Tables 3-2A, 3-4A, Appendix III, Table III-1-5, and 2008 

ammonia inventory from Appendix V, Table V-4-2.
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B. Air Quality Modeling

1. Requirements for Air Quality Modeling

CAA section 189(a)(1)(B) requires each State in which a Moderate area is located to 

submit a plan that includes a demonstration either (i) that the plan will provide for attainment by 

the applicable attainment date, or (ii) that attainment by that date is impracticable. 

Air quality modeling is used to establish attainment emissions targets, the combination of 

emissions of PM2.5 and PM2.5 precursors that the area can accommodate and still attain the 

standard, and to assess whether the proposed control strategy will result in attainment of the 

standard. Air quality modeling is performed for a base year and compared to air quality 

monitoring data collected during that year in order to determine model performance. Once the 

performance is determined to be acceptable, future year changes to the emissions inventory are 

simulated with the model to determine the relationship between emissions reductions and 

changes in ambient air quality. To project future design values, the model response to emission 

reductions, in the form of Relative Response Factors (RRFs), is applied to monitored design 

values from the base year.

For demonstrating attainment, the EPA’s recommendations for model input preparation, 

model performance evaluation, use of the model output for the attainment demonstration, and 

modeling documentation are described in Guidance on the Use of Models and Other Analyses for 

Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, EPA454/B-07-002, April 2007 (“Modeling Guidance”), as amended by “Update to the 24 Hour PM2.5

NAAQS Modeled Attainment Test,” Memorandum dated June 28, 2011, from Tyler Fox, Air 

Quality Modeling Group, Office of Air Quality Planning and Standards, EPA to Regional Air 

Program Managers, EPA (“Modeling Guidance Update”).22 As discussed below, the Modeling 

Guidance recommends supplemental air quality analyses. These may be used as part of a Weight 

of Evidence analysis (WOEA), which assesses attainment projections by considering evidence 

other than the main air quality modeling attainment test.

The EPA has not issued modeling guidance specific to impracticability demonstrations 

but believes that a state seeking to make such a demonstration generally should provide air 

quality modeling similar to that required for an attainment demonstration. The main difference is 

that for an impracticability demonstration, the implementation of the SIP control strategy 

(including RACM) does not result in attainment of the standard by the Moderate area attainment 

date. 

 

22 The EPA modeling guidance is available on EPA’s SCRAM web site, web page:

http://www.epa.gov/scram001/guidance_sip.htm; direct links:

http://www.epa.gov/scram001/guidance/guide/final-03-pm-rh-guidance.pdf and

http://www.epa.gov/ttn/scram/guidance/guide/Update_to_the_24- hour_PM25_Modeled_Attainment_Test.pdf.
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For an attainment demonstration, a thorough review of all modeling inputs and 

assumptions (including consistency with EPA guidance) is especially important, since the 

modeling must ultimately support a conclusion that the plan (including its control strategy) will 

provide for timely attainment of the applicable NAAQS. In contrast, for an impracticability 

demonstration, the end point is a reclassification to Serious, which triggers the requirement for a 

new Serious Area attainment plan with a new air quality modeling analysis, and a new control 

strategy. See CAA section 189(b)(1). Thus, the Serious Area planning process would provide an 

opportunity to refine the modeling analysis and/or correct any technical shortcomings in the 

impracticability demonstration. Therefore, the burden of proof will generally be lower for an 

impracticability demonstration compared to an attainment demonstration. 

2. Air Quality Modeling in the 2012 PM2.5 Plan and 2015 Supplement

The 2012 PM2.5 Plan’s attainment demonstration used photochemical modeling with the 

Community Multiscale Air Quality (CMAQ) model, with routinely available meteorological 

and air quality data as input. The Plan discusses air quality modeling in Chapter 5, “Future Air 

Quality” and in detail in Appendix V, Modeling and Attainment Demonstrations.

 

In its letter dated July 28, 2015, the SCAQMD requested that EPA reclassify the South 

Coast Air Basin as Serious nonattainment for the 24-hour PM2.5 NAAQS based on monitoring 

data indicating that attainment is not practicable by the Moderate area attainment date, which is 

December 31, 2015. SCAQMD staff also requested that EPA treat the 2012 PM2.5 Plan and 

2015 Supplement,23 together with the air quality data provided in the letter, as a demonstration 

that the area cannot practicably attain by the Moderate area attainment date. 

The data provided in the July 28, 2015 letter indicates that the Mira Loma air quality 

monitoring station exceeds the 24-hour PM2.5 NAAQS, and preliminary ambient 24-hour PM2.5

measurements at that station for the first quarter of 2015 indicate that the Basin will not attain 

the NAAQS by the moderate area deadline of 2015. The letter attributes the inability to attain 

the NAAQS largely to the lack of rainy days in January and February of 2014 and 2015, which 

experienced 33 percent of the average rainfall. The District also discussed the effect of the 

drought on air quality in the 2015 Supplement.24

Based on the request from the SCAQMD, the modeled attainment demonstration 

provided in the Plan, the 2015 Supplement, and the monitoring data provided in the July 28, 

2015 letter, we are evaluating the State’s submittal as an impracticability demonstration. 

a. Conceptual Description

 

23 Draft Supplement to the 24-Hour PM2.5 State Implementation Plan for the South Coast Air Basin, January 2015.

24 Ibid.
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A conceptual description is a qualitative way of characterizing the nature of an area’s 

nonattainment problem. It can be helpful for developing a modeling protocol and in identifying 

potential stakeholders. It can also influence the choice of air quality model, modeling domain, 

grid cell size, priorities for quality assuring and refining emissions estimates, and the choice of 

initial diagnostic tests to identify potentially effective control strategies. In general, a 

conceptual description is useful for helping a state identify priorities and allocate resources in 

performing a modeled attainment demonstration.

The Modeling Guidance lists 13 elements that should be addressed in the conceptual 

description at pp. 128-130. These are:

1. nature of nonattainment problem (e.g., local versus regional)

2. relative importance of primary and secondary components of PM2.5

3. most prevalent components of measured PM2.5

4. components of measurements versus emissions

5. areas with large gradients

6. indications of limiting precursor for secondary formation

7. monitored violations at locations subject to mesoscale wind patterns (e.g., at a coastline)

differing from the general wind flow

8. recent changes in PM emissions in or near the nonattainment area

9. trends in design values or other air quality indicators that have accompanied emissions 

changes

10. spatial patterns to trends in design values or other air quality indicators

11. past modeling results

12. distinctive meteorological measurements coinciding with exceedances

13. correlations of PM or components with each other and other pollutants
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The Plan’s conceptual model is discussed in 2. Chemical Composition of PM2.5 in the 

South Coast, above. The EPA finds that the conceptual description of the PM2.5 problem in 

provided in the Plan is adequately documented, convincing, and forms an adequate basis for 

the development of the modeling protocol and the air quality analysis work itself.

b. Modeling Protocol

A modeling protocol should detail and formalize the procedures for conducting all phases 

of the modeling study, such as describing the background and objectives for the study, creating 

a schedule and organizational structure for the study, developing the input data, conducting 

model performance evaluations, interpreting modeling results, describing procedures for using 

the model to demonstrate whether proposed strategies are sufficient to attain the NAAQS, and 

producing documentation to be submitted for EPA Regional Office review and approval. The 

Modeling Guidance at pp. 133-134 describes a minimum list of topics to be addressed in the 

modeling protocol:

1. Overview of Modeling/Analysis Project 

a. Management structure

b. Technical committees or other communication procedures to be used 

c. Participating organizations

d. Schedule for completion of attainment demonstration

e. Description of the conceptual model for the nonattainment area (or Class I area(s))

2. Model and Modeling Inputs

f. Rationale for the selection of air quality, meteorological, and emissions models 

g. Modeling domain

h. Horizontal and vertical resolution

i. Specification of initial and boundary conditions 

j. Episode selection

k. Description of meteorological model setup 

l. Development of emissions inputs

m. Geographic area identified for application of the attainment test(s)

n. Methods used to quality-assure emissions, meteorological, and other model inputs

3. Model Performance Evaluation

o. Description of the ambient air quality data base 

p. Description of the evaluation procedures

q. Identification of possible diagnostic testing that could be used to improve model 

performance
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4. Supplemental Analyses

r. Description of the additional analyses to be completed to corroborate the model 

attainment test

s. Outline of the plans for conducting a weight of evidence determination, should it be 

necessary

5. Procedural Requirements

t. Identification of how modeling and other analyses will be archived and documented

u. Identification of specific deliverables to EPA Regional Office

2012 PM2.5 Plan Modeling Protocol25

Table V-2-1 in Appendix V of the 2012 PM2.5 Plan provides a side-by-side comparison of 

the 2012 PM2.5 Plan and 2007 AQMP modeling protocols. The differences between the 

modeling structure focus on a limited number of areas. In general, changes to emissions 

inventories, future year simulations and episode selection evaluation are specific to the base 

year selected and the level of the non-attainment designation. As such, these changes are 

expected to occur as part of each modeling update. The more substantive changes to the 2012 

PM2.5 Plan protocol reflect the use of CMAQ as the primary modeling platform, Weather 

Research and Forecasting as the meteorological modeling platform, and the changes to the size 

of the modeling region, vertical structure and grid size. For this set of modeling analyses, 

CMAQ was selected as the primary dispersion modeling platform. One element in the decision 

to use CMAQ as the primary modeling platform was the fact that it was a publicly-available 

model with numerous computational features and ongoing support in the modeling community. 

When evaluated for possible use in the attainment demonstration, both CMAQ and CAMx 

exhibited similar model performance in predicting 24-hour and annual PM2.5 levels. CMAQ 

however tended to predict monitored ozone concentrations with higher accuracy than CAMx. 

The migration to WRF from MM5 (a mesoscale meteorological model) as the primary 

meteorology modeling tool follows its ongoing use as the mainstay in weather forecasting by 

the National Weather Service, and its continuing development and support by the National 

Oceanic and Atmospheric Administration and U.S. EPA.

The Protocol covers the topics listed above, although some meteorological and air quality

model analyses lack detail. EPA finds the Protocol to be an adequate basis for the Plan’s 

modeling work.

c. Air Quality Model Selection

A model should meet several general criteria for it to be considered in the development of 

an attainment demonstration (Modeling Guidance, p. 136). These general criteria are consistent 

with requirements in 40 CFR § 51.112 and 40 CFR part 51, Appendix W, EPA’s Guideline on 

 

25 2012 PM2.5 Plan, Appendix V, Table V-2-1.
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Air Quality Models. The EPA does not recommend a specific model for use in PM2.5 attainment 

demonstrations. At present, no single model has been extensively tested and shown to be 

clearly superior to its alternatives. Thus, 40 CFR Part 51 Appendix W does not identify a 

preferred model for use in attainment demonstrations for the PM2.5 standards. Based on the 

language in Appendix W, models used for these purposes should meet requirements in the 

Appendix for alternative models.

States should use a non-proprietary model, that is, a model whose source code is 

available for free (or for a reasonable cost) and whose code can be revised by the state in order 

to perform diagnostic analyses and/or to improve the model’s ability to describe observations in 

a credible manner. A model should meet several additional prerequisites before being used to 

support an attainment demonstration. It should be:

1. revised in response to a scientific peer review,

2. appropriate for the specific application on a theoretical basis,

3. used with a data base which is adequate to support its application,

4. shown to have performed well in past ozone or PM modeling applications (or if it is the 

first application, then the state should note why it believes the new model is expected to 

perform sufficiently); and

5. applied consistently with a protocol on methods and procedures. 

In the 2012 PM2.5 Plan, CMAQ was selected as the primary dispersion modeling platform 

based on the CMAQ is publicly-available model with numerous computational features and 

ongoing support in the modeling community. In addition, when evaluated for possible use in the 

attainment demonstration, both CMAQ and CAMx exhibited similar model performance in 

predicting 24-hour and annual PM2.5 levels. CMAQ however tended to predict monitored ozone 

concentrations with higher accuracy than CAMx. 

The EPA finds that the choice of the CMAQ model is adequately justified because the 

rationale provided in the plan meets the 5 requirements listed above. The database, past 

performance, and protocol are discussed in more detail in the plan and below. The EPAsponsored CMAQ is explicitly mentioned in the Modeling Guidance (p. 138) as being a

suitable model. The ability of CMAQ to predict monitored ozone concentrations with 

higher accuracy than CAMx is important because it provides a consistent platform for 

modeling ozone and particulate matter in the South Coast Air Basin. 

d. Episode Selection

The Modeling Guidance recommends one of two possible approaches in modeling for the 

24-hour PM2.5 NAAQS (Modeling Guidance, p. 147):
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1) Model every day for a full year (or multiple years). This is recommended for both 

dispersion modeling of primary PM2.5 components and photochemical modeling of 

secondary and primary components. Many areas that violate the 24-hour PM2.5 NAAQS 

will also violate the annual PM2.5 NAAQS. Therefore, full year modeling may already exist 

or be planned for the annual NAAQS attainment test. Modeling at least a full year will also 

help ensure that a sufficient number of days is included in the relative reduction factor 

(RRF) calculations.

2) Model episodes when high PM2.5 concentrations occur. Similar to modeling for the ozone 

NAAQS, episodes should be selected where PM2.5 concentrations are greater than the 

NAAQS (in this case, the 2006 standard of 35 μg/m3) and are close to the baseline design 

value (the design value in the planning baseline year). Also similar to ozone modeling, data 

analyses can be completed to help select a variety of meteorological episodes which lead to 

high PM2.5 concentrations. In some cases, very limited conditions may lead to high 24-hour 

average PM2.5 concentrations, and in other cases there may be a wide variety of conditions. 

The specific situation in each nonattainment area will determine the number of episodes 

and the time periods which need to be modeled. For example, if exceedance-level PM2.5

concentrations in an area only occur in the winter, then a limited number of winter days can 

be modeled. In other areas, exceedance days may occur in all seasons. We also recommend 

that the modeling “focus on the high end of the distribution of days in each quarter, (e.g. the 

top 10% of PM2.5 days) assuming that the high days are representative of days that violate 

the NAAQS.” (Modeling Guidance Update, p. B-1).

For modeling purposes, “base case” means the historical period that is simulated in the air 

quality modeling, including its meteorology, air quality, and emissions inventory. This period is 

chosen during the episode selection process, based on representative meteorology and air quality, 

and the availability of meteorological, air quality, and emission inventory data for input to the 

modeling. The term “baseline” refers to the starting point for controls are applied; it can be the 

same year as the base case, or it could be a period convenient for planning purposes, e.g. because 

of emission inventory availability. (CARB refers to this as the “reference year”.)

The modeling approach in the plan used the first approach of modeling every day for an 

entire year. CMAQ simulations were conducted for each day in 2008. The simulations included 

8784 consecutive hours from which daily 24-hour average PM2.5 concentrations (0000-2300 

hours) were calculated. The EPA finds the modeling approach of modeling every day in 2008 to 

be adequate.

e. Domain, Domain Size, and Spatial Resolution

i. Domain Size

The principal determinants of model domain size are the nature of the PM2.5 problem and 

the scale of the emissions which impact the nonattainment area. Isolated nonattainment areas that 

are not affected by regional transport of PM and its precursors may be able to use a relatively 

small domain. Some areas of the western U.S. may fall into this category. The modeling domain 

should be designed so that all major upwind source areas that influence the downwind 

nonattainment area are included in the modeling domain. The influence of boundary conditions 

should be minimized to the extent possible (Modeling Guidance, p. 153).
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In domain size and spatial resolution is discussed in Chapter 2 of Appendix V in the 2012 

PM2.5 Plan. The most significant changes to the modeling analyses in South Coast’s 2012 PM2.5

Plan, compared with that defined in the 2007 PM2.5 Plan, occur in the size of the domain, 

reduced grid size and increased vertical structure. First and foremost, both PM2.5 and ozone will 

be simulated together using the same domain specification. The size of the domain has been 

expanded 65 km further west to attempt to incorporate clean boundaries into the modeling 

region, and 40 km to the south to include a greater percentage of northern Mexico emissions.26

See Figure II-B-1.

FIGURE II-B-1. South Coast Modeling Domain27 (Source: South Coast 2012 PM2.5 Plan, 

Appendix V, Figure V-2-2)

ii. Horizontal Resolution

The EPA recommends that states use grid cell sizes as large as 12 kilometers (km) for 

urban scale applications addressing secondary components of particulate matter. However, in 

addressing the primary components of PM2.5, in some cases, cells as small as 4 km (or possibly 

smaller) may be needed. Alternatively, large sources of primary PM can be modeled with a 

 

26 2012 PM2.5 Plan, Appendix V, p. V-2-2.

27 2012 PM2.5 Plan, Appendix V, p. V-2-5.
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dispersion model or a combination of grid and dispersion models. For the regional outer nest 

of the domain, grid cells as large as 36 km may be used (Modeling Guidance, p. 157).

In the South Coast 2012 attainment plan modeling, the grid size has been reduced from 5 

x 5 km to 4 x 4 km. The reduced grid size better enabled the merging of the statewide 

emissions inventory, which is set at the 4 km grid scale based on a Lambert Conformal 

projection.28

Another clear benefit of the modification to the grid size was the smoother coupling of 

the meteorological modeling field development.29 The WRF analyses are initialized from the 

National Centers for Environmental Prediction (NCEP) model output at 36 km grid level, then 

scaled downward based on a 3:1 scaling ratio to a 12 km grid inner-modeling domain covering 

most of California to set the regional meteorological boundary conditions for the 4 km grid 

modeling domain

iii. Vertical Layers

There is no specified minimum number of vertical layers needed in an attainment 

demonstration. The vertical resolution will vary depending on the application. Greater 

resolution allows more precise estimation of mixing heights and avoids unrealistic step 

increases in mixing; alignment with the layers in the meteorological model can affect accuracy; 

the lowest layer should generally be no more than 50 meters thick; resolution above the 

boundary layer can generally be coarser. Recent applications of one atmosphere models (with 

model tops at 100 millibars (mb)) have used anywhere from 12 to 21 vertical layers with 8-15 

layers approximately within the boundary layer (below 2500 m) and 4-6 layers above the 

Planetary Boundary Layer (PBL) (Modeling Guidance p. 159). 

Table II-B-1 below indicates the vertical layers used in the 2012 PM2.5 Plan.

Table II-B-1. 2012 PM2. 5 Plan Modeling Vertical Layer Structure30

WRF

Layer

Index

Mid-Point

Height (m)

CMAQ

Layer

Index

Mid-Point

Height (m)

 

28 2012 PM2. 5 Plan, Appendix V, p. V -2-5

29 2012 PM2.5 Plan, Appendix V, p. V-2- 6

30 2012 PM2.5 Plan, Appendix V, p. V-2-7, Table V-2-3.
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30 19268 15 19268

29 17355

28 15755

27 14337 14 14337

26 13028

25 11791

24 10598

23 9429

22 8271 13 8271

21 7118

20 5994

19 4992

18 4153

17 3449 12 3449

16 2858

15 2361

14 1944 11 1944

13 1595

12 1302

11 1057

10 851 10 851

9 681 9 681

8 538 8 538

7 418 7 418

6 318 6 318

5 235 5 235

4 165 4 165

3 107 3 107

2 59 2 59

1 18 1 18

The layer structure in the vertical domain for the modeling region has been increased to 

15 layers from the previous the eight layers used in the CAMx PM2.5 attainment demonstration 

simulations. Table V-2-3 in Appendix V of the 2012 PM2.5 Plan provides a definition of the 15 

layer vertical structure used in the air quality simulations. Also listed is the corresponding 30 

layer structure of the WRF modeling vertical domain that matches the CMAQ domain at the 

top height. Table II-B-2 indicates the coordinates of the modeling domain used in the 2012 

PM2.5 Plan.

TABLE II-B-2.31 Final 2012 PM2.5 Plan Modeling Domain

 

31 2012 PM2.5 Plan, Appendix V, p. V-2-5, Table V-2-2.
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The EPA finds the domain to be adequate, and consistent with EPA Modeling Guidance. 

