Reply to Attn Of: AWT-107

MEMORANDUM

DATE: April 2, 2014

SUBJECT: Technical Support Document for the Central Puget Sound Maintenance Area, 

Section 110(a)(1) Ozone Maintenance Plan 

FROM: Keith Rose, Environmental Scientist

TO: Docket EPA-R10-OAR-2008-0122

TABLE OF CONTENTS

I. Purpose

II. Background

III. Review of the Maintenance Plan

IV. Evaluation of the Maintenance Plan

V. Conclusion

VI. Recommended Agency Action

I. Purpose 

This technical support document (TSD) provides information supporting EPA’s action to 

approve the State of Washington’s January 10, 2008 State Implementation Plan (SIP) revision of 

a Section 110(a)(1) Ozone Maintenance Plan for the Central Puget Sound Area. This TSD 

documents how the maintenance plan in this SIP revision meets the Clean Air Act (CAA) 

110(a)(1) requirements, and demonstrates that the Central Puget Sound area will be able to 

remain in attainment with both the 1997 and 2008 Ozone NAAQS through 2015. 

II. Background

Ozone is a summertime air pollution problem. It is formed when photochemical precursors react 

with sunlight in the atmosphere. Precursors include volatile organic compounds (VOC) and 

nitrogen oxides (NOx), with some influence by carbon monoxide (CO). These precursors come 

from anthropogenic sources such as mobile sources, industrial and commercial solvent use, as 

well as natural biogenic sources. Levels of ozone are usually highest in the afternoon because of 

intense sunlight, increased temperatures, and the precursors have had a longer period of time to 

react and form ozone. Ozone levels are also highly affected by weather conditions. 

Atmospheric chemical dispersion modeling has repeatedly shown that the Puget Sound urban 

area is “VOC-limited,” which means that reducing VOC emissions most effectively reduces 

ambient concentrations of ozone at the locations of greatest concentration.
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Elevated ozone concentrations can cause reduced lung function and respiratory irritation, and can 

aggravate asthma. People with respiratory conditions should limit outdoor exertion if ozone 

levels are high. Ozone has also been linked to impaired immune system function and groundlevel ozone can also damage agricultural crops and forests, interfering with their ability to 

produce food and grow. In the Puget Sound region, the hot sunny days that are favorable for 

ozone formation also tend to have light north-to-northwest winds. Ozone has typically been 

transported 10 to 30 miles downwind from the original source by the time the highest 

concentrations have formed in the afternoon and early evening. Highest ozone concentrations 

are measured in towns such as North Bend and Enumclaw, which are the communities 

downwind of the Seattle-Tacoma urban area.

On November 15, 1990, the CAA Amendments of 1990 were enacted. Under section 107(d)(1) 

of the CAA, EPA designated the Central Puget Sound area, which includes all of Pierce County, 

almost all of King County except the northeast corner, part of Snohomish County, and lands 

within the Puyallup, Tulalip, Muckleshoot, Stillaguamish, and Nisqually Reservations, as 

nonattainment because the area violated the 1-hour ozone standard, 0.12 parts per million (ppm), 

during the period of 1989-1991. Because of this violation, the Central Puget Sound area was 

classified as "marginal" under section 181(a)(1) of the CAA. On January 28, 1993, the State of 

Washington Department of Ecology (Ecology) submitted a State Implementation Plan (SIP) for 

compliance with the 1-hour ozone NAAQS. Ecology submitted an Ozone Maintenance Plan and 

redesignation request for the Central Puget Sound area on March 4, 1996. On September 26, 

1996, the Central Puget Sound area was re-designated to attainment for ozone, and the ozone 

maintenance plan for this area was approved. 

In 1997 EPA changed the ozone NAAQS to 0.08 ppm for the three-year average of the annual 

fourth highest 8-hour average ozone concentration, and in 2008 EPA revised the ozone standard 

to 0.075 ppm for the three-year average of the annual fourth highest 8-hour average ozone 

concentration. Since 1997 there have been no violations of either 8-hour ozone standard at any 

ozone monitoring site in the Puget Sound area.

On January 10, 2008 Ecology submitted for approval under section 110 of the CAA a revised 8-

hour ozone maintenance plan for the Central Puget Sound area. This plan was developed by the 

Puget Sound Clean Air Agency (PSCAA) with collaboration from Ecology. Throughout this 

document the submitting agency is referred to as Ecology, recognizing that air quality 

management in this area is shared between Ecology and PSCAA.

