Puget Sound 8-Hour Ozone

110(a)(1) Maintenance Plan 

Puget Sound Clean Air Agency

1904 3rd Ave, Ste 105, Seattle, WA 98101

John Anderson 

May 2007
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Summary

According to Environmental Protection Agency (EPA) guidance1, the Puget Sound Clean Air 

Agency must prepare a federal Clean Air Act Section 110(a)(1) maintenance plan for the 8-hour 

ozone standard. The EPA requires the Agency to submit this plan by June 15, 2007.

The Agency has met all requirements for this 8-hour maintenance plan as shown beginning on page 

5. Additionally, air monitoring within the Agency’s jurisdiction has not measured any violations of

EPA’s 8-hour ozone standard since its adoption in 1998. The Agency has conducted photochemical 

dispersion modeling for multiple ozone episodes, predicting attainment into future years up to 2015. 

This modeling has repeatedly shown that the Puget Sound area is likely to remain in attainment with 

the current 8-hour standard. 

General Background

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

with sunlight. 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 are usually highest in the summer afternoons because of the intense sunlight and 

the time required for ozone to form. Ozone levels are highly affected by weather. Atmospheric 

chemical dispersion modeling has repeatedly shown that the Puget Sound urban area is “VOClimited,” which means that reducing VOC emissions most effectively reduces ambient 

concentrations of ozone at the locations of greatest concentration.

Elevated ozone concentrations can cause reduced lung function and respiratory irritation, and can 

aggravate asthma2. People with respiratory conditions should limit outdoor exertion if ozone levels 

are high. Ozone has also been linked to immune system effects and ground-level ozone can also 

damage agricultural crops and forests, interfering with their ability to produce food and grow3.

In the Puget Sound region, the hot sunny days 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 areas such as North Bend and Enumclaw, 

the communities downwind of large urban areas. 

Ozone State Implementation Plan & Maintenance Plan History

The original "Plan for the Implementation, Maintenance and Enforcement of National Ambient Air 

Quality Standards in the State of Washington" was submitted in January 28, 1972 [40 CFR 52.2470

Subpart WW--Washington State Implementation Plan]. A Transportation Control Plan was 

submitted on April 13, 1973 and then revised May 13, 1973 [40 CFR 52.2470(7) and (8)]. A 

revision was made to the Seattle-Tacoma ozone non-attainment area plan on June 24, 1982 [40 CFR 

52.2470(22)]. On July 16, 1982 the Seattle-Tacoma ozone non-attainment area plan was revised to 

include the then Puget Sound Air Pollution Control Agency's Regulation II adopted by their Board 

on March 13, 1980 to provide for control of photochemically reactive volatile organic compounds 

(VOC) and conformity procedures for evaluating federal projects for consistency with the Seattle-
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Tacoma ozone plan [40 CFR 52.2470(27)]. Regulation II revisions through December 13, 1984

were incorporated into the SIP [40 CFR 52.2470(35)].

On November 15, 1990, the Clean Air Act Amendments of 1990 (CAA) were enacted. Under 

section 107(d)(1) of the CAA, EPA designated, in conjunction with the Governor of Washington,

the Puget Sound area as nonattainment for ozone because the area violated the 1-hour ozone 

standard during the period from 1989-1991. The Puget Sound area was classified as "marginal" 

under section 181(a)(1) of the CAA. On January 28, 1993 the State of Washington submitted a 

State Implementation Plan (SIP) for compliance with the ozone NAAQS. The Puget Sound Clean 

Air Agency Regulation II revisions through October 18, 1993 and December 8, 1994 were 

incorporated into the SIP [40 CFR 52.2470(43) and (53)]. On March 4, 1996, the State submitted 

the Central Puget Sound Redesignation Request and Ozone Maintenance Plan adopted February 6, 

1996 including base year 1990 emission inventories of precursors of ozone for King, Pierce and 

Snohomish counties [40 CFR 52.2470(63) and (66)]. Regulation II revisions through August 6, 

1996 were incorporated into the SIP [40 CFR 52.2470(71)]. On September 25, 1996 the Puget 

Sound area ozone State Implementation Plan (SIP) was revised to incorporate the Puget Sound 

area's centralized, test only, biennial vehicle inspection and maintenance program overseen by the 

Washington State Department of Ecology using its Systems Control contractor4. On September 26, 

1996, Puget Sound was re-designated to attainment for ozone and the ozone maintenance plan was 

approved5. 