The inner domain meets all of the Modeling Guidance domain characteristics listed above for 

spatial resolution and layer thickness.

f. Initial and Boundary Conditions

If there is no larger regional model application available, then we recommend that 

background boundary conditions be used to specify initial and boundary concentrations for the 

attainment demonstration modeling. However, concentration fields derived from a larger domain 

regional or global chemistry model (i.e., the nesting approach) is considered more credible than 

the assumption of static concentrations, since the pollutant concentration fields reflect simulated 

atmospheric chemical and physical processes driven by assimilated meteorological observations. 

Therefore, the EPA recommends using boundary conditions derived from a regional or global 

scale model, whenever possible. We also recommend using a ramp-up period by beginning a 

simulation prior to the period of interest to diminish the importance of initial conditions. The 

recommended ramp-up period is at least 5-10 days for PM2.5. Diagnostic testing which indicates 

a large impact on the model results from initial or boundary conditions may indicate that the 

domain is not large enough or the ramp-up period is too short. In either case, it should generally 

be assumed that initial and boundary conditions do not change in the future. The use of altered 

initial or boundary conditions in the future year should be documented and justified (Guidance, 

p. 153).

As discussed in Chapter 4 of Appendix V of the 2012 PM2.5 Plan, the initial concept for 

establishing boundary conditions for the regional modeling analyses focused on using global 

chemical simulation model output to define key species concentrations at the edge of the 

modeling domain. The Model for Ozone and Related Chemical Tracers (MOZART) was selected 

to provide the characterization. However, after evaluation, it was discontinued in favor of using a 

U.S. EPA “clean boundary32 approach that has been incorporated in previous attainment 

demonstrations.33 The boundary conditions are listed in Table II-B-3. Boundary Profile 

Concentrations, below.

 

32 Guideline For Regulatory Application of the Urban Airshed Model, USEPA, 1991

33 2012 PM2.5 Plan, Appendix V, p. V-4-10.

Projection

Lambert Conformal

Latitude of Origin Projection 37 N

Modeling Domain 156 x 102 x 18

Vertical Layer Structure Variable up to 50 hPa (mb)

Central Meridian 120.5 W

Standard Parallel 30 N, 60 N

Horizontal Grid Size 4 km x 4 km

Southwest Origin (-84 km, -552km)
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This decision was discussed in greater detail in Chapters 1 and 3 of Appendix V of the 

2012 PM2.5 Plan. Lateral and vertical boundary conditions were designated using an “U.S. EPA 

clean boundary profile.” The analysis tested the use of MOZART (Model of Ozone and Related 

Chemical Tracers, [Horowitz, L.W., et. Al., 2003]), global chemical simulation model output to 

specify the lateral and vertical boundary conditions used for the CMAQ modeling. Grid scale 

matching using MOZART at 60 x 60 km compared with the CMAQ 4 x 4 km grid introduced 

significant uncertainty to the boundary concentration profiles and subsequent regional 

simulations. Background simulations including the MOZART boundary specification while 

excluding anthropogenic emissions depicted large variations in background concentrations. 

Discussions conducted at the Scientific Technical Modeling Peer Review Advisory Group 

suggested that a finer scale MOZART output might dampen the variable impact to the regional 

air quality simulations. While this recommendation was acknowledged, the resources and time 

requirements needed to generate new global modeling output were prohibitive. The final 

simulations reverted to the more stable clean boundary assumption.

Table II-B-3. Boundary Profile Concentrations (ppb)34

SAPRC99 Species (ppb) SAPRC99 Species (ppb)

HCHO 0.930 ARO1 0.210

CCHO 0.530 ARO2 0.070

RCHO 0.250 OLE1 0.180

0.020 OLE2 e-13

MEOH 0.100

ETOH 0.050 O3 40.0

ETHE 0.180 CO 200.

ALK1 2.500

ALK2 2.300 NO 0.100

ALK3 0.930 NO2 (surf) 2.000

ALK4 e-13 NO2 (aloft) 0.100

ALK5 e-13

The EPA finds the boundary conditions procedures adequate for this demonstration that 

attainment by the Moderate area attainment date is impracticable, although the basis for this 

selection was sparsely documented. EPA expects more complete documentation of boundary 

condition evaluation and selection for an attainment demonstration, given that the resource and 

time constraints needed to generate new global modeling output should be less.

Meteorological Model

i. Meteorological Model Selection

 

34 2012 PM2.5 Plan, Appendix V, p. V-4-12.
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A description of the methods used to generate the meteorological fields should be 

included in the modeling protocol. In cases in which standard meteorological modeling (e.g. 

MM5, RAMS (Regional Atmospheric Modeling System) or WRF in a retrospective analysis 

model is not used, the EPA recommends that a detailed description of the technique that will be 

used to generate the three-dimensional meteorological fields be shared with the appropriate 

EPA Regional Office prior to conducting the air quality modeling analysis (Modeling 

Guidance, p. 161).

The meteorological model selection is discussed in Chapter 3 of Appendix V of the 2012 

PM2.5 Plan. The Final 2012 AQMP regional modeling relied on WRF model applications for 

2008. The migration to WRF was based on two factors: First, WRF is the state-of-the-art 

meteorological forecast model used by the NWS and scientific community. It is under continual 

review and benefits from updates to critical modeling parameters. In moving to a new 

meteorological model, several analyses were conducted to compare WRF and MM5 

meteorological fields to confirm the portability of the CMAQ modeling system to the new 

model.

The Plan describes the meteorological model, the comparison between WFR and MM5, 

the selection of the vertical stability parameterization, land use, and initial and boundary 

conditions used in the 24-hour PM2.5 attainment demonstration. Based on the model 

performance evaluation presented in the plan, the EPA finds that the meteorological model 

choice is adequately justified.

ii. Meteorological Model Domain

Most attainment demonstrations will cover large areas and use nested grids. The 

outermost grid should capture all upwind areas that can reasonably be expected to influence 

local concentrations of PM2.5. In terms of selecting an appropriate meteorological modeling 

domain, a state should extend the grid 3 to 6 cells beyond the domains of each air quality 

modeling grid to avoid boundary effects. For example, if 4 km grid cells are to be used in the 

fine portion of a nested regional air quality model, then the meteorological fields at this detail 

would need to extend 12-24 km beyond the bounds of the 4 km grid used for air quality 

predictions. In terms of grid resolution, the EPA recommends that the dynamic meteorological 

models use the same grid resolution as desired for the air quality model applications. In some 

cases, however, this may not be feasible. One possible reason for modeling with meteorology 

using a different grid resolution is in the case of unacceptable model performance from the 

meteorological model at the desired grid resolution. In other instances, the need for finer 

resolution may be emissions-driven more than meteorologically-driven and the costs do not 

warrant the generation of additional resolution in the meteorological data. In these specific 

situations, it is recommended that the air quality model application use available results from 

meteorological models on the next coarser scale (i.e., 36 km for a desired 12 km estimate, 12 

km for a desired 4 km estimate). The coarse grid meteorological fields can be mapped to the 

more finely resolved air quality modeling domain.
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The Meteorological Model Domain is discussed in Chapter 3 of the plan. WRF 

simulations were conducted with three nested domains of which grid resolutions were 36, 12 and 

4 km. The innermost domain has 163 by 115 grid points in abscissa and ordinate, respectively, 

which spans 652 km by 460 km in east-west and north-south directions, respectively. 

Geographically, the domain encompasses the greater Los Angeles and suburban areas, its 

surrounding mountains, and seas off the coast of the Basin as shown in Figure II-B-2, below. The 

relative locations and sizes of the three nested grids are shown as well. 

Figure II-B-2. Three nested modeling domains employed in the WRF simulations35

iii. Physics Options

Most meteorological models have a suite of physics options that allows users to select 

how a given feature will be simulated. For example, there may be several options for specifying 

the planetary boundary layer scheme or the cumulus parameterization. In many situations, the 

 

352012 PM2.5 Plan, Appendix V. p. V-3-2.
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optimal configuration cannot be determined without performing an initial series of sensitivity 

tests which consider various combinations of physics options over specific time periods and 

regions. While these tests may not ultimately conclude that any one configuration is clearly 

superior at all times and in all areas, it is recommended that these sensitivity tests be completed, 

as they should lead to a modeling analysis that is best-suited for the domain and period being 

simulated. Typically, the model configuration which yields predictions that provide the best 

statistical match with observed data over the most cases (episodes, regions, etc.) is the one that 

should be chosen, although other more qualitative information can also be considered in 

choosing a model configuration. Additionally, model configurations should be designed to 

account for the pollutants and time periods that are of most interest. As an example, a 

wintertime PM simulation in the Midwest (with high measured nitrate concentrations) may 

need a meteorological model configuration that employs a land-surface model that properly 

handles snow-covered fields and their effects on boundary layer humidities and temperatures.

The physics option selection process and sensitivity tests are discussed in Chapter 3 of 

the plan. YSU was chosen as the planetary boundary layer (PBL) scheme for the current 

attainment demonstration. Three land surface models (LSM) were considered for WRF 

modeling: the five-layer thermal diffusion scheme, and the Noah and Pleim-Xiu schemes. By 

comparison to the effect of using different PBL schemes, modifications to the LSM caused 

significant responses in near surface variables. First, wind was generally overpredicted during 

the daytime and under-predicted during the nighttime. The difference between the two schemes 

was signified during the nocturnal stable period, which occurred in temperature predictions as 

well. As for wind, the Noah showed a better agreement with observations, while temperature 

prediction was worse. The 5-layer slab model agreed better with the measurements, as evident 

in the warmer surface temperature fields and the convective boundary layer predicted to be 

deeper in the Noah scheme

The EPA finds that the meteorological domain and model physics options are acceptable

and consistent with EPA Modeling Guidance.

h. Meteorological Model Performance

The EPA recommends that states devote appropriate effort to the process of evaluating 

the meteorological inputs to the air quality model, as we believe good meteorological model 

performance will yield more confidence in the predictions from the air quality model. This 

evaluation should determine if the meteorological model output fields represent a reasonable 

approximation of the actual meteorology that occurred during the modeling period. This can be 

done via an operational evaluation (i.e., quantitative, statistical, and graphical comparisons). A 

second objective of the evaluation should be to identify and quantify the existing biases and 

errors in the meteorological predictions in order to allow for a downstream assessment of how 

the air quality modeling results are affected by issues associated with the meteorological data. 

This evaluation can be done via a more phenomenological assessment (i.e., generally 

qualitative comparisons of observed features versus their depiction in the model data) 

(Modeling Guidance, p. 163).
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Operational Evaluation (Modeling Guidance, p. 163): The operational evaluation results 

should focus on the values and distributions of specific meteorological parameters as paired 

with and compared to observed data. The observation-model matching should be paired as 

closely as possible in space and time. Typical statistical comparisons of the key meteorological 

parameters will include: comparisons of the means, mean bias, mean normalized bias, mean 

absolute error, mean absolute normalized error, root mean square error (systematic and 

unsystematic), and an index of agreement. For modeling exercises over large domains and 

entire seasons or years, we recommend that the operational evaluation be broken down into 

individual segments such as geographic sub-regions and/or months/seasons to allow for a more 

comprehensive assessment of the meteorological strengths and weaknesses.

Phenomenological Evaluation (Modeling Guidance, p. 167): Within the conceptual description 

of a particular modeling exercise, EPA recommends that a state identify and qualitatively rank 

in importance the specific meteorological parameters that influence air quality. When 

evaluating meteorological models or any other source of meteorological data, the focus of the 

phenomenological evaluation should be on those specific meteorological phenomena that are 

thought to strongly affect air pollution formation and transport within the scope of a specific 

analysis. It is expected that this event-oriented evaluation will need to summarize model 

performance in terms of statistical metrics such as probability of detection and false alarm rate. 

As an example of a potential phenomenological analysis, many regional air quality modeling 

exercises attempt to assess the effects of transport of emissions from one area to a downwind 

area with an intent to establish source-receptor relationships. For these types of modeling 

analyses, accurate transport wind trajectories are needed to properly establish these sourcereceptor linkages. In this type of model application, a useful event-based meteorological 

evaluation would be to compare model-derived trajectories versus those based on ambient data 

to determine what error distance can be associated with the model fields.

The statistical performance evaluation is discussed in detail in Chapter 3 and Attachment 

1: WRF METSTAT Model Graphical Performance Statistics of Appendix V of the 2012 PM2.5

Plan. A set of statistical variables were generated using the METSTAT software to evaluate the 

WRF modeling performance quantitatively. The list of statistical parameters included bias, gross 

error and root mean square error and the Index of Agreement (IOA). The IOA was calculated 

following the approach of Willmont (1981). This metric condenses all the differences between 

model estimates and observations within a given analysis region and for a given time period 

(hourly and daily) into one statistical quantity. 

Overall, the daily WRF simulation for 2008 provided representative meteorological

fields that well characterized the observed conditions. The EPA finds the meteorological model

performance is adequate.

i. Emissions Inventory

Air quality modeling requires emissions inputs for base case, baseline, and future 

modeling years. Preparation of emissions data for air quality models for the base and future years 

requires several steps. First, a state needs to compile base-year inventories for its modeling 
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region (e.g., the state and tribal areas in the modeling grid). For PM model applications, 

emissions inventories should include emissions of anthropogenic and biogenic VOC (speciated), 

NOx, carbon monoxide, SO2, NH3, PM2.5 (speciated), and PM coarse (PMC). Second, modelers 

must collect ancillary data associated with the inventories, which describes the spatial, temporal, 

and chemical speciation information about the emissions inventory. Third, modelers use the 

ancillary data for emissions modeling. Emissions models spatially, temporally, chemically, and 

vertically allocate emissions inventories to the resolution needed by the air quality model. 

Fourth, modelers must collect data on growth rates and existing control programs for use in 

projecting the base year emissions inventories to the future year, and then use an emissions 

model to prepare that future year inventory data for input to the air quality model. Fifth, 

emissions inventories that reflect the emissions reductions needed for attainment will have to be 

prepared for air quality modeling.

Chapter 3 of Appendix V of the 2012 PM2.5 Plan provides the baseline and controlled 

modeling emissions inventories used for modeling and alternative analyses. The CMAQ 

simulations were based on the annual average inventory, with adjustments made for weekly and 

daily temperature variations. A brief characterization of the annual day emissions used for the 

modeling analysis follows is discussed. An extensive discussion of the overall emissions 

inventory is summarized in Appendix III of the Final 2012 AQMP. The EPA finds the modeling

emissions inventory preparation procedures were adequate.

j. Air Quality Model Performance

PM2.5 consists of many components and is typically measured with a 24-hour averaging 

time. The individual components of PM2.5 should be evaluated individually. In fact, it is more 

important to evaluate the components of PM2.5 than to evaluate total PM2.5 itself. Apparent good 

performance for total PM2.5 does not indicate whether modeled PM2.5 is predicted for the right 

reasons (the proper mix of components). If performance of the major components is good, then 

performance for total PM2.5 should also be good. The EPA recommends calculating statistics for 

components of PM2.5 and PM2.5 precursors. Useful metrics include mean fractional bias and 

mean fractional error, normalized mean bias, and normalized mean error. Formulas for 

estimating these metrics are given in the Modeling Guidance (Modeling Guidance, p. 203-204). 

Other statistics such as mean bias, mean error, root mean square error, correlation coefficients, 

etc. should also be calculated to the extent that they provide meaningful information.

Since modeling for the PM2.5 NAAQS will likely require modeling different times of 

year, season-specific statistics and graphic displays are helpful for evaluating and diagnosing 

model performance. Statistics and graphics can be averaged for various time scales. For example, 

statistical metrics and scatter plots can show daily averaged ambient modeled pairs, monthly 

averaged pairs, quarterly (or seasonal averaged) pairs, or annual average pairs. Each of these 

averaging times can provide useful information. The EPA recommends a range of different 

averaging times for annual or seasonal modeling. At a minimum, a state should examine daily 

averaged pairs and seasonal (or quarterly) averaged pairs. Because statistics and plots tend to 

look “better” as the averaging time increases from daily to monthly to quarterly to annual, daily 
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pairs should always be examined to ensure a detailed look at model performance on the time 

scale of the Federal Reference Method (FRM) and Speciation Trends Network (STN) 

measurements (24-hour average).

Soccer plots provide a convenient way to display a summary of model performance 

(including bias and error at the same time). Bugle plots36 have variable bias and error goals, 

based on ambient concentrations. This allows for a higher percentage error and bias at very low 

concentrations. This recognizes the fact that models often have difficulty in accurately predicting 

near background concentrations and may be useful to prioritize examination of model 

performance within and near the non-attainment area(s) of interest. Additionally, priority may be 

placed on examination of the days that are potentially used in the attainment test (e.g., the days 

with ambient concentrations above 35 μg/m3for the 2006 24-hour PM2.5 NAAQS.)

The performance evaluation is presented in Chapter 5 of Appendix V of the 2012 PM2.5 Plan.

The CMAQ 2008 base-year 24-hour PM2.5 Component Species performance statistics are 

presented. The analysis includes predicted concentrations and observations for the six component 

species and total mass at the 6 SASS sites, as well as estimates of bias and error for each 

component at each monitoring site. 

The three western Basin Los Angeles County sites analyzed had a total mass absolute 

prediction accuracy that exceeded 25 percent of the observed average. Prediction accuracy 

estimated for the three remaining sites measured approximately 20 percent or lower. In general, 

normalized bias was lowest for nitrate and highest for sulfate. The only systematic bias was 

evident for EC, whereby the tendency was to under predict observations.

One element observed during the 2008 simulation evaluation was that the eastern portion 

of the Basin predicted low concentrations of secondary aerosols when high wind “Santa Ana” 

conditions were observed. This generalized wind condition also impacted the western portion of 

the Basin but to a lesser extent. The days impacted by the high winds were clustered in the first 

and fourth quarters. 

The plan also discusses the base-year model performance stress test evaluation. EPA’s 

modeling guidance as well as the draft modeling protocol outline a series of basic stress tests that 

can be applied to the base case simulation to determine the level of sensitivity of model 

performance to key parameters defining the simulations. These stress tests include modifying the 

boundary conditions, and introducing gross changes in the meteorological and emissions 

profiles. The goal for these analyses is to see if any one factor is unduly biasing model 

performance and in doing so jeopardizing the validity of the analysis. The plan presents the suite 

of performance stress tests applied to the CMAQ (and CAMx) PM2.5 simulations. The results of 

the tests are not presented, be the summary of the outcome of the CMAQ testing indicated that 

 

36 Fractional error and bias tend to be large at small concentrations, since then the uncertainty can be nearly as big as

the concentration. Since fractional error varies relatively slowly with concentration, but then grows larger at low

concentrations, the shape of the plot resembles a long tube with a flared end at low concentrations, reminiscent of a 

bugle.
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the model responded in an expected manner to the changes in simulation parameters and 

emissions profiles outlined in the stress tests.

The EPA finds the air quality model performance is adequate. More complete 

documentation of the stress test evaluation results would have been desirable.

k. Modeled Attainment Test

A modeled attainment test is an exercise in which an air quality model is used to simulate 

current and future air quality. If future estimates of PM2.5 concentrations are less than the 

NAAQS, then this element of the attainment test is satisfied. The EPA’s recommended test is 

one in which model estimates are used in a relative rather than absolute sense. That is, we take 

the ratio of the model’s future to current (baseline) predictions at monitors. We call these ratios 

relative response factors (RRF). Future PM2.5 concentrations are estimated at existing 

monitoring sites by multiplying a modeled relative response factor at locations near each 

monitor by the observation-based, monitor-specific, baseline design value. The resulting 

predicted future concentrations are compared to the NAAQS.