This maintenance plan demonstrates how Ecology intends to remain in attainment with the 1997 

and 2008 8-hour ozone NAAQS through 2015 for the Central Puget Sound area. The

maintenance plan contains a base-year inventory for 2002, and demonstrates that emissions will 

not be greater than the base year in 2015. The proposed maintenance plan commits to tracking 

progress and identifies measures that would be available to promptly correct any ozone NAAQS 

violation. Ecology’s SIP submittal addresses all the CAA requirements for SIP submittals under 

CAA Section 110(a)(1). Additionally, Ecology’s submittal also addresses the requirements of 

CAA section 110(l) and CAA section 193. 

III. Review of the Maintenance Plan

A. What are the components of a section 110(a)(1) 8-hour ozone Maintenance Plan?
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CAA section 110(a)(1) requires states to submit plans to EPA which provide for the 

implementation, maintenance and enforcement of NAAQS standards in each air quality control 

region within the state. On May 20, 2005, EPA issued guidance that applies to areas that are 

designated maintenance for the 1-hour ozone NAAQS but unclassifiable/attainment for the 8-

hour ozone standard. The purpose of that guidance was to identify required elements of a 

maintenance plan that would meet the requirements in section 110(a)(1) of the CAA. The 

guidance identifies five required components of an 8-hour ozone maintenance plan, which are:

1. Attainment Inventory – The plan should include an attainment inventory based on actual 

“typical summer day” emissions of volatile organic compounds (VOCs) and nitrogen oxides 

(NOx) for a 10-year maintenance period. For purposes of an attainment emissions inventory, the 

state must choose any one of the three years in which the 8-hour ozone attainment designation 

was based. As many states are already required to develop an inventory for 2002 under EPA’s 

Consolidated Emissions Reporting Rule (67 FR 39602), EPA recommends that states use that 

year as the attainment emission inventory base year for the section 110(a)(1) Maintenance Plan. 

Ecology used 2002 as the base year for the Puget Sound attainment inventory.

2. Maintenance Demonstration – The plan should demonstrate how the area will remain in 

compliance with the 8-hour ozone NAAQS for a period of 10 years following the effective date 

of designation as unclassifiable/attainment. For areas with an effective date of designation for the 

8-hour NAAQS of June 15, 2004, the maintenance plan must project attainment through 2014 or 

beyond. Maintenance may also be demonstrated by modeling future ozone concentrations on a 

typical summer day based on a future projected emission inventory. In the Central Puget Sound 

ozone maintenance plan, Ecology demonstrated attainment by projecting emission inventories 

for 2015, and modeling ozone concentrations for 2015 based on these projected inventories. 

3. Ambient Air Quality Monitoring - The plan should include a commitment by the state to 

continue to operate air quality monitors, and collect quality assured data, in accordance with 40 

CFR Part 58 to verify continued attainment of the 8-hour ozone standard.

4. Contingency Plan – The plan should include contingency measures to reduce emissions that 

can be implemented as expeditiously as practicable in the event of a violation of the 8-hour 

ozone NAAQS. 

5. Verification of Continued Attainment – The plan should indicate how the state intends on 

tracking and verifying progress toward attainment in the maintenance plan. This is necessary 

because the emissions projections made for the maintenance demonstration depend on 

assumptions of point, area and mobile source growth, and need to be verified. 

B. Components of the Central Puget Sound 8-hour ozone Maintenance Plan

1. Attainment Inventory – In its SIP submittal, Ecology provided a comprehensive emissions 

inventory for VOCs and NOx using 2002 as the base year for attainment. The effective year of 

the 8-hour ozone initial designation was 2004, and therefore Ecology projected emissions for 

ozone precursors to the year 2015, which is 10 years or beyond the effective date of the initial

designation. In the maintenance plan, Ecology included information on anthropogenic source

categories of VOCs and NOx, including point sources, on-road sources, nonroad sources, and 
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area sources. Projected emissions from these source categories were determined based on the 

following assumptions:

a. All point source emissions were held constant from 1999 values through 2015.

b. Area source emissions were based on population and economic growth factors applied to 

base year. Stationary area source projection factors ranged from 0.24 for residential coal 

combustion to 1.51 for liquefied petroleum gas. 

c. Non-road vehicle source emissions were estimated using the NONROAD model with 

Reid Vapor Pressures (RVP) of 7.8 and 8.7 to address both a low RVP scenario and a 

high RVP scenario.

d. Marine vessel emissions (a subset of the non-road category) were projected from 1999 to 

2015 using a projection factor of 2 based on the projected dramatic increase in the units 

of cargo shipped to Washington ports over this period. 

e. On-road mobile source emissions were based on model runs of EPA’s MOBILE 6.2 

using projected future vehicle miles traveled. 