On August 5, 20046 EPA approved Washington's demonstration that the Central Puget Sound area 

will maintain air quality standards for ozone through the year 2016. It also updated and enhanced 

the State Implementation Plan (SIP) by adding two ozone contingency measures, incorporated by 

reference: (1) Puget Sound Clean Air Agency (PSCAA) Regulation I, Section 8.06, Outdoor 

Burning Ozone Contingency Measure and (2) PSCAA Regulation II, Section 2.10, Gasoline Station 

Ozone Contingency Measure7.

Historic Monitoring & Federal Standards

The national ambient air quality standard in place during 1972 through 1978 was achieved when no 

more than one 1-hour average of total photochemical oxidants concentration exceeded 0.08 ppm. In 

the Puget Sound area the number of hours exceeding this standard during 1972 through 1978 ranged 

from 0 to 37 annually. The chart below shows that this standard was exceeded in 1972, 1974-1976 

and 1978.
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Puget Sound Photochemical Oxidants

Number of Hours Above 0.08 ppm

(The Standard Allows Only 1 Hour)

12

0

12

37

19

1

14

0

5

10

15

20

25

30

35

40

1972 1973 1974 1975 1976 1977 1978

During 1979 through 1997, the ambient standard was changed by EPA. The standard was achieved 

when no more than one day, annually, has 1-hour average ozone concentrations above 0.12 ppm. 

The number of days, annually, exceeding this standard during 1979 through 1997 ranged from 0 to 

3.9. The chart below shows that this standard was exceeded during 1979-1983, 1985-1986, and 

1990-1992.

Puget Sound Ozone

Monitored Last 3-Year Average # Days 1-hr Value > 0.12 ppm

(The Standard Requires Less Than 1.0)

3.9

2.1

1.9

1.3 1.3

0

1 1

0.7 0.7

0.5

1.3 1.3

1

0

0.7 0.7

0 0 0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1979198019811982198319841985198619871988198919901991199219931994199519961997

Current Monitoring & Federal Standards

From 1998 through 2006 the ambient standard was changed to be achieved when the three-year 

average of the annual fourth highest 8-hour average ozone concentration at each monitor did not 

exceed 0.08 parts per million (ppm). This standard has not been violated from 1998 through 2006

at any monitor in the Puget Sound region. The chart below shows that this 8-hour standard has
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never been exceeded. The chart shows maximum 8-hour concentrations at the Enumclaw Mud 

Mountain monitoring, the highest ozone site in our jurisdiction. The pink line shows the design 

value, the 3-year average of the 4th highest concentration, while the dotted line shows the federal 

standard of 0.08 ppm. This line has stayed relatively flat, ranging from 0.068 to 0.076 ppm. Note 

that EPA rounding conventions requires truncating both the hourly measurements and the resulting 

8-hour averages yielding the following results for the 1998 through 2006 time period:

Ozone Measured at Mud Mountain Road, Enumclaw

4 Highest 8-Hour Concentrations

and 3-Year Average of 4th Highest

0.074

0.072

0.073

0.071

0.068

0.069

0.076

0.00

0.03

0.06

0.09

0.12

0.15

1998 1999 2000 2001 2002 2003 2004 2005 2006

Year Concentration ppm

8-Hour Ozone

3-Year Average of 4th Highest Annual Concentration vs Standard

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year 8-Hour Average Concentration Parts per Million (ppm)

 8-Hour Federal Standard

LAG - Pack Forest (FH)

ENU - Highway 410 (BU)

LKS - Lk Sammamish Park (DN)

SEA - Beacon Hill (BW)

ENU - Mud Mountain Rd (DF)

NHB - North Bend (DG)

YEL - Yelm (VK)
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8-hour Ozone Concentrations by Site

For further reference, see the Puget Sound Clean Air Agency's web site monitoring mapping tool at 

<http://trendgraphing.pscleanair.org/TrendGraphing.aspx>.
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The circles on the map above represent ozone monitoring sites maintained by the Department of 

Ecology - the two letters are codes used for identification. Highest ozone concentrations are 

typically recorded at the DF (Enumclaw Mud Mountain) monitor. The other monitoring site codes 

are listed above in parentheses in the "8-hour Ozone Concentrations by Site" graph.

Required 8-Hour Ozone Maintenance Plan

According to the May 20, 2005 EPA guidance, the Puget Sound Clean Air Agency must prepare a 

federal Clean Air Act Section 110(a)(1) maintenance plan for the 8-hour ozone standard because all 

of Pierce County, all of King County except a small portion on the northeast corner and the western 

portion of Snohomish County were designated as unclassifiable/attainment for the 8-hour ozone 

standard and had an approved maintenance plan for the 1-hour ozone standard on June 15, 2005. 

