Bryan W. Shaw, Ph.D., Chairman 

Buddy Garcia, Commissioner 

Carlos Rubinstein, Commissioner 

- . : ~~·.-> .:.\ \ .: I· 

!d:~ fJLr.;·u:i: 

. !· 

Mark R. Vickery, P.G., Executive Director 10 APR -9 Pii 1:55 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

Protecting Texas bg Reducing and Preventing Pollution 

April6,2010 

Docket No. 2009-0802-SIP, Project No. 2009-017-SIP-NR ~ 

Docket No. 2009-0932-RUL, Rule Project No. 2009-006-101-EN · 

Docket No. 2009-0867-RUL, Rule Project No. 2009-019-101-EN 

A1 Armendariz, PhD, Regional Administrator 

U.S. Environmental Protection Agency- Region 6 

1445 Ross Avenue 

Dallas, Texas 75202-2733 . 

Dear Dr. Armendariz: 

On March 10, 2010, the Texas Commission on Environmental Quality (Commission) adopted revisions to the 

State Implementation Plan (SlP) for the control of ozone air pollution for the Houston-Galveston-Brazoria 

(HGB) area. 

The Commission adopted amendments to 30 Texas Administrative Code (TAC) Chapter 101, Subchapter A, 

General Rules, Section 101.1; and Subchapter H, Emissions Banking and Trading, Division 6, Highly Reactive 

Volatile Organic Compound Emissions Cap and Trade Program, Sections 101.390 - 101.394, 101.396, and 

101.399 - 101.401; 30 TAC Chapter 101, Subchapter H, Emissions Banking and Trading, Division 3, Mass 

Emissions C and Trade Pro Sections 101.350 101.351 and 101.353 and co · revisions to the 

SlP; and GB Attsinment Demonstration SlP Revision for the 1997 Ei t-Hour Ozone Standard. These rule 

changes and SIP revisions demonstrate that the HGB area will attain the 1997 eight-hour ozone National 

Ambient Air Quality Standard by June 15, 2019. 

Enclosed are the proposed revisions to the SlP, a public hearing certification, a complete record of the public 

hearings, and the accompanying orders.· I look forward to your expeditious approval of these SlP revisions. 

Sincerely, 

B ~,;ktw.--· B~haw,PhD. Chairman 

BWS/jmm 

Enclosures 

cc: The Honorable Rick Perry, Governor ofTexas 

Mr. Toby Baker, Office ofBudget, Planning and Policy, Office of the Governor 

Mr. Mark R Vickery, P.G., Executive Director, Texas Cor!unission on Environmental Quality 

P.O. Box 13087 Austin, Texas 78711-3087 512-239'1000 1ntemet address: www.tceq.state.tx.us 
Texas Commission on Environmental Quality 

Public Hearings 

October 28-29, 2009 

Houston-Galveston-Brazoria (HGB) 

Attainment Demonstration SIP Revision 

for the 1997 Eight-Hour Ozone Standard 

Project Number 2009-017-SIP-NR 

Volume 1 of 2 
PUBLIC 

NOTIFICATION AND 

PROPOSAL 
PUBLIC NOTIFICATION 

Notification to the public of the proposed revision was conducted by the following procedures: 

1 . Publication of notice of public hearings in the following newspapers on the date listed: 

Austin American-Statesman, September 28, 2009 

Houston Chronicle, September 28, 2009 

2. Publication of the Notice of Public Hearings in the October 9, 2009, issue of the Texas Register 

(34 TexReg 7132) 

3. Correspondence forwarding the notice of public hearing to the following officials and agencies: 

Speaker of the House 

Lieutenant Governor 

Alamo Area Council of Governments 

Capital Area Planning Council 

City of Austin, Mayor's Office 

City of El Paso 

City of Houston, Mayor's Office 

City of Victoria Planning Department 

Dallas Department of Environmental and Health Services 

Dallas Department of Aviation 

East Texas Council of Governments 

El Paso Metropolitan Planning Organization 

Federal Highway Administration 

Fort Worth Environmental Management Department 
Galveston County Health District 

Houston Department of Health and Human Services 

Harris County Public Health and Environmental Services 

Houston-Galveston Area Council 

North Central Texas Council of Governments 

South East Texas Regional Planning Commission 

Texas Department of Transportation 

Texas Transportation Institute 

Travis County Judge 

Arkansas Department of Pollution Control and Ecology 

Louisiana Department of Environmental Quality 

New Mexico Environmental Department 

Oklahoma Department of Environmental Quality 

U.S. Environmental Protection Agency 
Example of Newspaper Classified Ad 

Houston Chronicle, September 28,2009 
(TCEQ) for proposed Registration N , 40243, to construct and operate 

a Type V municipal solid waste trans station. The proposed facility, 

River City Recycles, will be located 000 Daffan Lane, Austin, Texas 

78724, in Travis County. This facil is requesting authorization to 

recycle and transfer municipal solid aste which includes construction 

and demolition waste. The regi 'on application is available for 

viewing and copying at the TCEQ gion 11 Office, 2800 S. lli 35, 

Suite 100, Austin, Travis County, 78704-5712. 

PUBLIC COMMENT/PUBLIC ME 

or written requests for a public m · must be submitted to the Office 

of Chief Clerk at the address include in the information section below. 

Comments may also be received if a ublic meeting is held on the facility. A public meeting will be held by he executive director if requested 

by a member of the legislature who epresents the general area where 

the development is to be located, or f there is a substantial public interest in the proposed development purpose of the public meeting 

is for the public to provide input for nsideration by the commission, 

and for the' applicant and the comm · sion staff to provide information 

to the public. A public meeting is t a contested case hearing. The 

executive director will review and ider public comments and written requests for a public meeting su mitted prior to the notice of final 

determination. The executive dire is not required to file a response 

to comments. 

EXECUTIVE DIRECTOR ACTIO . The executive director shall, after review of an application for regi tion, determine if the application will be approved or denied in hole or in part. If the executive 

director acts on an application, the 'efclerk shall mail or otherwise 

transmit notice of the action and an xplanation of the opportunity to 

file a motion to reconsider the exec 've director's decision. The chief 

clerk shall mail this notice to the o and operator, the public interest 

counsel, to adjacent landowners as own on the required land ownership map and landowners list, and other persons who timely filed 

public comment in response to pub ic notice. Not all persons on the 

mailing list for this notice will recei e the notice letter from the Office 

of the Chief Clerk. 

INFORMATION. Written public 

on the permanent mailing list fo this application should be submitted to the Office of the Chief lerk, MC 105, TCEQ, P.O. Box 

13087, Austin, TX 78711-3088 or electronically submitted to 

http://wwwS.tceq.state.tx.uslecmn index.cfm. Individual members 

of the general public may contact e Office of Public Assistance at 

1-800-687-4040. General info ·on regarding the TCEQ can be 

found at our web site at www.tce .state.tx.us. Further information 

may also be obtained from Ms. n Rodewald at the address stated 

above or by calling (512) 832-83 

TRD-200904422 

LaDonna Castanuela 

Chief Cleric 

Texas Commission on Environmen 

Flied: September 30, 2009 

• 

Notice of Public Hearings on 

Chapter I 0 I and to the State 

• 

oposed Revisions to 30 TAC 

plementation Plan 

The Texas Commission on Enviro ental Quality (commission) will 

conduct concurrent public he · to receive testimony regarding 

proposed revisions to 30 TAC Cha r 10 I, General Air Quality Rules, 

Subchapter A, Definitions, and Su hapter H, Emissions Banking and 

Trading, Division 6, Highly-Re 've Volatile Organic Compound 

Emissions Cap and Trade Pro , and corresponding revisions to 

the state implementation plan (S ) under the requirements of Texas 

34 TexReg 7132 October 9, 2009 Texas Register 

Health and Safety Code, §382.017; exas Government Code, Chapter 

2001, Subchapter B; and 40 Code fFederal Regulations §51.102, of 

the United States Environmental P tection Agency (EPA) concerning 

SIPs. 

The proposed amendments to C pter 101, Subchapter A, §101.1, 

Definitions, would update the de nition of volatile organic compound to link the 30 TAC defini on with the current definition in 

40 Code of Federal Regulations d correct the reportable quantity 

for 1,1,1,2,3,3,3-heptaftuoroprop . The proposed amendment to 

Chapter 101, Subchapter H, Div ion 6, Highly-Reactive Volatile 

Organic Compound Emissions Ca and Trade Program, would also 

reduce the total cap amount of al wances and revise the allocation 

methodology of allowances for p 'cipants in the Highly-Reactive 

Volatile Organic Compound Emiss· ns Cap and Trade Program. (Rule 

Project No. 2009-006-101-EN) 

Public hearings for this proposed lemaking and corresponding SIP 

revision are scheduled in conjun n with the proposed amendments 

to Chapter 101, Subchapter H, Di ision 3, Mass Emissions Cap and 

Trade (MECn program; and Cha ter 115, Subchapter E, Division 4, 

Offset Lithographic Printing at the allowing times and locations: October 28, 2009, 2:00p.m. and 6:00 .m., in Conference Room A at the 

Houston-Galveston Area Council, 555 Tunmons Lane, Houston; and 

in Austin on October 29, 2009, 1: 0 p.m. and 3:00p.m., at the Texas 

Commission on Environmental Q ity complex, Building E, Room 

201S, 12100 Park 35 Circle. The hearings will be structured for the 

receipt of oral or written commen by interested persons. Registration 

will begin 30 minutes prior to eac hearing. Individuals may present 

oral statements when called upon order of registration. There will 

be no open discussion during the earing; however, commission staff 

members will be available to disc the proposals 30 minutes before 

each hearing and will answer que 'ons before and after the hearing. 

Persons planning to attend the he · g, who have special communication or other accommodation n ds, should contact Charlotte Horn, 

Texas Register Team (512) 239-0 9. Requests should be made as far 

in advance as possible. 

Comments may be submitted to Jessica Rawlings, Texas Register 

Team, Office of Legal Services, 1i xas Commission on Environmental 

Quality, MC 205, P.O. Box 130 7, Austin, Texas 78711-3087, or 

faxed to (512) 239-4808. Ele ·c comments may be submitted at 

www5.tceq.state.tt.us/ruleslecom ents/. File size restrictions may apply to comments being submitted ia the eComments system. Copies 

of the proposed rules can be o · ed from the commission's Web site 

at http://www.tceq.state.tt.us/nav. leslpropose_adopt.html. Copies 

of the proposed SIP revisions d all appendices can be obtained 

from the commission's Web site t http:/lwww.tceq.state.tt.us/imp/ementationlair/sip/Hottop.html F r further information regarding the 

proposed rules and SIP revisio please contact Ray Schubert, Air 

Quality Planning Section, at (512 239-6615. 

TR0-200904274 

Robert Martinez 

Oiredor, Environmental Law Divis n 

Texas Commission on Environme tal Quality 

Filed: September 25, 2009 

• • • 

Notice of Public Hearings on Proposed Revisions to 30 TAC 

Chapters lOI and II5 and to the State Implementation Plan 

The Texas Commission on Environmental Quality (commission) will 

conduct public hearings to receive testimony regarding proposed 

revisions to 30 TAC Chapter 101, General Air Quality Rules, and 

30 TAC Chapter 115, Control of Air Pollution from Volatile Organic 
Compounds and corresponding revisions to the state implementation 

plan (SIP) under the requirements of Texas Health and Safety Code, 

§382.017; Texas Government Code, Chapter 2001, Subchapter B; and 

40 Code of Federal Regulations §5 1.1 02, and the United States Envi· 

ronmental Protection Agency (EPA) concerning SIPs. Additionally, 

the commission will also receive testimony regarding the proposed 

eight-hour ozone attainment demonstration and rea.Sonable further 

progress (RFP) demonstration for the Houston-Galveston-Brazoria 

(HGB) area. 

The proposed amendment to Chapter 101, Subchapter H, Division 3, 

Mass Emissions Cap and Trade (MECn Program, would revise the 

definition of "Uncontrolled design capacity" to provide additional flexibility for certain stationary diesel engines and clarify both site and facility applicability. In addition, the proposed amendment would maintain the integrity of the nitrogen oxides (NO.) cap in the HGB ozone 

nonattainment area and minimize increases in the NO. cap by discontinuing the acceptance oflate ECT-3 forms, Level of Activity Certification, from major sources of NO. submitted after March 30, 2010. 

(Rule Projeet No. 2009-019-101-EN) 

The proposed amendment to Chapter 101, Subchapter H, Division 

6, Highly-Reactive Volatile Organic Compound Emissions Cap and 

Trade Program, would reduce the total cap amount of allowances and 

revise the allocation methodology of allowances for participants in the 

Highly-Reactive Volatile Organic Compound (HRVOC) Emissions 

Cap and Trade Program. A proposed amendment to § 101.1 would also 

update the definition of volatile organic compound (VOC) to link the 

30 TAC definition with the current definition in 40 Code of Federal 

Regulations and correct the reportable quantity for 1,1,1,2,3,3,3-heptafluoropropane. (Rule Project No. 2009-ooci-101-EN) 

The proposed amendments to Chapter 115, Subchapter E, Division 4, 

Offset Lithographic Printing, would reduce the VOC content limits on 

fountain solutions used by sources that are subject to the existing Chapter 115 rules. The proposed rulemaking would also limit the VOC 

content of fountain and cleaning solutions used by certain sources that 

are exempt from the existing Chapter 115 rules. (Rule Projeet No. 

2008-019-115-EN) 

The proposed HGB Attainment Demonstration SIP revision contains 

Federal Clean Air Act-required SIP elements, including a photochemical modeling analysis, a weight of evidence analysis, a reasonable 

available control technology (RACT) analysis, a reasonably available 

control measures (RACM) analysis, a motor vehicle emissions budget (MVEB) for 2018, and a contingency plan. In addition, the Houston-Galveston Area Council bas committed to emissions reductions 

through the Voluntary Mobile Emission Reduction Program and implementation of transportation control measures. The proposed revision also describes the concurrently proposed rule revisions in Chapters 101 and 115. The commission is also soliciting comments on whether it is appropriate to perform a 1997 eight-hour ozone standard 

mid-course review analysis, and, if so, what elements should be contained in the analysis. The commission is also seeking input on the 

appropriate date to submit the mid-course review. (Rule Projeet No. 

2009-017-SIP-NR) 

The proposed HGB Eight-Hour Ozone Nonattainment Area RFP SIP 

revision demonstrates that the 18 percent ozone precursor emissions reduction requirement will be met for the analysis period of2002 to 2008, 

9 percent between 2009 and 2011, 9 percent between 2012 and 2014, 

9 percent between 2015 and 2017, 3 percent in 2018, and 3 percent 

for contingency purposes. This revision also includes a revised MVEB 

for the milestone years 2008, 2011, 2014, 2017, and 2018. No new 

on-road mobile source controls have been adopted as part of the plan. 

However, on-road mobile source emissions inventories have been updated using the latest available data and the EPA's MOBILE6 inventory 

development tool. As a result of the required mobile source emission 

inventory updates, the MVEBs are updated as part of this SIP revision. 

(Rule Projeet No. 2009-018-SIP-NR) 

Public hearings on these proposals will be held at the following times 

and locations: October 28, 2009, 2:00 p.m. and 6:00 p.m., in Conference Room A at the Houston-Galveston Area Council, 3555 Tunmons 

Lane, Houston; and in Austin on October 29, 2009, 3:00p.m., at the 

Texas Commission on Environmental Quality complex, Building E, 

Room 201 S, 12100 Park 35 Circle. The hearings will be structured for 

the receipt of oral or written comments by interested persons. Registration will begin 30 minutes prior to each hearing. Individuals may 

present oral statements when called upon in order of registration. There 

will be no open discussion during the hearing; however, commission 

staff members will be available to discuss the proposals 30 minutes before each hearing and will answer questions before and after the hear· 

in g. 

Persons planning to attend the bearing, who have special communi· 

cation or other accommodation needs, should contact Charlotte Hom, 

Texas Register Team (512) 239-0779. Requests should be made as far 

in advance as possible. 

Comments may be submitted to Jessica Rawlings, Texas Register 

Team, Office of Legal Services, Texas Commission on Environmental 

Quality, MC 205, P.O. Box 13087, Austin, Texas 78711-3087, or 

faxed to (512) 239-4808. Electronic comments may be submitted at 

www5.tceq.state.tx.uslruleslecommentsl. File size restrictions may 

apply to comments being submitted via the eComments system. All 

comments sbould reference tbe rule or SIP projeet number tbat 

the comment pertains to: Rule Project No. 2009-019-101-EN 

for the proposed MECT rule amendments, Rule Projeet No. 

2009-ooci-101-EN for tbe proposed HRVOC rule amendments, 

Rule Projeet No. 2008-019-115-EN for tbe proposed VOC rule 

amendments, SIP Projeet No. 2009-017-SIP-NR for the proposed 

HGB Attainment Demonstration SIP revision and SIP Projeet 

No. 2009-018-SIP-NR for tbe proposed HGB RFP SIP revision. 

Comments must be received by November 9, 2009. Copies of 

the proposed rules can be obtained from the commission's Web site 

at http:llwww.tceq.state.tx.uslnav/ruleslpropose _ adopt.html. Copies 

of the proposed SIP revisions and all appendices can be obtained 

from the commission's Web site at hltp:llwww.tceq.state.t:x.IIS!implementationlairlsip/Hottop.html. For further information regarding the 

proposed rules and SIP revisions, please contact Ray Schubert, Air 

Quality Planning Section, at (512) 239-6615. 