Table 1 shows the VOC and NOx emission inventories for 2002, and table 2, based on the above 

growth assumptions, shows the VOC and NOx emission inventories for 2015. 

Table 1: Central Puget Sound 2002 Attainment Inventories (tons/day)

Source Category NOx VOC

Onroad Mobile 301 220

Nonroad Mobile 113 92

Stationary Area 14 157

Point Sources 18 5

Total 446 474

Table 2

Central Puget Sound 2015 Maintenance Demonstration, Typical Summer Day (tons/day)

Source Category NOx VOC

Onroad Mobile 100 81

Nonroad Mobile 271 70

Stationary Area 13 172

Point Sources 27 17

Total 411 346

These tables show a projected 8% reduction in NOx between 2002 and 2015, and a projected 

27% reduction in VOCs between 2002 and 2015. The 2002 Consolidated Emissions Reporting 

Rule (CERR) emissions data submitted by Ecology and PSCAA to EPA’s National Emission 

Inventory (NEI) were used as the basis for the 2002 attainment year inventory. Figure 1 shows 

the trends of NOx and VOC emissions from 1998 through 2015. 
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Figure 1: Central Puget Sound 1998 through 2015 Emission projections used for 

Maintenance Demonstration (tons/day)

The technical appendices submitted with Ecology’s Maintenance Plan contain more detailed 

information on the emissions inventories for each source category. Emissions for all source 

categories were calculated following EPA guidance and are properly documented in the 

appendix titled “2002 Emission Inventory – Seasonal” of the Maintenance Plan

2. Maintenance Demonstration – The proposed Maintenance Plan must demonstrate 

maintenance of the 8 hour ozone NAAQS to 2014 or beyond. The Central Puget Sound Area

Maintenance Plan meets this criterion by first demonstrating that the inventories of ozone 

precursors in 2015 will be below the 2002 attainment year. Specifically, VOC emissions are 

projected to decrease from 474 tons/year in 2002, to 420 tons/year in 2005, and to 346 tons/year 

in 2015. NOx emissions are projected to decrease from 446 tons/year in 2002, to 390 tons/year in 

2005, and to 411 tons/year in 2015. Even though there is a slight increase in NOx emissions 

between 2005 and 2015, there is an overall decrease in NOx emissions of 35 tons/year between 

2002 and 2015. The second demonstration is that the highest 3-year average of the 4th highest 

ozone value (the ozone design value) in the Central Puget Sound Area in 2015 is projected to be 

below the 2008 ozone NAAQS. 

Ecology initially conducted a maintenance demonstration by using dispersion modeling to show 

that the Puget Sound area will remain in compliance with the 8-hour ozone standard through 

2015. This demonstration was included as an appendix to the maintenance plan and is titled,

“Ozone Modeling for Maintenance Plan Revision for Puget Sound in Western Washington” 

(October 2001). This analysis shows that even with an increase in total NOx emissions between 

2005 and projected 2015, the downward trend in VOC emissions leads to lower ozone 

concentrations and continued compliance with the ozone NAAQS.

Ozone Summer Day NOx and VOC Emissions

0

100

200

300

400

500

600

NOx VOC NOx VOC NOx VOC NOx VOC

1998 tons/day 2002 tons/day 2005 tons/day 2015 tons/day

Onroad Mobile

Nonroad Mobile

Stationary Area

Point Sources

Total
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In order to demonstrate continued maintenance with the ozone NAAQS through 2015, Ecology 

and PSCAA conducted a second dispersion modeling to more accurately estimate the 

comprehensive impacts of emission growth, weather patterns, estimate of future emissions of 

VOCs and NOx from offshore marine vessels, and the transport of ozone precursors from areas 

outside of the State of Washington on ozone concentrations in the Central Puget Sound area. 

This ozone modeling was included in an appendix to the maintenance plan titled, “Modeling 

Analysis of Future Emission Scenarios for Ozone Impacts in the Puget Sound Area” (August 

2006). Based on this modeling, the highest ozone design value for 2015 in the Puget Sound area 

was projected to be 0.068 parts per million (ppm). This modeling confirms the previous 

modeling results which indicated that the Puget Sound area will maintain attainment with the 

current ozone NAAQS through 2015. These most recent modeling results are shown in Table 3. 