The PM2.5 attainment test reflects the fact that PM2.5 is a mixture. In the test, ambient 

PM2.5 is divided into major species components, so EPA’s test is called the Speciated Modeled

Attainment Test (SMAT). There is mass associated with sulfates, nitrates, ammonium, organic 

carbon, elemental carbon, particle-bound water, other primary inorganic particulate matter, and 

passively collected mass. Note that FRM monitors do not measure the same components and do 

not retain all of the PM2.5 that is measured by routine speciation samplers, and therefore cannot 

be directly compared to speciation measurements from the STN. By design, the FRM mass 

measurement does not retain all ammonium nitrate and other semi-volatile materials (negative 

sampling artifacts) and includes particle-bound water associated with sulfates, nitrates and 

other hygroscopic species (positive sampling artifacts). This results in concentrations (and 

percent contributions to PM2.5 mass) which may be different than the ambient levels of some 

PM2.5 chemical constituents. Therefore, we recommend a SMAT technique which uses an FRM 

mass construction methodology which results in reduced nitrates (relative to the amount 

measured by routine speciation networks), higher mass associated with sulfates and nitrates 

(reflecting water included in gravimetric FRM measurements) and a measure of organic 

carbonaceous mass which is derived from the difference between measured PM2.5 and its nonorganic carbon components. This approach is sometimes called SANDWICH, for sulfate, 

adjusted nitrate, derived water, inferred carbonaceous material balance approach (Modeling 

Guidance, p. 47).

The modeled attainment test in the plan was based on the following steps:

1. A separate RRF is calculated for each monitoring site for each of the PM2.5 components 

(except passive mass, represented by a field blank concentration of 0.3-0.5 μg/m3). 

2. Future PM2.5 design values are estimated at existing monitoring sites by multiplying modeled 

RRFs near each monitor by the observed component-specific design value. This latter quantity 
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is estimated using measured site-specific design values for PM2.5 in concert with available 

measured composition data.

3. Future site-specific PM2.5 design values at a site are estimated by adding the future year 

values of the seven PM2.5 components. If all future site-specific PM2.5 design values are less 

than or equal to the concentration specified in the NAAQS, the test is passed (Modeling 

Guidance, pp. 15-16). 

The future year modeling for the 2012 PM2.5 Plan is discussed in Chapter 5 of Appendix 

V. A set of RRFs were generated for each future year simulation. RRFs were generated for the 

ammonium ion (NH4), nitrate ion (NO3), sulfate ion (SO4), organic carbon (OC), elemental 

carbon (EC) and a combined grouping of crustal, sea salts and metals (Others). A total of 24 

RRFs were generated for each future year simulation. Water vapor was determined using U.S. 

EPA’s regression model approximation of the AIM model based on simulated concentrations of 

the ammonium, nitrate and sulfate ions.

Future year concentrations of the six component species were calculated by applying the 

model generated quarterly RRFs to the speciated 24-hour PM2.5 (FRM) data sorted by quarter 

for each of the five years used in the design value calculation. The 32 days in each year were 

then re-ranked to establish a new 98th percentile concentration. The resulting future year 98th 

percentile concentrations for the 5-years were subjected to weighted averaging for the attainment 

demonstration. Future year PM2.5 24-hour average design values are presented for 2014, and 

2019 to (1) demonstrate the future baseline concentrations if no further controls are 

implemented; (2) identify the amount of air quality improvement needed to advance the 

attainment date to 2014; and (3) confirm the attainment demonstration with implementation of 

the proposed PM2.5 control strategy. The results are presented in Table II-B-4, CMAQ 2014 24-

hour PM2.5 Controlled Predictions (in μg/m3).

TableII-B-4: CMAQ 2014 24-hour PM2.5 Controlled Predictions (μg/m3)

Locations NH4 NO3 SO4 OC EC Others Water Blank Mass

Anaheim 2.89 7.52 2.20 6.61 2.79 3.53 1.45 0.50 27.49

S. Long Beach 2.96 6.86 2.52 5.55 3.06 1.98 1.37 0.50 24.79

Fontana 4.71 11.80 1.86 5.26 3.27 3.45 2.10 0.50 32.94

N. Long Beach 3.76 8.24 3.39 5.79 2.80 2.08 1.70 0.50 28.27

Los Angeles 4.56 10.49 3.32 5.62 2.68 2.64 2.00 0.50 31.80

Mira Loma 4.92 12.84 1.96 5.61 2.88 3.24 2.33 0.50 34.28

Rubidoux 4.71 12.95 1.95 4.73 2.47 2.77 2.44 0.50 32.51

Source: 2012 Plan, Appendix V., page V-5-40
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The EPA finds the Plan’s attainment test procedure to be adequate for the 

impracticability demonstration.

l. Unmonitored Area Analysis

In addition to a modeled attainment demonstration, the EPA recommends use of an 

unmonitored area analysis (UAA). This type of analysis is intended to ensure that a control 

strategy leads to reductions in ozone or PM2.5 at other locations which could have base year and 

future baseline (projection year) design values exceeding the NAAQS if a monitor were 

deployed there.

The UAA should identify areas where future year design values are predicted to be 

greater than the NAAQS. The UAA for a particular nonattainment area is intended to address 

potential problems within or near that nonattainment area. The analysis should include, at a 

minimum, all nonattainment counties and counties surrounding the nonattainment area (located 

within the state). In order to examine unmonitored areas in all portions of the domain, the EPA 

recommends that a state use interpolated spatial fields of ambient data combined with gridded 

modeled outputs (Modeling Guidance, p. 29).

Gradient adjusted spatial fields are first created for the base year. Future year estimates 

can then be created by applying gridded RRFs to the gradient adjusted spatial fields. The basic 

steps are as follows (Modeling Guidance, p. 30):

1. Interpolate base year ambient data to create a set of spatial fields.

2. Adjust the spatial fields using gridded model output gradients (base year values).

3. Apply gridded model RRFs to the gradient adjusted spatial fields.

4. Determine if any unmonitored areas are predicted to exceed the NAAQS in the future.

As described earlier in this chapter, speciation profiles from Speciation Air Sampling 

System (SASS) sites in adjacent or collocated grid cells are used in the formal attainment 

demonstration for Mira Loma and also South Long Beach.37 With interpolation of the SASS 

speciation profiles, attainment demonstrations can be directly conducted for the remaining grid 

cells where FRM mass data has been collected over the 5-year period (2006-2010). To date, no 

specific test has been proposed by the EPA to address testing attainment at grid cells where no 

speciated and/or FRM data is available. The form of the revised attainment test adds 

 

37 2012 PM2.5 Plan, Appendix V, p. V-5-44.
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complication in that it requires assessing the impacts for 32 days per year, for five years, at 

each unmonitored grid cell.

The methodology used to assess the unmonitored grid cell impact follows. First, a subset 

of the full modeling domain covering the Basin was selected for the analysis. The western most 

grid column (70) was aligned with coastal Los Angeles. The eastern most column (100) 

touched Banning Pass, the southern boundary was located in row 45 in northern San Diego, and 

the northern most row (65) corresponding to the northern portion of the San Fernando Valley 

extending across the San Gabriel and San Bernardino Mountains. A review of the 24-hour 

PM2.5 FRM data and design values from sites located outside of this inner domain indicated 

that concentrations were significantly lower than in those observed in the primary nonattainment portion of the Basin. 

The next task included spatial interpolation (1/r) of the six SASS speciation splits to 

define the split profiles for each grid cell. The split percentages were then multiplied by the 

simulation-derived RRFs, for each of the four seasons. FRM data, based on every third day 

sampling from 21 Basin monitoring sites which were extracted from the EPA’s Air Quality 

System database for each year of the 5-year period. The highest 8 concentrations sampled in 

each quarter were selected to generate a data set that included 160 days. The data for each day 

were then interpolated throughout the inner-domain using an inverse distance weighted scheme 

(1/r) to develop a matrix of grid-specific 24-hour PM2.5 concentrations for all 160 days. Note 

that extraction of data on a frequency of every third day was selected so that there was 

consistency in the numbers of FRM data samples used in the analysis. In general, the number of 

valid yearly samples using the third day extraction was between 100-150 days, and thus 

allowed the analysis to focus on the projected 3rd highest value (of the 32 days evaluated) in 

each year as the 98th percentile value. 

The interpolated FRM data were then multiplied by the seasonally sorted, RRFinterpolated species fractions to project the future year 24-hour PM2.5 distribution for each of 

the five years. The attainment calculation then tested the weighted 5-year average 98th 

percentile concentration at each grid. Table V-5-23, shown below, provides a summary of the 

unmonitored area analysis. Listed are the top 15 projected grid cell center concentrations for 

the 2014 controlled scenario and the respective 2008 interpolated center grid concentration. 

The second set of columns provides the list of grid cells with the maximum projected 2014 

controlled 24-hour PM2.5 design value modeled as if every grid in the Basin had Mira Loma’s 

species profile. This calculation was conducted to test the distance-weighted interpolation 

hypothesis and the impacts of varying species profiles and RRFs.

The interpolated 2008 grid center design values and 2014 projected determined from the 

unmonitored area analysis lined up closely with the station design values. The 2014 controlled 

maximum projected 24-hour PM2.5 design value of 31.2 μg/m3 occurred at the center of the 

Mira Loma grid cell (89,58). Since no cell in the modeling domain was projected to have a 

2014 controlled design value above that of cell (89,58), the Basin passes the unmonitored area 

portion of the 24-hour PM2.5 attainment demonstration.
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This analysis demonstrates that the relative response to the control program is more 

effective in the Eastern Basin while portions of the western Basin do not exhibit the equivalent 

response to the implementation of the proposed control strategy.

The EPA finds that the UAA is adequate for purposes of the impracticability

demonstration.

m. Weight of Evidence

States should perform complementary analyses of air quality, emissions and 

meteorological data and consider modeling outputs other than the results of the attainment test. 

Such analyses are instrumental in guiding an air quality modeling application. The results of 

corroboratory analyses may sometimes be used in a weight of evidence determination to show 

that attainment is likely despite modeled results, which may be inconclusive. The further the 

attainment test is from being passed (i.e., the higher the modeled pollutant levels are above 

attainment levels), the more compelling contrary evidence produced by corroboratory analyses 

must be to draw a conclusion different from that implied by the modeled attainment test results. 

(Modeling Guidance, p. 17). Supplemental analyses could include additional modeling using 

alternative models and inputs, modeling apportionment and process analysis tools, alternative 

metrics (such as change in the number of grid cells above the NAAQS), trends in ambient air 

quality, trends in emissions, receptor modeling, and indicator species approaches.

The weight of evidence in the plan is based on trends in emissions. The plan concluded 

that while the projected NOx and direct PM2.5 emissions trends decrease at a reduced rate 

between 2012 and 2019, it is clearly evident that the overall significant reductions will continue 

to result in lower nitrate and direct particulate contributions to 24-hour PM2.5 design values.

The EPA finds that the weight of evidence presented in the plan is adequate for purposes 

of the impracticability demonstration. 

3. Data in the July 28, 2015, Request to U.S. EPA to Reclassify the South Coast Air Basin as 

Serious Nonattainment for the 24-hour PM2.5 National Ambient Air Quality Standard (NAAQS)

In a letter dated July 28, 2015, the SCAQMD requested that the EPA reclassify the South 

Coast Air Basin as a Serious nonattainment area for the 24-hour PM2.5 NAAQS based on 

monitoring data indicating attainment is not practicable by the December 31, 2015 attainment 

date. SCAQMD staff also requested that the EPA approve any applicable elements in the 

Moderate SIP submitted previously and consider the data submitted herewith in conjunction with 

the 2012 and 2015 submittals as a demonstration that the area cannot practicably attain by the 

Moderate area date. 
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Air quality measured at the Mira Loma air quality monitoring station exceeds the 24-hour 

PM2.5 NAAQS, and preliminary ambient 24-hour PM2.5 measurements at that station for the 

first quarter of 2015 indicate that the Basin will not attain the NAAQS by the moderate area 

statutory deadline of 2015. The letter attributes the inability to attain the NAAQS largely to the 

lack of rainy days in January and February of 2014 and 2015, which experienced 33 percent of 

average rainfall. The effect of the drought on air quality was also discussed in the Draft 

Supplement to the 24-Hour PM2.5 State Implementation Plan for the South Coast Air Basin.38

4. Weight of Evidence in the Supplement to the 24-Hour PM2.5 State Implementation Plan for 

the South Coast Air Basin

The Supplement provided an update to the analysis and a discussion of the drought’s 

impact on air quality.39 The west coast of the U.S. has experienced a severe drought for the past 

several years with 2013 annual rainfall total measured at Downtown Los Angeles of 3.6 inches, 

far below the 14.9 inch long term average. 

 Rainfall events of 0.01 inches of rain or more were 25 percent lower than the average of 

28 days typically occurring during the 1st and 4th quarters of the year. 

 Under the drought conditions, Mira Loma 24-hour PM2.5 98th percentile concentrations 

experienced a reversal in the long-term trend of declining concentrations rising from a 

2012 value of 35.1 μg/m3 to 37.5 in 2013. 

 Based on a conservative analysis of the impact of rain fall events on the 98th percentile 

concentration, the drought accounted for roughly 1.6 μg/m3 additional mass to the 

observed 98th percentile concentration.40

A discussion of the rain event-concentration impact was provided in Attachment B to the 

2015 Supplement, and is discussed below. Based on this analysis, the SCAQMD anticipated 

that the 2014 Basin 24-hour PM2.5 design value (measured at Mira Loma) based on the 2012-

2014 3-year average of the 98th percentile concentration will exceed 35.4 μg/m3due to the 

observed continuation of the drought.

Background

The 2014 attainment demonstration was based on simulated RRFs applied to a weighted 

2008 design value. The 5-year weighted PM2.5 design value incorporated 98th percentile 

concentrations from 2006 through 2010. The five-year period used for the design calculation 

covered a meteorological period, when assessed for the frequency of rainfall events and 

precipitation accumulations, was essentially average compared to the long term (50+ year) 

 

38 Draft Supplement to the 24-Hour PM2.5 State Implementation Plan for the South Coast Air Basin, January 2015

39 2015 Supplement, Attachment A, p. A-2.

40 Ibid. (?)
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statistics. As a consequence, the 2014 projected 24-hour PM2.5 design value for Mira Loma 

assumed a similar window of average precipitation events and rainfall totals with the 

concurrent natural pollution dispersion potential associated with the unstable weather.

Through October, the drought continued and only 8 rain days were observed at 

Downtown Los Angeles in 2014. More specifically, no rain fell in January with only two days 

of minor precipitation in February before the 26th of the month. Note that historically, the 

majority of exceedances of the standard occur between November and February. 

SCAQMD evaluated the impact of the drought on 24-hour PM2.5 levels by first 

developing a methodology to correct for variations in rainfall frequency and then applying that 

methodology to the trend of ambient PM2.5 to determine the likelihood of future compliance.

Accounting for Seasonal Variations in Rainfall Frequency

As described above, the West Coast of the U.S. has been impacted by a multi-year 

drought that has reduced the frequency of rain events and increased the likelihood for 

atmospheric stagnation. A question has arisen as to what would be the impact to the 2015 

attainment demonstration if the drought continues beyond 2014. To assess this potential 

situation, an algorithm was generated to adjust the predicted annual PM2.5 98th percentile 

concentration based on the deviation from the average expected rain frequency.

Estimating the Impact of the Drought on the PM2.5 Trend

The supplemental analysis first presents the 24-hour PM2.5 data for the Mira Loma design 

site including the observed 98th percentile concentration from 2006 through 2013 and the three 

year average design value for 2008 through 2013. It then outlines the steps to estimate the 

drought impact to the observed Mira Loma annual 98th percentile concentration and the 

methodology to estimate the impact to both 2014 and 2015.

The EPA finds that the weight of evidence presented in the supplement to the plan useful 

for the purpose of the impracticability demonstration, because it contributes to the 

understanding of current air quality and the drought’s impact on air quality. 

5. Conclusion on Air Quality Modeling

Given the Plan’s extensive discussion of modeling procedures, tests, and performance 

analyses consistent with EPA’s guidance in the Modeling Protocol, and the good model 

performance, EPA finds that the modeling is adequate for purposes of supporting the RACM 

demonstration, the RFP demonstration, and the demonstration of impracticability in the 2012 

PM2.5 Plan and Supplement.
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C. PM2.5 Precursors

1. Requirements for the Control of PM2.5 Precursors

The composition of PM2.5 is complex and highly variable due in part to the large 

contribution of secondary PM2.5 to total fine particle mass in most locations, and to the 

complexity of secondary particle formation processes. A large number of possible chemical 

reactions, often non-linear in nature, can convert gaseous SO2, NOx, VOC and ammonia to 

PM2.5, making them precursors to PM2.5.

41 Formation of secondary PM2.5 may also depend on 

atmospheric conditions, including solar radiation, temperature, and relative humidity, and the 

interactions of precursors with preexisting particles and with cloud or fog droplets.

42

The 2007 PM2.5 Implementation Rule contained rebuttable presumptions concerning the 

four PM2.5 precursors applicable to attainment plans and control measures related to those plans.

See 40 CFR 51.1002(c). Although the rule included presumptions that states should address SO2

and NOx emissions in their attainment plans, it also included presumptions that regulation of 

VOCs and ammonia was not necessary. Specifically, in 40 CFR 51.1002(c), the EPA provided, 

among other things, that a state was “not required to address VOC [and ammonia] as . . . PM2.5 

attainment plan precursor[s] and to evaluate sources of VOC [and ammonia] emissions in the 

state for control measures,” unless the state or the EPA provided an appropriate technical 

demonstration showing that emissions from sources of these pollutants “significantly contribute” 

to PM2.5 concentrations in the nonattainment area. 40 CFR 51.1002(c)(3), (4); see also 2007 

PM2.5 Implementation Rule, 72 FR 20586 at 20589-97 (April 25, 2007).

In NRDC, however, the D.C. Circuit remanded the EPA’s 2007 PM2.5 Implementation 

Rule in its entirety, including the presumptions concerning VOC and ammonia in 40 CFR 

51.1002. See NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013). Although the court expressly

declined to decide the specific challenge to these presumptions (see 706 F.3d at 437, n. 10 

(D.C. Cir. 2013)), the court cited CAA section 189(e)

43 to support its observation that 

“[a]mmonia is a precursor to fine particulate matter, making it a precursor to both PM2.5 and 

PM10” and that “[f]or a PM10 nonattainment area governed by subpart 4, a precursor is 

presumptively regulated.” 706 F.3d at 436, n. 7 (citing CAA section 189(e)). Consistent with 

the NRDC decision, EPA now interprets the Act to require that under subpart 4, a state must

evaluate all PM2.5 precursors for regulation unless the state provides a demonstration adequate

to rebut the presumption for a particular precursor in a particular nonattainment area. 

The provisions of subpart 4 do not define the term “precursor” for purposes of PM2.5, 

nor do they explicitly require the control of any specifically identified particulate matter (PM) 

 

41 EPA, Air Quality Criteria for Particulate Matter (EPA/600/P-99/002aF, October 2004), Chapter 3.

42 EPA, Regulatory Impact Analysis for the Final Revisions to the National Ambient Air Quality Standards for

Particulate Matter (EPA-452/R-12-005, December 2012), p. 2-1. 

43 Section 189(e) of the CAA states that “[t]he control requirements applicable under plans in effect under this part 

for major stationary sources of PM10 shall also apply to major stationary sources of PM10 precursors, except where 

the Administrator determines that such sources do not contribute significantly to PM10 levels which exceed the 

standard in the area.”
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precursor. The statutory definition of “air pollutant,” however, provides that the term 

“includes any precursors to the formation of any air pollutant, to the extent the Administrator 

has identified such precursor or precursors for the particular purpose for which the term ‘air 

pollutant’ is used.” CAA section 302(g). The EPA has identified SO2, NOx, VOC, and 

ammonia as precursors to the formation of PM2.5. Accordingly, the attainment plan 

requirements of subpart 4 presumptively apply to emissions of all four precursor pollutants

and direct PM2.5 from all types of stationary, area, and mobiles sources, except as otherwise 

provided in the Act (e.g. CAA section 189(e)).