TRD-200904267 

Robert Martinez 

Diredor, Environmental Law Division 

Texas Commission on Environmental Quality 

Filed: September 25, 2009 

• • • 

Notice of Public Hearings on oposed Revisions to 30 TAC 

Chapter 115 and to the State I plementation Plan 

The Texas Commission on En · ental Quality (commission) will 

conduct public bearings to rece e testimony regarding proposed 

revisions to 30 TAC Chapter 10 , General Air Quality Rules, and 

30 TAC Chapter 11 5, Control of · Pollution from Volatile Organic 

Compounds and corresponding isions to the state implementation 

plan (SIP) under the requiremen of Texas Health and Safety Code, 

§382.017; Texas Government C de, Chapter 2001, Subchapter B; 

and 40 Code of Federal Regulati ns §5 1.1 02, and the United States 

Environmental Protection Agen (EPA) concerning SIPs. Additionally, the commission will al receive testimony regarding the 

IN ADDITION October 9, 2009 34 TexReg 7133 
Bryan W. Shaw, Ph.D., Chairman 

Buddy Garcia, Commissioner 

Carlos Rubinstein, Commissioner 

Mark R. Vickery, P.G., Executive Director 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

Protecting Texas by Reducing and Preventing Pollution 

NOTICE OF PUBLIC HEARINGS BY THE 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

ON PROPOSED REviSIONS TO 30 TAC CHAPTERS 101 AND 115, AND TO THE STATE 

IMPLEMENTATION PLAN 

The Texas Commission on Environmental Quality (commission) will conduct public hearings to receive 

testimony regarding proposed revisions to 30 TAC Chapter 101, General Air Quality Rules, and 30 T AC 

Chapter 115, Control of Air Pollution from Volatile Organic Compounds and corresponding revisions to 

the state implementation plan (SIP) under the requirements of Texas Health and Safety Code, §382.017; 

Texas Government Code, Chapter 2001, Subchapter B; and 40 Code of Federal Regulations §51.1 02, and 

the United States Environmental Protection Agency (EPA) concerning SIPs. Additi.onally, the 

commission will also receive testimony regarding the proposed eight-hour ozone attainment 

demonstration and reasonable further progress (RFP) demonstration for the Houston-Galveston-Brazoria 

(HGB) area. 

The proposed amendment to Chapter 101, Subchapter H, Division 3, Mass Emissions Cap and Trade 

(MECT) Program, would revise the definition of "Uncontrolled design capacity" to provide additional 

flexibility for certain stationary diesel engines and clarify both site and facility applicability. In addition, 

the proposed amendment would maintain the integrity of the nitrogen oxides (NOx) cap in the HGB 

ozone nonattainment area and minimize increases in the NOx cap by discontinuing the acceptance of late 

ECT-3 forms, Level of Activity Certification, from major sources of NOx submitted after March 30, 

2010. (Rule Project No. 2009-019-101-EN) 

The proposed amendment to Chapter 101, Subchapter H, Division 6, Highly-Reactive Volatile Organic 

Compound Emissions Cap and Trade Program, would reduce the total cap amount of allowances and 

revise the allocation methodology of allowances for participants in the Highly-Reactive Volatile Organic 

Compound (HRVOC) Emissions Cap and Trade Program. A proposed amendment to §101.1 would also 

update the definition of volatile organic compound (VOC) to link the 30 TAC definition with the current 

defmition in 40 Code of Federal Regulations and correct the reportable quantity for 1,1,1,2,3,3,3-

heptafl.uoropropane. (Rule Project No. 2009-006-101-EN) 

The proposed amendments to Chapter 115, Subchapter E, Division 4, Offset Lithographic Printing, would 

reduce the VOC content limits on fountain solutions used by sources that are subject to the existing 

Chapter 115 rules. The proposed rulemaking would also limit the VOC content of fountain and cleaning 

solutions used by certain sources that are exempt from the existing Chapter 115 rules. (Rule Project No. 

2008-019-115-EN) 

The proposed HGB Attainment Demonstration SIP revision contains Federal Clean Air Act-required SIP 

elements, including a photochemical modeling analysis, a weight of evidence analysis, a reasonable 

available control technology (RACT) analysis, a reasonably available control measures (RACM) analysis, 

a motor vehicle emissions budget (MVEB) for 2018, and a contingency plan. In addition, the HoustonGalveston Area Council has committed to emissions reductions through the Voluntary Mobile Emission 

Reduction Program and implementation of transportation control measures. The proposed revision also 

describes the concurrently proposed rule revisions in Chapters 101 and 115. The commission is also 

Pn Rm 1~0R7 Anc;tin TPY:o~ 7R71 VlOR7 :; 1 ?.-?.~G- 1 non 
soliciting comments on whether it is appropriate to perform a 1997 eight-hour ozone standard mid-course 

review analysis, and, if so, what elements should be contained in the analysis. The commission is also 

seeking input on the appropriate date to submit the mid-course review. (Rule Project No. 2009-017-SIPNR) . 

The proposed HGB Eight-Hour Ozone Nonattainment Area RFP SIP revision demonstrates that the 18 

percent ozone precursor emissions reduction requirement will be met for the analysis period of 2002 to 

2008, 9 percent between 2009 and 2011, 9 percent between 2012 and 2014,9 percent between 2015 and 

2017, 3 percent in 2018, and 3 percent for contingency purposes. This revision also includes a revised 

MVEB for the milestone years 2008, 2011, 2014, 2017, and 2018. No new on-road mobile source 

controls have been adopted as part of the plan. However, on-road mobile source emissions inventories 

have been updated using the latest available data and the EPA's MOBU.E6 inventory development tool. 

As a result of the required mobile source emission inventory updates, the MVEBs are updated as part of 

this SIP revision. (Rule Project No. 2009-018-SIP-NR) 

Public hearings on these proposals will be held at the following times and locations: October 28, 2009, 

2:00 p.m. and 6:00 p.m., in Conference Room A at the Houston-Galveston Area Council, 3555 Timmons 

Lane, Houston; and in Austin on October 29, 2009, 3:00 p.m., at the Texas Commission on 

Environmental Quality complex, Building E, Room 201S, 12100 Park 35 Circle. The hearings will be 

structured for the receipt of oral or written comments by interested persons. Registration will begin 30 

minutes prior to each hearing. Individuals may present oral statements when called upon in order of 

registration. There will be no open discussion during the hearing; however, commission staff members 

will be available to discuss the proposals 30 minutes before each hearing and will answer questions before 

and after the hearing. 

Persons planning to attend the hearing, who have special communication or other accommodation needs, 

should contact Charlotte Hom, Texas Register Team (512) 239-0779. Requests should be made as far in 

advance as possible. 

Comments may be submitted to Jessica Rawlings, Texas Register Team, Office of Legal Services, Texas 

Commission on Environmental Quality, MC 205, P.O. Box 13087, Austin, Texas 78711-3087, or faxed to 

(512) 239-4808. Electronic comments may be submitted at www5.tceq.state.tx.uslruleslecommentsl. File 

size restrictions may apply to comments being submitted via the eComments system. All comments 

should reference the rule or SIP project number that the comment pertains to: Rule Project No. 

2009-019-101-EN for the proposed MECT rule amendments, Rule Project No. 2009-006-101-EN for 

the proposed HRVOC rule amendments, Rule Project No. 2008-019-115-EN for the proposed VOC 

rule amendments, SIP Project No. 2009-017-SIP-NR for the proposed HGB Attainment 

Demonstration SIP revision and SIP Project No. 2009-018-SIP-NR for the proposed HGB RFP SIP 

revision. Comments must be received by November 9, 2009. Copies of the proposed rules can be 

obtained from the commission's Web site at http://www.tceq.state.tx.uslnav/ruleslpropose_adopt.html. 

Copies of the proposed SIP revisions and all appendices can be obtained from the commission's Web site 

at http:/lwww.tceq.state.tx.uslimplementationlair/sip/Hottop.html. For further information regarding the 

proposed rules and SIP revisions, please contact Ray Schubert, Air Quality Planning Section, at (512) 

239-6615. 

Issued in Austin, Texas, on September 23, 2009. 
REVISION TO THE STATE IMPLEMENTATION PLAN 

FOR THE CONTROL OF OZONE AIR POLLUTION 

HOUSTON-GALVESTON-BRAZORIA 1997 EIGHT-HOUR OZONE STANDARD 

NONATTAINMENT AREA 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

P.O. BOX 13087 

AUSTIN, TEXAS 78711-3087 

Houston-Galveston-Brazoria Attainment Demonstration 

State Implementation Plan Revision for the 1997 Eight-Hour Ozone Standard 

PROJECT NO. 2009-017-SIP-NR 

Proposed 

September 23, 2009 
This page is intentionally left blank.
EXECUTIVE SUMMARY 

The United States Environmental Protection Agency (EPA) reclassified the eight-county 

Houston-Galveston-Brazoria (HGB) area from a moderate to a severe nonattainment area for the 

1997 eight-hour ozone National Ambient Air Quality Standard (NAAQS) effective on October 

31, 2008. The HGB eight-county area includes Brazoria, Chambers, Fort Bend, Galveston, 

Harris, Liberty, Montgomery, and Waller Counties. The EPA set April 15, 2010, as the date for 

the state to submit a state implementation plan (SIP) revision addressing the severe ozone 

nonattainment area requirements of the 1990 Federal Clean Air Act Amendments (FCAA). The 

HGB area must attain the 1997 eight-hour ozone standard of 0.08 parts per million (ppm) as 

expeditiously as practicable but no later than the attainment date of June 15, 2019. Since 

emission reductions needed for attainment must be implemented by the beginning of the ozone 

season immediately preceding the HGB area’s attainment date, implementation of controls need 

to be made by 2018, which is the attainment year for modeling.

This SIP revision addresses ozone formation in the HGB area, the precursor emissions of nitrogen 

oxides (NOX) and volatile organic compounds (VOC), the control strategies that are to be 

implemented, the quantity of emission reductions associated with each strategy, and when these 

reductions will occur. Based on photochemical modeling and an evaluation of corroborative 

evidence, ozone measurements in the HGB area are predicted to be compliant with the 1997 

eight-hour ozone NAAQS by June 15, 2019. 

The existing measures to control ozone formation in the HGB area that have been adopted in 

previous SIP revisions center on: 

• approximately 80 percent NOX emission reductions from point sources through the Mass 

Emission Cap and Trade (MECT) program; 

• NOX emission reductions from on-road and non-road sources through the vehicle 

inspection and maintenance (I/M) program, the Texas Emission Reduction Plan (TERP), 

and the Texas Low Emission Diesel (TxLED) program; 

• highly reactive volatile organic compounds (HRVOC) controls through the associated 

HRVOC Emission Cap and Trade (HECT) program; and 

• VOC controls. 

See Chapter 4, Control Strategies and Required Elements, Section 4.2, Existing Control 

Measures for a complete list of control measures. 

Despite the significant decreases in one-hour and eight-hour ozone design values and in NOX and 

VOC emissions in the HGB area, further reductions are needed to bring the area into attainment 

of the 1997 eight-hour ozone NAAQS. Even as key ozone-targeting regulatory programs have 

reduced the number and magnitude of ozone exceedances, the area of exceedance, and the 

population exposed to exceedances, economic and population growth continue to create air 

quality challenges for the HGB area. 

This submittal contains proposed new state and local control measures. The Houston-Galveston 

Area Council (H-GAC), as the regional metropolitan transportation planning agency for the HGB 

area, has identified three voluntary programs that will aid in the improvement of the HGB area’s 

air quality. The H-GAC’s commitment for NOX emissions reductions from the Voluntary Mobile 

Emission Reduction Program (VMEP) is 2.25 tons per day (tpd). The H-GAC has also identified 

transportations control measures (TCMs) that have been or will be implemented in the 

 i
nonattainment area. By the start of the 2018 ozone season, these TCMs will reduce NOX

emissions in the HGB area by 0.015 tpd. 

Photochemical modeling analysis demonstrates that a 25 percent reduction of the HECT cap on 

the total Harris County HRVOC allocation would contribute to attainment of the 1997 eight-hour 

ozone NAAQS by reducing the future 2018 ozone design values at all HGB monitors. 

Accordingly, this SIP revision contains a proposed 25 percent reduction in the total HRVOC 

allowance cap and revision to the HRVOC allocation methodology. The HECT program will 

continue to be applicable only in Harris County. 

This plan demonstrates attainment using photochemical modeling that includes the existing and 

proposed control strategies previously listed. The demonstration also relies on weight of 

evidence (WoE) corroborative analysis and additional control measures not explicitly accounted 

for in the photochemical modeling (see Chapter 5, Weight of Evidence). 

This SIP revision includes base case modeling of representative ozone exceedance episodes that 

occurred during 2005 and 2006. In general, the model performance evaluation of the base cases 

for 2005 and 2006 indicates the modeling is suitable for use in conducting the modeling 

attainment test. The modeling attainment test was applied by modeling a 2006 baseline year and 

2018 future year to project 2018 eight-hour ozone design values. Only two regulatory monitors, 

Deer Park (DRPK) and Bayland Park (BAYP), and one non-regulatory monitor, Wallisville 

(WALV), are projected to have modeled 2018 eight-hour ozone design values greater than the 

1997 eight-hour ozone NAAQS. 

Modeling analyses of the sensitivity of the 2018 projected eight-hour ozone design values to 

emission reductions of NOX and VOC generally indicate that the ozone design values are more 

sensitive to NOX reductions than VOC. However, the sensitivity of ozone design values to 

reductions in HRVOC is much greater than for other VOC. 

Table ES-1: Summary of 2006 Baseline, 2018 Future Year, and 2018 Control Strategy 

Anthropogenic Modeling Emissions for HGB lists the anthropogenic modeling emissions in tons 

per day (tpd) by source category for the 2006 baseline, 2018 future year, and the 2018 control 

strategies for NOX and VOC. The differences in modeling emissions between the 2006 baseline 

and the 2018 future year reflect the net of growth and existing controls. The existing controls 

include both state and federal measures that have already been promulgated. The differences in 

modeling emissions between the 2018 future year and the 2018 control strategy reflect the 

proposed controls. These proposed controls include NOX reductions from both the VMEP 

measures and TCMs, and the 25 percent reduction in the Harris County total HRVOC cap for the 

HECT program. 

 ii
Table ES-1: Summary of 2006 Baseline, 2018 Future Year, and 2018 Control Strategy 

Anthropogenic Modeling Emissions for HGB 

2006 Baseline 2018 Future Year 2018 Control Strategy 

NOX VOC CO NOX VOC CO NOX VOC CO 

Source 

Type 

(tpd) (tpd) (tpd) 

Point 172.16 208.34 126.22 162.75 309.46 182.10 162.75 306.77 182.10 

On-road 197.28 99.39 1115.23 50.76 50.39 733.17 49.21 50.39 733.17 

Non-road 78.85 75.97 772.94 35.65 59.56 893.84 34.95 59.56 893.84 

Off-road 73.55 6.05 53.25 85.72 6.93 44.71 85.72 6.93 44.71 

Area 36.35 528.99 134.59 42.04 650.09 158.99 42.04 650.09 158.99 

Totals 558.19 918.74 2202.23 376.92 1076.43 2012.81 374.67 1073.74 2012.81 

Note: VOC is reported as sum of CB05 species 

Table ES-2: Summary of 2006 Baseline, 2018 Future Year, and 2018 Control Strategy EightHour Ozone Design Values for BAYP and DRPK Monitors lists the eight-hour ozone design 

values in parts per billion (ppb) for the 2006 baseline (DVB), 2018 baseline future year (DVF), 

and 2018 control strategy for the two regulatory monitors with model-projected 2018 eight-hour 

ozone design values greater than the 1997 eight-hour ozone NAAQS. However, 18 regulatory 

monitors have model-projected 2018 eight-hour ozone design values less than the 1997 eighthour ozone NAAQS. Since the modeling cannot provide an absolute prediction of future year 

ozone design values, additional information from corroborative analyses are used in assessing 

whether the area will attain the standard in the future year. 

Table ES-2: Summary of Modeled 2006 Baseline, 2018 Future Year, and 2018 Control 

Strategy Eight-Hour Ozone Design Values for BAYP and DRPK Monitors 

Monitor 

Site Code 

Monitor 

Designation 

2006 

DVB

 (ppb) 

2018 Baseline 

DVF 

(ppb) 

2018 Control Strategy 

DV 

(ppb) 

DRPK Deer Park (CAMS 35) 92.0 88.2 87.9 

BAYP Bayland Park (CAMS 53) 96.7 87.0 86.9 

Note: The 2006 DVB is different from the 2006 regulatory design value (DVR). Figure 3-1: Baseline 

Design Value Calculation Illustration in Chapter 3, Photochemical Modeling, illustrates how DVBs are 

calculated using the three DVRs containing 2006 data. The 2006 DVR is the average of the fourth high 

ozone values from 2004, 2005, and 2006. 

This SIP revision provides ozone reduction trends analyses and supplementary data to 

demonstrate that the HGB eight-county nonattainment area will attain the 1997 eight-hour ozone 

standard of 0.08 ppm (84 parts per billion (ppb)). The EPA’s April 2007 “Guidance on the Use 

of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, 

PM2.5, and Regional Haze” states that a weight of evidence demonstration is allowed when the 

future design value is at or below 87.9 ppb. The quantitative and qualitative corroborative 

analyses in Chapter 5, Weight of Evidence, support a conclusion that this SIP revision 

demonstrates attainment of the 1997 eight-hour ozone NAAQS. 