This plan is required to be submitted no later than June 15, 2007.

This 8-hour ozone maintenance plan contains the required elements:

(1) An actual summer day VOC and NOx emission inventory for calendar year 20028. 

The documentation of this inventory is available from the EPA website9. A summary of two 

ozone modeling emission inventories and average summer day estimates from two base year 

annual emission inventories is shown below. After 1996, the trend is downward for total 

emissions of VOC, which is the controlling pollutant for ozone in the Puget Sound area.

0

100

200

300

400

500

600

1996 1998 2002 2005

VOC tons/day

Ozone Summer Day VOC Emissions

Onroad Mobile

Nonroad Mobile

Stationary Area

Point Sources

Total
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0

100

200

300

400

500

600

1996 1998 2002 2005

NOx tons/day

Ozone Summer Day NOx Emissions

Onroad Mobile

Nonroad Mobile

Stationary Area

Point Sources

Total

The emission charts above come from the following references:

1996 Ozone Modeling for Maintenance Plan Revision for Puget Sound in Western Washington, pages 93-

94, 7/13/9610

This ozone summer day modeling inventory was used to construct hourly emission estimates over a 5

kilometer grid system to test ozone strategies in comparison with a July 11-14, 1996, ozone episode. 

Link-base vehicle miles traveled estimates came from the regional planning organization Puget Sound 

Regional Council and emission factor were derived from a modified EPA MOBILE5b model. 

Vehicle registration distribution was modified to track older than default vehicles in the Puget Sound 

area, based on data from the Washington State Department of Licensing. In addition, parameters 

were specified for two vehicle inspection and maintenance program scenarios. Emissions were also 

projected to 2015.

1998 Modeling Analysis of Future Emission Scenarios for Ozone Impacts in the Puget Sound Area, pages 

77-78, 7/29/9811

This ozone summer day modeling inventory was used to construct hourly emission estimates over a 4 

kilometer grid system to test ozone strategies in comparison with a July 22-28, 1998, ozone episode. 

Link-base vehicle miles traveled estimates came from the regional planning organization Puget Sound 

Regional Council and emission factors were derived from the EPA MOBILE6.2 model. Vehicle 

registration distribution was modified to track older than default vehicles in the Puget Sound area, 

based on data from the Washington State Department of Licensing. In addition, parameters were 

specified for six vehicle inspection and maintenance program scenarios. Emissions were also 

projected to 2015 to analyze expected growth in the marine sector and the eventual removal of the 

voluntary gasoline low Reid Vapor Pressure gasoline program.

2002 2002 Emission Inventory Appendix--Seasonal,12

The 2002 National Emission Inventory was prepared by EPA headquarters except for data submitted 

by the Puget Sound Clean Air Agency on point sources, fireplace/woodstove emissions and land 

clearing burning. A final version of this inventory and documentation may be found on EPA's 

website9. For this ozone 110 maintenance plan a spreadsheet was prepared that seasonally adjusts 

each source category of emissions to yield average summer day emissions in 2002. On-road mobile 

estimates were made using MOBILE6.2 based on EPA's default NMIM inventory and non-road 

emission estimates were made using the NONROAD model.

2005 All Air Pollution Sources 2005--Seasonal13
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(2) A maintenance demonstration10 was conducted in 2001 which showed that the Puget 

Sound area would remain in compliance with the 8-hour ozone standard by ensuring that 

VOC and NOx emissions will remain below attainment levels for calendar years 2005 through 

2015. In 2006 another ozone modeling exercise was conducted11, which confirms the previous 

modeling results indicating that the region is likely to maintain attainment with the current ozone 

national ambient air quality standard. It is expected that total on-road mobile sources emissions 

may decrease, while emission from the maritime-related sources may increase from 2006 through 

2015. Even with a small increase in total NOx emissions in the final time period segment between 

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

concentrations and confirm continued compliance with the existing 8-hour standard of 0.08 ppm. 

This latest modeling ozone effort focused on an ozone episode which occurred in Puget Sound 

during July 22-28, 1998. This episode recorded the highest ozone levels in recent history in the 

Puget Sound area and had the most extreme meteorology available. During this episode the 8-hour 

average ozone concentrations observed downwind of Seattle reached 111 ppb. Air quality during 

this period was simulated using the Mesoscale Meteorology model version 5/Sparse Matrix 

Operator Kernel Emissions Modeling System/Community Multi-scale Air Quality modeling System 

(MM5/SMOKE/CMAQ). Future design values, used to compare to the federal 8-hour ozone 

standard, were calculated at values less than 84 ppb and demonstrated that Puget Sound monitoring 

sites remain in federal attainment status in 2015. The highest design value was 68 ppb for the 

Enumclaw Weyerhaeuser Mill and Pack Forest monitoring sites. Sensitivity analysis model runs 

were made to insure the validity of the conclusions. In addition the modeling system was used to 

test the difference between continuing and discontinuing the voluntary low RVP gasoline program 

and found the increase to be less than 0.3 ppb in predicted daily maximum 8-hour ozone 

concentrations. Given the overall decease in on-road mobile VOC emissions, the voluntary low 

RVP gasoline program impact is considered inconsequential in future years.