Section 189(e) of the Act requires that the control requirements for major stationary

sources of direct PM10 also apply to major stationary sources of PM10 precursors, except where

the Administrator determines that such sources do not contribute significantly to PM10 levels 

that exceed the standard in the area. Section 189(e) contains the only express exception to the

control requirements under subpart 4 (e.g., requirements for RACM and RACT, BACM and 

BACT, most stringent measures, and NSR) for sources of direct PM2.5 and PM2.5 precursor

emissions. Although section 189(e) explicitly addresses only major stationary sources, the EPA 

interprets the Act as authorizing it to also determine, under appropriate circumstances, that 

regulation of certain PM2.5 precursors from other source categories in a given nonattainment 

area is not necessary. For example, under the EPA’s longstanding interpretation of the control

requirements that apply to stationary, area, and mobile sources of PM10 precursors area-wide 

under CAA section 172(c)(1) and subpart 4 (see General Preamble, 57 FR 13498 at 13539-42), 

a state may demonstrate in a SIP submittal that control of a certain precursor pollutant is not 

necessary in light of its insignificant contribution to ambient PM2.5 levels in the nonattainment 

area.

44

We are evaluating the South Coast PM2.5 Plan in accordance with the presumption

embodied within subpart 4 that all PM2.5 precursors must be addressed in the state’s evaluation 

of potential control measures, unless the state adequately demonstrates that emissions of a

particular precursor do not contribute significantly to ambient PM2.5 levels that exceed the PM2.5

NAAQs in the nonattainment area.

2. Evaluation of Precursors in 2012 PM2.5 Plan and 2015 Supplement

The 2012 PM2.5 Plan discusses the five primary pollutants that contribute to the mass of 

the ambient aerosol (i.e., ammonia, NOx, SOx, VOC, and directly emitted PM2.5), and states that 

various combinations of reductions in these pollutants could all provide a path to clean air.45 The

Plan assesses and presents the relative value of each ton of precursor emission reductions, 

considering the resulting ambient microgram per cubic meter improvements in PM2.5 air 

quality.

46 As presented in the weight of evidence discussion, trends of PM2.5 and NOx emissions 

 

44 Courts have upheld this approach to the requirements of subpart 4 for PM10. See, e.g., Assoc. of Irritated

Residents v. EPA, et al., 423 F.3d 989 (9th Cir. 2005).

45 2012 PM2.5 Plan, Appendix V, p. V-5-51 and Appendix V, Attachment 8, Relative Contributions of Precursor 

Emissions Reductions to Simulated Controlled Future-Year 24-hour PM2.5 Concentrations.

46 2012 PM2.5 Plan, Appendix V, Attachment 8, Relative Contributions of Precursor Emissions Reductions to 

Simulated Controlled Future-Year 24-hour PM2.5 Concentrations.
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suggest a direct response between lower emissions of PM2.5 and NOx and improved air quality. 

The Community Multi-Scale Air Quality model (CMAQ) simulations in the Plan provide a set of 

response factors for direct PM2.5, SOx, NOx, and VOCs, based on improvements to ambient 24-

hour PM2.5 levels resulting from reductions of each pollutant. The contribution of ammonia 

emissions is embedded as a component of the SOx and NOx factors since ammonium nitrate and

ammonium sulfate are the resultant particulate species formed in the atmosphere. 

The 2012 PM2.5 Plan and 2015 Supplement describe how reductions in NOx, SO2, VOC 

and ammonia emissions contribute to attainment of the PM2.5 standard in the South Coast area 

and contains the District’s evaluation of available control measures for all four of these PM2.5

precursor pollutants, in addition to direct PM2.5, consistent with the regulatory presumptions 

under subpart 4. The Plan also contains a discussion of the Nonattainment New Source review 

(NNSR) control requirements applicable to major stationary sources under CAA section 189(e) 

(see 2015 Supplement at Attachment E), which we are not addressing in this proposal.47 We 

discuss the state’s evaluation of potential control measures for direct PM2.5, NOx, SO2, VOC and 

ammonia in section II.D, “Reasonably Available Control Measures/Reasonably Available 

Control Technology.” 

 

47 In a separate rulemaking to approve revisions to SCAQMD’s nonattainment New Source Review (NNSR) 

program, the EPA determined that the control requirements applicable under the SCAQMD SIP to major stationary 

sources of direct PM2.5 also apply to major stationary sources of NOx, SOx, and VOC, and that major stationary 

sources of ammonia do not contribute significantly to PM2.5 levels which exceed the PM2.5 standards in the area. See 

80 FR 24821, May 1, 2015. This rulemaking addressed the control requirements of CAA section 189(e) only for 

NNSR purposes and not for attainment planning purposes under subpart 1 and 4 of part D, title I of the Act.
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D. Reasonably Available Control Measures/Reasonably Available Control 

Technology (RACM/RACT)

1. Requirements for RACM/RACT

The general subpart 1 attainment plan requirement for RACM and RACT is described in 

CAA section 172(c)(1), which requires that attainment plan submissions “provide for the 

implementation of all reasonably available control measures as expeditiously as practicable 

(including such reductions in emissions from existing sources in the area as may be obtained 

through the adoption, at a minimum, of reasonably available control technology) and shall 

provide for attainment” of the NAAQS. The attainment planning requirements specific to PM2.5

under subpart 4 likewise impose upon states an obligation to develop attainment plans that 

require RACM on sources of direct PM2.5 and those PM2.5 precursors determined to be subject to 

the RACM/RACT requirement. CAA section 189(a)(1)(C) requires that Moderate area PM2.5

SIPs contain provisions to assure that RACM are implemented by no later than 4 years after 

designation of the area. The EPA reads CAA sections 172(c)(1) and 189(a)(1)(C) together to 

require that attainment plans for Moderate nonattainment areas must provide for the 

implementation of RACM and RACT for existing sources of PM2.5 and PM2.5 precursors in the 

nonattainment area as expeditiously as practicable but no later than 4 years after designation.48

Under the RACM and RACT requirements, all available controls should be evaluated, and 

reasonable controls should be adopted.

The terms RACM and RACT are not specifically defined in the Act, nor do the 

provisions of subpart 4 specify how states are to meet the RACM and RACT requirements. In 

longstanding guidance, however, the EPA has interpreted the RACM requirement to include any 

potential control measure for a point, area, on-road and non-road emission source that is 

technologically and economically feasible (General Preamble at 13540). The EPA has 

historically defined RACT as the lowest emission limitation that a particular stationary source is 

capable of meeting by the application of control technology (e.g., devices, systems, process 

modifications, or other apparatus or techniques that reduce air pollution) that is reasonably 

available considering technological and economic feasibility. See General Preamble at 13541 and 

57 FR 18070, 18073-74 (April 28, 1992). 

An evaluation of technological feasibility should include consideration of factors such as 

a source’s process and operating conditions, raw materials, physical plant layout, and non-air 

quality and energy impacts (i.e., increased water pollution, waste disposal, and energy 

requirements. (57 FR 18070, 18073).

An evaluation of economic feasibility should include consideration of factors such as cost 

per ton of pollution reduced (cost-effectiveness), capital costs, and annualized cost (57 FR 

18070, 18074). Absent other indications, the EPA presumes that it is reasonable for similar 

sources to bear similar costs of emissions reductions. Economic feasibility of RACM and RACT 

is thus largely informed by evidence that other sources in a source category have in fact applied 

the control technology, process change, or measure in question in similar circumstances. Id.

 

48 This interpretation is consistent with guidance provided in the General Preamble at 13540.
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2. RACM/RACT Analysis in the 2012 PM2.5 Plan and 2015 Supplement

The 2012 PM2.5 Plan’s RACM/RACT evaluation for direct PM2.5, NOx, VOC, NH3 and 

SOx sources is presented in Appendix VI and in Attachment D to the 2015 Supplement. SCAG’s 

RACM analysis for mobile sources is detailed in Appendix IV-C (“Regional Transportation 

Strategies and Control Measures”). CARB’s RACM evaluation for mobile sources is included in 

Appendix VI of the 2012 PM2.5 Plan.

The evaluation of potential controls is presented by pollutant and then by rule type/source 

category. For stationary and area source categories, the comparison to recently-issued EPA 

CTGs is broken down by the current District rule or rules that apply to that source category. See

2012 PM2.5 Plan, Appendix VI, and 2015 Supplement, Attachment D).

For the 2012 PM2.5 Plan, the District, CARB and SCAG each undertook a process to 

identify and evaluate potential measures that could contribute to expeditious attainment of the 

PM2.5 standards in the South Coast nonattainment area. We describe these processes below. 

The District conducted a multi-step process to identify candidate RACM measures for for 

the 2012 PM2.5 Plan that are technologically and economically feasible. The first step was to

conduct a 2012 Air Quality Technology Symposium in September of 2011. Technical experts 

from a wide variety of areas and the public were invited to provide new and innovative concepts 

to assist the South Coast area with attaining the PM and ozone NAAQS. The District also 

conducted ongoing outreach to engage stakeholders in the process. The following concepts were 

proposed as a result of these efforts:

 promote zero or near-zero emission technologies and provide incentives for mobile 

source and goods movement equipment upgrades,

 further reduce VOC emissions from coatings, solvents, and various consumer 

products focusing on reformulations or alternatives to VOC-based solvents,

 conduct a technology review for NOx RECLAIM, and further reduce NOx emissions 

through the use of low NOx burners, fuel cells, biogas, and distributed power 

generation, 

 address energy-climate change and co-benefits, the need for electricity storage, or 

new fossil-fueled peaking plants, to compensate for fluctuation in renewable energy 

supply, and use outreach to promote energy efficiency,

 influence consumer behavior, expand carpools, increase gas taxes, and promote 

multiagency collaboration.

The second step in the District’s RACM process was to look at EPA’s list of suggested 

control measures for PM2.5 nonattainment areas described in the 2007 PM2.5 Implementation 

Rule. The District summarized the results of this analysis in Table VI-3, Appendix VI of the 

2012 PM2.5 Plan. This analysis shows that the District either has a pre-existing rule or has

developed a control measure for the 2012 PM2.5 Plan to address each of EPA’s suggested types 

of measures.
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The third step in the District’s RACM process involved analyzing the District’s rules for 

compliance with the RACT standard. The results of this analysis are summarized in Table VI-4, 

Appendix VI (page VI-10) of the 2012 PM2.5 Plan. The District further supplemented these

analyses in the 2015 Supplement, Attachment D, Tables D-4 to D-8 to address RACM and 

RACT requirements for direct PM2.5 and all PM2.5 precursors, and to provide reasoned 

justifications for control measures that were not adopted. A few examples of RACT-level rules 

in the South Coast include Rules 1146 and 1146.1, which control NOx from industrial and 

institutional boilers, Rule 1133.3, greenwaste composting, which in addition to providing a 

RACT level of control, also controls fugitives, Rule 1171, Solvent Cleaning, and Rule 1130, 

Graphic Arts.49

As part of these evaluations, the District compared its SIP rules with current rules,

regulations and control measures implemented in other nonattainment areas. Specifically, the 

District re-evaluated all of its source category-specific rules and compared the requirements in 

these rules to more than 100 rules from four other air districts in California (San Joaquin Valley, 

Sacramento Metropolitan, Ventura, and San Francisco Bay Area), the Dallas-Fort Worth and 

Houston-Galveston areas in Texas, New York, and New Jersey. A summary of this analysis is 

presented in the 2012 PM2.5 Plan, Appendix VI, Table VI-5 and in the 2015 Supplement, 

Attachment D. Table VI-5 identifies those rules from other areas that, based on the District’s 

review, may be more stringent in some respects than South Coast rules. With respect to rules

1115, 1130, and 1168, the Plan states the District’s intention to provide further analyses at a later 

time. See 2012 PM2.5 Plan, Appendix VI, p. VI-9. Attachment D to the 2015 Supplement 

includes an updated RACM/RACT analysis with additional information on RACM for ammonia

sources. The 2015 Supplement also states that the District will further evaluate Rule 1115 and

Rule 1168, and notes that Rule 1130 was recently amended to address the applicable CTG. See

2015 Supplement, Attachment D, Table D-1 on p. D-5. 

According to the District, several of the requirements in South Coast Rule 1115, Motor 

Vehicle Assembly Line Coating Operations, are not as stringent as the recommendations in the 

2008 EPA CTG for a few coating processes emitting > 15 lbs/day. The two facilities subject to 

Rule 1115, however, have very small emissions, a total of about 0.02 tpd of VOC.50 See 2015 

Supplement, Attachment D, page D-29. In December 2009, we approved Rule 1168, Adhesive 

and Sealant Applications, as satisfying VOC RACT requirements under CAA section 182(b)(2) 

 

49 The technical support documents for EPA’s rulemaking actions on these rules are available at: 

http://yosemite.epa.gov/r9/r9sips.nsf/AgencyProvision/5F5287B726E9E6F488257D790004839A/$file/1146+and+1

146+1+June+2014.pdf?OpenElement, 

http://yosemite.epa.gov/r9/r9sips.nsf/AgencyProvision/5AD85F69581DEB9388257AC50057D806?OpenDocument, 

http://yosemite.epa.gov/r9/r9sips.nsf/AgencyProvision/F65EA6DB0E3F7F06882579210082BE8C?OpenDocument, 

and 

http://yosemite.epa.gov/r9/r9sips.nsf/AgencyProvision/865FFD6DBAC8018F88257E82007BA257/$file/1130+Jun+

2015.pdf?OpenElement.

50 We note that 0.02 tpd is about 0.0044 percent of the total VOC inventory of 451 tpd for 2014. See section II.A of 

the TSD. See email correspondence from Joseph Cassmassi, SCAQMD, to Stanley Tong, US EPA Region 9, dated 

November 25, 2014 in the docket for today’s action.
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(see 74 FR 67821, December 21, 2009). In 2014, the District amended South Coast Rule 1130, 

Graphic Arts, to reduce fountain solution VOC content to 16-85 g/L with optional control device 

efficiency of 90-95% consistent with EPA’s current CTG recommendations. On July 14, 2015, 

EPA approved the revised SC Rule 1130 as satisfying VOC RACT requirements under CAA 

section 182(b)(2). (See 80 FR 40915.)

The RACM analyses and demonstrations conducted by CARB and SCAG for 

transportation and mobile source control measures are included in Appendix IV-C and its 

Attachment as well as the Attachment to Appendix VI of the 2012 PM2.5 Plan. CARB has unique 

authority under the CAA to adopt standards for most categories of on- and off-road engines and 

vehicles, subject in most instances to a waiver or authorization by EPA under CAA section 209. 

The State of California has been a leader in the development of some of the most stringent 

control measures nationwide for on-road and off-road mobile sources and the fuels that power 

them. As part of its 2007 State Strategy as revised in 2009 and 2011 to support attainment plans 

in California for PM2.5 and 8-hour ozone, CARB undertook an extensive public consultation 

process to identify potential SIP measures. New measures adopted by CARB focused on 

cleaning up the in-use fleet, and increasing the stringency of emissions standards for a number of 

engine categories, fuels, and consumer products. CARB continues to expand its mobile source 

program to further reduce emission of direct PM2.5 and PM2.5 precursors. For example, in 

January 2012, CARB adopted the Advanced Clean Car program.51

SCAG focused its analysis on transportation control measures (TCMs) in the 2012-2035 

Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS), and the analysis 

and results are described in Appendix IV-C of the 2012 PM2.5 Plan, “Regional Transportation 

Strategy and Control Measures.” This evaluation considered transportation-related measures 

identified in section 108(f) of the CAA and measures adopted in other nonattainment areas of the 

country. SCAG provided a justification for measures that were determined to be infeasible for 

implementation in the South Coast nonattainment area. See 2012 PM2.5 Plan, Appendix IV-C.

The inventory for ammonia, provided in Appendix V of the 2012 PM2.5 Plan, indicates 

that the largest sources of ammonia include fuel combustion, waste disposal, miscellaneous 

sources, industrial sources, livestock, composting, domestic, and on-road mobile emissions. See

Table D-1 (referencing 2012 PM2.5 Plan at Appendix V, page V-4-2). The 2012 PM2.5 Plan and 

2015 Supplement identify five measures that control ammonia emissions sources in the South 

Coast. The five rules are Rule 223, Emissions Reduction Permits from Large Confined Animal 

Feeding Operations (adopted June 2, 2006); Rule 1105.1, Reductions of PM-10 and Ammonia 

Emissions from Fluid Catalytic Cracking Units (adopted November 7, 2003); Rule 1127, 

Emissions Reductions from Livestock Waste (adopted August 6, 2004); Rule 1133.2, Emission

Reductions from Co-Composting Operations (adopted January 10, 2003); and Rule 1133.3, 

Emission Reductions from Greenwaste Composting Operations (adopted July 8, 2011).

 

51 See 78 FR 2112 (January 9, 2013).
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Table D-1. South Coast Ammonia Emissions Inventory for 2008 (tpd)

Source Category Ammonia Emissions 

Livestock 18.6

Soil 1.8

Domestic 25.1

Landfill 3.6

Composting 17.8

Fertilizer 1.5

Sewage Treatment 0.2

Wood Combustion 0.1

Industrial 20.2

On-Road Mobile 19.9

Off-road Mobile 0.1

TOTAL 108.9

Source: 2012 PM2.5 Plan, Appendix V, Table V-4-2.

 Rule 223, Emissions Reduction Permits from Large Confined Animal Feeding Operations 

(LCAF), is a work practice rule to control VOC and ammonia emissions from LCAFs. It 

requires operators and/or owners to implement management practices (e.g., feed according to 

National Research Council of the National Academy of Sciences guidelines, clean manure 

from corrals at least four times per year, land incorporate manure within 72-hours of 

removal, and allow liquid manure to stand in field no more than 24 hours after irrigation) for 

different components of the CAF operation, such as feeding, milking parlors, 

housing/bedding, manure management and land application. 

EPA approved Rule 223 into the SIP on July 13, 2015 (see 80 FR 39966). In our technical 

support document (TSD) for that rulemaking action, we recommended that the District 

consider, at its next rulemaking opportunity, control provisions similar to those in SJV Rule 

4570 in 2010 (approved by EPA at 77 FR 2228, January 17, 2012), including lowering the 

threshold for rule applicability from 1,000 milk cows to 500 milk cows per facility, and from 

650,000 broilers/ducks and layers to 400,000. 

 Rule 1105.1, Reductions of PM10 and Ammonia Emissions from Fluid Catalytic Cracking 

Units (FCCU), is designed to limit PM10 and ammonia emissions from fluid catalytic 

cracking units at oil refineries. The rule sets emission limits for PM10 and ammonia slip that 

result from the combination of FCCU emissions and ammonia injection used with 

electrostatic precipitators (ESP) to control FCCU emissions. Once in the atmosphere, 

ammonia emissions react with other compounds to produce secondary PM. The rule requires 
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EPA- Region 9 Page 59

oil refineries to implement control technologies to meet the emissions limits including but 

not limited to dry and wet ESPs, sulfur oxide reducing agents, selective catalytic reduction, 

selective non-catalytic reduction, and wet gas scrubbers. EPA approved this rule into the SIP

on January 4, 2006 (see 71 FR 241). 

 Rule 1127, Emissions Reductions from Livestock Waste, requires dairies (and other types of 

dairy-cattle operations) to implement specific best management practices for manure 

management and disposal, and sets requirements for approving a facility as a manure 

processing operation. Specific requirements for ammonia include cleaning manure from 

corrals at least four times a year, disposing of manure only at approved manure processing 

operations, and applying it on agricultural land approved for that purpose. The EPA 

approved this rule into the SIP on May 23, 2013 (see 78 FR 30768).

 Rule 1133.2, Emission Reductions from Co-Composting Operations, requires all new or 

existing co-composting operations to compost in an enclosure that meets certain technical 

requirements (e.g., inward face velocity of air through each opening shall be at least 100 feet 

per minute unless the opening contains closure seals), cure using an aeration system 

operating under negative pressure for no less than 90 percent of blower operating cycle, and 

vent the exhaust to an emission control system with a control efficiency for both VOC and 

ammonia of at least 80 percent, by weight, or submit a compliance plan for new operations 

that demonstrates an overall emission reduction for both VOC and ammonia of 80 percent, 

by weight, based on emission factors specified in the rule. For existing operations, the 

required emission reduction is 70 percent, by weight, for both ammonia and VOC. Rule 

1133.2 also specifies required compliance plan elements. EPA approved this rule into the 

SIP on July 21, 2004 (see 69 FR 43518).