This revision also includes FCAA-required SIP elements, including a reasonably available control 

measures (RACM) analysis, a reasonably available control technology (RACT) analysis, a motor 

vehicle emissions budget (MVEB), and a contingency plan. For the MVEB, see Table ES-3: 

 iii
2018 Attainment Demonstration Motor Vehicle Emissions Budget for the Eight-County HGB 

Area. 

Table ES-3: 2018 Attainment Demonstration Motor Vehicle Emissions Budget 

for the Eight-County HGB Area 

Eight-County HGB Area Summer Weekday Emissions (tpd)

NOX VOC 2018 MVEB 49.22 45.97 

The Texas Commission on Environmental Quality (TCEQ) is committed to developing and 

applying the best science and technology towards addressing and reducing ozone formation in 

HGB and other nonattainment areas in Texas. This SIP revision also includes a description of 

how the TCEQ continues to use new technology, such as infrared VOC imaging to identify and 

control unaddressed or under-addressed pollution sources, to investigate possible emission 

reduction strategies, and other practical methods to continue making progress in air quality 

improvement. For more information, see Chapter 6, Ongoing and Future Initiatives. 

 iv
SECTION V: LEGAL AUTHORITY

A. General

The Texas Commission on Environmental Quality (TCEQ) has the legal authority to implement, 

maintain, and enforce the National Ambient Air Quality Standards (NAAQS) and to control the 

quality of the state’s air, including maintaining adequate visibility. 

The first air pollution control act, known as the Clean Air Act of Texas, was passed by the Texas 

Legislature in 1965. In 1967, the Clean Air Act of Texas was superseded by a more 

comprehensive statute, the Texas Clean Air Act (TCAA), found in Article 4477-5, Vernon’s 

Texas Civil Statutes. The legislature amended the TCAA in 1969, 1971, 1973, 1979, 1985, 1987, 

1989, 1991, 1993, 1995, 1997, 1999, 2001, 2003, 2005, 2007, and 2009. In 1989, the TCAA was 

codified as Chapter 382 of the Texas Health & Safety Code. 

Originally, the TCAA stated that the Texas Air Control Board (TACB) is the state air pollution 

control agency and is principal authority in the state on matters relating to the quality of air 

resources. In 1991, the legislature abolished the TACB effective September 1, 1993, and its 

powers, duties, responsibilities, and functions were transferred to the Texas Natural Resource 

Conservation Commission (TNRCC). With the creation of the TNRCC, the authority over air 

quality is found in both the Texas Water Code and the TCAA. Specifically, the authority of the 

TNRCC is found in Chapters 5 and 7. Chapter 5, Subchapters A - F, H - J, and L, include the 

general provisions, organization, and general powers and duties of the TNRCC, and the 

responsibilities and authority of the executive director. This chapter also authorizes the TNRCC 

to implement action when emergency conditions arise, and to conduct hearings. Chapter 7 gives 

the TNRCC enforcement authority. In 2001, the 77th Texas Legislature continued the existence 

of the TNRCC until September 1, 2013, and changed the name of the TNRCC to the Texas 

Commission on Environmental Quality (TCEQ). In 2009, the 81st Texas Legislature, during a 

special session, amended § 5.014 of the Texas Water Code, changing the expiration date of the 

TCEQ to September 1, 2011, unless continued in existence by the Texas Sunset Act. 

The TCAA specifically authorizes the TCEQ to establish the level of quality to be maintained in 

the state’s air and to control the quality of the state’s air by preparing and developing a general, 

comprehensive plan. The TCAA, Subchapters A - D, also authorize the TCEQ to collect 

information to enable the commission to develop an inventory of emissions; to conduct research 

and investigations; to enter property and examine records; to prescribe monitoring requirements; 

to institute enforcement proceedings; to enter into contracts and execute instruments; to formulate 

rules; to issue orders taking into consideration factors bearing upon health, welfare, social and 

economic factors, and practicability and reasonableness; to conduct hearings; to establish air 

quality control regions; to encourage cooperation with citizens’ groups and other agencies and 

political subdivisions of the state as well as with industries and the federal government; and to 

establish and operate a system of permits for construction or modification of facilities. 

Local government authority is found in Subchapter E of the TCAA. Local governments have the 

same power as the TCEQ to enter property and make inspections. They also may make 

recommendations to the Commission concerning any action of the TCEQ that affects their 

territorial jurisdiction, may bring enforcement actions, and may execute cooperative agreements 

with the TCEQ or other local governments. In addition, a city or town may enact and enforce 

ordinances for the control and abatement of air pollution not inconsistent with the provisions of 

the TCAA and the rules or orders of the Commission. 

 v
Subchapters G and H of the TCAA authorize the TCEQ to establish vehicle inspection and 

maintenance programs in certain areas of the state, consistent with the requirements of the federal 

Clean Air Act; coordinate with federal, state, and local transportation planning agencies to 

develop and implement transportation programs and measures necessary to attain and maintain 

the NAAQS; establish gasoline volatility and low emission diesel standards; and fund and 

authorize participating counties to implement vehicle repair assistance, retrofit, and accelerated 

vehicle retirement programs. 

B. Applicable Law

The following statutes and rules provide necessary authority to adopt and implement the State 

Implementation Plan (SIP). The rules listed below have previously been submitted as part of the 

SIP. 

Statutes

All sections of each subchapter are included, unless otherwise noted. 

 

TEXAS HEALTH & SAFETY CODE, Chapter 382 September 1, 2009 

 

TEXAS WATER CODE September 1, 2009 

Chapter 5: Texas Natural Resource Conservation Commission 

Subchapter A: General Provisions 

Subchapter B: Organization of the Texas Natural Resource Conservation Commission 

Subchapter C: Texas Natural Resource Conservation Commission 

Subchapter D: General Powers and Duties of the Commission 

Subchapter E: Administrative Provisions for Commission 

Subchapter F: Executive Director (except §§ 5.225, 5.226, 5.227, 5.2275, 5.231, 5.232, and 

5.236) 

Subchapter H: Delegation of Hearings 

Subchapter I: Judicial Review 

Subchapter J: Consolidated Permit Processing 

Subchapter L: Emergency and Temporary Orders (§§ 5.514, 5.5145, and 5.515 only) 

Subchapter M: Environmental Permitting Procedures (§ 5.558 only) 

Chapter 7: Enforcement 

Subchapter A: General Provisions (§§ 7.001, 7.002, 7.00251, 7.0025, 7.004, and 7.005 only) 

Subchapter B: Corrective Action and Injunctive Relief (§ 7.032 only) 

Subchapter C: Administrative Penalties 

Subchapter D: Civil Penalties (except §7.109) 

Subchapter E: Criminal Offenses and Penalties: §§ 7.177, 7.179-7.183 

Rules

All of the following rules are found in 30, Texas Administrative Code, as of the following 

effective dates: 

Chapter 7: Memoranda of Understanding, § 7.110 and § 7.119 May 2, 2002 

Chapter 19: Electronic Reporting March 1, 2007 

Chapter 35, Subchapters A-C, K: Emergency and Temporary Orders and Permits; Temporary 

Suspension or Amendment of Permit Conditions July 20, 2006 

 vi
Chapter 39: Public Notice, §§ 39.201; 39.401; 39.403(a) and (b)(8)-(10); 

39.405(f)(1) and (g); 39.409; 39.411 (a), (b)(1)-(6) and (8)-(10), (c)(1)-(6), 

and (d); 39.413(9), (11), (12), and (14); 39.418(a) and (b)(3) 

and (4); 39.419(a), (b), (d), and (e); 39.420(a), (b) and (c)(3) and (4); 

 39.423 (a) and (b); 39.601-39.605 March 29, 2006 

Chapter 55: Requests for Reconsideration and Contested Case Hearings; 

Public Comment, §§ 55.1; 55.21(a)-(d), (e)(2), (3), and (12), (f), and 

(g); 55.101(a), (b), and (c)(6)-(8); 55.103; 55.150; 55.152(a)(1), (2), 

and (6) and (b); 55.154; 55.156; 55.200; 55.201(a)-(h); 55.203; 

55.205; 55.209, and 55.211 March 29, 2006 

Chapter 101: General Air Quality Rules January 1, 2009 

Chapter 106: Permits by Rule, Subchapter A June 30, 2004 

Chapter 111: Control of Air Pollution from Visible Emissions and 

 Particulate Matter July 19, 2006 

Chapter 112: Control of Air Pollution from Sulfur Compounds July 16, 1997 

Chapter 113: Standards of Performance for Hazardous Air Pollutants 

 and for Designated Facilities and Pollutants May 14, 2009 

Chapter 114: Control of Air Pollution from Motor Vehicles June 26, 2008 

Chapter 115: Control of Air Pollution from Volatile Organic Compounds July 19, 2007 

Chapter 116: Permits for New Construction or Modification May 29, 2008 

Chapter 117: Control of Air Pollution from Nitrogen Compounds March 4, 2009 

Chapter 118: Control of Air Pollution Episodes March 5, 2000 

Chapter 122: § 122.122: Potential to Emit December 11, 2002 

Chapter 122: § 122.215: Minor Permit Revisions June 3, 2001 

Chapter 122: § 122. 216: Applications for Minor Permit Revisions June 3, 2001 

Chapter 122: § 122.217: Procedures for Minor Permit Revisions December 11, 2002 

Chapter 122: § 122.218 Minor Permit Revision Procedures for Permit 

Revisions Involving the Use of Economic Incentives, Marketable 

Permits, and Emissions Trading June 3, 2001 

 vii
SECTION VI. CONTROL STRATEGY 

A. Introduction (No change) 

B. Ozone (Revised) 

 1. Dallas-Fort Worth (No change) 

 2. Houston-Galveston-Brazoria (Revised) 

 Chapter 1: General

 Chapter 2: Anthropogenic Emissions Inventory (EI) Description 

 Chapter 3: Photochemical Modeling 

 Chapter 4: Control Strategies and Required Elements 

 Chapter 5: Weight of Evidence 

 Chapter 6: Ongoing and Future Initiatives 

 3. Beaumont-Port Arthur (No change) 

 4. El Paso (No change) 

 5. Regional Strategies (No change) 

 6. Northeast Texas (No change) 

 7. Austin Area (No change) 

 8. San Antonio Area (No change) 

C. Particulate Matter (No change) 

D. Carbon Monoxide (No change) 

E. Lead (No change) 

F. Oxides of Nitrogen (No change) 

G. Sulfur Dioxide (No change) 

H. Conformity with the National Ambient Air Quality Standards (No change) 

I. Site Specific (No change) 

J. Mobile Sources Strategies (No change) 

K. Clean Air Interstate Rule (No change) 

L. Transport (No change) 

M. Regional Haze (No change) 

 viii
LIST OF ACRONYMS 

ACT Alternative Control Techniques 

AERR Air Emissions Reporting Requirements 

AGL Above Ground Level 

AIRS Aerometric Information Retrieval System 

APCA Anthropogenic Precursor Culpability Assessment 

APU Auxiliary Power Unit 

ARD Acid Rain Database 

auto-GC Automated Gas Chromatograph 

AWO American Waterways Operators 

BACT Best Available Control Technology 

BAYP Houston Bayland Park Monitor (CAMS 53) 

BCCA-AG Business Coalition for Clean Air-Appeal Group 

BELD Biogenic Emissions Landuse Data 

BMP Best Management Practices 

BPA Beaumont-Port Arthur 

C35C Clinton Monitor (CAMS 403/CAMS 113/CAMS 304) 

CAIR Clean Air Interstate Rule 

CAMS Continuous Air Monitoring Station 

CAMx Comprehensive Air Model with Extension 

CARB California Air Resources Board 

CEMS Continuous Emission Monitoring Systems 

CENRAP/RPO Central Regional Air Planning Association/Regional Planning 

Organization 

CFFP Clean Fuel Fleet Program 

CFR Code of Federal Regulations 

CFV Clean Fuel Vehicles 

ClNO2 Nitryl Chloride 

CLU Common Land Unit 

CNR2 Conroe Relocated (CAMS 78) 

CO Carbon Monoxide 

CTAC Chemical Transportation Advisory Committee 

CTG Control Technique Guidelines 

DACM AirCheckTexas Drive a Clean Machine 

DERC Discrete Emissions Reduction Credit 

DFW Dallas-Fort Worth 

DIAL Differential Absorption Lidar 

DMA Marine Distillate Fuel A 

DMX Marine Distillate Fuel X 

DOAS Differential Optical Absorption Spectroscopy 

DRE Destruction and Removal Efficiency 

DRPK Deer Park Monitor (CAMS 35/139) 

DV Design Value 

DV18 2018 Ozone Design Value 

 ix
DVB Baseline Year Ozone Design Value 

DVF Future Design Value 

EBI Euler Backward Iterative 

ECA Emissions Control Area 

EDAS Ecosystem Dynamics and the Atmosphere Section 

EE/RE Energy Efficiency and Renewable Energy 

EGAS Economic Growth Analysis System 

EGU Electric Generating Unit 

EI Emissions Inventory 

EIQ Emissions Inventory Questionnaires 

EPA United States Environmental Protection Agency 

EPS3 Emissions Processing System version 3 

ERC Emissions Reduction Credit 

ESL Energy Systems Laboratory 

ETH Ethylene 

FCAA Federal Clean Air Act 

FDDA Four-Dimensional Data Assimilation 

FIP Federal Implementation Plan 

FMVCP Federal Motor Vehicle Control Program 

FORM Formaldehyde 

GALV Galveston Airport Monitor (CAMS 34/CAMS 109/CAMS 154) 

GAPP GEWEX Americas Prediction Project 

GCIP GEWEX Continental International Project 

GEWEX Global Energy and Water Cycle Experiment 

GloBEIS Global Biosphere Emissions and Interactions System 

GOES Geostationary Operational Environmental Satellite 

g/kW–hr Grams per Kilowatt Hour 

GREASD Greatly Reduced Execution and Simplified Dynamics 

GWEI Gulf-wide Emissions Inventory 

HALC Aldine Monitor (CAMS 8) 

HB House Bill 

HCHV Channelview Monitor (CAMS 15/CAMS 115) 

HCQA Croquet Monitor (CAMS 409) 

HDDV Heavy-Duty Diesel Vehicle 

HECT Highly Reactive Volatile Organic Compound Emissions Cap and Trade 

H-GAC Houston-Galveston Area Council 

HGB Houston-Galveston-Brazoria 

HNWA Northwest Harris County Monitor (CAMS 26) 

HO2 Hydroperoxy Radical 

HOEA Houston East Monitor (CAMS 1) 

HONO Nitrous Acid 

hp Horsepower 

HPMS Highway Performance Monitoring System 

HRM Haden Road Monitor (CAMS 603) 

 x
HROC TCEQ Houston Regional Office Monitor (CAMS 81) 

HRVOC Highly Reactive Volatile Organic Compounds 

HSMA Houston Monroe Monitor (CAMS 406) 

HTCA Houston Texas Avenue Monitor (CAMS 411) 

HYSPLIT Hybrid Single Particle Lagrangian Integrated Trajectory 

I/M Inspection and Maintenance 

IAF Ike Adjustment Factor 

I-DOAS Imaging Differential Optical Absorption Spectroscopy 

IMO International Maritime Organization 

IOLE Internal Olefins 

ISOP Isoprene 

JPL Jet Propulsion Laboratory 

km Kilometer 

KV Vertical Diffusivity Coefficient 

kW Kilowatts 

LDAR Leak Detection and Repair 

LDEQ Louisiana Department of Environmental Quality 

LEADS Leading Environmental Analysis and Display System 

LIRAP Low Income Vehicle Repair Assistance, Retrofit, and Accelerated 

Vehicle Retirement Program 

LULC Land-Use/Land-Cover 

LYNF Lynchburg Ferry Monitor (CAMS 1015) 

m/s Meters per Second 

MACP Manvel Croix Park Monitor (CAMS 84) 

MACT Maximum Achievable Control Technology 

MARPOL Annex VI of the International Convention for the Prevention of 

Pollution from Ships 

MCR Mid-Course Review 

MECT Mass Emissions Cap and Trade 

METDAT Omnibus Meteorological Database 

MGO Marine Gas Oil 

MM5 Fifth Generation Meteorological Model 

MMS Minerals Management Services 

MNB Mean Normalized Bias 

MNGE Mean Normalized Gross Error 

MOZART Model for Ozone and Related Chemical Tracers 

mph Miles per Hour 

MVEB Motor Vehicle Emissions Budget 

MW Megawatt 

NAAQS National Ambient Air Quality Standard 

NAM North American Model 

NASA National Aeronautics and Space Administration 

NCAR National Center for Atmospheric Research 

NCEP National Center for Environmental Prediction 

NEI National Emissions Inventory 

 xi
ng/J Nanogram per Joule 

NMIM National Mobile Inventory Model 

NO Nitric Oxide 

NO2 Nitrogen Dioxide 

NOAA National Oceanic and Atmospheric Administration 

NOX Nitrogen Oxides 

NOY Total Reactive Nitrogen 

NPL National Physical Laboratory 

NSR New Source Review 

NTIG New Technology Implementation Grants 

O3 Ozone 

OGV Oceangoing Vessel 

OH Hydroxyl Radical 

OLE Olefins 

OSAT Ozone Source Apportionment Technology 

OSD Ozone Season Day 

P3 The NOAA WP-3D Orion 

PAMS Photochemical Assessment Monitoring Station 

PAR Photosynthetically-Active Solar Radiation 

PBL Planetary Boundary Layer 

PEI Periodic Emissions Inventory 

PFC Portable Fuel Container 

PiG Plume-in-Grid 

PM2.5 Particulate Matter of 2.5 Microns and Less 

ppb Parts per Billion 

ppbC Parts per Billion, Carbon 

ppm Parts per Million 

PPM Piecewise Parabolic Method 

psi Pounds per Square Inch 

PUCT Public Utility Commission of Texas 

QQ Quantile-Quantile 

R2 Correlation Coefficient 

RACM Reasonably Available Control Measures 

RACT Reasonably Available Control Technology 

REMI Regional Economic Models, Inc. 