Ozone Summer Day VOC Emissions

0

100

200

300

400

500

600

1998 2002 2005 2015

Onroad Mobile

Nonroad Mobile

St at ionary Area

Point Sources

Tot al

 

Ozone Summer Day NOx Emissions

0

100

200

300

400

500

600

1998 2002 2005 2015

Onr oad Mobile

Nonr oad Mobile

Stationar y Ar ea

Point Sour ces

Total

2015 Modeling Analysis of Future Emission Scenarios for Ozone Impacts in the Puget Sound Area 11, 

pages 77-78, 7/29/98

Projections were made to 2015 based on the base year 1999 emission inventory.
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(3) A commitment to continue adequate ozone monitoring to demonstrate compliance with 

the 8-hour ozone standard. Ecology commits to continuing to monitor for 8-hour ozone 

concentrations and to show comparisons of these values to the 8-hour ozone standards.

(4) A contingency plan is in place that will ensure that any violation of the 8-hour ozone 

standard would be promptly addressed. The Puget Sound Clean Air Agency regulations for two 

contingency measures were adopted December 19, 2002 and were included in the revised State 

Implementation Plan on August 5, 20046. Both the outdoor burning and the gasoline marketing 

contingency measure regulations are triggered by a written finding from EPA of a quality assured 

violation of the standard and that future violations can reasonably be addressed through 

implementation of the regulations. 

Outdoor Burning Ozone Contingency Measure (PSCAA Regulation I, Section 8.06):

Step 1--EPA, in consultation with the Puget Sound Clean Air Agency and Ecology, 

makes a written finding that a quality-assured ozone standard violation has occurred and 

that prevention of future violations can be reasonably addressed through implementation 

of Regulation I, Section 8.06.

Step 2--Puget Sound Clean Air Agency provides public notice of EPA's written finding 

by November 1st.

Step 3--Effective July 1

st following the public notice of the written finding outdoor 

burning is unlawful within King, Kitsap, Pierce or Snohomish counties during the months 

of July through August.

Gasoline Station Ozone Contingency Measure (PSCAA Regulation II, Section 2.10):

Step 1--EPA, in consultation with the Puget Sound Clean Air Agency and Ecology, 

makes a written finding that a quality-assured ozone standard violation has occurred and 

that prevention of future violations can be reasonably addressed through implementation 

of Regulation II, Section 2.10.

Step 2--Puget Sound Clean Air Agency provides public notice of EPA's written finding 

by November 1st.

Step 3--Effective May 1st following the public notice of the written finding it shall be 

unlawful for any person to cause or allow the transfer of gasoline from a transport tank 

into a stationary storage tank at a gasoline station that uses coaxial Stage 1 vapor 

recovery systems and dispenses 600,000 gallons or more of gasoline per year unless a 

California Air Resources Board (CARB) Stage I system, approved after July 1, 2002, is 

installed within one year of the May 1st date and operated in accordance with CARB 

system certification requirements.
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(5) Puget Sound Clean Air Agency is required by EPA to update the VOC and NOx emission 

inventories for 2008, 2011 and 2014. Puget Sound Clean Air Agency commits to preparing 

summer day emission inventories for the interim years of 2008, 2011 and 2014 and comparing these 

emission inventory results with the modeling emission inventories to ensure continued compliance 

with the 8-hour ozone ambient air quality standard. If values in the total VOC and NOx emissions 

for 2008, 2011 or 2014 exceed linearly interpolated values between 1998 and 2015 used in the 

ozone modeling, an analysis will be made by the Puget Sound Clean Air Agency to determine the 

probability of continued compliance with the ozone 8-hour standard. Even though the comparison 

is made in the total emissions, emissions by major source category are listed below to show the 

trends by category. Rounding differences have caused some column totals to show slight variances. 