 Rule 1133.3, Emission Reductions from Greenwaste Composting Operations, requires all 

new or existing greenwaste (includes foodwaste) composting facilities to cover, water and 

turn active phase compost piles according to specific requirements (e.g., cover for seven 

days, turn only when top of pile is sufficiently wet, based on test method) to minimize VOC 

and ammonia emissions. If total foodwaste throughput exceeds 5,000 tons per year, any 

active pile with more than 10 percent foodwaste must be controlled by a device with an 

overall system control efficiency of 80 percent, by weight, each for VOC and ammonia 

emissions. EPA approved this rule into the SIP on November 29, 2012 (see 77 FR 71129).

In addition, for livestock waste, the 2012 PM2.5 Plan and 2015 Supplement indicate the 

District will evaluate control measure BCM-04, Further Ammonia Reductions from Livestock 

Waste, as a potential ammonia control measure. Phase I of this control measure, scheduled for 

the 2015-2016 timeframe, involves a technology assessment. The technical assessment will 

evaluate the technical and economic feasibility of applying sodium bisulfate (SBS) at local 

dairies in the South Coast. SBS application has been shown to be an effective method for 

reducing ammonia from fresh manure. (See 2012 PM2.5 Plan, Appendix IV, page IV-A-32). The 

Supplement states that rule development will follow if controls are determined to be technically 

feasible and cost-effective. See 2015 Supplement, page F-1 and Table F-1. 
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We are proposing to reclassify the South Coast from Moderate to Serious nonattainment for the 

2006 PM2.5 standard. A final reclassification to Serious will trigger the requirement in CAA 

section 189(b)(1)(B) for the submittal of a SIP providing for the implementation of Best 

Available Control Measures (BACM),52 among other things, within 18 months. As part of the 

District’s development of a BACM control strategy for direct PM2.5 and those precursors subject 

to evaluation for potential controls in the South Coast (NOx, SO2, VOC, and ammonia), we

encourage the District to consider additional measures previously identified by EPA and the 

public in comments on the 2012 PM2.5 Plan, 2015 Supplement, and other individual rules and 

plans, as well as other potential innovative measures for reducing emissions. As part of this 

process, we suggest that the District consult with other state/local agencies and environmental 

and industry stakeholders. 

Examples of potential rule revisions include:

 lowering the curtailment threshold for Rule 445 (Wood Burning Devices), and further 

revising Rule 445 by requiring old wood burning stoves be changed out upon home 

resale, retrofitting wood burning fireplaces with natural gas fireplaces upon major home 

remodeling, and requiring homes that use wood burning as their sole source of heat 

demonstrate that they maintain a device that meets EPA Phase II emission limits, 

 revising Rule 1140 (Abrasive Blasting) to have a 20% opacity limit,

 expanding coverage of Rule 1118, Refinery Flares, to include flares at large oil 

production facilities, similar to San Joaquin Rule 4311,

 lowering the threshold for rule applicability in Rule 223 from 1,000 milk cows to 500 

milk cows per facility, and from 650,000 broilers/ducks and layers to 400,000, and 

 evaluating/encouraging the use of warm-mix asphalt over hot-mix asphalt on public and 

private roads and lots.

Condensable Fraction of Direct PM2.5 Emissions

EPA’s 2007 PM2.5 implementation rule states that “[a]fter January 1, 2011, for purposes 

of establishing emissions limits under 51.1009 and 51.1010, States must establish such limits 

taking into consideration the condensable fraction of direct PM2.5 emissions.” 40 CFR 

51.1002(c). The South Coast 2012 AQMP and 2015 Supplement rely on several SIP-approved 

rules regulating direct PM emissions as part of the PM2.5 control strategy (e.g., Wood Burning 

Fireplaces (Rule 445, adopted March 7, 2008, most recently revised May 3, 2013), Wood Stoves 

and Under-Fired Charbroilers (Rule 1138, adopted November 14, 1997), and Particulate Matter 

(PM) Control Devices (Rule 1155, adopted December 4, 2009). See 2015 Supplement, 

 

52 The EPA defines BACM as, among other things, the maximum degree of emissions reduction achievable for a 

source or source category, which is determined on a case-by-case basis considering energy, environmental, and 

economic impacts. See Addendum at 42010, 42014. BACM must be implemented for all categories of sources in a 

serious PM2.5 nonattainment area unless the State adequately demonstrates that a particular source category does not 

contribute significantly to nonattainment of the PM2.5 standard. See id. At 42011, 42012.
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Attachment F, Table F-1 and letter dated July 25, 2014 transmitting SC Rule 1155 to EPA. As 

part of our action on any rules that regulate direct PM2.5 emissions, we evaluate the emission 

limits in the rule to ensure that they appropriately address CPM, as required by 40 CFR 

51.1002(c). We note that the SIP-approved version of Rule 1138 requires testing according to 

the District’s Protocol, which requires measurement of both condensable and filterable PM in 

accordance with SCAQMD Test Method 5.1. See Rule 1138 (adopted Nov. 14, 1997, approved 

July 11, 2011, see 66 FR 36170), paragraph (c)(1) and (g) and SCAQMD Protocol paragraph 

3.1.53 We also note that the SIP-approved version of Rule 1155 requires measurement of both 

condensable and filterable PM in accordance with SCAQMD Test Methods 5.1, 5.2, or 5.3 as 

applicable. See Rule 1155 (adopted Dec. 4, 2009, approved March 16, 2015, see 80 FR 13495),

paragraph (e)(6).54 

3. Evaluation and Proposed Action

We find that the process followed in the 2012 PM2.5 Plan and 2015 Supplement to 

identify RACM/RACT is generally consistent with the EPA’s recommendations in the General 

Preamble. The process included compiling a comprehensive list of potential control measures for 

sources of direct PM2.5, NOx, VOC, SO2, and ammonia in the South Coast. This list included

measures suggested in public comments on the Plan. See 2012 PM2.5 Plan, Appendices VI and 

IV-C. As part of this process, the District, CARB, and SCAG evaluated potential controls for all 

relevant source categories for economic and technological feasibility, and provided justifications

for the rejection of certain identified measures. Id. After completing this evaluation, the District 

stated its intent to analyze potential rule improvements with respect to rules 1115, 1130, and 

1168. See 2012 PM2.5 Plan, Chapter 4 and Appendices VI, IV-A, and IV-C, and 2015 

Supplement, Attachment D. Since submittal of the 2012 PM2.5 Plan in February 2013, the 

District has strengthened, adopted and submitted Rule 1130, which EPA approved on July 14, 

2015 (see 80 FR 40915). The EPA approved Rule 1168 as satisfying VOC RACT on December 

21, 2009 (see 74 FR 67821). With respect to Rule 1115, as noted above, the emissions inventory 

for these sources is very small. 

We have reviewed the District’s determination in the 2012 PM2.5 Plan and 2015 

Supplement that its stationary and area source control measures represent RACM/RACT for 

direct PM2.5, NOx, VOC, NH3 and SO2. Our rulemaking actions on District rules generally 

provide the bases for our conclusions that the emission limits and/or other control requirements

in the rules represent a RACT level of control, at minimum, for the relevant source categories.

55

 

53 See SCAQMD Protocol, Determination of Particulate and Volatile Organic Compound Emissions from 

Restaurant Operations, November 14, 1997 (available at 

http://yosemite.epa.gov/R9/R9Testmethod.nsf/0/3D4DEB4D21AB4AAF882570AD005DFF69/$file/SC%20Rest%2

0emiss.pdf).

54 See SCAQMD Test Method 5.1, Determination of Particulate Matter Emissions from Stationary Sources Using a 

Wet Impingement Train, March 1989 (available at http://aqmd.gov/tao/methods/stm/stm-005-1.pdf); SCAQMD Test 

Method 5.2, Determination of Particulate Matter Emissions from Stationary Sources Using Heated Probe and 

Filter, March 1989 (available at http://aqmd.gov/tao/methods/stm/stm-005-2.pdf); and SCAQMD Test Method 5.3, 

Determination of Particulate Matter Emissions from Stationary Sources Using an in-Stack Filter, October 2005 

(available at http://aqmd.gov/tao/methods/stm/stm-005-3.pdf).

55 A full list of the District’s rules, including citations to our most recent final or proposed rulemaking on each rule 

can be found in Appendix A to this TSD. 
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We also reviewed the potential additional control measures that the District considered, 

including those identified by public commenters during the State/District rulemaking processes, 

and believe that the District adequately justified its conclusions with respect to each of these 

measures.

Finally, we have reviewed the analysis of current and potentially available controls for 

both on-road and off-road mobile sources in Appendices IV-C and VI, as well as the Attachment 

to Appendix VI. As we have noted in previous actions on South Coast plans,

56 California is a 

leader in the development and implementation of stringent control measures for on-road and offroad mobile sources. Its current program addresses the full range of mobile sources in the South 

Coast through regulatory programs for both new and in-use vehicles and through incentive grant 

programs. See 2012 PM2.5 Plan, Appendix III, Table III-1-3. The District has also adopted 

measures to reduce emissions from mobile sources including its Surplus Opt-in for NOx (SOON)

rule (Rule 2449) and on-road mobile sources including its employer trip reduction rule (Rule 

2202) and has a well-funded incentive grants program focused on mobile sources. See 2012 

PM2.5 Plan, Chapter 4. Overall, we believe that the State, District, and MPO programs provide 

for the implementation of RACM for emissions of direct PM2.5 and PM2.5 precursors from 

mobile sources in the South Coast.

For the foregoing reasons, we propose to find that the 2012 PM2.5 Plan and 2015 

Supplement provide for the implementation of all RACM/RACT that can be implemented prior 

to the applicable Moderate area attainment date as required by CAA sections 189(a)(1)(C) and 

172(c)(1), and to approve the RACM/RACT demonstration in the South Coast 2012 PM2.5 Plan 

and 2015 Supplement.

57

 

56 See the proposed approvals of the South Coast 2007 [8-hour] Ozone Plan at 76 FR 57872, 57879 (September 16, 

2011) and the 2007 AQMP addressing the 1997 PM2.5 NAAQS at 76 FR 41562. 41570 (July 14, 2011).

57 The 2012 PM2.5 Plan is the latest in a series of air quality plans and control strategies that the District, CARB and 

SCAG have developed to provide for attainment of the NAAQS in the South Coast. These plans include the 2003 

PM10 Plan (approved 70 FR 69081 (November 14, 2005)); the 2003 Extreme [1-hour] Ozone Attainment Plan 

(approved 74 FR 10176 (March 8, 2009); the 2007 [8-hour] Ozone Plan (approved 77 FR 12674 (March 1, 2012)); 

the 2007 State Strategy for the 1997 Ozone and PM2.5 standards (approved 76 FR 69928 (November 9, 2011)); the 

2007 PM2.5 SIP as revised in 2009 and 2011 (approved 66 FR 69928 (November 9, 2011)); and the RACT SIP 

submitted in 2007 (approved 73 FR 76947 (December 18, 2008)). In each of our rulemakings on these Plans, we 

approved a RACM and/or RACT demonstration that addressed one or more PM2.5 precursors. 
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E. Major Stationary Source Control Requirements Under CAA Section 

189(e)

1. Requirements for Major Stationary Sources of PM2.5 Precursors

CAA section 189(e) specifically requires that the control requirements applicable to 

major stationary sources of direct PM2.5 also apply to major stationary sources of PM2.5

precursors, except where the Administrator determines that such sources do not contribute 

significantly to PM2.5 levels that exceed the standard in the area (see General Preamble at 13539 

and 13541 to 42). The control requirements applicable to major stationary sources of direct PM2.5

and PM2.5 precursors in a Moderate PM2.5 nonattainment area include, at minimum, the 

requirements of a nonattainment new source review (NNSR) permit program meeting the 

requirements of CAA section 172(c)(5) (see CAA 189(a)(1)(A)). 

2. Evaluation of Major Source Control Requirements in the 2012 PM2.5 Plan and 2015 

Supplement

In Attachment E to the 2015 Supplement, the District addressed the NNSR control 

requirements that apply to major stationary sources of direct PM2.5 and PM2.5 precursors in the 

South Coast nonattainment area. 

3. Evaluation and Proposed Action

In a separate rulemaking to approve revisions to SCAQMD’s NNSR permit program,

EPA evaluated the District’s discussion of control requirements applicable to major stationary 

sources (Attachment E of the 2015 Supplement) and determined that the District’s SIP-approved

NNSR program satisfies the requirements of CAA section 189(e) for direct PM2.5 and all PM2.5

precursors.

58

 Accordingly, in this action, EPA is not addressing the NNSR control requirements 

that apply to major stationary sources of direct PM2.5 and PM2.5 precursors in the South Coast 

area under CAA section 189(e). 

 

58 See n. 27, supra.
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F. Adopted Control Strategy 

1. Requirements for Control Strategies

CAA section 110(a)(2)(A) provides that each SIP “shall include enforceable emission 

limitations, and other control measures, means or techniques... as well as schedules and 

timetables for compliance, as may be necessary or appropriate to meet the applicable 

requirements of the Act.” Section 172(c)(6) of the Act, which applies to nonattainment area SIPs, 

is virtually identical to section 110(a)(2)(A).59 Measures necessary to meet RACM/RACT and 

the additional control requirements under section 172(c)(6) must be adopted by the State in an 

enforceable form (General Preamble at 13541) and submitted to the EPA for approval into the 

SIP under CAA section 110.

Commitments approved by the EPA under CAA section 110(k)(3) are enforceable by the 

EPA and citizens under CAA sections 113 and 304, respectively. In the past, the EPA has 

approved enforceable commitments and courts have enforced actions against states that failed to 

comply with them.

60 Additionally, if a state fails to meet its commitments, the EPA may make a 

finding of failure to implement the SIP under CAA section 179(a)(4), which starts an 18-month 

period for the state to correct the non-implementation before mandatory sanctions are imposed.

Once the EPA determines that circumstances warrant use of an enforceable commitment, 

the EPA considers three factors in determining whether to approve the use of an enforceable 

commitment to meet a CAA requirement: (a) does the commitment address a limited portion of 

the CAA-required program; (b) is the state capable of fulfilling its commitment; and (c) is the 

commitment for a reasonable and appropriate period of time.61 

2. Control Strategy in the South Coast 2012 PM2.5 Plan and 2015 Supplement

For purposes of evaluating the South Coast 2012 PM2.5 Plan and 2015 Supplement, we 

have divided the measures relied on to satisfy the applicable control requirements into two 

categories: baseline measures and control strategy measures.

As the term is used here, baseline measures are federal, State, and District rules and 

regulations adopted prior to June 2012 for District rules and prior to August 2011 for CARB 

rules (i.e., prior to the development of the 2012 PM2.5 Plan) that continue to achieve emissions 

 

59 The language in sections 110(a)(2)(A) and 172(c)(6) is quite broad, allowing a SIP to contain any enforceable 

“means or techniques” that EPA determines are “necessary or appropriate” to meet CAA requirements, such that the 

area will attain as expeditiously as practicable but no later than the designated date. Furthermore, the express 

allowance for “schedules and timetables” demonstrates that Congress understood that all required controls might not 

have to be in place when a SIP is approved.

60 See, e.g., American Lung Ass'n of N.J. v. Kean, 670 F. Supp. 1285 (D.N.J. 1987), aff'd, 871 F.2d 319 (3rd Cir. 

1989); NRDC, Inc. v. N.Y. State Dept. of Env. Cons., 668 F. Supp. 848 (S.D.N.Y. 1987); Citizens for a Better Env't 

v. Deukmejian, 731 F. Supp. 1448, recon. granted in par, 746 F. Supp. 976 (N.D. Cal. 1990); Coalition for Clean Air 

v. South Coast Air Quality Mgt. Dist., No. CV 97-6916-HLH, (C.D. Cal. Aug. 27, 1999).

61

 Courts have upheld EPA’s use of this “three-factor test” to ensure that a state’s use of such commitments is a 

limited component of a comprehensive strategy for attaining the NAAQS. See BCCA Appeal Group v. EPA, 355 

F.3d 817 (5th Cir. 2003), reh’g denied, 2004 U.S. App. LEXIS 215 (5th Cir., January 8, 2004) and Environmental 

Defense v. EPA, 369 F.3d 193 (2d Cir. 2004).
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reductions through the current attainment year of 2015 and beyond.

62 The Plan describes many 

of these measures in Chapter 4 and in Appendices III, IV-A, IV-C, and VI. Reductions from 

these baseline measures are incorporated into the baseline inventory and reductions from the 

District measures in particular are quantified in Appendix III, Table III-2-2B. According to the 

Plan, these measures provide most of the emissions reductions projected to occur between the 

base year of 2008 and the Moderate area attainment date of 2015 and, based on the modelpredicted level of emission reductions needed to meet the 2006 PM2.5 standard in the South 

Coast, the majority of the reductions needed to meet that standard. See 2012 PM2.5 Plan, Chapter 

4 and Appendix V and 2015 Supplement, Attachment A.

According to the Plan, these measures provide most the emissions reductions projected to 

occur between the base year of 2008 and the modeled attainment year of 2015. See 2012 PM2.5

Plan, Chapter 4 and Appendix V and 2015 Supplement, Attachment A.

Control strategy measures are the new rules, rule revisions, commitments and other 

measures that provide the additional increment of emissions reductions needed beyond the 

baseline measures to provide for attainment, to demonstrate RFP, to meet the RACM/RACT

requirement, or to provide for contingency measures. We discuss the control strategy measures 

and commitments in this section. District baseline measures are listed in Appendix A of this 

TSD.

The District included several new measures in the 2012 PM2.5 Plan and 2015 Supplement

to provide for attainment of the 2006 PM2.5 NAAQS. First, the District committed to adopt, 

submit, and implement amendments to two District rules (Rule 444 and Rule 445) to reduce 

direct PM2.5 emissions from open burning and residential wood burning activities. See 2012 

PM2.5 Plan, p. 4-8, Table 4-2 and SCAQMD Governing Board Resolution 12-19 (Dec. 7, 2012), 

p. 8, as revised by 2015 Supplement, Attachment F, Table F-1 and SCAQMD Governing Board 

Resolution 15-2 (Feb. 19, 2015). Second, the District committed to achieve 11.7 tpd of direct 

PM2.5 emission reductions by 2015, either from these two amended rules or from substitute 

measures as necessary to address any shortfall in emission reductions. Id. Third, the District 

committed to carry out technology assessments to address emissions from under-fired 

charbroilers and livestock waste in 2015-2016 and 2017, respectively. Id. Finally, the District 

committed to adopt revisions to its NOx RECLAIM program to achieve an additional 2 tpd of

NOx emission reductions in 2015, as a contingency measure, and to adopt backstop measures 

related to ports and port-related facilities in 2015. Id. Following the State’s submittal of the 

2012 PM2.5 Plan to EPA in 2013, the District adopted amendments to Rule 444 and Rule 445 and 

on June 11, 2013, the District submitted these revised rules to EPA for SIP approval, consistent 

with its commitments in the Plan. All of these measures and commitments are listed in Table F-1

below. 

 

62 These measures are typically rules that have compliance dates that occur after the adoption date of a plan and 

mobile source measures that achieve reductions as older engines are replaced through attrition (e.g., through fleet 

turnover).
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Table F-1. SCAQMD 2012 PM2.5 Plan and 2015 Supplement Specific Rule

Commitments

District Rule 

Number Measure Number & Description Adoption Date

Implementati

on Date

Emission 

Reductions

444 Further Reductions from Open 

Burning63 2013 May 3, 2013 4.6 tpd PM2.5

445 Further Reductions from Residential 

Wood Burning64 2013 May 3, 2013 7.1 tpd PM2.5

1138 Emissions Reductions from Underfired Charbroilers 2017 N/A TBD

1127 Further Ammonia Emissions From 

Livestock Waste

2015-2016

Technology 

Assessment

N/A TBD

2002 Further NOx Reductions from 

RECLAIM 2015 N/A 2 tpd NOx

4001

Backstop Measures for Indirect Sources 

of Emissions from Ports and Portrelated Facilities2015 N/A N/A

Source: 2012 PM2.5 Plan, Chapter 4, Table 4-2, as amended by 2015 Supplement, Attachment F, Table F-1.