rpm Revolutions per Minute 

RFP Reasonable Further Progress 

ROP Rate-of-Progress 

RRF Relative Response Factor 

RRFD Relative Response Factor Denominator 

RRFN Relative Response Factor Numerator 

RV Research Vessel 

RVP Reid Vapor Pressure 

 xii
SB Senate Bill 

SBFP Seabrook Friendship Park Monitor (CAMS 45) 

SCR Selective Catalytic Reduction 

SECO State Energy Conservation Office 

SEER Seasonal Energy Efficiency Ratio 

SEP Supplemental Environmental Project 

SETPMTC Southeast Texas Photochemical Modeling Technical Committee 

SGIA Smart Growth Implementation Assistance 

SHARP Study of Houston Atmospheric Radical Precursors 

SHWH Shell Westhollow Monitor (CAMS 410) 

SI Special Inventory 

SIP State Implementation Plan 

SO2 Sulfur Dioxide 

SOF Solar Occultation Flux 

SST Sea Surface Temperature 

STARS State of Texas Air Reporting System 

TAC Texas Administrative Code 

TACB Texas Air Control Board 

TAMU Texas A&M University 

TCAA Texas Clean Air Act 

TCEQ Texas Commission on Environmental Quality 

TCM Transportation Control Measure 

TDM Travel Demand Model 

TERP Texas Emission Reduction Plan 

TexAER Texas Air Emissions Repository 

TexAQS 2000 Texas Air Quality Study 2000 

TexAQS II Texas Air Quality Study 2006 

TexN Texas NONROAD 

THSC Texas Health and Safety Code 

TKE Mellor-Yamada Turbulent Kinetic Energy 

TNMHC Total Nonmethane Hydrocarbons 

TNRCC Texas Natural Resource Conservation Commission 

TOMS Total Ozone Mapping Spectrometer 

TOPAZ Tunable Optical Profiler for Aerosol and oZone 

tpd Tons per Day 

tpy Tons per Year 

TSE Truck Stop Electrification 

TTI Texas Transportation Institute 

TXCT Texas City Monitor (CAMS 620) 

TxLED Texas Low Emission Diesel 

UH University of Houston 

UPA Unpaired Peak Accuracy 

USGS United States Geological Survey 

UTC Coordinated Universal Time 

 xiii
UT-CSR University of Texas Center for Space Research 

VMEP Voluntary Mobile Emission Reduction Program 

VMT Vehicle Miles Traveled 

VOC Volatile Organic Compounds 

WALV Wallisville Monitor (CAMS 617) 

WDIR Wind Direction 

WoE Weight of Evidence 

WSPD Wind Speed 

 xiv
TABLE OF CONTENTS 

Executive Summary 

List of Acronyms 

Table of Contents 

List of Appendices 

List of Tables 

List of Figures 

Chapter 1: General 

1.1 Background 

1.2 Introduction 

 1.2.1 One-Hour Ozone National Ambient Air Quality Standard (NAAQS) History 

 1.2.1.1 December 2000 

 1.2.1.2 September 2001 

 1.2.1.3 December 2002 

 1.2.1.4 December 2004 

 1.2.1.5 EPA Approval of the One-Hour Ozone Attainment Demonstration 

 1.2.2 Eight-Hour Ozone NAAQS History 

 1.2.2.1 May 23, 2007 

 1.2.3 Existing Ozone Control Strategies 

 1.2.4 2010 Proposed Revision 

1.3 Health Effects 

1.4 Stakeholder Participation and Public Hearings 

 1.4.1 Local Program Control Strategy Development Meetings

 1.4.2 TCEQ SIP and Control Strategy Development Stakeholder Meetings 

 1.4.3 Public Hearings and Comment Information 

1.5 Social and Economic Considerations 

1.6 Fiscal and Manpower Resources 

Chapter 2: Anthropogenic Emissions Inventory (EI) Description 

2.1 Introduction 

 2.1.1 EI Improvement 

2.2 Point Sources 

2.3 Area Sources 

2.4 Non-Road Mobile Sources 

2.5 On-Road Mobile Sources 

Chapter 3: Photochemical Modeling 

3.1 Introduction 

 3.1.1 Overview of the Ozone Photochemical Modeling Process 

 3.1.2 Ozone Modeling 

 3.1.3 Base Case Modeling 

 3.1.4 Future Year Modeling 

3.2 Episode Selection 

 xv
 3.2.1 EPA Guidance for Episode Selection 

 3.2.2 HGB Ozone Episode Selection Process 

3.3 Meteorological Model 

 3.3.1 Modeling Domains 

 3.3.2 Model (MM5) Configuration 

 3.3.3 MM5 Application and Performance 

3.4 Modeling Emissions 

 3.4.1 Biogenic Emissions 

 3.4.2 Base Cases 

 3.4.2.1 Point Sources 

 3.4.2.2 On-Road Mobile Sources 

 3.4.2.3 Non- and Off-Road Mobile Sources 

 3.4.2.4 Area Sources 

 3.4.2.5 Base Case Summary 

 3.4.3 2006 Baseline 

 3.4.3.1 Point Sources 

 3.4.3.2 On-Road Mobile Sources 

 3.4.4 2018 Future Base and Control Strategy 

 3.4.4.1 Point Sources 

 3.4.4.2 On-Road Mobile Sources 

 3.4.4.3 Non- and Off-Road Mobile Sources 

 3.4.4.4 Area Sources 

 3.4.5 2006 and 2018 Modeling Emissions Summary for HGB 

3.5 Photochemical Modeling 

 3.5.1 Modeling Domains and Horizontal Grid Cell Size 

 3.5.2 Vertical Layer Structure 

 3.5.3 Model Configuration 

 3.5.4 Model Performance Evaluation 

 3.5.4.1 Performance Evaluations Overview 

 3.5.4.2 Operational Evaluations 

 3.5.4.3 Diagnostic Evaluations 

3.6 Baseline (2006) and Future Case (2018) Modeling 

 3.6.1 2006 Baseline Modeling 

 3.6.2 Future Baseline Modeling 

 3.6.2.1 Matrix Modeling 

 3.6.2.2 Modeling Sensitivities: Emissions Reductions within 100 and 200 km 

of HGB 

3.6.2.3 Ozone Source Apportionment Tool and Anthropogenic Precursor 

Culpability Analysis 

 3.6.3 Future Case Modeling with Controls 

3.6.3.1 25 Percent HECT Cap Reduction 

 3.6.3.2 VMEP Reductions 

3.7 Modeling Archive and References 

3.7.1 Modeling Archive 

 3.7.2 Modeling References 

Chapter 4: Control Strategies and Required Elements 

4.1 Introduction 

4.2 Existing Control Measures 

4.3 Updates to Existing Control Measures 

4.3.1 Mass Emissions Cap and Trade (MECT) Program 

 xvi
 4.3.2 Repeal of State Portable Fuel Container Rule 

 4.3.3 Clean Fuel Fleet Requirement 

4.4 Reasonably Available Control Technology (RACT) Analysis 

4.4.1 General Discussion 

 4.4.2 NOX RACT Determination 

 4.4.3 VOC RACT Determination 

 4.4.3.1 CTG Documents That Are Not Applicable to the HGB Area 

 4.4.3.2 CTG Documents That Do Not Represent RACT for the HGB Area 

4.4.3.3 CTG Documents That a RACT Determination Cannot Be Made at This 

Time 

 4.4.3.4 CTG Documents That Represent RACT for the HGB Area 

4.5 Reasonably Available Control Measures Analysis 

4.5.1 General Discussion 

 4.5.2 Results of RACM Analysis 

4.6 New Control Measures 

4.6.1 Stationary Sources 

4.6.1.1 HECT Cap Reduction and Allowance Reallocation 

 4.6.2 Local Programs 

4.6.2.1 Transportation Control Measures 

 4.6.2.2 Voluntary Mobile Emission Reduction Programs 

4.7 Motor Vehicle Emissions Budget (MVEB) 

4.8 Monitoring Network 

4.9 Contingency Plan 

4.10 References 

Chapter 5: Weight of Evidence 

5.1 Quantitative Corroborative Analysis 

 5.1.1 Introduction 

5.2 Corroborative Analysis: Modeling 

 5.2.1 Solving Modeling Problems 

 5.2.1.1 Industrial Point Source Emission Inventory Issues 

 5.2.1.2 Modeling of Emissions Events 

 5.2.1.3 Resolution of Photochemical Modeling Grids 

 5.2.1.4 Incommensurability and Model Performance Evaluation 

 5.2.1.5 Ensemble Modeling 

 5.2.1.6 Vertical Distribution of Ozone 

 5.2.1.7 Photolysis Discrepancies Due to Improper Placement of Clouds 

 5.2.1.8 Radical Shortage 

 5.2.2 Model Performance Evaluations: Implications of the Model Performance of the 

Current SIP Modeling 

 5.2.3 Model Response to Proposed Controls: Additional Ways to Measure Progress 

 5.2.4 Conclusion 

5.3 Air Quality Trends in the HGB Area 

 5.3.1 Ozone Trends 

 5.3.2 Ozone Trends at Regulatory and Non-Regulatory Monitors 

 5.3.3 Trends in the Strength of Observed Ozone Gradients in the HGB Area 

 5.3.4 The Impact of Hurricane Ike on Ozone Observations in the HGB Area 

 5.3.4.1 Approach 

5.3.4.2 Results 

 5.3.5 NOX Trends 

 5.3.6 Ambient VOC Concentrations 

 xvii
 5.3.7 Geographic Patterns in Ambient HRVOC Concentrations Near the Houston Ship 

Channel 

 5.3.8 Ambient Total VOC Concentrations 

 5.3.9 Meteorologically Adjusted Ozone Trends 

 5.3.10 Background Ozone Concentrations: Transport of Ozone into the HGB Area 

 5.3.11 Transport and Surface Wind Trajectories 

 5.3.12 Background Ozone in Texas 

 5.3.13 Air Quality Trends Conclusions 

5.4 Qualitative Corroborative Analysis 

5.4.1 Introduction 

5.4.2 Federal Preemption Issues 

5.4.2.1 Federal Assignment 

5.4.3 Additional Measures 

5.4.3.1 New International Marine Diesel Engine and Marine Fuel Standards for 

Oceangoing Vessels and Emissions Control Areas 

5.4.3.2 SmartWay Transport Partnership and the Blue Skyways Collaborative 

5.4.3.3 Control of VOC Emissions from Flash Emissions 

5.4.3.4 Energy Efficiency and Renewable Energy (EE/RE) Measures 

 5.4.3.5 Clean Air Interstate Rule (CAIR) 

 5.4.3.6 Texas Emission Reduction Plan (TERP) 

5.4.3.7 Low Income Vehicle Repair Assistance, Retrofit, and Accelerated 

Vehicle Retirement Program (LIRAP) 

 5.4.3.8 Clean School Bus Program 

 5.4.3.9 81st Texas Legislature, 2009 

 5.4.3.10 American Waterways Operators Tank Barge Emissions Best 

Management Practices 

 5.4.3.11 Local Initiative Projects 

5.4.3.12 Other Local Programs 

5.5 Conclusions 

5.6 References 

Chapter 6: Ongoing and Future Initiatives 

6.1 Introduction 

6.2 Ongoing Work 

 6.2.1 Flare Task Force 

6.2.2 Technologies for Detecting VOC 

6.2.2.1 Optical Gas Imaging Technology 

6.2.2.2 Open Path Sensing Technology 

 6.2.2.3 DIAL Remote Sensing Technology 

 6.2.2.4 Helicopter-Mounted DIAL Imaging System 

 6.2.2.5 Flare Study 

 6.2.2.6 Study of Houston Atmospheric Radical Precursors (SHARP) 

6.3 Future Initiatives 

 6.3.1 Mid-Course Review (MCR) 

 6.3.2 2008 Ozone National Ambient Air Quality Standard (NAAQS) 

Appendices 

 xviii
LIST OF APPENDICES 

Appendix Appendix Name

Appendix A Meteorological Modeling for the HGB Attainment Demonstration SIP 

Appendix B Emissions Modeling for the HGB Attainment Demonstration SIP 

Appendix C CAMx Modeling for the HGB Attainment Demonstration SIP 

Appendix D Reasonably Available Control Technology Analysis 

Appendix E Reasonably Available Control Measure Analysis 

Appendix F Evaluation of Mobile Source Control Strategies for the HoustonGalveston-Brazoria State Implementation Plan (With Detailed 

Strategies), Prepared for Houston-Galveston Area Council, Prepared by 

ENVIRON International Corporation 

Appendix G Transportation Control Measures for the HGB Attainment 

Demonstration SIP Revision for the 1997 Eight-Hour Ozone Standard 

(Excerpt from Evaluation of Mobile Source Control Strategies for the 

Houston-Galveston-Brazoria State Implementation Plan) 

Appendix H Voluntary Mobile Emission Reduction Program for the HGB Attainment 

Demonstration SIP Revision for the 1997 Eight-Hour Ozone Standard 

(Excerpt from Evaluation of Mobile Source Control Strategies for the 

Houston-Galveston-Brazoria State Implementation Plan) 

Appendix I Corroborative Analysis for the HGB Attainment Demonstration SIP 

Appendix J Recommendations for Best Management Practices to Control and 

Reduce Inadvertent Cargo Vapor Emissions in the Tank Barge 

Community 

 xix
LIST OF TABLES 

Number Table Name

Table 1-1 Proposed Rule Revisions 

Table 1-2 H-GAC Public and Stakeholder Meeting Dates 

Table 3-1 Selected Episodes 

Table 3-2 Eight-Hour Ozone Design Values and Number of Exceedance Days During 

Selected Episodes 

Table 3-3 Selected MM5 Modeling Schemes 

Table 3-4 2005 and 2006 Meteorological Modeling Episodes 

Table 3-5 Average HGB Percent Accuracy for all Meteorological Modeling Episodes 

Table 3-6 EPS3 Emissions Processing Modules 

Table 3-7 2005 and 2006 Episode Days for Emissions Modeling 

Table 3-8 2005 and 2006 Base Case Episode Point Source Modeling Emissions for HGB 

Table 3-9 Summary of the Development of On-Road Mobile Sources Emissions 

Table 3-10 2005 and 2006 Base Case Episode On-Road Modeling Emissions for HGB 

Table 3-11 2005 and 2006 Base Case Episode Non- and Off-Road Modeling Emissions for 

HGB 

Table 3-12 2005 and 2006 Base Case Episode Anthropogenic Modeling Emissions for HGB 

Table 3-13 Summary of 2006 Baseline and 2018 Future Base, and 2018 Control Strategy 

Anthropogenic Modeling Emissions for HGB 

Table 3-14 CAMx Vertical Layer Structure for 2 km and 4 km Fine Grids 

Table 3-15 CAMx Vertical Layer Structure for Intermediate and Coarse Grids 

Table 3-16 2000 Baseline Design Value Calculation for Retrospective Analysis 

Table 3-17 2000 Projected DVs Compared with Calculated DVs 

Table 3-18 2006 DVB, RRF Denominator (RRFD), and Number of 2006 Baseline Modeled 

Days Averaged 

Table 3-19 Summary of 2006 Baseline Modeling, RRF, and Future Design Values 

Table 3-20 VOC, NOX, and VOC+NOX Emissions Reductions Needed to Model Attainment 

 xx
Table 3-21 200 km NOX Reduction Modeling Sensitivity 

Table 3-22 200 km VOC Reduction Modeling Sensitivity 

Table 3-23 OSAT/APCA Source Groups and Regions Defined 

Table 3-24 HECT Modeling Sensitivity Results 

Table 3-25 HECT and VMEP Modeling Sensitivity Results 

Table 4-1 Existing Ozone Control Measures Applicable to the HGB Eight-County 

Nonattainment Area 

Table 4-2 2018 Attainment Demonstration MVEB for the Eight-County HGB Area 

Table 4-3 2019 Contingency Demonstration for the HGB Area 

Table 5-1 Changes in the Area and Population Affected by an Eight-Hour Ozone Design 

Value Greater than or Equal to 85 ppb in Response to Growth and Controls 

Table 5-2 Eight-Hour Ozone Design Values (in ppb) for Each Regulatory Monitor in the 

HGB Area 

Table 5-3 One-Hour Ozone Design Values (in ppb) for Each Regulatory Monitor in the 

HGB Area 

Table 5-4 Number of Days with a 1997 Eight-Hour Ozone Exceedance 

Table 5-5 Number of Days with a One-Hour Ozone Exceedance 

Table 5-6 Eight-Hour Ozone Design Values at Regulatory and Non-Regulatory Monitors 

Table 5-7 One-Hour Ozone Design Values at Regulatory and Non-Regulatory Monitors 

Table 5-8 Exceedance Days at Regulatory and Non-Regulatory Monitors, 2003 through 

2008 

Table 5-9 Monitors Recording the Annual Maximum One-Hour Ozone Design Value 

Table 5-10 List of the Number of Days HGB Ozone Regulatory and Non-Regulatory 

Monitors were Not Operating Before and After the Landfall of Hurricane Ike 

Table 5-11 Alternative Fourth-High Daily Peak Eight-Hour Ozone Concentration 

Calculations Using Different Ike Adjustment Factors (IAFs) 