The VOC emissions in tons per summer day calculated from interpolation between 1998 and 2015 

ozone modeling values are shown below:

VOC Emission 

Source Category

1998 tpd 2005 tpd 2008 tpd 2011 tpd 2014 tpd 2015 tpd

Area 155 158 162 165 169 172

Point 17 17 17 17 17 17

Non-road 128 116 105 93 82 70

On-road 240 207 177 147 117 87

Biogenic 433 433 433 433 433 433

Total 973 934 896 857 819 780

The VOC emissions in tons per summer day from the seasonally adjusted draft 2005 emission 

inventory are:

VOC Emission Source Category 2005 tpd

Area 176

Point 11

Non-road 81

On-road 154

Biogenic 433

Total 855

Note that total the 2005 VOC emissions in the draft emission inventory of 855 tons per day are less 

that the interpolated 934 tons per day so that no additional determination in 2005 of continued 

compliance with the 8-hour ozone standard would be required, even though the draft inventory area 

source category of 176 tpd exceeds the interpolated 158 tpd.
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The NOx emissions in tons per summer day calculated from interpolation between 1998 and 2015 

ozone modeling values are shown below:

NOx Emission 

Source Category

1998 tpd 2005 tpd 2008 tpd 2011 tpd 2014 tpd 2015 tpd

Area 14 14 14 13 13 13

Point 27 27 27 27 27 27

Non-road 211 223 235 247 259 271

On-road 312 270 227 185 142 100

Biogenic 2 2 2 2 2 2

Total 567 536 506 475 445 414

The NOx Emissions in tons per summer day from the seasonally adjusted draft 2005 emission 

inventory:

NOx Emission Source Category 2005 tpd

Area 7

Point 21

Non-road 111

On-road 232

Biogenic 2

Total 373

Note that total 2005 NOx emissions in the draft emission inventory of 373 tons per day is less that 

the interpolated 536 tons per day so that no additional determination in 2005 of continued 

compliance with the 8-hour ozone standard would be required.

Therefore, as noted above, the Puget Sound Clean Air Agency has met the requirements of the 

ozone 110 SIP guidance document and shows continued compliance of the existing 0.08 ppm 8-

hour ozone National Ambient Air Quality Standard through 2015. 
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References

 

1

EPA. "Maintenance Plan Guidance Document for Certain 8-hour Ozone Areas Under Section 110(a)(1) of Clean Air Act." 

Research Triangle Park, N.C.: 20 May 2005.

2 EPA. “Ozone and Your Health,” http://www.airnow.gov/index.cfm?action=static.ozone2#3

3 EPA. “Health and Environmental Effects of Ground-Level Ozone,” http://www.epa.gov/ttn/oarpg/naaqsfin/o3health.html

4

Federal Register. September 25, 1996. Approval and Promulgation of Air Quality Implementation Plans; Washington; Revision to 

the State Implementation Plan Vehicle Inspection and Maintenance Programs. Pages 50235-50238, effective 9-25-96. 

5

Federal Register. September 26, 1996. Approval and Promulgation of Implementation Plans and Redesignation of Puget Sound, 

Washington for Air Quality Planning Purposes: Ozone. Pages 50438-50443, effective 11-25-96.

6

Federal Register. August 5, 2004. Approval and Promulgation of State Implementation Plans: State of Washington; Central Puget 

Sound Carbon Monoxide and Ozone Second 10-Year Maintenance Plans. Pages 47365-47366, effective 9-7-04. 

7

Puget Sound Clean Air Agency. Regulation I, Section 8.06 and Regulation II, Section 2.10. Seattle, WA: 19 December 2002.

8

Puget Sound Clean Air Agency. "Ozone Summer Day Emission Inventories" spreadsheet. Seattle, WA: 2 May 2007. [Ozone 

Summer Day Emission Inventories.xls]

9 EPA. 2002 National Emission Inventory, ftp://ftp.epa.gov/EmisInventory/2002finalnei

10 Lamb, Brian et al. of Washington State University; Sally Otterson et al. of Washington State Department of Ecology 

and Naydene Maykut of Puget Sound Clean Air Agency. Ozone Modeling for Maintenance Plan Revision for Puget 

Sound in Western Washington. Pullman, Lacey and Seattle, WA: 15 October 2001.

11 Lamb, Brian et al. of Washington State University; Sally Otterson et al. of Washington State Department of Ecology 

and Kathy Himes et al. of Puget Sound Clean Air Agency. Modeling Analysis of Future Emission Scenarios for 

Ozone Impacts in the Puget Sound Area. Pullman, Lacey and Seattle, WA: August 2006.

12 Anderson, John of Puget Sound Clean Air Agency. "2002 Emission Inventory Appendix--Seasonal" spreadsheet. 

Seattle, WA, 1 May 2007. 

13

 [In preparation]