Table 3: Maintenance Demonstration

Projected 2015 8-hour ozone design values for the Puget Sound area

Monitoring Site 1996-2000 Design 

Value (ppm)

Relative Reduction 

Factor

2015 Design Value 

(ppm)

Enumclaw 0.0756 0.901 0.068

Lake Sammamish 0.0603 0.970 0.058

Pack Forest 0.073 0.936 0.068

3. Ambient Air Quality Monitoring – Ecology and PSCAA commit to operate an ozone air 

quality monitoring network in accordance with 40 CFR 58 to verify maintenance of the 8-hour 

ozone standard in the Central Puget Sound area. Any modification to the ambient air monitoring 

network, such as removal of duplicative or unnecessary monitors, will be identified in the 

Washington annual monitoring network plan for EPA approval. In the case of proposed network 

reductions, proposed network modifications would be accompanied by technical and statistical 

analysis sufficient to document that a given monitor may be removed because it is unnecessary 

or duplicative. In accordance with 40 CFR 58, the annual monitoring network plans, and the 5-

year monitoring network assessments, will be subject to the approval of the EPA Regional 

Administrator. 

4. Contingency Plan – Section 110(a)(1) of the CAA requires that the state develop a 

contingency plan which will ensure that any violation of a NAAQS is promptly corrected. The 

purpose of the contingency plan is to adopt measures, outlined in the maintenance plan, that 

would assure continued attainment in the event of a violation of the 8-hour ozone NAAQS. The 

maintenance plan should identify the events that would “trigger” the adoption and 

implementation of any contingency measures, the specific contingency measures that would be 

adopted and implemented, and the schedule for adopting and implementing these measures. 

There are two contingency measures identified in this maintenance plan. They are PSCAA 

Regulation I, Section 8.06, Outdoor Burning Ozone Contingency Measure, and PSCAA 

Regulation II, Section 2.10, Gasoline Station Ozone Contingency Measure. Both the outdoor 

burning and the gasoline station contingency regulations are triggered by a written finding from 
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EPA of a quality assured violation of the ozone NAAQS, and that future violations can 

reasonable be addressed through implementation of these regulations. These regulations were 

included as contingency measures in the ozone second 10-year maintenance plan for the Central 

Puget Sound area and were approved by the EPA on August 5, 2004 (69 FR 47364 and 69 FR 

47365).

5. Verification of Continued Attainment – Ecology and PSCAA will continue to monitor 

ambient air quality ozone levels in the Central Puget Sound area during the ozone season (May 

through September) using the ozone monitoring network as described in Ecology’s annual 

ambient air monitoring network plan approved by EPA. Ecology and PSCAA will update 

countywide emission inventories in the National Emissions Inventory every three years as 

required by the Consolidated Emission and Reporting Rule (CERR). If ambient ozone levels 

begin to significantly increase above baseline levels, Ecology and PSCAA will compare CERR 

updates with the 2002 and 2015 emissions inventories and reevaluate the assumptions used in the 

2015 emissions projections to determine if they are still valid. 

IV. Evaluation of the Central Puget Sound 8-hour Ozone Maintenance Plan

The EPA has determined that the Central Puget Sound Ozone Maintenance Plan adequately 

addressed the five required elements for a 110(a)(1) maintenance plan including: an attainment 

year emission inventory, a maintenance demonstration for 2014 or beyond, a commitment to 

operate an ozone air quality monitoring network in accordance with 40 CFR 58 to verify 

maintenance of the 8-hour ozone NAAQS in the Central Puget Sound area, contingency 

measures to be triggered if the ozone NAAQS were to be violated, and verification of attainment 

through ambient air monitoring and updating of countywide emission inventories in the National 

Emissions Inventory every three years. In addition, historical monitoring shows that the Central 

Puget Sound area has been in compliance with all other criteria air pollutant NAAQS since the 

1980s. Additionally, EPA’s evaluation of the impacts of the changes proposed in this 

maintenance plan has determined that these changes will not cause an increase in direct or 

precursor emissions that will interfere with the attainment or maintenance of any other NAAQS.

Therefore, an approval of this plan revision will not interfere with any applicable requirement 

concerning attainment or maintenance of any applicable NAAQS. Therefore, approval of the 

State of Washington’s section 110(a)(1) 8-hour Ozone Maintenance Plan for the Central Puget 

Sound area is recommended.

V. Conclusion and Recommended Action 

This SIP revision satisfies all applicable CAA requirements for an acceptable 110(a)(1) 8-hour 

ozone maintenance plan, and therefore should be approved.