Table 5-12 Observed and Expected Design Values, Recalculated to Account for Hurricane 

Ike 

Table 5-13 NOX Values in the HGB Area by Year 

 xxi
Table 5-14 Median and 90th Percentile Hourly NOX Values 

Table 5-15 Auto-GC Monitors in the Houston Ship Channel Area 

Table 5-16 Parameter Estimates of Monthly Geometric Mean Concentrations Trends 

Table 5-17 Geometric Mean Ethylene for Key Wind Direction Lobes at Eastern Houston 

Ship Channel Monitors 

Table 5-18 Geometric Mean Propylene Concentrations for Key Wind Directions at Eastern 

Houston Ship Channel Monitors 

Table 5-19 Parameter Estimates of Monthly Geometric Mean TNMHC Concentration 

Trends Houston Ship Channel Area Auto-GC Monitors 

Table 5-20 Area Ozone Monitoring Sites with Long-Term Data 

Table 5-21 Summary Statistics for Meteorologically Adjusted Ozone Trends from 1996 to 

2007 

Table 5-22 Ozone Statistics for HYSPLIT Back Trajectory Clusters 

Table 5-23 Average Maximum Ozone and 95 Percent Confidence Intervals 

Table 5-24 Monitors Selected for Background Transport Analysis 

Table 5-25 Range of Monthly 90th Percentile Daily Peak Hourly Ozone Concentrations for 

Subject Wind Directions 

Table 5-26 Parameter Estimates for Regression of West Orange C9 on Mauriceville 

C642/C311/C665 

Table 5-27 New MARPOL Annex VI Emission Standards for Marine Diesel Engines 

 xxii
LIST OF FIGURES 

Figure Figure Name

Figure 1-1 One-Hour and 1997 Eight-Hour Ozone Design Values and HGB Area Population 

Figure 3-1 Baseline Design Value Calculation Illustration 

Figure 3-2 Eight-Hour Ozone Exceedance Days in HGB and Other Areas of Texas 

Figure 3-3 Hourly Average Resultant Winds; Eight-Hour Exceedance Days, August through 

September 1998 through 2006 

Figure 3-4 2005 and 2006 Non-TexAQS II Modeling Episodes 

Figure 3-5 2006 TexAQS II Modeling Episodes 

Figure 3-6 Map Depicting Regulatory Monitors in the HGB Area 

Figure 3-7 MM5 Modeling Domains 

Figure 3-8 Meteorological Modeling Performance 

Figure 3-9 An Example of Day-Specific Biogenic Emissions 

Figure 3-10 2006 Baseline and 2018 Future Base, and 2018 Control Strategy Anthropogenic 

NOX and VOC Modeling Emissions for HGB 

Figure 3-11 CAMx Modeling Domains 

Figure 3-12.a Peak Eight-Hour Ozone Concentration, Measured versus Modeled for the 2005 

Episode Days 

Figure 3-12.b Peak Eight-Hour Ozone Concentration, Measured versus Modeled for the 2006 

Episode Days 

Figure 3-13.a Mean Normalized Gross Error (MNGE) and Bias (MNB) for 2005 Episode Days 

Figure 3-13.b Mean Normalized Gross Error (MNGE) and Bias (MNB) for 2006 Episode Days 

Figure 3-14 TexAQS II Monitoring Sites Outside HGB/BPA 

Figure 3-15 Time Series of Hourly Ozone Concentrations for Episode bc05ep0 at the CNR2, 

HNWA, and WALV Monitors 

Figure 3-16 Time Series of Hourly Ozone Concentrations for Episode bc05ep0 at the GRVL 

and LACT Rural Monitors 

Figure 3-17 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor for 

the bc05ep0 Episode 

 xxiii
Figure 3-18 Tile Plots of Daily Maximum Eight-Hour Ozone Concentrations for 

May 27 and 31 and June 1 through 2, 2005 

Figure 3-19 Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the DRPK, 

HCQA, and MACP Monitors 

Figure 3-20 Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the GRVL 

and LACT Rural Monitors 

Figure 3-21 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc05ep1 Episode 

Figure 3-22 Tile Plots of Daily Maximum Eight-Hour Ozone Concentrations for 

June 20 through 23, 2005 

Figure 3-23 Time Series of Hourly Ozone Concentrations for Episode bc05ep2 at the BAYP, 

HROC, and TXCT Monitors 

Figure 3-24 Time Series of Hourly Ozone Concentrations for Episode bc05ep2 at the GRVL, 

LACT, and SAGA Rural Monitors 

Figure 3-25 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the TXCT Monitor for 

the bc05ep2 Episode 

Figure 3-26 Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for July 28, 

August 1 through 2, and August 4, 2005 

Figure 3-27 Time Series of Hourly Ozone Concentrations for Episode bc06ep0 at the HROC, 

SHWH, and WALV Monitors 

Figure 3-28 Time Series of Hourly Ozone Concentrations for Episode bc06ep0 at the GRVL, 

LACT, and SAGA Rural Monitors 

Figure 3-29 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor for 

the bc06ep0 Episode 

Figure 3-30 Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for June 

5, 8 through 9, and 14, 2006 

Figure 3-31 Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the BAYP, 

DRPK, and HSMA Monitors 

Figure 3-32 Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the GRVL, 

LACT, and SAGA Rural Monitors 

Figure 3-33 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc06aqs1 Episode 

Figure 3-34 Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for August 17 

and 31, and September 1 and 7, 2006 

 xxiv
Figure 3-35 Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the CNR2, 

DRPK, and GALC Monitors 

Figure 3-36 Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the GRVL, 

LACT, and SAGA Rural Monitors 

Figure 3-37 Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc06aqs2 Episode 

Figure 3-38 Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for September 20 

and 27, and October 6 and 11, 2006 

Figure 3-39 Comparison of Modeled and P3 Observed Ozone (O3), August 31, 2006, 14:16 to 

15:33 CST 

Figure 3-40 TOPAZ-Observed and Modeled Ozone Concentrations on August 31, 2006 

Figure 3-41 Comparison of Ozone Concentrations Observed by the RV Ron Brown with 

Modeled Concentrations, August 31, 2006, 08:00 to 16:30 

Figure 3-42 Comparison of Modeled and Observed Vertical Ozone Profiles from Two Sonde 

Launches at UH Campus and One Sonde Launch from the Ron Brown in the 

Gulf of Mexico, August 31, 2006 

Figure 3-43 Comparison of P3 Measurements with Base Case and Enhanced Flare Emissions; 

observed ethylene (Panel A), formaldehyde (Panel B), and ozone (Panel C) 

compared to modeled concentrations using (left) the base case inventory, and 

(right) the base case inventory with 10X flare VOC emissions, minus the 

HRVOC reconciliation 

Figure 3-44 Log-Log Plots of Observed vs. Modeled Ethylene at Deer Park September 

19 through October 11, 2006; with (Left) base case inventory, and (Right) base 

case inventory with 10X flare emissions minus the HRVOC reconciliation 

Figure 3-45 Daily Peak Modeled Eight-Hour Ozone Concentrations with Base Case 

Inventory (Left) and 10X Flare Inventory (Center); the difference between the 

two plots (Flare 10X – Reg 10) is shown at right 

Figure 3-46 Mean Observed NOX Concentrations at HGB Monitors as a Percentage of 

Wednesday Mean Values, May 15 through October 15, 2005 through 2008 

Figure 3-47 Observed and Modeled Daily Peak Eight-Hour Ozone Concentrations as a 

Percentage of Wednesdays 

Figure 3-48 Near Monitoring Site Grid Cell Array Size 

Figure 3-49 DVF versus NOX and/or VOC Emissions Reduction Response Curves for the 

BAYP, DRPK, and WALV Monitors 

Figure 3-50 Map of Counties within 100 km (Red) and 200 km (Orange) of the Eight-County 

HGB Area 

 xxv
Figure 3-51 OSAT and APCA Results for BAYP 

Figure 3-52 OSAT and APCA Results for DRPK 

Figure 3-53 OSAT and APCA Results for WALV 

Figure 5-1 Ozone Design Values for the HGB Area 

Figure 5-2 Eight-Hour Ozone Design Value Statistics for All Monitors in the HGB Area 

Figure 5-3 One-Hour Ozone Design Value Statistics for All Monitors in the HGB Area 

Figure 5-4 Number of Monitors and Ozone Exceedance Days in the HGB Area 

Figure 5-5 Number of 1997 Eight-Hour Ozone Exceedance Days by Monitor 

Figure 5-6 Number of One-Hour Ozone Exceedance Days by Monitor 

Figure 5-7 1997 Eight-Hour Ozone Exceedance Days in the HGB Area 

Figure 5-8 Distributions of Eight-Hour Ozone Design Values at Regulatory and NonRegulatory Monitors in the HGB Area 

Figure 5-9 Distributions of One-Hour Ozone Design Values at Regulatory and NonRegulatory Monitors in the HGB Area 

Figure 5-10 1997 Eight-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory 

Monitors, 2003 through 2008 

Figure 5-11 One-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory Monitors, 

2003 through 2008 

Figure 5-12 Eight-Hour Ozone Design Values for 2000, 2005, and 2008 

Figure 5-13 Time of Day of Peak Hourly Ozone on Low and High Ozone Days 

Figure 5-14 Trends in the Strength of Ozone Gradients Measured in the HGB Area from 1995 

through 2008 

Figure 5-15 The Number of Occurrences of One-Hour Increases in Ozone Greater Than 40 

ppb/hr in the HGB Area for the Subset of Monitors with Long Historical Records 

Figure 5-16 Number of Days that Exceeded the 1997 Eight-Hour Ozone NAAQS by Month 

from 2000 through 2008 

Figure 5-17 Frequency of Daily Peak Eight-Hour Ozone Values for All Ozone Monitoring 

Sites in Texas, September 2006 

Figure 5-18 Frequency of Daily Peak Eight-Hour Ozone Values for All Ozone Monitoring 

Sites in Texas, September 2008 

 xxvi
Figure 5-19 Daily Peak Hourly NOX in the HGB Area 

Figure 5-20: Median NOX Concentrations in the HGB Area 

Figure 5-21 Houston Ship Channel Auto-GC Monitors and 2006 Reported Point Source 

HRVOC Emissions Points and Plant Boundaries 

Figure 5-22 Monthly Geometric Mean Ethylene Concentrations at the Eight Houston Ship 

Channel Monitors, July 1995 through December 2008 

Figure 5-23 Monthly Geometric Mean Propylene Concentrations at the Eight Houston Ship 

Channel Monitors, July 1995 through December 2008 

Figure 5-24 Geometric Mean Ethylene Concentration at Western Houston Ship Channel 

Monitors 

Figure 5-25 Geometric Mean Ethylene Concentrations at Eastern Houston Ship Channel 

Monitors 

Figure 5-26 Geometric Mean Propylene Concentration at Eastern Houston Ship Channel 

Monitors 

Figure 5-27 Geometric Mean Propylene Concentration at Western Houston Ship Channel 

Monitors 

Figure 5-28 Monthly Geometric Mean TNMHC Concentrations, July 1995 through 

December 2008 

Figure 5-29 90th Percentile TNMHC Concentration in the HGB Area 

Figure 5-30 Actual Mean Eight-Hour Ozone Concentrations (Blue Line) and Mean EightHour Predicted Concentrations with the Non-Meteorological Trend Removed 

(Red Line) 

Figure 5-31 Residual Meteorologically Adjusted Eight-Hour Ozone Concentrations Trend 

Figure 5-32 Six Clusters Found Using HYSPLIT Backward Trajectory Clustering Algorithm 

Figure 5-33 Cluster 0 Backward Trajectories 

Figure 5-34 Means of Six 60-Hour Backward Trajectory Clusters 

Figure 5-35 Sites Used in Ozone Area Maximum and Background Determination 

Figure 5-36 Average Maximum Ozone and 95 Percent Confidence Intervals 

Figure 5-37 Relationship Between Minimum and Maximum Ozone Concentrations 

Figure 5-38 Distributions of End Points from HYSPLIT 48-Hour Back Trajectories 

 xxvii
 xxviii

Figure 5-39 Mauriceville C642/C311/C65 and West Orange C9/A141 Monitors 

Figure 5-40 Karnack C85 Monitor 

Figure 5-41 Hamshire C64/C654 Monitor 

Figure 5-42 Selected Statistics for the West Orange C9 Monitor 

Figure 5-43 Selected Statistics for the Mauriceville C642/C311/C665 Monitor 

Figure 5-44 Selected Statistics for the Karnack C85 Monitor 

Figure 5-45 Selected Statistics for the Hamshire C64/C654 Monitor 

Figure 5-46 Scatter-plot of 90th Percentile Hourly Values at West Orange C9 and 

Mauriceville C642/C311/C6 
1-1

CHAPTER 1: GENERAL 

1.1 BACKGROUND 

The “History of the Texas State Implementation Plan (SIP),” a comprehensive overview of the 

SIP revisions submitted to the United States Environmental Protection Agency (EPA) by the 

State of Texas, is available at the following Web site: 

http://www.tceq.state.tx.us/implementation/air/sip/sipintro.html#History. 

1.2 INTRODUCTION

The Houston-Galveston-Brazoria (HGB) area’s hot, sunny climate, large urban population 

activities, and extensive, highly concentrated industrial complex provide the ingredients for ozone 

formation: sunlight, nitrogen oxides (NOX), and volatile organic compounds (VOC). The 

Houston area’s significant biogenic VOC emissions and complex meteorology, which includes 

land/sea breeze air parcel recirculation, complicate air quality modeling. Economic and 

population growth continue to create air quality challenges for the HGB area. However, key 

ozone-targeting regulatory programs have reduced the number and magnitude of ozone 

exceedances, the area of exceedance, and the population exposed to exceedances. 

1.2.1 One-Hour Ozone National Ambient Air Quality Standard (NAAQS) History 

The EPA established the one-hour ozone NAAQS of 0.08 parts per million (ppm) in the April 30, 

1971, issue of the Federal Register (36 FR 8186). The EPA revised the one-hour ozone standard 

to 0.12 ppm in the February 8, 1979, issue of the Federal Register (44 FR 4202). The eightcounty HGB area, defined as Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, 

Montgomery, and Waller Counties, was first designated as a nonattainment area for the one-hour 

ozone NAAQS established by the Federal Clean Air Act (FCAA) in the November 6, 1991, issue 

of the Federal Register (56 FR 56694). The HGB area was classified as a Severe-17 

nonattainment area, which required it to attain the one-hour ozone NAAQS by November 15, 

2007. The one-hour ozone NAAQS was revoked in the June 15, 2005, issue of the Federal 

Register (69 FR 23951). 

The following summaries of HGB area one-hour ozone SIP revisions are provided to give context 

and greater understanding of the complex issues involved in HGB’s ozone challenge. For a 

summary of ozone SIP revisions in the HGB area prior to December 2000, please refer to the 

“History of the Texas State Implementation Plan (SIP),” mentioned in Section 1.1 of this chapter. 

1.2.1.1 December 2000

The Post-1999 Rate-of-Progress (ROP) and Attainment Demonstration SIP for the 

Houston/Galveston Ozone Nonattainment Area revision contained rules and photochemical 

modeling analyses in support of the HGB one-hour ozone attainment demonstration. The 

majority of the emission reductions identified in this revision resulted from an overall 90 percent 

reduction in point source NOX implemented through 30 Texas Administrative Code (TAC) 

Chapter 117 and the Mass Emissions Cap and Trade (MECT) program in 30 TAC Chapter 101. 

A modeling analysis, which showed a 141 parts per billion (ppb) peak ozone level, indicated a 

shortfall of 91 tons per day (tpd) in NOX emissions reductions that were necessary, but not readily 

available, for an approvable attainment demonstration. In addition, the revision contained a post1999 ROP plan for the milestone years 2002 and 2005, as well as the attainment year 2007, and 

transportation conformity motor vehicle emissions budgets (MVEBs) for NOX and VOC. The 

SIP revision also contained enforceable commitments to implement further measures (in support 

of the HGB area’s attainment demonstration and to remedy the estimated 91 tpd shortfall), 

Voluntary Mobile Emission Reduction Program (VMEP) measures, as well as a commitment to 

perform and submit a mid-course review (MCR) to the EPA. 
1-2

1.2.1.2 September 2001

The Post-1999 ROP and Attainment Demonstration Follow-Up SIP for the 

Houston/Galveston Ozone Nonattainment Area revision included the following elements: 1) 

corrections to the ROP table/budget for the years 2002, 2005, and 2007 due to a mathematical 

error; 2) incorporation of a change to the idling restriction control strategy, which clarified that 

the operator of a rented or leased vehicle is responsible for compliance with the requirements in 

situations where the operator of a leased or rented vehicle is not employed by the owner of the 

vehicle; 3) incorporation of revisions to the clean diesel fuel rules to provide greater flexibility in 

complying with the rule requirements while preserving the emission reductions previously 

represented; 4) incorporation of a stationary diesel engine rule; 5) incorporation of revisions to 

the point source NOX rules; 6) incorporation of revisions to the NOX emissions cap and trade 

rules; 7) removal of the construction equipment operating restriction and the accelerated purchase 

requirement for Tier 2/Tier 3 heavy-duty equipment; 8) replacement of the Tier 2/Tier 3 rules 

with the Texas Emission Reduction Plan (TERP); 9) layout of the MCR process that detailed how 

the state would fulfill the commitment to obtain the additional emission reductions necessary to 

demonstrate attainment of the one-hour ozone standard in the HGB area; and 10) replacement of 

the 2007 ROP MVEB to be consistent with the attainment demonstration MVEB. 