3. Evaluation and Conclusions

The Plan provides for the majority of the emissions reductions necessary for attainment 

to be achieved from baseline measures. These reductions come from a combination of District,

State and federal stationary and mobile source measures.65 Over the past four decades, the 

District has adopted or revised almost 100 prohibitory rules that limit emissions of NOx, SO2, 

ammonia, VOC, and particulate matter from stationary sources. See Appendix A of this TSD. 

The vast majority of these rules are currently SIP-approved and as such, their emissions 

reductions are fully creditable in attainment-related SIPs. The District’s most recent amendments 

to Rule 444 and Rule 445 further tighten the District’s control strategy for direct PM2.5

emissions. California has also adopted standards for many categories of on- and off-road 

vehicles and engines as well as standards for gasoline and diesel fuels. 

The State’s mobile source measures fall into two categories: measures for which the State 

has obtained or has applied to obtain a waiver of federal pre-emption under CAA section 209 

 

63 Approved on September 26, 2013, see 78 FR 59249.

64 Ibid.

65 These federal measures include EPA’s national emissions standards for heavy duty diesel trucks (66 FR 5001 

(January 18, 2001)), certain new construction and farm equipment (Tier 2 and 3 non-road engines standards, 

63 FR 56968 (October 23, 1998) and Tier 4 diesel non-road engine standards, 69 FR 38958 (June 29, 2004)), and 

locomotives (63 FR 18978 (April 16, 1998) and 73 FR 37045 (June 30, 2008)). States are allowed to rely on 

reductions from federal measures in attainment and RFP demonstrations and for other SIP purposes.
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(“section 209 waiver measures” or “waiver measures”) and those for which the State is not 

required to obtain a waiver (“non-waiver measures” or “SIP measures”).

Under the Clean Air Act, the EPA is charged with establishing national emission limits 

for mobile sources. States are generally preempted from establishing such limits except for 

California, which can establish these limits subject to EPA waiver or authorization under CAA 

section 209 (referred to herein as “waiver measures”). Over the years, the EPA has issued 

waivers or authorizations for many mobile source regulations adopted by CARB. California 

attainment and maintenance plans rely on emissions reductions from implementation of the 

waiver measures through use of emissions models such as EMFAC, and the South Coast 2012 

PM2.5 Plan is no exception.

Historically, the EPA has allowed California to take credit for such “waiver” measures 

even though the waiver measures themselves (i.e., CARB’s regulations) have not been adopted 

and approved as part of the California SIP. However, a recent decision by the Ninth Circuit 

Court of Appeals held that the EPA’s longstanding practice in this regard was at odds with the 

CAA requirement that state and local emissions limits relied upon to meet the NAAQS be 

enforceable by EPA or private citizens through adoption and approval of such limits in the SIP.66

In response to the court’s decision, CARB has adopted the necessary waiver measures as 

revisions to the California SIP and submitted them to EPA for approval.67 EPA intends to propose 

action on these waiver measures in a separate rulemaking. Once approved as part of the SIP, the 

measures will be enforceable by the EPA or private citizens under the CAA. In today’s action, the 

EPA is proposing to approve certain elements of the 2012 PM2.5 Plan and 2015 Supplement in part 

based on our expectation that these waiver measures will soon become federally enforceable as a 

result of our approval of the measures as part of the SIP.

Non-waiver measures include improvements to California’s inspection and maintenance 

(I/M) program, SmogCheck, and cleaner burning gasoline and diesel regulations as well as the 

District’s stationary source and mobile source rules. 

As discussed above, we generally consider three factors in determining whether to 

approve the use of enforceable commitments to meet a CAA requirement. In this case, however, 

the 2012 PM2.5 Plan and 2015 Supplement do not rely on either the rule amendment 

commitments or the emission reduction commitments in its impracticability demonstration, 

RACM demonstration, RFP demonstration, or quantitative milestones, or to meet any other CAA 

requirement. Therefore, we do not need to apply this three-factor test before proposing to 

approve the District’s commitments into the SIP. Approval of these commitments will strengthen 

the SIP and contribute to the SIP’s purpose of “eliminating or reducing the severity and number 

of violations of the [PM2.5 NAAQS] and achieving expeditious attainment of such standards.” 

See CAA 176(c)(1)(A). 

We are proposing to approve the District’s commitments to adopt and implement specific 

control measures identified in Table 4-2 in the South Coast 2012 AQMP (as amended March 4, 

2015 by Table F-1 in Attachment F of the 2015 Supplement), and to achieve specified NOx

emission reductions, to the extent that these commitments have not yet been fulfilled. 

 

66

 See Committee for a Better Arvin v. EPA, 786 F.3d 1169 (9th Cir. 2015). 

67 See letter dated August 14, 2015, from Richard W. Corey, Executive Officer, California Air Resources Board, to 

Jared Blumenfeld, Regional Administrator, EPA Region 9.
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Specifically, we are proposing to approve the District’s commitments to: (1) carry out a 

technology assessment to address emissions from under-fired charbroilers by 2017, (2) conduct a 

technology assessment for livestock waste by 2016, (3) adopt revisions to its NOx RECLAIM 

program or other enforceable control measures to achieve an additional 2 tpd of NOx emission 

reductions in 2015, and 4) adopt backstop measures for indirect sources of emissions from ports 

and port-related facilities. See 2012 PM2.5 Plan, p. 4-8, Table 4-2 and SCAQMD Governing 

Board Resolution 12-19 (Dec. 7, 2012), pp. 7-8, as revised by 2015 Supplement, Attachment F, 

Table F-1 and SCAQMD Governing Board Resolution 15-2 (Feb. 19, 2015), pp. 2-3.

With respect to the commitments to adopt Rules 444 and 445 and to achieve 11.7 tpd of 

direct PM2.5 emission reductions, the District has satisfied these commitments by submitting the 

fully adopted rules to EPA on June 11, 2013, together with technical documentation to support 

its conclusion that these rules will achieve 11.7 tpd of direct PM2.5 emission reductions in 2015.68

EPA approved Rule 444 and Rule 445 on September 26, 2013 (see 79 FR 59249).69

 

68 See “Rule Evaluation Form,” South Coast Rules 444 and 445, and South Coast Air Quality Management District, 

Draft Final Staff Report, Proposed Amended Rule 445 – Wood-Burning Devices, Proposed Amended Rule 444 –

Open Burning, May 2013, pp. 15-16.

69 See letter dated June 11, 2013, from Edie Chang, Deputy Executive Officer, California Air Resources Board, to 

Jared Blumenfeld, Regional Administrator, EPA Region 9, transmitting South Coast Rules 444 and 445.
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G. Demonstration that Attainment by the Moderate Area Attainment Date is 

Impracticable

1. Requirements for Attainment/Impracticability of Attainment Demonstrations

CAA section 189(a)(1)(B) requires that each Moderate area attainment plan include a 

demonstration that the plan provides for attainment by the latest applicable Moderate area 

deadline or, alternatively, that attainment by the latest applicable attainment date is

impracticable. A demonstration that the plan provides for attainment must be based on air quality 

modeling, and the EPA generally recommends that a demonstration of impracticability also be 

based on air quality modeling consistent with EPA’s modeling guidance (General Preamble at 

13538).70

CAA section 188(c) states, in relevant part, that the Moderate area attainment date “shall 

be as expeditiously as practicable but no later than the end of the sixth calendar year after the 

area’s designation as nonattainment....” For the South Coast area, which was initially designated 

as nonattainment for the 2006 PM2.5 standard effective December 14, 2009, the applicable 

Moderate area attainment date under section 188(c) is as expeditiously as practicable but no later 

than December 31, 2015.

In SIP submissions to demonstrate impracticability, the State should document that its 

required control strategy in the attainment plan represents the application of RACM/RACT to 

existing sources. The EPA believes it is appropriate to require adoption of all available control

measures that are reasonable (i.e., technologically and economically feasible) in areas that do not 

demonstrate timely attainment, even where those measures cannot be implemented within the 4-

year timeframe for implementation of RACM under CAA section 189(a)(1)(C). The 

impracticability demonstration will then be based on a showing that the area cannot attain by the 

applicable attainment date, notwithstanding implementation of the required controls.

2. Impracticability Demonstration for the 2012 PM2.5 Plan and 2015 Supplement

By letter dated July 28, 2015, the District requested that the EPA reclassify the South 

Coast Air Basin to “Serious” for the 2006 PM2.5 NAAQS. The letter provided preliminary 2015 

air quality monitoring data for the Mira Loma monitoring station supporting a conclusion that 

attainment of the 2006 PM2.5 standard by December 31, 2015 in the South Coast is 

impracticable.71

Based in part on the information contained in this letter and in the 2012 PM2.5 Plan and 

Supplement, we have conducted an analysis of recent PM2.5 monitoring data for the South Coast 

PM2.5 nonattainment area.72 For this analysis, the EPA used certified data for 2013, 2014 and 

 

70 For more information on the applicable air quality modeling requirements, please see section II.B of the TSD.

71 See letter dated July 28, 2015, from Barry R. Wallerstein, Executive Officer, SCAQMD, to Elizabeth Adams, 

Acting Director, Air Division, US Environmental Protection Agency, Region 9.

72 See Memorandum dated August 21, 2015 from Michael Flagg, U.S. EPA, Region 9 Air Quality Analysis Office, 

to South Coast Docket EPA-R09-OAR-2015-0204, Subject: Practicability of South Coast 2015 Attainment of the 

2006 24-hour PM NAAQS (“Flagg Memo”).
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preliminary data available for 2015.73 Although the State and District originally intended for the 

2012 PM2.5 Plan and 2015 Supplement to demonstrate that the area would attain the 2006 PM2.5

NAAQS by the Moderate area attainment date of December 31, 2015, more recent monitoring 

data show that 24-hour PM2.5 levels in the South Coast, with a current design value (2012-2014) 

of 38 μg/m3 at the Mira Loma monitoring site, continue to be above the 35 μg/m3level of the 

2006 PM2.5 standard, and the recent trends in the South Coast’s 24-hour PM2.5 levels are not 

consistent with a projection of attainment by the end of 2015.

The EPA calculated the maximum allowed 2015 concentrations for all monitors in the 

area, and compared them to the estimated 2015 98th percentile. If the estimated 2015 98th

percentile was greater than the maximum allowed 2015 98th percentile concentration, the EPA 

considered attainment at that monitoring site impracticable. For each monitor, the EPA 

estimated the 2015 98th percentile from the 2015 data available in AQS as of August 2015, based 

a number of assumptions.74 The EPA assumed that the concentrations measured during the 

remainder of 2015 would be no higher than those already recorded, so the 98th percentile could 

be chosen from among the already recorded data. This is a conservative assumption for assessing 

the impracticability of attainment, since future concentrations and 98th percentiles could be 

higher than recorded values. 

The EPA’s analysis showed that during 2015, two monitoring sites (Rubidoux and Mira 

Loma-Van Buren) had estimated 98th percentiles greater than the maximum allowed 98th

percentile concentration for 2015, which indicates that attainment of the 2006 24-hour PM2.5 

NAAQS by the end of 2015 is impracticable.

In a separate analysis, EPA assumed that Rubidoux and Mira Loma-Van Buren collected 

a minimum of 351 daily samples (i.e. consistent with an everyday sampling frequency) in 2015, 

which would allow for selection of the 8th highest recorded value as the 98th percentile for 2015. 

This assumption resulted in selection of the lowest 98th percentile value possible for 2015, 

making the analysis more conservative than the previous approach. Even under this assumption, 

both Rubidoux and Mira Loma-Van Buren had estimated 2015 98th percentiles greater than the 

maximum allowed 2015 98th percentile.

 

73 Some data in the 2nd, 3rd, and 4th quarter of 2014 may have been impacted by a temporary lab closure and other 

issues at SCAQMD and are under current review. As a precautionary measure, we conducted an additional analysis 

on the impracticability of attaining by December 31, 2015 that completely excluded these data. The outcome of the 

analysis further supported the impracticability of attainment by the applicable attainment date. See Attachment to 

Flagg Memo, under “24-Hour Practicability” tab.

74 EPA also assumed that the sampling rate observed so far would continue throughout the year; this yielded an 

estimate of the number of total samples expected for 2015, and allowed for selection of the corresponding rank of 

the daily data available to use as the 98th percentile in accordance with 40 CFR part 50, appendix N, section 4.5. 
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3. Evaluation and Proposed Action

Our conservative assessment of recent PM2.5 air quality data indicates that attainment of 

the 2006 PM2.5 standard in the South Coast by December 31, 2015 is impracticable. We have 

also evaluated the RACM/RACT demonstration in the 2012 PM2.5 Plan and 2015 Supplement 

and find that it provides for the expeditious implementation of all RACM that may feasibly be 

implemented at this time, consistent with the requirements of CAA sections 172(c)(1) and 

189(a)(1)(C) for the 2006 PM2.5 NAAQS in the South Coast. See section II.D of this TSD. 

Implementation of this RACM/RACT control strategy appears, however, to be insufficient to 

bring the South Coast area into attainment by December 31, 2015.

Based on this evaluation, we propose to approve the State’s demonstration in the 2012 

PM2.5 Plan and 2015 Supplement that attainment of the 2006 PM2.5 standard by the Moderate 

area attainment date in the South Coast is impracticable, consistent with the requirements of 

CAA section 189(a)(1)(B)(ii). Based on this proposal, we propose to reclassify the South Coast 

as Serious nonattainment, which would trigger requirements for the State to submit a Serious 

area plan consistent with the requirements of subparts 1 and 4 of part D, Title I of the Act (see 

Section III of this TSD).
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H. Reasonable Further Progress and Quantitative Milestones

1. Requirements for Reasonable Further Progress and Quantitative Milestones

CAA section 172(c)(2) requires nonattainment area plans to provide for reasonable 

further progress (RFP). In addition, CAA section 189(c) requires PM2.5 nonattainment area SIPs

to include quantitative milestones to be achieved every 3 years until the area is redesignated to 

attainment and which demonstrate reasonable further progress (RFP), as defined in CAA section 

171(1). Section 171(1) defines RFP as “such annual incremental reductions in emissions of the 

relevant air pollutant as are required by [Part D] or may reasonably be required by the 

Administrator for the purpose of ensuring attainment of the applicable [NAAQS] by the 

applicable date.” Neither subpart 1 nor subpart 4 of part D, title 1 of the Act requires that a set 

percentage of emissions reductions be achieved in any given year for purposes of satisfying the 

RFP requirement.

RFP has historically been met by showing annual incremental emission reductions 

sufficient generally to maintain at least linear progress toward attainment by the applicable 

deadline (Addendum at 42015). As discussed in the EPA’s guidance in the Addendum, requiring 

linear progress in reductions of direct PM2.5 and any individual precursor in a PM2.5 plan may be 

appropriate in situations where: 

 the pollutant is emitted by a large number and range of sources,

 the relationship between any individual source or source category and overall air quality 

is not well known, 

 a chemical transformation is involved (e.g., secondary particulate significantly 

contributes to PM2.5 levels over the standard), and/or

 the emission reductions necessary to attain the PM2.5 standard are inventory-wide. Id.

The EPA’s guidance in the Addendum at 42105 recommends that requiring linear 

progress is less appropriate in other situations, such as:

 where there is a limited number of sources of direct PM2.5 or a precursor,

 where the relationships between individual sources and air quality are relatively well 

defined, and/or

 where the emission control systems utilized (e.g., at major point sources) will result in 

swift and dramatic emission reductions. Id.

In nonattainment areas characterized by any of these latter conditions, RFP may be better 

represented as step-wise progress as controls are implemented and achieve significant reductions 

soon thereafter. For example, if an area’s nonattainment problem can be attributed to a few major 

sources, EPA guidance indicates that “RFP should be met by ‘adherence to an ambitious 

compliance schedule’ which is likely to periodically yield significant emission reductions of 

direct PM2.5 or a PM2.5 precursor.” (Addendum at 42015.)

Plans for PM2.5 nonattainment areas should include detailed schedules for compliance 

with emission regulations in the area and provide corresponding annual emission reductions to

be realized from each milestone in the schedule (Addendum at 42016). In reviewing an 
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attainment plan under subpart 4, the EPA evaluates whether the annual incremental emission 

reductions to be achieved are reasonable in light of the statutory objective of timely attainment. 

Section 189(c) provides that the quantitative milestones submitted by a state for an area 

also must be consistent with RFP for the area. Thus, the EPA determines an area’s compliance 

with RFP in conjunction with determining its compliance with the quantitative milestone 

requirement. Because RFP is an annual emission reduction requirement and the quantitative 

milestones are to be achieved every 3 years, when the state demonstrates compliance with the 

quantitative milestone requirement, it will demonstrate that RFP has been achieved during each 

of the relevant 3 years. Quantitative milestones should consist of elements that allow progress 

toward attainment to be quantified or measured. Specifically, states should identify and submit 

quantitative milestones providing for the amount of emissions reductions adequate to achieve the 

NAAQs by the applicable attainment date (see Addendum at 42016). Implementation of control 

measures comprising the RFP plan may provide a means for satisfying the quantitative milestone 

requirement (see id.). The Act requires states to include RFP and quantitative milestones even 

for areas that cannot practicably attain.

2. RFP Demonstration and Quantitative Milestones in the 2012 PM2.5 Plan and 2015 Supplement

South Coast’s 2012 PM2.5 Plan was originally developed in accordance with the 

requirements of subpart 1 and the 2007 PM2.5 Implementation Rule (see 75 FR 20586, April 25, 

2007), which did not require a submittal of a separate RFP plan where the State submits a plan 

demonstrating attainment within five years of the date of designation (see 40 CFR 51.1009(b)). 

Because the 2012 PM2.5 Plan as originally adopted (in December 2012) included the State’s 

demonstration of attainment by December 14, 2014, which is five years from the date of 

designation,75 the Plan does not include a separate RFP demonstration. 

Following the D.C. Circuit’s January 2013 decision remanding the 2007 PM2.5

Implementation Rule (see NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013)) and the EPA’s June 

2014 promulgation of Moderate area classifications in the deadline and classifications rule (see 

79 FR 31566, June 2, 2014), the District developed the 2015 Supplement to address the 

applicable subpart 4 requirements for the 2006 PM2.5 NAAQS. By the time the State and District

submitted this Supplement to EPA in early 2015, less than a year remained before the December 

31, 2015 Moderate area attainment date applicable to the area under subpart 4, and ambient air 

quality monitoring data indicated the area was very close to attaining the 2006 PM2.5 standard. 

 

75 Section 172(a)(2)(A) of the CAA states, in relevant part, that the attainment date for a nonattainment area “shall 

be the date by which attainment can be achieved as expeditiously as practicable, but no later than 5 years from the 

date such area was designated nonattainment under section [107(d)].” Because the EPA designated South Coast as 

nonattainment for the 2006 24-hour standard effective December 14, 2009 (74 FR 58688, November 13, 2009), 

under subpart 1 the area was required to attain this standard no later than December 14, 2014.
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See 2015 Supplement, p. 4. Accordingly, the 2015 Supplement does not contain a separate RFP 

or quantitative milestone demonstration.

3. Evaluation and Proposed Action

As a result of the NRDC decision remanding the 2007 PM2.5 Implementation Rule, the 

EPA has considered whether the 2012 PM2.5 Plan and 2015 Supplement meet the RFP 

requirement in section 172(c)(2) of the Act and proposes to find that they do.

The 2012 PM2.5 Plan demonstrates that all RACM/RACT are being implemented as 

expeditiously as practicable and identifies projected emission levels for 2014 that reflect full 

implementation of the State’s and District’s RACM/RACT control strategy for the area.76 The

Plan also shows steady reductions in direct PM2.5, NOx, VOC, SOx, and ammonia emissions 

during the 2008-2014 period. Figures IIH-1 and IIH-2 show the emissions trajectories for direct 

PM2.5 and each PM2.5 precursor addressed in the control strategy which indicate generally linear 

reductions. We propose, therefore, to approve the 2012 PM2.5 Plan and 2015 Supplement as 

satisfying the requirement for RFP in CAA section 172(c)(2) for the 2006 PM2.5 standard.

With respect to quantitative milestones, the EPA is proposing to establish December 31, 

2014 as the starting point for the first 3-year period under CAA section 189(e) for the 2006 PM2.5

standard in the South Coast. This date is the due date for the State’s submittal of attainmentrelated SIPs necessary to satisfy the Moderate area requirements applicable to the South Coast 

area.77 Accordingly, the first quantitative milestone date for the South Coast area would be 

December 31, 2017 (3 years after December 31, 2014). Because this date falls well after the 

applicable Moderate area attainment date for the area, which is December 31, 2015, we propose 

to find that quantitative milestones are not necessary in this particular Moderate area plan. If, 

however, EPA either finalizes this proposal to reclassify the South Coast area as Serious 

nonattainment for the 2006 PM2.5 standard or determines that the area has failed to attain by the 

December 31, 2015 attainment date, the State and District will be required to submit a Serious 

area plan that contains, among other things, quantitative milestones that demonstrate RFP at each 

milestone date, starting December 31, 2017 and at subsequent 3-year intervals until the area is 

redesignated to attainment.

 

76 See 2012 PM2.5 plan at Chapter 4, pp. 4-4 through 4-13, Table 4-7, and Appendix III, Table III-2-2B (“Emission 

Reductions (Tons per Day) in the Baseline by District Rules”). 

77 Subpart 4 requires states to submit attainment plans within 18 months after nonattainment designations (CAA 

189(a)(2)). Due to unusual circumstances, however, the EPA has by rule created a later deadline for submittal of 

attainment plan submission date for the 2006 PM2.5 NAAQS in order to provide states a reasonable amount of time 

to address the requirements of subpart 4 consistent with the NRDC decision. See 79 FR 31566 (June 2, 2014).
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Source for Figures IIH-1 and IIH-2: 2012 AQMP, Chapter 3, Tables 3-2A, 3-4A, Appendix III, Table III-1-5, and 

2008 ammonia inventory from Appendix V, Table V-4-2. 

0

100

200

300

400

500

600

700

800

2008 2014

tons per day (tpd)

year

Figure IIH-1. Reduction in Overall NOx and VOC Emissions, 

2008-2014

NOx VOC

0

20

40

60

80

100

120

2008 2014

tons per day (tpd)

year

Figure IIH-2. Reduction in Overall PM2.5, SOx, and Ammonia 

Emissions, 2008-2014

PM2.5 SOx NH3
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I. Contingency Measures

1. Requirements for Contingency Measures

Under CAA section 172(c)(9), PM2.5 plans must include contingency measures to be 

implemented if an area fails to meet RFP (“RFP contingency measures”) or fails to attain the 

PM2.5 NAAQS by the applicable attainment date (“attainment contingency measures”). Under 

subpart 4, however, the EPA interprets section 172(c)(9) in light of the specific requirements for 

particulate matter nonattainment areas. Section 189(b)(1)(A) differentiates between attainment 

plans that provide for timely attainment and those that demonstrate that attainment is 

impracticable. Where the SIP includes a demonstration that attainment by the applicable 

attainment date is impracticable, the state need only submit contingency measures to be 

implemented if an area fails to meet RFP.78

The purpose of contingency measures is to continue progress in reducing emissions while 

the SIP is being revised to meet the missed RFP milestone or to provide for attainment.

The principal requirements and recommendations for contingency measures are:

 Contingency measures must be fully adopted rules or control measures that are 

ready to be implemented quickly upon failure to meet RFP or failure of the area to 

meet the standard by its attainment date.

 The SIP should contain trigger mechanisms for the contingency measures, specify 

a schedule for implementation, and indicate that the measures will be 

implemented without further action by the state or by the EPA. In general, we

expect all actions needed to effect full implementation of the measures to occur 

within 60 days after the EPA notifies the state of a failure.

 Contingency measures should consist of control measures for the area that are not 

relied on to demonstrate attainment or RFP. 

 The measures should provide for emissions reductions equivalent to 

approximately one year of reductions needed for RFP calculated as the overall 

level of reductions needed to demonstrate attainment divided by the number of 

years from the base year to the attainment year.

See General Preamble at 13543 and Addendum at 42014.

2. Contingency Measures in the 2012 PM2.5 Plan and 2015 Supplement

Contingency measures for failure to attain are described in Chapter 6, pages 6-7 to 6-13 

of the 2012 PM2.5 Plan. The 2012 PM2.5 Plan and 2015 Supplement do not include contingency 

measures for failure to meet RFP.

 

78 The EPA does not interpret the requirement for failure-to-attain contingency measures to apply to Moderate PM2.5

nonattainment areas that cannot practicably attain the NAAQS by the statutory attainment date. Rather, the EPA 

believes it is appropriate for the state to identify and adopt attainment contingency measures as part of the Serious 

area attainment plan that it will develop once the EPA reclassifies the area (Addendum at 42015).
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3. Evaluation and Proposed Action

Because we are proposing to approve the State’s demonstration that attainment by the 

applicable Moderate area attainment date of December 31, 2015 is impracticable in the South 

Coast and to reclassify the area to serious, contingency measures for failure to attain are not 

required as part of this Moderate area plan. Upon reclassification of the South Coast area as a 

Serious area, California will be required to adopt attainment contingency measures as part of the 

Serious area attainment plan for the 2006 PM2.5 NAAQS.

We propose to find that the RFP contingency measure requirement for any RFP 

milestone year prior to 2014 is now moot as applied to the South Coast PM2.5 nonattainment 

area. The sole purpose of RFP contingency measures is to provide continued progress if an area 

fails to meet its RFP goal. Failure to meet any milestone year target prior to 2014 would have 

required California to implement RFP contingency measures in the South Coast and to revise the 

2012 PM2.5 Plan to assure that it still provided for attainment by the applicable attainment date of 

December 31, 2015. In this case, however, the 2012 PM2.5 Plan and 2015 Supplement 

demonstrate that actual emission levels in the years leading up to 2014 were consistent with RFP 

for direct PM2.5 and all four precursor pollutants (NOx, SOx, VOC and ammonia) regulated in 

the 2012 PM2.5 Plan. Accordingly, RFP contingency measures no longer have meaning or 

purpose, and therefore EPA proposes to find that the requirement for them is now moot. 
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J. Motor Vehicle Emissions Budgets

1. Requirements for Motor Vehicle Emissions Budgets

CAA section 176(c) requires Federal actions in nonattainment and maintenance areas to

conform to the SIP’s goals of eliminating or reducing the severity and number of violations of 

the NAAQS and achieving expeditious attainment of the standards. Conformity to the SIP’s 

goals means that such actions will not: (1) cause or contribute to violations of a NAAQS, (2) 

worsen the severity of an existing violation, or (3) delay timely attainment of any NAAQS or any 

interim milestone.

Actions involving Federal Highway Administration (FHWA) or Federal Transit 

Administration (FTA) funding or approval are subject to the EPA’s transportation conformity 

rule, codified at 40 CFR part 93, subpart A. Under this rule, MPOs in nonattainment and 

maintenance areas coordinate with state and local air quality and transportation agencies, EPA, 

FHWA, and FTA to demonstrate that an area’s RTP and transportation improvement programs 

(TIP) conform to the applicable SIP. This demonstration is typically done by showing that 

estimated emissions from existing and planned highway and transit systems are less than or equal 

to the motor vehicle emissions budgets (budgets) contained in all control strategy SIPs. An 

attainment, maintenance, or RFP SIP should include budgets for the attainment year, each 

required RFP year, or the last year of the maintenance plan, as appropriate. Budgets are generally 

established for specific years and specific pollutants or precursors and must reflect all of the 

motor vehicle control measures contained in the attainment and RFP demonstrations 

(40 CFR § 93.118(e)(4)(v)).

PM2.5 plans should identify motor vehicle emission budgets for direct PM2.5 and all 

significant PM2.5 precursors for each RFP milestone year and the attainment year, if the plan 

demonstrates attainment. All direct PM2.5 SIP budgets should include direct PM2.5 motor vehicle 

emissions from tailpipe, brake wear, and tire wear. A state must also consider whether reentrained paved and unpaved road dust or highway and transit construction dust are significant 

contributors and should be included in the direct PM2.5 budget. See 40 CFR § 93.102(b) and 

§ 93.122(f) and the conformity rule preamble at 69 FR 40004, 40031–40036 (July 1, 2004). 

2. Motor Vehicle Emissions Budgets in the 2012 PM2.5 Plan and 2015 Supplement

The 2015 Supplement revised the attainment demonstration in the 2012 PM2.5 Plan to 

identify December 31, 2015 as the applicable attainment date, and included revised budgets for 

2015 for directly emitted PM2.5, NOx, and VOC. See 2015 Supplement, Attachment C, Table C1. These budgets reflect average annual daily emissions and are calculated using EMFAC2011, 

the currently approved mobile source emission model for California, and transportation activity 

from SCAG’s adopted 2012 Regional Transportation Plan (RTP), consistent with the 

methodology for developing the emissions inventories used in the attainment demonstration. 

Reductions from incentive measures were removed from the budgets, and off-model reductions 

for reformulated gasoline (RFG) and SmogCheck (California’s inspection and maintenance 

program) which were not in EMFAC2011 were included in the budgets, consistent with the 

emissions inventory used in the attainment demonstration. 

The direct PM2.5 budgets included tailpipe, brake wear, and tire wear emissions as well as

paved and unpaved road dust and road construction dust. No budgets for SO2 were included in 
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the 2012 PM2.5 Plan or 2015 Supplement because on-road emissions of SO2 are a small part (11

percent) of the total SO2 inventory. No budgets for ammonia were included in the 2012 PM2.5

Plan or 2015 Supplement. 

3. Conclusion and Proposed Actions 

We are not acting on the motor vehicle emission budgets for direct PM2.5, NOx, and VOC

in the 2012 PM2.5 Plan or 2015 Supplement. We have previously approved motor vehicle 

emissions budgets for the 1997 annual and 24-hour PM2.5 standards (76 FR 69928, 69951

(November 9, 2011)), and these budgets will continue to apply in the South Coast for

transportation conformity purposes for these standards. The same budgets will also continue to 

apply for the 2006 24-hour PM2.5 standard until we finalize our approval of new budgets in the 

Serious area plan for the 2006 PM2.5 NAAQS or find those budgets adequate. The budgets 

approved in 2011 will continue to apply in the South Coast for determining transportation 

conformity for the 1997 PM2.5 annual and 24-hour standards.79

 

79 In 2012, the EPA revised the annual PM2.5 standard, lowering its level from 15 μg/m3

to 12 μg/m3(78 FR 3086 

(January 15, 2013). We finalized designations for the 2012 standard in December, 2014 and these designations 

became effective April 15, 2015. See 80 FR 2206, January 15, 2015. For purposes of the 2012 PM2.5 standard, the 

regional conformity test requirements for all nonattainment and maintenance areas in 40 CFR 93.109 will apply one 

year after the effective date of EPA’s nonattainment designations in accordance with section 93.102(d) and until the 

effective date of revocation of such NAAQS.
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K. General Conformity Budgets

1. Requirements for General Conformity

Conformity is required under CAA section 176(c) to ensure that federal actions are 

consistent with (“conform to”) the purpose of the SIP. Conformity to the purpose of the SIP 

means that federal activities will not cause new air quality violations, worsen existing violations, 

or delay timely attainment of the relevant NAAQS or interim reductions and milestones. 

Conformity applies to areas that are designated nonattainment and to maintenance areas.

Section 176(c)(4) of the CAA establishes the framework for general conformity. The 

EPA first promulgated general conformity regulations in November 1993 (40 CFR part 51, 

subpart W, 40 CFR part 93, subpart B). Subsequently we revised the general conformity 

regulations on April 5, 2010 (75 FR 17254). Besides ensuring that federal actions not covered by 

the transportation conformity rule will not interfere with the SIP, the general conformity 

regulations encourage consultation between the federal agency and the state or local air pollution 

control agencies before and during the environmental review process, as well as public 

notification of and access to federal agency conformity determinations, and allows for air quality 

review of individual federal actions.

The general conformity regulations provide three phases: (A) applicability analysis, (B) 

conformity determination, and (C) review process. The applicability analysis phase under 40 

CFR § 93.153 is used to determine whether a Federal action requires a conformity determination 

for a specific pollutant. If a conformity determination is needed, Federal agencies can use one of 

several methods to show that the project conforms to the SIP. In an area without a State 

Implementation Plan (SIP), a federal action may be shown to "conform" by demonstrating there 

will be no net increase in emission in the nonattainment or maintenance area from the Federal 

action.

In an area with a SIP, conformity to the applicable SIP can be demonstrated in one of 

several ways. For actions where the direct and indirect emissions exceeds the rates in 40 CFR §

93.153(b), the federal action can include mitigation efforts to bring emissions to levels below the

thresholds or they can show that the action will conform by meeting any of the following 

requirements:

 By showing that the net emission increases caused by an action are included in the SIP,

 By documenting that the State agrees to include the emission increases in the SIP,

 Through offsetting the action’s emissions in the same or nearby area of equal or greater 

classification, or

 Through an air quality modeling demonstration in some circumstances.

The general conformity regulations at 40 CFR 93.161 allow state and local air quality 

agencies working with federal agencies with large facilities (e.g., commercial airports, ports and 

large military bases) that are subject to the general conformity regulations to develop and adopt 

an emissions budget for those facilities in order to facilitate future conformity determinations. 

Such a budget, referred to as a facility-wide emission budget, may be used by federal agencies to 

demonstrate conformity as long as the total facility-wide budget level identified in the SIP is not 

exceeded.
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According to 40 CFR 93.161, the state or local agency responsible for implementing and 

enforcing the SIP can develop and adopt an emissions budget to be used for demonstrating 

conformity under 40 CFR 93.158(a)(1). The facility-wide budget must (1) be for a set time 

period; (2) cover the pollutants or precursors of the pollutants for which the area is designated 

nonattainment or maintenance; (3) the budgets are specific about what can be emitted on an 

annual or seasonal basis; (4) the emissions from the facility along with all other emissions in the 

area will not exceed the total SIP emissions budget for the nonattainment or maintenance area; 

(5) specific measures are included to ensure compliance with the facility-wide budget, such as 

periodic reporting requirements or compliance demonstrations when the Federal agency is taking 

an action that would otherwise require a conformity determination; (6) the budget must be 

submitted to EPA as a SIP revision; and (7) the SIP revision must be approved by EPA. Having 

or using a facility-wide emissions budget does not preclude a Federal agency from demonstrating 

conformity in any other manner allowed by the conformity rule.

2. General Conformity Budget in the 2012 PM2.5 Plan and 2015 Supplement

The 2012 PM2.5 Plan addresses general conformity beginning on page II-2-52 of 

Appendix III. The District identified the de minimis thresholds for general conformity in the 

South Coast as 10 tpy of VOC and NOx because of its designation and classification as a severe 

ozone nonattainment area, and 100 tpy of PM2.5 because of its designation and classification as a 

moderate PM2.5 nonattainment area.80 The District examined historical records and noted that 

projects requiring general conformity determinations had historically not exceeded the PM2.5 de 

minimis levels. The main pollutant of concern during project construction was NOx, and to a 

lesser extent, VOC. To streamline the general conformity process for projects and to facilitate 

general conformity determinations, VOC and NOx general conformity budgets of 1 tpd of NOx 

and 0.2 tpd of VOC were established on an annual basis from 2013 to 2030. These general 

conformity budgets will be tracked via a tracking system that the District sets up for projects 

subject to general conformity determinations. The District will count project emissions towards 

the applicable general conformity budget until the budget has been used. Any unused portions 

will not carry forward from year to year. Once the budget is used, federal projects can still 

demonstration conformity using other provisions in the conformity rule. And federal projects that 

emit criteria pollutants or pollutant precursors other than those for which general conformity 

budgets are established will still need to demonstrate conformity for those pollutants or 

precursors. 

3. Evaluation and Proposed Action

We propose to approve the general conformity budgets in the 2012 PM2.5 Plan for NOx 

and VOC for 2013 to 2030 as meeting the requirements of the CAA and the general conformity 

rule. If we finalize our approval of these budgets, Federal agencies can use these budgets to 

demonstrate that their projects conform to the SIP through a letter from the State and District 

 

80 Final reclassification of the South Coast area as Serious nonattainment for the 2006 PM2.5 standard may lower the 

de minimis threshold under the CAA’s General Conformity requirements (40 CFR part 93, subpart B) from 100 tpy 

to 70 tpy for PM2.5 and PM2.5 precursors. See 80 FR 15339 at 15441; see also Section III of this TSD.
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confirming that the project’s emissions are accounted for in the SIP’s general conformity 

budgets. The District will be responsible for tracking emissions from all projects against the 

budgets. Once the budgets are exhausted, future federal projects will need to demonstrate 

conformity using a different method.
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III. Proposed Reclassification as Serious Nonattainment and 

Serious Area SIP Requirements
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A. Proposed Reclassification as Serious and Applicable Attainment Date

Section 188 of the Act outlines the process for classification of PM2.5 nonattainment areas 

and establishes the applicable attainment dates. Under the plain meaning of the terms of section 

188(b)(1) of the Act, the EPA has general authority to reclassify at any time before the 

applicable attainment date any area that the EPA determines cannot practicably attain the 

standard by such date. Accordingly, section 188(b)(1) of the Act is a general expression of 

delegated rulemaking authority. In addition, subparagraphs (A) and (B) of section 188(b)(1) 

mandate that the EPA reclassify “appropriate” PM10 nonattainment areas at specified time frames 

(i.e., by December 31, 1991 for the initial PM10 nonattainment areas, and within 18 months after 

the SIP submittal due date for subsequent nonattainment areas). These subparagraphs do not 

restrict the EPA’s general authority but simply specify that, at a minimum, it must be exercised 

at certain times.81

We have reviewed recent PM2.5 monitoring data for the South Coast available in the 

EPA’s Air Quality System (AQS) database. These data show that 24-hour PM2.5 levels in the 

South Coast continue to be above 35 μg/m3, the level of the 2006 PM2.5 standard, and the recent 

trends in the South Coast’s 24-hour PM2.5 levels are not consistent with a projection of 

attainment by the end of 2015. (See Memorandum dated August 21, 2015, Michael Flagg, US 

EPA Region 9, Air Quality Analysis Office). 

In accordance with section 188(b)(1) of the Act, the EPA is proposing to reclassify the 

South Coast area from Moderate to Serious nonattainment for the 2006 24-hour PM2.5 standard

of 35 μg/m3, based on the EPA’s determination that the South Coast area cannot practicably 

attain this standard by the applicable attainment date of December 31, 2015.

 

81 For a general discussion of EPA’s interpretation of the reclassification provisions in section 188(b)(1) of the Act,

see the General Preamble, 57 FR 13498 at 13537-38 (April 16, 1992).
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Under section 188(c)(2) of the Act, the attainment date for a Serious area “shall be as 

expeditiously as practicable but no later than the end of the tenth calendar year beginning after the 

area’s designation as nonattainment....” The South Coast area was designated nonattainment for 

the 2006 PM2.5 standard effective December 14, 2009.82 Therefore, upon final reclassification of 

the South Coast area as a Serious nonattainment area, the latest permissible attainment date under 

section 188(c)(2) of the Act, for purposes of the 2006 PM2.5 standard in this area, will be 

December 31, 2019. 