Despite the NOX measures adopted in the December 2000 SIP revision and the stationary diesel 

engine rules included in the September 2001 SIP revision, an estimated 56 tpd NOX reduction 

shortfall remained. The state committed to address the remaining shortfall through the MCR 

process. The EPA approved the December 2000 and September 2001 submittals in the 

November 14, 2001, issue of the Federal Register (66 FR 57160). 

1.2.1.3 December 2002

In January 2001, the Business Coalition for Clean Air-Appeal Group (BCCA-AG) and several 

regulated companies challenged the December 2000 HGB SIP revision and the 90 percent NOX 

reduction requirement from stationary sources. Among other things, BCCA-AG contended that 

the last 10 percent of the NOX emissions reductions were not cost effective and that the ozone 

plan would fail because the Texas Commission on Environmental Quality (TCEQ) did not 

account for VOC emissions associated with upset conditions. In May 2001, the parties agreed to 

a stay in the case, and Judge Margaret Cooper, Travis County District Court, signed a Consent 

Order, effective June 8, 2001. The order required the commission to perform an independent and 

thorough analysis of the causes of rapid ozone formation events and to identify potential 

mitigating measures not yet included in the HGB attainment demonstration. 

In compliance with the Consent Order, the commission conducted a scientific evaluation based in 

large part on aircraft data collected by the Texas Air Quality Study 2000 (TexAQS 2000). The 

TexAQS 2000 was a comprehensive research project, conducted in August and September 2000, 

involving more than 40 research organizations and over 200 scientists that studied ground-level 

ozone air pollution in the HGB and east Texas regions. These and other studies suggested that 

the HGB area’s high ozone events can be attributed, in part, to the presence of significant 

reactivity in the airshed. An analysis of automated gas chromatograph data revealed that four 

highly reactive volatile organic compounds (HRVOC) were frequently responsible for high 

reactivity days: ethylene, propylene, 1,3-butadiene, and butenes. As such, these compounds 

were selected as the best candidates for HRVOC emission controls. Analysis showed that the 

ozone control strategy involving limits on emissions of ethylene, propylene, 1,3-butadiene, and 

butenes from industrial sources, in conjunction with an 80 percent reduction in industrial or point 

source NOX, was equivalent or better in terms of air quality benefit than the previous ozone 

control strategy (a 90 percent point source NOX emissions reduction requirement alone). 

Therefore, in December 2002, the TCEQ adopted a SIP revision that replaced 10 percent of 

industrial point source NOX emissions reductions with industrial source HRVOC controls. 

HRVOC is defined in 30 TAC Chapter 115 as ethylene, propylene, 1,3-butadiene, and all isomers 

of butene for Harris County and ethylene and propylene for the other seven counties in the HGB 

area. The result was an industrial source ozone control strategy that relies on an 80 percent 
1-3

reduction in NOX emissions through Chapter 117 and the MECT program, and HRVOC rules in 

Chapter 115 that better quantify and reduce emissions of HRVOC from four key industrial 

sources: fugitives, flares, process vents, and cooling tower heat exchange systems. The HRVOC 

fugitive emission controls are more stringent leak detection and repair requirements for 

components in HRVOC service such as valves and flanges. The HRVOC rules for flares, process 

vents, and cooling tower heat exchange systems are performance-based and emphasize 

monitoring, recordkeeping, reporting, and enforcement, rather than establishing individual unit 

emission rates. Site-wide HRVOC emission caps were established and adopted in the SIP for 

sites subject to the HRVOC rules for flares, process vents, and cooling tower heat exchange 

systems. The December 2002 SIP revision exchanging the two strategies for the one strategy met 

the FCAA, §110(l) requirement, which allows a revision of the SIP where that revision would not 

interfere with reasonable further progress toward attainment of the NAAQS. 

1.2.1.4 December 2004

As previously noted in Section 1.2.1.1 of this chapter, in December 2000, the TCEQ committed 

to perform an MCR to ensure attainment of the one-hour ozone standard. The MCR process 

provided the opportunity to update emissions inventory data, use current modeling tools, and 

enhance the photochemical grid modeling. The data gathered from the TexAQS 2000 was used 

to improve the photochemical modeling of the HGB area. These technical improvements 

provided a more comprehensive understanding of the ozone challenge in the HGB area that is 

necessary to develop an attainment plan. In early 2003, as the TCEQ was preparing to move 

forward with the MCR, the EPA announced its plans to begin implementation of the 1997 eighthour ozone standard. The EPA published its proposed implementation rule for the 1997 eighthour ozone standard in the June 2, 2003, issue of the Federal Register (68 FR 32802). In the 

same timeframe, the EPA formalized its intentions to designate areas for the 1997 eight-hour 

ozone standard by April 15, 2004, requiring states to reassess their efforts and control strategies 

to address this new standard in a revised plan to be submitted to the EPA by June 2007. 

Recognizing that existing one-hour nonattainment areas would soon be subject to the 1997 eighthour ozone standard and in an effort to efficiently manage the state’s limited resources, the TCEQ 

developed an approach that addressed the outstanding obligations under the one-hour ozone 

standard while beginning to analyze eight-hour ozone issues. 

The TCEQ’s one-hour ozone SIP revision commitments that were addressed in the December 

2004 HGB Ozone Nonattainment Area SIP revision include: completion of a one-hour ozone 

MCR; performance of modeling; adoption of measures sufficient to fill the shortfall of NOX

reductions; adoption of measures sufficient to demonstrate attainment; revision of the MVEB 

using the EPA’s MOBILE6 model; and revision of the VMEP measures. 

The December 2004 revision reflected a shift from primarily reducing industrial emissions of 

NOX to reducing both industrial emissions of NOX and industrial point source HRVOC. This 

revision included measures to ensure compliance with the specific strategies to control HRVOC 

emissions and replaced the site-wide caps adopted in the SIP with the HRVOC Emissions Cap 

and Trade (HECT) program in 30 TAC Chapter 101. The HECT program is an annual cap and 

trade program developed to provide sources compliance flexibility in meeting the control 

requirements for flares, process vents, and cooling tower heat exchange systems in 30 TAC 

Chapter 115. Sites subject to the program are required to possess an HRVOC allowance for each 

ton of HRVOC emissions. Sites have the option to trade excess HRVOC allowances on the open 

market. The December 2004 SIP revision also reflected the repeal of the motor vehicle idling 

rules and modified certain recordkeeping requirements of the general VOC fugitive emission 

rules to make them apply only to sources of HRVOC fugitive emissions. 

1.2.1.5 EPA Approval of the One-Hour Ozone Attainment Demonstration

The EPA published its approval of the HGB nonattainment area one-hour ozone attainment 

demonstration in the September 6, 2006, issue of the Federal Register (71 FR 52656). Also in a 

separate action, the EPA concurrently approved rules for the control of HRVOC, the HECT 

program, the MECT program, and the emissions reduction credit banking and trading program, 
1-4

and conditionally approved rules for the discrete emissions reduction credit banking and trading 

program. 

1.2.2 Eight-Hour Ozone NAAQS History 

In 1997, the EPA revised the health-based NAAQS for ozone, setting it at 0.08 ppm averaged 

over an eight-hour time frame. The final 1997 eight-hour ozone NAAQS was published in the 

Federal Register on July 18, 1997 (62 FR 38856), and became effective on September 16, 1997. 

On April 30, 2004, the EPA finalized its attainment/nonattainment designations and promulgated 

the first phase of its implementation rule for the 1997 eight-hour ozone standard (69 FR 23951). 

These actions became effective on June 15, 2004. The EPA classified the HGB area as a 

moderate nonattainment area for the standard under the 1990 FCAA (42 United States Code, 

§§ 7401 et seq.). The TCEQ was required to submit a SIP revision for the 1997 eight-hour ozone 

NAAQS to the EPA by June 15, 2007, and demonstrate attainment of the standard by June 15, 

2010. In the November 29, 2005, issue of the Federal Register (70 FR 71612) the EPA published 

its second phase of the implementation rule for the 1997 eight-hour ozone NAAQS, which 

addressed the control obligations that apply to areas designated nonattainment for the standard. 

The commission adopted the 1997 eight-hour ozone nonattainment area SIP revision and the 

reasonable further progress SIP revision for the HGB area on May 23, 2007. These SIP revisions 

were the first step in addressing the 1997 eight-hour ozone standard in the HGB area. The TCEQ 

demonstrated reasonable further progress toward attaining the 1997 eight-hour ozone standard 

and committed to attaining the 1997 standard as expeditiously as practicable and developing an 

HGB 1997 eight-hour ozone attainment demonstration SIP revision. 

On June 15, 2007, these two revisions to the Texas SIP and a letter from the governor of Texas 

requesting that the HGB ozone nonattainment area be reclassified from a moderate nonattainment 

area to a severe nonattainment area were submitted to the EPA. The EPA granted the governor’s 

request to voluntarily reclassify the HGB ozone nonattainment area from a moderate to a severe 

nonattainment area for the 1997 ozone NAAQS in the October 1, 2008, issue of the Federal 

Register (73 FR 56983). The EPA set April 15, 2010, as the date for the state to submit a revised 

SIP addressing the severe ozone nonattainment area requirements of the FCAA. The area’s new 

attainment date for the 1997 eight-hour ozone standard is as expeditiously as practicable but no 

later than June 15, 2019. 

1.2.2.1 May 23, 2007

On May 23, 2007, the commission adopted the HGB 1997 Eight-Hour Ozone Nonattainment 

Area SIP revision. This SIP revision contained the reasonably available control technology 

(RACT) analysis, additional VMEP commitments, and the Texas 2002 Periodic Emissions 

Inventory for the HGB Ozone Nonattainment Area. This SIP revision also included rule 

revisions to 30 TAC Chapter 114 to add marine diesel fuels to the definition of diesel fuels that 

are subject to the Texas Low Emission Diesel Rule and to 30 TAC Chapter 115 to control 

underestimated, unreported, or underreported VOC emissions from tank landings, flash 

emissions, and degassing of storage tanks, transport vessels, and marine vessels with liquid heels. 

In an associated rulemaking project, 30 TAC Chapter 117 was reformatted and the 10 nanogram 

per Joule (ng/J) heat input NOX standard for residential water heaters was repealed in accordance 

with House Bill (HB) 965, 79th Texas Legislature, 2005. The emission standard of 40 ng/J NOX

was retained. 

This revision also described ongoing efforts to develop the eight-hour ozone attainment 

demonstration including a new modeling episode using days from 2005 and 2006, the continued 

implementation of increasingly lower federal on-road and non-road engine standards, and further 

research and consideration of additional control strategies. 

The HGB 1997 Eight-Hour Ozone Nonattainment Area Reasonable Further Progress SIP 

revision, also adopted by the commission on May 23, 2007, demonstrates that the reasonable 

further progress 15 percent reduction requirement would be met for the analysis period of 2002 - 
2008. Demonstration of reasonable further progress is based on the guidelines in the second 

phase of the EPA’s 1997 eight-hour ozone implementation rule. On April 22, 2009, the EPA 

published a direct final approval of the reasonable further progress SIP revision, its associated 

MVEBs, and the 2002 base year emissions inventory (74 FR 18298). 

1.2.3 Existing Ozone Control Strategies 

Existing ozone control strategies and VMEP measures, discussed in Chapter 4, Control Strategies 

and Required Elements, Section 4.2, Existing Control Measures show key control strategies for 

complying with both the one-hour and eight-hour ozone NAAQS in the HGB nonattainment area. 

Existing control strategies targeted to the one-hour standard are expected to continue to reduce 

emissions of ozone precursors in the HGB area and positively impact progress toward attainment 

of the 1997 eight-hour ozone standard. The one-hour and 1997 eight-hour ozone design values 

for the HGB area from 1991 to 2008 are illustrated in Figure 1-1: One-Hour and 1997 EightHour Ozone Design Values and HGB Area Population. Both design values have decreased over 

the past 18 years. The 2008 one-hour ozone design value was 147 ppb, representing a 33 percent 

decrease from the value for 1991 (220 ppb). The 2008 eight-hour ozone design value was 91 

ppb, a 24 percent decrease from the 1991 value of 119 ppb. These decreases occurred despite a 

47 percent increase in area population, as shown in the Figure 1-1: One-Hour and 1997 EightHour Ozone Design Values and HGB Area Population. 

1-5

220

210

200 202

189 188

199 196 203 199

119 116

104 110 114 116 116 112 110 107 102 101 103 103 96 91

185

147 153 153

170 169 175 175

1-Hr DV

117 118

0

40

80

120

160

200

240

199119921993199419951996199719981999200020012002200320042005200620072008

Design Value

(ppb)

0

1

2

3

4

5

6

Population 

(Millions)

*Source: Ozone -- EPA's AQS database.

1991-2008 Population --http://www.census.gov/popest/archives/1990s/MA-99-03b.txt and http://www.census.gov/popest/counties/CO-EST2008-popchg2000_2008.html

One-Hour NAAQS: 125 ppb

Estimated 

Population

Eight-Hour NAAQS: 85 ppb

8-Hr DV

Figure 1-1: One-Hour and 1997 Eight-Hour Ozone Design Values and HGB Area 

Population 

1.2.4 2010 Proposed Revision 

The EPA reclassification of the HGB area as a severe nonattainment area for the 1997 eight-hour 

ozone NAAQS became effective on October 31, 2008. Severe nonattainment areas are required 

to attain the 1997 eight-hour ozone standard as expeditiously as practicable but no later than June 

15, 2019. The state must submit a SIP revision addressing the severe ozone nonattainment area 

requirements of the FCAA by April 15, 2010. 
1-6

This SIP revision demonstrates attainment of the 1997 eight-hour ozone NAAQS using a 

photochemical modeling analysis and a weight of evidence corroborative analysis. This submittal 

contains proposed new state and local control measures. The Houston-Galveston Area Council 

(H-GAC), as the regional metropolitan transportation planning agency for the HGB area, has 

identified VMEP measures and transportation control measures for NOX emission reductions. 

Photochemical modeling analysis demonstrates that a 25 percent reduction of the HECT cap on 

the total Harris County HRVOC allocation would contribute to attainment of the 1997 eight-hour 

ozone NAAQS by reducing the future 2018 ozone design values at all HGB monitors. 

Accordingly, this SIP revision contains a proposed 25 percent reduction in the total HECT 

allowance cap and revision of the HRVOC allocation methodology. The HECT program will 

continue to be applicable only in Harris County. 

This SIP revision also contains the RACT analysis, the reasonably available control measures 

(RACM) analysis, updates to existing control measures, contingency measures, and the MVEB. 

The plan also describes ongoing technological research and development as well as future 

initiatives. 

The HGB Reasonable Further Progress SIP Revision for the1997 Eight-Hour Ozone Standard 

(Project No. 2009-018-SIP-NR), which demonstrates the FCAA requirement of interim 

reductions of ozone precursors through the 2019 attainment date, is being proposed in a 

concurrent action. 

Table 1-1: Proposed Rule Revisions contains the project number, title, and description of 

proposed rule revisions to 30 TAC Chapters 101 and 115 that are associated with this SIP 

revision. Additional information regarding these rule revisions is included in Chapter 4: Control 

Strategies and Required Elements. 
1-7

Table 1-1: Proposed Rule Revisions 

Rule Project Number Title Description 

2009-019-101-EN MECT Program Cap 

Integrity for the HGB 

Eight-Hour Ozone 

Nonattainment Area 

The proposed revision to the MECT program would 

ensure the integrity of the modeled HGB 

nonattainment area cap by prohibiting the issuance 

of allowance allocations to major sources that did 

not submit the required Level of Activity 

Certification forms by the compliance date in 30 

TAC §101.360. This proposed rule change would 

not reduce the current NOX cap in the HGB 

nonattainment area. 

2009-006-101-EN HECT Program Cap 

Reduction and Allowance 

Reallocation 

The proposed revisions to the HECT program cap 

rule would propose a 25 percent reduction in the 

total HRVOC allowance cap and revisions to the 

HRVOC allocation methodology. The HECT 

program was adopted by the commission as an 

ozone control measure for the HGB area on 

December 1, 2004. The HECT program is 

applicable only in Harris County. 

2008-019-115-EN VOC Control Technique 

Guidelines (CTG) Update 

The proposed revisions to 30 TAC Chapter 115, 

Subchapter E, Division 4 would limit the VOC 

content of solvents used by offset lithographic 

printing facilities located in the HGB area and 

would implement the CTG recommendations to 

reduce the VOC content of the fountain solutions 

and cleaning materials used by such facilities. 

Additionally, the proposed revisions would expand 

the current rule applicability to include smaller 

sources not currently subject to the rule. The 

proposed revisions are to satisfy RACT for the 

2006 federal CTG document for offset lithographic 

and letterpress printing operations. 

The commission is soliciting comments on whether it is appropriate to perform a 1997 eight-hour 

ozone MCR analysis for the HGB area, and, if so, what elements should be contained in the 

analysis. The commission is also seeking input on the appropriate date to submit the MCR. 

1.3 HEALTH EFFECTS 

In 1997, the EPA revised the NAAQS for ozone from a one-hour to an eight-hour standard. To 

support the 1997 eight-hour ozone standard, the EPA provided information indicating that health 

effects can occur at levels lower than the previous standard and at exposure times longer than one 

hour. Exposure to ambient ozone can cause asthma in some people. Repeated exposures to 

ozone can make people more susceptible to respiratory infection and lung inflammation and can 

aggravate preexisting respiratory diseases, such as bronchitis and emphysema.