Under section 188(e) of the Act, a state may apply to EPA for a single extension of the 

Serious area attainment date by up to 5 years, which EPA may grant if the State satisfies certain 

conditions. Before EPA may extend the attainment date for a Serious area under section 188(e), the 

State must: (1) apply for an extension of the attainment date beyond the statutory attainment date; 

(2) demonstrate that attainment by the statutory attainment date is impracticable; (3) have 

complied with all requirements and commitments pertaining to the area in the implementation 

plan; (4) demonstrate to the satisfaction of the Administrator that the plan for the area includes the 

most stringent measures that are included in the implementation plan of any State or are achieved 

in practice in any State, and can feasibly be implemented in the area; and (5) submit a 

demonstration of attainment by the most expeditious alternative date practicable.83

B. Clean Air Act Requirements for Serious PM2.5 Nonattainment Area Plans

Upon reclassification as a Serious nonattainment area for the 2006 PM2.5 NAAQS, 

California will be required to submit additional SIP revisions to satisfy the statutory requirements 

that apply to Serious PM2.5 nonattainment areas, including the requirements of subpart 4 of part D, 

title I of the Act.

The Serious area SIP elements that California will be required to submit are as follows:

1. provisions to assure that the best available control measures (BACM), including best 

available control technology (BACT) for stationary sources, for the control of direct PM2.5

and PM2.5 precursors shall be implemented no later than 4 years after the area is reclassified 

(CAA section 189(b)(1)(B));

2. a demonstration (including air quality modeling) that the plan provides for attainment as 

expeditiously as practicable but no later than December 31, 2019, or where the State is 

seeking an extension of the attainment date under section 188(e), a demonstration that 

attainment by December 31, 2019 is impracticable and that the plan provides for attainment 

by the most expeditious alternative date practicable and no later than December 31, 2024

(CAA sections 188(c)(2) and 189(b)(1)(A)); 

 

82 See 74 FR 58688 (November 13, 2009).

83 For a discussion of EPA’s interpretation of the requirements of section 188(e), see “State Implementation Plans for 

Serious PM10 Nonattainment Areas, and Attainment Date Waivers for PM10 Nonattainment Areas Generally; 

Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990,” 59 

FR 41998 (August 16, 1994) (hereafter “Addendum”) at 42002; 65 FR 19964 (April 13, 2000) (proposed action on 

PM10 Plan for Maricopa County, Arizona); 66 FR 50252 (October 2, 2001) (proposed action on PM10 Plan for 

Maricopa County, Arizona); 67 FR 48718 (July 25, 2002) (final action on PM10 Plan for Maricopa County, Arizona); 

and Vigil v. EPA, 366 F.3d 1025, amended at 381 F.3d 826 (9th Cir. 2004) (remanding EPA action on PM10 Plan for 

Maricopa County, Arizona but generally upholding EPA’s interpretation of CAA section 188(e)).
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3. plan provisions that require reasonable further progress (RFP) (CAA 172(c)(2));

4. quantitative milestones which are to be achieved every 3 years until the area is redesignated 

attainment and which demonstrate RFP toward attainment by the applicable date (CAA 

section 189(c)); 

5. provisions to assure that control requirements applicable to major stationary sources of 

PM2.5 also apply to major stationary sources of PM2.5 precursors, except where the state 

demonstrates to the EPA’s satisfaction that such sources do not contribute significantly to 

PM2.5 levels that exceed the standard in the area (CAA section 189(e));

6. a comprehensive, accurate, current inventory of actual emissions from all sources of PM2.5

and PM2.5 precursors in the area (CAA section 172(c)(3));

7. contingency measures to be implemented if the area fails to meet RFP or to attain by the

applicable attainment date (CAA section 172(c)(9)); and

8. A revision to the nonattainment new source review (NNSR) program to lower the 

applicable “major stationary source”84 thresholds from 100 tons per year (tpy) to 70 tpy 

(CAA section 189(b)(3)).

Final reclassification of the South Coast area as Serious nonattainment for the 2006 PM2.5

standard may also lower the de minimis threshold under the CAA’s General Conformity 

requirements (40 CFR part 93, subpart B) from 100 tpy to 70 tpy for PM2.5 and PM2.5 precursors. 

See 80 FR 15339 at 15441.

The EPA recently issued a proposed rulemaking to provide guidance to states on the 

attainment planning requirements in subparts 1 and 4 of part D, title I of the Act that apply to areas 

designated nonattainment for PM2.5.

85 In the interim, before the PM2.5 implementation rule is 

finalized, EPA encourages the State to review the proposed rulemaking as well as the General 

Preamble and Addendum for guidance on how to implement these statutory requirements in the 

South Coast PM2.5 nonattainment area.86

C. Statutory Deadline for Submittal of the Serious Area Plan

For an area reclassified as a Serious nonattainment area before the applicable attainment 

date under CAA section 188(b)(1), section 189(b)(2) requires the State to submit the required 

BACM provisions “no later than 18 months after reclassification of the area as a Serious Area” and 

to submit the required attainment demonstration “no later than 4 years after reclassification of the 

area to Serious.” Section 189(b)(2) establishes outer bounds on the SIP submission deadlines and 

does not preclude the EPA’s establishment of earlier deadlines as necessary or appropriate to 

assure consistency among the required submissions and to implement the statutory requirements.

If a final reclassification of the South Coast PM2.5 nonattainment area to Serious becomes 

effective by early 2016, the Act provides the State with up to 18 months after this date (i.e., until 

 

84 For any Serious area, the terms “major source” and “major stationary source” include any stationary source that 

emits or has the potential to emit at least 70 tons per year of PM10 (CAA sections 189(b)(3)).

85 See 80 FR 15339, “Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan 

Requirements,” March 23, 2015.

86 See generally the General Preamble, 57 FR 13498 (April 16, 1992) and Addendum, 59 FR 41998 (August 16, 1994).
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mid-2017) to submit the required BACM provisions. Because an up-to-date emissions inventory 

serves as the foundation for a state’s BACM and BACT determinations, the EPA also proposes to 

require the State to submit the emissions inventory required under CAA section 172(c)(3) within 

18 months after the effective date of final reclassification. Similarly, because an effective 

evaluation of BACM and BACT measures requires evaluation of the precursor pollutants that must 

be controlled to provide for expeditious attainment in the area, if the State chooses to submit an 

optional precursor insignificance demonstration to support a determination to exclude a PM2.5

precursor from the required control measure evaluations for the area, the EPA proposes to require 

the State to submit any such demonstration by this same date. An 18-month timeframe for 

submission of these plan elements is consistent with both the timeframe for submission of BACM 

provisions under CAA section 189(b)(2) and the timeframe for submission of subpart 1 plan 

elements under section 172(b) of the Act.87

The EPA proposes to require the State to submit the attainment demonstration required 

under section 189(b)(1)(A) and the remaining attainment-related plan elements no later than three 

years after the effective date of final reclassification or by December 31, 2018, whichever is 

earlier. The attainment-related plan elements that we propose to require within the same 3-year 

timeframe as the attainment demonstration are: (1) the RFP demonstration required under section 

172(c)(2); (2) the quantitative milestones required under section 189(c); (3) any additional control 

measures necessary to meet the requirements of section 172(c)(6); and (4) the contingency 

measures required under section 172(c)(9). Although section 189(b)(2) generally provides for up 

to 4 years after a discretionary reclassification for the State to submit the required attainment 

demonstration, it is appropriate in this case for the EPA to establish an earlier SIP submission 

deadline to assure timely implementation of the statutory requirements. 

The EPA designated the South Coast area as nonattainment for the 2006 PM2.5 standard 

effective December 14, 2009.88 On January 4, 2013, the D.C. Circuit Court of Appeals issued its 

decision in NRDC remanding EPA’s 2007 PM2.5 Implementation Rule and directing the EPA to 

repromulgate it in accordance with the requirements of subpart 4.89 In response to the NRDC

decision, the EPA undertook a rulemaking to classify all PM2.5 nonattainment areas as Moderate 

nonattainment and begin implementing the PM2.5 NAAQS under subpart 4. Effective July 2, 2014, 

the EPA classified all areas previously designated nonattainment for the 1997 and/or 2006 PM2.5

NAAQS as Moderate nonattainment under subpart 4 and established a December 31, 2014 

deadline for states to submit Moderate area SIP elements required for these areas.90 These unusual 

circumstances have significantly shortened the timeframes ordinarily allowed under the Act for the 

 

87 Section 172(b) requires EPA to establish, concurrent with nonattainment area designations, a schedule extending no 

later than 3 years from the date of the nonattainment designation for states to submit plans or plan revisions meeting 

the applicable requirements of sections 110(a)(2) and 172(c) of the CAA.

88 74 FR 58688 (November 13, 2009).

89 NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013). 

90 79 FR 31566 (June 2, 2014). EPA notes that some states had already made SIP submissions intended to meet 

applicable nonattainment plan requirements as interpreted in the remanded 2007 PM2.5 Implementation Rule. 

Accordingly, the new SIP submission deadline provided the opportunity for states to revise or supplement their prior 

submissions, as necessary or appropriate to meet subpart 4 requirements.
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EPA and the states to address the statutory SIP requirements following reclassification of an area 

from Moderate to Serious nonattainment under subpart 4.91

Our proposal to require the State to submit the attainment demonstration and other 

attainment-related plan elements no later than three years after reclassification or by December 31, 

2018, whichever is earlier, is supported by the overall structure and purpose of the attainment 

planning requirements in part D, title I of the Act. Section 188(b)(1) provides the EPA with 

discretionary authority to reclassify an area as Serious nonattainment at any time before the 

applicable attainment date, based on a determination that the area cannot practicably attain the 

NAAQS by the Moderate area attainment date. Under normal circumstances, where the EPA 

reclassifies an area within 3 years after its designation as nonattainment, as contemplated in CAA 

section 188(b)(1)(B),92 the required BACM provisions would be due no later than 18 months after 

reclassification (i.e., no later than 4.5 years after designation) and the required attainment 

demonstration would be due no later than 4 years after reclassification (i.e., no later than 7 years 

after designation).93 In these circumstances, the Serious area attainment demonstration would be 

due at least 3 years before the outermost Serious area attainment date for the area,94 thus providing 

the EPA with sufficient time to evaluate the submitted plan well in advance of the statutory 

attainment date. However, in situations such as this, where the EPA reclassifies an area pursuant 

to its discretionary reclassification authority later than 3 years after the area’s designation as 

nonattainment, it is appropriate for the EPA to consider the outermost Serious area attainment date 

applicable to the area in setting a deadline for the State to submit the required elements of the 

Serious area attainment plan. 

Upon reclassification as Serious, the South Coast PM2.5 nonattainment area will be subject 

to a Serious area attainment date no later than December 31, 2019.95 Sections 189(b)(1)(A) and 

189(c) of the Act require the State to submit a demonstration that the plan provides for attainment 

of the PM2.5 standard by this date, including quantitative milestones which are to be achieved 

every 3 years until the area is redesignated attainment and which demonstrate reasonable further 

progress toward attainment by this date. If the EPA reclassifies the South Coast area effective in 

early 2016 and allows the State 4 years following reclassification (i.e., potentially until early 2020) 

to submit the attainment demonstration and related plan elements, these Serious area plan 

 

91 For areas designated nonattainment after November 15, 1990, section 188(b)(1)(B) of the Act requires that EPA 

“reclassify appropriate areas within 18 months after the required date for the State’s submission of a SIP for the 

Moderate Area.” Read together with section 189(a)(2)(B), which requires states to submit Moderate Area plans within 

18 months after nonattainment designations, section 188(b)(1)(B) generally contemplates that EPA would reclassify 

appropriate areas as Serious nonattainment no later than 36 months (3 years) after initial nonattainment designations. 

Under these circumstances, the required Serious area attainment demonstration would normally be submitted no later 

than 7 years after initial designation (4 years after reclassification), which is 3 years before the latest permissible 

attainment date under CAA section 188(c)(2).

92 Id.

93 CAA section 189(b)(2). By contrast, for an area that is reclassified as Serious by operation of law after the 

applicable attainment date, which may be as late as the end of the 6th year after the area’s designation as nonattainment 

(CAA section 188(b)(1)), the state must submit both the BACM provisions and the Serious area attainment 

demonstration no later than 18 months after reclassification. Id.

94 Under CAA section 188(c)(2), the latest permissible attainment date for a Serious PM2.5 nonattainment area is no 

later than the end of the tenth calendar year beginning after the area’s designation as nonattainment.

95 Id.
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provisions would not be due until after the latest permissible statutory attainment date for the area 

(December 31, 2019) has come and gone. Thus, under such circumstances, allowing the maximum 

4-year timeframe for submission of the required attainment demonstration and related plan 

elements would frustrate the statutory design and severely constrain the EPA’s ability to ensure 

that the State is implementing the applicable statutory requirements in a timely manner. 

Therefore, it is appropriate for the EPA to require California to submit the required 

attainment demonstration and other attainment-related plan elements no later than 3 years after 

final reclassification or by December 31, 2018, whichever is earlier, so that the EPA has adequate 

time to review and act on the State’s submission prior to the latest permissible attainment date for 

the area under section 188(c)(2), which is December 31, 2019. This timeframe for the required 

Serious area plan submissions is appropriate to assure consistency among the required submissions 

and to implement the statutory requirements in a timely manner.

Finally, the EPA proposes to require that the State submit revised nonattainment NSR 

program requirements no later than 18 months after final reclassification. The Act does not specify 

a deadline for the State’s submission of SIP revisions to meet nonattainment NSR program 

requirements to lower the “major stationary source” threshold from 100 tons per year (tpy) to 70 

tpy (CAA section 189(b)(3)) and to address the control requirements for major stationary sources 

of PM2.5 precursors (CAA section 189(e))96 following reclassification of a Moderate PM2.5

nonattainment area as Serious nonattainment under subpart 4. Pursuant to the EPA’s gap-filling 

authority in CAA section 301(a) and to effectuate the statutory control requirements in section 189 

of the Act, the EPA proposes to require the State to submit these nonattainment NSR SIP 

revisions, as well as any necessary analysis of and additional control requirements for major 

stationary sources of PM2.5 precursors, no later than 18 months after the effective date of final 

reclassification of the South Coast area as Serious nonattainment for the 2006 PM2.5 standard. This 

due date will ensure that necessary control requirements for major sources are established well in 

advance of the required attainment demonstration. An 18-month timeframe for submission of the 

NNSR SIP revisions also aligns with the statutory deadline for submission of BACM and BACT 

provisions and the broader analysis of PM2.5 precursors for potential controls on existing sources in 

the area. 

 

96 Section 189(e) requires that the control requirements applicable to major stationary sources of PM2.5 also apply to 

major stationary sources of PM2.5 precursors, except where the state demonstrates to EPA’s satisfaction that such 

sources do not contribute significantly to PM2.5 levels that exceed the standard in the area.
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D. Reclassification of Reservation Areas of Indian Country97

Seven Indian tribes are located within the boundaries of the South Coast PM2.5

nonattainment area. These tribes are listed in Table III-2 below.

Table III-2. Indian Tribes Located in South Coast PM2.5 Nonattainment Area

Cahuilla Band of Indians

Morongo Band of Cahuilla Mission Indians

Pechanga Band of Luiseno Mission Indians of the Pechanga Reservation

Ramona Band of Cahuilla

San Manuel Band of Serrano Mission Indians of the San Manuel Reservation

Santa Rosa Band of Cahuilla Indians

Soboba Band of Luiseno Indians

We have considered the relevance of our proposal to reclassify the South Coast area as 

Serious nonattainment for the 2006 PM2.5 standard to each tribe located within the South Coast

area. We believe that the same facts and circumstances that support the proposal for the non-Indian 

country lands also support the proposal for reservation areas of Indian country and any other area 

of Indian country where the EPA or a tribe has demonstrated that the tribe has jurisdiction located 

within the South Coast nonattainment area. The EPA is therefore proposing to exercise our 

authority under CAA section 188(b)(1) to reclassify areas of Indian country geographically located 

in the South Coast nonattainment area. Section 188(b)(1) broadly authorizes the EPA to reclassify 

a nonattainment area – including any Indian country located within such an area – that EPA 

determines cannot practicably attain the relevant standard by the applicable attainment date.

Directly-emitted PM2.5 and its precursor pollutants (NOx, SO2, VOC, and ammonia) are 

emitted throughout a nonattainment area and can be transported throughout that nonattainment 

area. Therefore, boundaries for nonattainment areas are drawn to encompass both areas with direct 

sources of the pollution problem as well as nearby areas in the same airshed. Initial classifications 

of nonattainment areas are coterminous with, that is, they match exactly, their boundaries. The 

EPA believes this approach best ensures public health protection from the adverse effects of PM2.5

pollution. Therefore, it is generally counterproductive from an air quality and planning perspective 

to have a disparate classification for a land area located within the boundaries of a nonattainment 

area, such as the reservation areas of Indian country contained within the South Coast PM2.5

 

97 “Indian country” as defined at 18 U.S.C. 1151 refers to: “(a) all land within the limits of any Indian reservation 

under the jurisdiction of the United States Government, notwithstanding the issuance of any patent, and, including 

rights-of-way running through the reservation, (b) all dependent Indian communities within the borders of the United 

States whether within the original or subsequently acquired territory thereof, and whether within or without the limits 

of a state, and (c) all Indian allotments, the Indian titles to which have not been extinguished, including rights-of-way 

running through the same.”
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nonattainment area. Moreover, violations of the 2006 PM2.5 standard, which are measured and 

modeled throughout the nonattainment area, as well as shared meteorological conditions, would 

dictate the same conclusion. Furthermore, emissions increases in portions of a PM2.5 nonattainment 

area that are left classified as Moderate could counteract the effects of efforts to attain the standard

within the overall area because less stringent requirements would apply in those Moderate portions

relative to those that would apply in the portions of the area reclassified to Serious. 

Uniformity of classification throughout a nonattainment area is thus a guiding principle and 

premise when an area is being reclassified. Equally, if the EPA believes it is likely that a given 

nonattainment area will not attain the PM2.5 standard by the applicable attainment date, then it may 

be an additional reason why it is appropriate to maintain a uniform classification within the area 

and thus to reclassify the reservation areas of Indian country and any other area where the EPA or 

a tribe has demonstrated that a tribe has jurisdiction together with the balance of the nonattainment 

area. In this particular case, we are proposing to determine, based on the State’s demonstration and 

current ambient air quality trends, that the South Coast nonattainment area cannot practicably 

attain the 2006 PM2.5 standard by its applicable Moderate area attainment date of December 31, 

2015. 

In light of the considerations outlined above that support retention of a uniformly-classified 

PM2.5 nonattainment area, and our finding that it is impracticable for the area to attain by the 

applicable attainment date, we propose to reclassify the areas of Indian country within the South 

Coast nonattainment area as Serious nonattainment for the 2006 PM2.5 standard.

The effect of reclassification would be to lower the applicable “major source” threshold for

purposes of the nonattainment new source review program and the Title V operating permit 

program from its current level of 100 tpy to 70 tpy (CAA sections 189(b)(3) and 501(2)(B)), thus 

subjecting more new or modified stationary sources to these requirements. The reclassification

may also lower the de minimis threshold under the CAA’s General Conformity requirements (40 

CFR part 93, subpart B) from 100 tpy to 70 tpy. Under the General Conformity requirements, 

Federal agencies bear the responsibility of determining conformity of actions in nonattainment and 

maintenance areas that require Federal permits, approvals, or funding. Such permits, approvals or 

funding by Federal agencies for projects in these areas of Indian country may be more difficult to 

obtain because of the lower de minimis thresholds. 

Given the potential implications of the reclassification, the EPA has contacted tribal 

officials to invite government-to-government consultation on this rulemaking effort.98 The EPA 

specifically solicits additional comment on this proposed rule from tribal officials. We note that 

although eligible tribes may seek EPA approval of relevant tribal programs under the CAA, none 

of the affected tribes will be required to submit an implementation plan to address this

reclassification.

 

98 We sent letters to seven tribal officials regarding government-to-government consultation on September 4, 2015 and 

September 30, 2015.