Children are at a relatively higher risk from exposure to ozone when compared to adults, since 

they breathe more air per pound of body weight than adults and because children’s respiratory 

systems are still developing. Children also spend a considerable amount of time outdoors during 

summer and during the start of the school year (August - October) when high ozone levels are 

typically recorded. Adults most at risk to ozone exposure are people working or exercising 

outdoors and individuals with preexisting respiratory diseases. 

1.4 STAKEHOLDER PARTICIPATION AND PUBLIC HEARINGS 

1.4.1 Local Program Control Strategy Development Meetings 

The TCEQ contracted with the H-GAC to identify possible local on-road and non-road mobile 

source control strategies. As part of this process, stakeholder meetings were held in the HGB 

area. Table 1-2: H-GAC Public and Stakeholder Meeting Dates lists the stakeholder meetings 
1-8

held by H-GAC and its subcontractor, ENVIRON International Corporation from May 2008 

through January 2009. These meetings gave the stakeholders and the public in the HGB area the 

opportunity to hear about and comment on the development of the local mobile source control 

strategies. 

Table 1-2: H-GAC Public and Stakeholder Meeting Dates 

Meetings Dates 

Airports/Airlines 5/22/08, 10/1/08, 1/6/09 

Railroads 6/12/08, 12/1/08 

Tug Boat Operators 12/3/08 

Public Meetings 7/10/08, 12/8/08 

Construction Industry 6/3/08, 12/15/08 

Ports/Marine Equipment 6/12/08, 6/19/08, 12/15/08 

Industrial Mobile Sources 8/13/08, 12/16/08, 1/8/09 

Local Governments 1/27/09 

1.4.2 TCEQ SIP and Control Strategy Development Stakeholder Meetings 

The TCEQ held two identical open-participation HGB Eight-Hour Ozone SIP Stakeholder Group 

meetings to discuss concepts of potential control strategies for the eight-county HGB ozone 

nonattainment area and to hear the public’s ideas on potential rulemaking concepts and provide 

the public an overview of the development of the HGB Attainment Demonstration SIP Revision 

for the 1997 Eight-Hour Ozone Standard. The meetings were held on March 25 and 26, 2008, at 

the Houston City Hall Annex. In these meetings, the TCEQ presented attendees with an update 

on the HGB Attainment Demonstration SIP Revision timeline, an update on modeling efforts, and 

a draft list of initial potential control strategy concepts for stationary, area, and mobile sources. 

The TCEQ held an additional stakeholder meeting to discuss the initial 2018 HGB modeling 

results, provide an update on the development status of the HGB SIP revision, and provide an 

update from H-GAC regarding potential local mobile source control strategies. This meeting was 

held on November 3, 2008, at H-GAC. Additional information on the HGB Eight-Hour Ozone 

SIP Stakeholder Group is available at: 

http://www.tceq.state.tx.us/implementation/air/sip/hgb_stakeholder.html. 

A meeting was held on May 15, 2008, at H-GAC to discuss the development of the HGB 

Attainment Demonstration SIP Revision for the 1997 Eight-Hour Ozone Standard and potential 

local control measures with local governments. Letters inviting participation were sent to the 15 

mayors of cities in the HGB area with populations greater than 20,000, the eight county judges, 

and the four Harris County commissioners. Notification was also sent to state representatives and 

senators representing the districts in the HGB area. Another meeting was held on July 22, 2008, 

at H-GAC to provide local governments information on the SIP revision, as well as discuss the 

process to identify potential measures that can be implemented at the local level. For this 

meeting, 109 letters inviting participation were sent to mayors of cities in the HGB area with 

populations of 20,000 or less. 
1-9

1.4.3 Public Hearings and Comment Information 

The commission will hold public hearings for this proposed SIP revision and associated 

rulemakings at the following times and locations: 

CITY DATE TIME LOCATION 

Houston October 28, 2009 2:00 P.M. Houston-Galveston Area Council 

3555 Timmons Lane 

Houston, TX 77027 

Conference Room A 

Houston October 28, 2009 6:00 P.M. Houston-Galveston Area Council 

3555 Timmons Lane 

Houston, TX 77027 

Conference Room A 

Austin October 29, 2009 3:00 P.M. TCEQ 

12100 Park 35 Circle 

Austin, TX 78753 

Building E, Room 201S 

The public comment period will open on October 9, 2009, and close on November 9, 2009. 

Written comments will be accepted via mail, fax, or through the eComments system. All 

comments should reference the “Houston-Galveston-Brazoria Attainment Demonstration State 

Implementation Plan Revision for the 1997 Eight-Hour Ozone Standard” and Project Number 

2009-017-SIP-NR. Comments may be submitted to Lola Brown, MC 206, State Implementation 

Plan Team, Chief Engineer’s Office, Texas Commission on Environmental Quality, P.O. Box 

13087, Austin, Texas 78711-3087 or faxed to (512) 239-5687. Electronic comments may be 

submitted at http://www5.tceq.state.tx.us/rules/ecomments. File size restrictions may apply to 

comments being submitted via the eComments system. Comments must be received by 

November 9, 2009. 

Copies of the proposed SIP revision and all appendices can be obtained from the TCEQ’s Web 

site at http://www.tceq.state.tx.us/implementation/air/sip/hgb.html#. 

1.5 SOCIAL AND ECONOMIC CONSIDERATIONS 

For a detailed explanation of the social and economic issues involved with any of the measures, 

please refer to the preambles that precede each rule package accompanying this SIP revision. 

1.6 FISCAL AND MANPOWER RESOURCES 

The state has determined that its fiscal and manpower resources are adequate and will not be 

adversely affected through the implementation of this plan. 
2-1 

CHAPTER 2: ANTHROPOGENIC EMISSIONS INVENTORY (EI) DESCRIPTION

2.1 INTRODUCTION 

The Air Emissions Reporting Requirements (AERR), published in the December 17, 2008, issue 

of the Federal Register (73 FR 76539), instruct states to submit EIs containing information 

regarding the emissions of criteria pollutants and criteria pollutant precursors (e.g., volatile 

organic compounds (VOC)). EIs are critical for the efforts of state, local, and federal agencies to 

attain and maintain the National Ambient Air Quality Standards (NAAQS). 

EIs provide data for a variety of air quality planning tasks, including establishing baseline 

emission levels, calculating emission reduction targets, control strategy development for 

achieving required emission reductions, emission inputs into air quality simulation models, and 

tracking actual emission reductions against the established emissions growth and control budgets. 

This chapter discusses general EI development for each of the AERR source categories. Chapter 

3, Photochemical Modeling details specific emissions inventories and emissions inputs developed 

for the Houston-Galveston-Brazoria (HGB) ozone photochemical modeling. 

2.1.1 EI Improvement 

The Texas Commission on Environmental Quality (TCEQ) EI reflects years of continuous 

emissions data improvement, including extensive point and area source inventory reconciliation 

with ambient emissions monitoring data. Since the Texas Air Quality Study 2000 (TexAQS 

2000), when ambient VOC concentrations were measured to be greater than EI estimates, EI 

improvements have targeted more accurate speciation and reporting of industrial VOC emissions. 

The following have significantly improved the HGB point source or area source inventory. 

• Implementation of the 30 Texas Administrative Code (TAC) Chapter 115 highly reactive 

volatile organic compounds (HRVOC) monitoring rules improved the HGB point source 

VOC inventory with measurements required of vents, cooling towers, and the streams to 

flares in HRVOC service.

• The Houston Advanced Research Center project H51C 

(http://www.harc.edu/Projects/AirQuality/Projects/Projects/H051C) identified thousands 

of tons of VOC flash emissions from upstream oil and gas operations in the HGB area 

that the TCEQ has added to the area source inventory. 

• A special landing loss EI was conducted that required the reporting of landing loss 

emissions from floating roof tanks. This special inventory also required regulated entities 

in the HGB area to revise their emissions inventories back to 2002, resulting in a 

reporting increase of approximately 7,000 to 8,000 tons of VOC per year (2002-2004). 

The episodic nature of these emissions is represented in the 2005 and 2006 ozone 

modeling based on site-specific activity data. 

• A month-long hourly EI of approximately 1,200 emissions sources at 125 industrial sites 

was conducted during the TexAQS II intensive period. These hourly data are integrated 

into the 2006 modeling episode, providing highly resolved hourly VOC and nitrogen 

oxides (NOX) emissions data for sources located in the HGB area. Monitored emissions 

data were collected for the majority of the VOC hourly emissions and all of the NOX

emissions rates. Because these sources are not included in the United States 

Environmental Protection Agency’s (EPA) Acid Rain database, these hourly data present 

an opportunity to model a unique and extensive set of monitoring data that characterizes 

the time-dependent nature of industrial ozone precursor emissions. 
2-2 

• The TCEQ Emissions Inventory Guidelines (RG-360A), a comprehensive guidance 

document which explains all aspects of the point source EI process is updated and 

published annually. The latest version of this document is available on the TCEQ’s Point 

Source Emissions Inventory Web site at: 

(http://www.tceq.state.tx.us/implementation/air/industei/psei/psei.html). Currently, six 

technical supplements provide detailed guidance on determining emissions from 

potentially underreported VOC emissions sources such as cooling towers, flares, and 

storage tanks. 

 

2.2 POINT SOURCES

Stationary point source emissions data are collected annually from sites that meet the reporting 

requirements of 30 TAC § 101.10. These sites include, but are not limited to, refineries, chemical 

plants, bulk terminals, and utilities. To collect the data, the TCEQ mails EI questionnaires (EIQ) 

to all sites identified as meeting the reporting requirements. Companies are required to report 

emissions data and to provide sample calculations used to determine the emissions. Information 

characterizing the process equipment, the abatement units, and the emission points is also 

required. All data submitted in the EIQ are reviewed for quality assurance purposes and then 

stored in the State of Texas Air Reporting System (STARS) database. At the end of the annual 

reporting cycle, point source emissions data are reported each year to the EPA for inclusion in the 

National Emissions Inventory (NEI). 

2.3 AREA SOURCES 

Area sources are stationary emission sources that are not included in the point source EI. Similar 

area sources such as plants, facilities, equipment, and/or processes are grouped into area source 

categories including, but not limited to, vehicle refueling, architectural coatings, auto refinishing, 

dry cleaning, municipal solid waste landfills, bakeries, residential fuel combustion, structural 

fires, wildfires, and open burning. 

Area source categories can further be characterized by the mechanism in which their emissions 

are released into the atmosphere: hydrocarbon evaporative emissions or fuel combustion 

emissions. Hydrocarbon evaporative emission sources include, but are not limited to, printing 

operations, industrial coatings, degreasing solvents, house painting, gasoline service station 

underground tank filling, and vehicle refueling operations. Fuel combustion emission sources 

include, but are not limited to, stationary source fossil fuel combustion at residences and 

businesses, outdoor burning, structural fires, and wildfires. Since area source categories represent 

individual emission sources that are small and numerous and that have not been inventoried as 

specific point or mobile sources, the EI for an area source category is developed for a specified 

geographic area by estimating the emissions collectively. 

The emissions from these area source categories, with some exceptions, may be calculated by 

applying an EPA-established emission factor (emissions per unit of activity) to the appropriate 

activity or activity surrogate responsible for generating emissions. Population is the most 

commonly used activity surrogate; examples of other activity data are the amount of gasoline sold 

in an area, employment by industry type, and acres of crop land. Activity data for an area source 

category is obtained via surveys, research, and/or investigations. Air emissions data from the 

different area source categories are collected, reviewed for quality assurance purposes, stored in 

the Texas Air Emissions Repository database system, and compiled to develop the statewide area 
2-3 

 source EI. This area source Periodic Emissions Inventory (PEI) is reported every third year 

(triennially) to the EPA for inclusion in the NEI; the TCEQ submitted the most recent PEI for 

calendar year 2005. 

2.4 NON-ROAD MOBILE SOURCES 

Non-road mobile sources include vehicles, engines, and equipment used for construction, 

agriculture, transportation, recreation, and many other purposes. Non-road vehicles are also 

referred to as off-road or off-highway vehicles that do not normally operate on roads or highways. 

This broad category is comprised of a diverse collection of machines, many of which are powered 

by diesel engines. Examples of non-road mobile sources include, but are not limited to: 

agricultural equipment, commercial and industrial equipment, construction and mining 

equipment, lawn and garden equipment, aircraft, locomotives, and commercial marine vessels. 

A Texas specific version of the EPA’s NONROAD 2005 model, called the Texas NONROAD 

(TexN) model, is used in calculating emissions from all non-road mobile equipment and 

recreational vehicles except aircraft, locomotives, and commercial marine vessels. Emissions for 

these three source categories are estimated using other EPA-approved methods and guidance 

documents. Airport emissions are calculated using the Federal Aviation Administration’s 

Emissions and Dispersion Modeling System, version 5.1. Locomotive emission estimates for 

Texas are based on specific fuel usage data derived from railway segment level gross ton mileage 

activity (line haul locomotives) and hours of operation (yard locomotives) provided directly by 

the Class I railroad companies operating in Texas. Data captured from the Automatic 

Identification System program is applied to the latest known emission factors to quantify 

emissions from commercial marine vessels.

2.5 ON-ROAD MOBILE SOURCES 

On-road mobile sources consist of automobiles, trucks, motorcycles, and other motor vehicles 

traveling on public roadways. Combustion-related emissions are estimated for vehicle engine 

exhaust, and evaporative hydrocarbon emissions are estimated for the fuel tank and other 

evaporative leak sources on the vehicle. The information necessary to estimate on-road mobile 

emissions is emission factors for each vehicle type, the estimated level of vehicle activity, and 

estimated roadway speed. 

Emission factors were developed using the newest version of the EPA's mobile emissions factor 

model, MOBILE6.2.03. Various inputs are provided to the model to simulate the vehicle fleet in 

each nonattainment area. Inputs used to develop localized emission factors include vehicle 

speeds, vehicle age distributions, local meteorological conditions, type of inspection and 

maintenance program in place, and local fuel properties. Emission factors are developed for all 

28 MOBILE6.2.03 vehicle types. 

The level of vehicle travel activity is developed using localized travel demand models (TDM) run 

by the Texas Transportation Institute, Texas Department of Transportation, or regional 

metropolitan planning organizations. The TDM have been validated using a large number of 

ground counts from traffic counters placed in various locations throughout Texas. Estimates of 

vehicle miles traveled (VMT) are often calibrated to outputs from the federal Highway 

Performance Monitor System, which is a model validated using a different set of traffic counters. 

VMT is allocated to the appropriate vehicle types using regional specific VMT mixes developed 

using ground counts and vehicle registration data. 
2-4 

Roadway speeds are needed to select the appropriate MOBILE6.2.03 emission factors. Roadway 

speeds are calculated by a post-processor to the TDM. The speed models use roadway capacity 

information, the estimated volumes from the TDM, and speed correlations based upon volume to 

capacity ratios to estimate roadway speeds. 

To develop on-road mobile emissions estimates, the speed specific MOBILE6.2.03 emission 

factors are multiplied by the VMT for each roadway link in the TDM network. 
3-1

CHAPTER 3: PHOTOCHEMICAL MODELING 

o 

ttainment of the 1997 eight-hour National Ambient Air Quality Standard (NAAQS) for ozone. 

rroborate the model results and support the adequacy of a proposed control 

trategy package. 

evision, submitted in December 

04, was approved by EPA on September 6, 2006. 

ossible to attain the eight-hour NAAQS in the HGB area by the prescribed 

ttainment date. 

lied to the previous ozone season. 

hus, 2018 is the attainment year used in the ozone modeling. 

Extensive use is made of the data collected during TexAQS II to evaluate the model’s 

3.1 INTRODUCTION 

This chapter describes modeling conducted in support of the Houston-Galveston-Brazoria (HGB) 

Attainment Demonstration State Implementation Plan (SIP) Revision for the 1997 Eight-Hour 

Ozone Standard. The HGB nonattainment area consists of Brazoria, Chambers, Fort Bend, 

Galveston, Harris, Liberty, Montgomery, and Waller Counties. The 1990 Federal Clean Air Act 

(FCAA) amendments require that attainment demonstrations be based on photochemical grid 

modeling or any other analytical methods determined by the United States Environmental 

Protection Agency (EPA) to be at least as effective. The EPA’s April 2007 “Guidance on the Use 

of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, 

PM2.5, and Regional Haze” (EPA, 2007; hereafter referred to as “modeling guidance”) 

recommends new procedures for determining whether a control strategy package will lead t

a

The current modeling guidance recommends several qualitative methods for preparing attainment 

demonstrations that acknowledge the limitations and uncertainties of photochemical models when 

used to project ozone concentrations into future years. First, the guidance recommends using 

model results in a relative sense and applying the model response to the observed ozone data. 

Second, the guidance recommends using available air quality, meteorology, and emissions data to 

develop a conceptual model for eight-hour ozone formation and to use that analysis in episode 

selection. Third, the guidance recommends using other analyses (Weight of Evidence) to 

supplement and co

s

The 1990 FCAA amendments established five classifications for ozone nonattainment areas 

based on the magnitude of the monitored one-hour ozone design values and established dates by 

which each classified area should attain the NAAQS. Based on the monitored one-hour ozone 

design value at that time, the HGB Consolidated Metropolitan Statistical Area (Brazoria, 

Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, and Waller counties) was 

classified severe-17, with an attainment date of November 15, 2007. Dating back to 1990, there 

have been six SIP revisions with supporting photochemical modeling addressing the one-hour 

ozone NAAQS. The most recent one-hour ozone HGB SIP r

20

 

With the change of the ozone NAAQS from a one-hour standard to an eight-hour standard, in 

April 2004, the EPA classified the HGB area as a moderate ozone nonattainment area with an 

attainment date of June 15, 2010. Ozone SIP revisions addressing the eight-hour ozone standard 

were due June 15, 2007. Ozone modeling and other analyses conducted by the Texas 

Commission on Environmental Quality (TCEQ) for the SIP revision resulted in a determination 

that it was not p

a

Therefore, the ozone SIP revision submitted to EPA on June 15, 2007, included a request to 

reclassify the area as severe nonattainment for the 1997 eight-hour ozone NAAQS, with an 

attainment date of June 15, 2019. Because the attainment date is early in the 2019 ozone season, 

the EPA has prescribed that the modeling attainment test be app

T

This attainment demonstration uses photochemical modeling in combination with corroborative 

analyses primarily associated with the 2000 and 2006 Texas Air Quality Studies (TexAQS 2000 

and TexAQS II, respectively) to support a conclusion that the HGB eight-county nonattainment 

area will attain the 0.08 parts per million (ppm) 1997 eight-hour ozone standard by June 15, 2019. 
performance and to improve unde

3-2

rstanding of the physical and chemical processes leading to 

zone formation in the HGB area. 

 The meteorological and emissions models 

rovide the major inputs to the air quality model. 

with 

ncentrations peaking during the day and falling during the night and early morning hours. 

 most effective tools to address both the chemical 

omplexity and the future case evaluation. 

 followed to evaluate the ozone in the urban 

rea and submitted the plan to the EPA for approval. 

 photochemical modeling and improving the science, the TCEQ selected 

pisodes to model. 

o

3.1.1 Overview of the Ozone Photochemical Modeling Process 

The modeling system is composed of a meteorological model, several emissions processing 

models, and a photochemical air quality model. 

p

Ozone is a secondary pollutant; it is not generally emitted directly into the atmosphere. Ozone is 

created in the atmosphere by a complex set of chemical reactions between sunlight and several 

primary (directly emitted) pollutants. The reactions are photochemical and require ultraviolet 

energy from sunlight. The primary pollutants fall into two groups, nitrogen oxides (NOX) and 

volatile organic compounds (VOC). In addition, carbon monoxide (CO) is also an ozone 

precursor, but much less effective than either NOX or VOC in forming ozone. As a result of these 

multiple factors, higher concentrations of ozone are most common during the summer 

co

 

Ozone chemistry is complex, involving hundreds of chemical compounds and chemical reactions. 

As a result, ozone cannot be evaluated using simple dilution and dispersion algorithms. Due to 

this chemical complexity, the modeling guidance strongly recommends using photochemical 

computer models to simulate ozone formation and evaluate the effectiveness of future control 

strategies. Computer simulations are the

c

3.1.2 Ozone Modeling 

Ozone modeling involves two major phases, the base case modeling phase and the future year 

modeling phase (with substeps in each phase). The purpose of the base case modeling phase is to 

evaluate the model’s ability to adequately replicate measured ozone and ozone precursor 

concentrations during recent periods with high ozone concentrations (base case episodes). The 

purpose of the future year modeling phase is to predict attainment year ozone design values, as 

well as evaluate the effectiveness of controls in reaching attainment. The TCEQ developed a 

modeling protocol (plan) describing the process to be

a

3.1.3 Base Case Modeling 

Base case modeling involves several steps. First, recent episodes are analyzed to determine what 

factors were associated with ozone formation in the area and whether those factors were 

consistent with the conceptual model. In consultation with the Southeast Texas Photochemical 

Modeling Technical Committee (SETPMTC), which serves in an advisory role for the technical 

aspects of applying

e

The next step is to generate and quality-assure the emissions and meteorological data for the 

selected episodes. Then the meteorological and emissions (NOX, VOC and CO) data are input to 

the photochemical model and the ozone photochemistry is simulated, resulting in predicted ozone 

and ozone precursor concentrations. Base case modeling results are evaluated by comparing 

them to the observed measurements of ozone and ozone precursors. Typically this step is an 

iterative process incorporating feedback from successive evaluations to ensure that the model is 

adequately replicating observations throughout the modeling episode. The adequacy of the model 

in replicating observations is assessed based on compliance with statistical and graphical 

measures as recommended in the modeling guidance. In addition to the recommended analyses, 

the TCEQ used the TexAQS II observations to extend its model performance evaluation to areas 

and chemical species not normally monitored. This extended analysis included use of monitoring 

data collected on aircraft and ship-based platforms. Satisfactory performance of the base case 
modeling provides

3-3

 a degree of reliability that the model can be used to predict future year ozone 

oncentrations (future year design values), as well as to evaluate the effectiveness of possible 

d control factors are developed based on the projected growth in the 

emand for goods and services and the reduction in emissions expected from state, local, and 

rs, and thus, the ratio of future year modeled ozone 

oncentrations to the baseline year concentrations provides a measure of the response of ozone 

sign value is greater than 84 ppb, then additional controls may be 

s in 

igure 3-1: Baseline Design Value Calculation Illustration 

c

control measures. 

3.1.4 Future Year Modeling 

Future year modeling involves several steps. The procedure for predicting future year ozone 

design values (attainment test) involves determining the ratio of the future year to the baseline 

year modeled ozone concentrations. This ratio is called the relative response factor (RRF). 

Whereas the emissions data for the base case modeling are episode-specific, the emissions data 

for the baseline year are based on typical ozone season emissions. Similarly, the emissions data 

for the future year are developed applying growth and control factors to the baseline year 

emissions. The growth an

d

federal control programs. 

Both the baseline and future years are modeled using their respective ozone season emissions and 

the base case episode meteorological data as inputs. The same meteorological data are used for 

modeling both the baseline and future yea

c

concentrations to the change in emissions. 

The future year ozone design value is calculated by multiplying the RRF by a baseline year ozone 

design value (DVB). The DVB is the average of the regulatory design values for the three 

consecutive years containing the baseline year (see Figure 3-1: Baseline Design Value 

Calculation Illustration). When the calculated future year ozone design value is less than or 

equal to 0.08 ppm (84 parts per billion (ppb)), this signifies modeled attainment. When the 

calculated future year ozone de

needed and the model can be used to test the effectiveness of various control measure

developing a control strategy. 

F
3-4

 criteria for selecting ozone episodes for eight-hour 

quently 

• Select periods during which observed eight-hour ozone concentrations are close to the 

y monitor; 

ring sites that are in violation of the NAAQS. 

igure 3-2: Eight-Hour Ozone Exceedance Days in HGB and Other Areas of Texas shows the 

frequency distribution of days with measured daily maximum eight-hour ozone concentrations 

greater than 84 ppb for the period 1991 through 2008. The distribution for the HGB area is 

somewhat bi-modal with a notable high frequency in the late May to early June period and the 

more prominent period of high frequency occurring from late August through September. 

3.2 EPISODE SELECTION 

3.2.1 EPA Guidance for Episode Selection 

The modeling guidance sets forth the primary

ozone attainment demonstration modeling: 

• Select a mix of episodes reflecting a variety of meteorological conditions that fre

correspond with observed eight-hour daily maximum ozone concentrations greater than 

84 ppb at different monitoring sites; 

eight-hour ozone design value at each ke

• Select periods for which extensive air quality/meteorological databases exist; and 

• Model a sufficient number of days so that the modeled attainment test can be applied at 

all of the ozone monito

3.2.2 HGB Ozone Episode Selection Process 

An episode selection analysis was performed to identify time periods with eight-hour ozone 

exceedance days that complied with the primary selection criteria. The analysis identified several 

episodes from 2005 and 2006. 

F
Eight-Hour Ozone Exceedance Days in Texas 

1991-2008

0

10

20

30

40

50

60

70

80

90

100

Early Jan

Late Jan

Early Feb

Late Feb

Early Mar

Late Mar

3-5

r Ozone Exceedance Days in HGB and Other Areas of Texas 

Notes: 

t Arthur 

ort Worth 

ande Valley 

LM = Tyler-Longview-Marshall 

ld intensive period. Table 

-1: Selected Episodes summarizes the dates of the selected episodes. 

 Selected Episodes 

Figure 3-2: Eight-Hou

AUS = Austin 

BPA = Beaumont-Por

CC = Corpus Christi 

DFW = Dallas-F

ELP = El Paso 

LRV = Lower Rio Gr

SAN = San Antonio 

T

In consultation with the SETPMTC, the TCEQ selected three episodes from 2005 and three 

episodes from 2006. Two of these occurred during the TexAQS II fie

3

Table 3-1:

Period of

Episode 

Number of 

Exceedance days 

5/19/05 through 6/3/05 8 

6/15/05 through 6/30/05 9 

7/26/05 through 8/8/05 8 

5/31/06 through 6/15/06 12 

8/15/06 through 9/14/06* 10 

9/19/06 through 11/11/06* 5

*TexAQS II field study intensive period 

These episodes contain 52 exceedance days with occurrences from late May to early October, the 

primary window during which high ozone concentrations have been historically observed, and 

cover the periods depicted in Figure 3-2: Eight-Hour Ozone Exceedance Days in HGB and Other EaLaEaLarly Apr Late Apr Early May Late May Early Jun Late Jun Early Jul Late Jul Early Aug Late Aug Early Sep te Sep rly Oct Late Oct Early Nov te Nov Early Dec Late Dec

Days

ELP

CC

LRV

HGB

DFW

TLM

BPA

AUS

SAN
3-6

e wind pattern 

haracterized by a diurnal clockwise rotational veering as depicted in Figure 3-3: Hourly 

ion the wind blew. The distance of a point from the origin represents 

e average wind speed in meters per second. The pink arrow indicates the daily average of all 24 

d 

ind pattern also frequently associated with eight-hour ozone exceedance days is characterized 

by a northerly morning to southerly afternoon flow reversal. Twenty-three of the 52 exceedance 

days exhibit this wind pattern. The selected episodes are consistent with the conceptual model. 

Areas of Texas. In addition, these episodes take advantage of the TexAQS II data and findings, 

including the August 1 through October 15, 2006, intensive field campaign. 

Selecting a large number of days also increases the likelihood that the distribution of days 

associated with various ozone-conducive wind patterns will be consistent with the conceptual 

model. The conceptual model of ozone formation in the HGB area (see Appendix C: CAMx 

Modeling for the HGB Attainment Demonstration SIP) suggests that th

c

Average Resultant Winds; Eight-Hour Exceedance Days, August through September 1998 

through 2006 is most often associated with eight-hour ozone exceedance days. 

Hourly average resultant winds are plotted in the figure. The x-axis represents the east-west 

component of the wind while the y-axis represents the north-south component. Each point on the 

loop represents an hour of the day. The red data point corresponds to midnight and the aqua point 

corresponds to noon. Wind vectors have two attributes, wind speed and direction, and these 

components were averaged across monitors for each hour of the day and then plotted. Each point 

represents the tail of that hour’s averaged resultant wind vector, and although not plotted, all the 

resultant wind vectors terminate at the origin. In other words, the direction from the point to the 

origin represents the direct

th

one-hour vectors, and the green halo around each point gives an indication of the variability of 

the data across monitors. 

Of the 52 exceedance days in the selected episodes, 25 days exhibit this wind pattern. A secon

w
3-7

eedance Days, August 

rough September 1998 through 2006 

um eight-hour ozone concentrations observed and the 

number of monitors exceeding 84 ppb. 

8-hour Exceedances 

Hourly Resultant Wind Vectors 170 days 

Vector Wind Speed in meters per second (m/s) -3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 00:00

12:00

Figure 3-3: Hourly Average Resultant Winds; Eight-Hour Exc

th

Figure 3-4: 2005 and 2006 Non-TexAQS II Modeling Episodes and Figure 3-5: 2006 TexAQS II 

Modeling Episodes show the daily maxim
Figure 3-4: 2005 and 2006 Non-TexAQS II Modeling Episodes 

Note: 8-h o3= eight-hour ozone

3-8
3-9

Figure 3-5: 2006 TexAQS II Modeling Episodes

33.0

41.4

56.6

68.8

65.8

56.8

44.2

50.2

76.8

43.0

45.2

42.5

43.4

56.0

64.3

95.5

113.6

89.7

51.6

75.5

73.7

71.2

44.1

67.9

45.5

26.5

30.0

29.7

72.7

80.8

127.1

121.8

83.7

88.7

79.8

63.9

87.9

110.5

81.1

47.4

41.5

46.0

70.0

89.0

118.9

44.8

36.7

24.6

43.0

60.4

86.7

56.9

27.7

29.8

45.0

58.3

78.4

90.5

60.9

67.1

48.0

59.1

51.0

70.6

82.0

6

14

1

14

25

11

12

1

8

12

152535455565758595

105115125135

20060801

20060804

20060807

20060810

20060813

20060816

20060819

20060822

20060825

20060828

20060831

20060903

20060906

20060909

20060912

20060915

20060918

20060921

20060924

20060927

20060930

20061003

hgb daily max 8-h ozone (ppb)

daily m ax # of sites >
3-10 

Table 3-2: Eight-Hour Ozone Design Values and Number of Exceedance Days During Selected 

Episodes lists the regulatory nonattainment monitors in the eight-county HGB area along with their 

2005 and 2006 eight-hour ozone design values and the number of days during the selected episodes 

for which the daily maximum eight-hour ozone was greater than 84 ppb. 

Table 3-2: Eight-Hour Ozone Design Values and Number of Exceedance Days During 

Selected Episodes 

Monitor 

Designation Site Code 

2005 Design 

Value (ppb) 

2006 Design 

Value (ppb) 

Number Days 

> 84ppb 

Houston East (CAMS 1) HOEA 87 83 7 

Aldine (CAMS 8) HALC 92 88 5 

Channelview (CAMS 15) HCHV 89 85 5 

Northwest Harris County 

(CAMS 26) HNWA 93 91 13 

Galveston Airport (CAMS 34) GALV 87 83 3 

Deer Park (CAMS 35) DRPK 100 96 10 

Seabrook Friendship Park (CAMS 

45) SBFP 92 90 8 

Houston Bayland Park 

(CAMS 53) BAYP 103 103 14 

Conroe Relocated (CAMS 78) CNR2 86 85 5 

TCEQ Houston Regional Office 

(CAMS 81) HROC 88 84 9 

Manvel Croix Park (CAMS 84) MACP 97 96 16 

Clinton (CAMS 403) C35C 95 85 1 

Houston Monroe (CAMS 406) HSMA 97 99 10 

Croquet (CAMS 409) HCQA 98 94 8 

Shell Westhollow (CAMS 410) SHWH 89 96 12 

Houston Texas Avenue 

(CAMS 411) HTCA 88 84 1 

Lynchburg Ferry (CAMS 1015) LYNF 96 89 8 

Note: CAMS = Continuous Ambient Monitoring Station 
3-11 

Figure 3-6: Map Depicting Regulatory Monitors in the HGB Area shows the location of the 

regulatory monitors in the eight-county HGB area. 

Figure 3-6: Map Depicting Regulatory Monitors in the HGB Area 

Even though there are 52 exceedance days in the 2005 and 2006 episodes, only a few of the 

regulatory monitors measured daily maximum eight-hour ozone concentrations of greater than 84 

ppb on 10 or more days. This reflects the complexity of ozone formation and distribution in the 

HGB area. For example, the Houston Texas Avenue (HTCA, CAMS 411) and TCEQ Houston 

Regional Office (HROC, CAMS 81) monitors are in fairly close proximity to one another, but the 

Houston Texas Avenue (CAMS 411) monitor measured a daily maximum eight-hour ozone 

concentration of greater than 84 ppb on only one day, while the TCEQ Houston Regional Office 

(CAMS 81) monitor measured it on nine days. The attainment test considers the modeled daily 

maximum eight-hour ozone concentration from an array of grid cells around the cell containing a 

monitor. By considering an array of grid cells around the monitor, rather than the single grid cell 

where the monitor is located, the likelihood of modeled concentrations exceeding 84 ppb is 

increased. This increases the number of days used in the attainment test (i.e., the RRF calculation). 

There were a few other ozone episodes during the 2005 and 2006 ozone season that were not 

developed due to unusual meteorological conditions. For example, exceedance days that occurred 

in late August and September of 2005 may have been influenced by hurricanes Katrina and Rita. 
3-12 

3.3 METEOROLOGICAL MODEL 

The TCEQ is using the Fifth Generation Meteorological Model (MM5, version 3.7.3) developed 

jointly by the National Center for Atmospheric Research (NCAR) and Pennsylvania State 

University (Grell et al., 1994). This model, supported by a broad user community including the 

Air Force Weather Agency, national laboratories, and academia, is being used extensively for 

regulatory air quality modeling analyses throughout the United States. 

3.3.1 Modeling Domains 

MM5 was configured with three two-way nested outer grids (108 kilometer (km), 36 km, and 12 

km horizontal resolution) to cover the United States and regional areas of interest. A one-way 

nested 4 km fine grid covering the eastern half of Texas was used to focus on metropolitan areas 

with air quality degradation, as shown in Figure 3-7: MM5 Modeling Domains. The extent of each 

of the MM5 modeling domains was selected to accommodate the embedding of the commensurate 

air quality modeling domains (see Section 3.5: PHOTOCHEMICAL MODELING). 

Vertically, MM5 is structured with 43 layers from the surface to approximately 20 km. Twenty 

layers are within the first 3,000 meters in order to resolve boundary layer phenomena. The same 

MM5 vertical layering structure is used for all of the domains. 

Range Grid Points 

Domain Easting (km) Northing (km) Easting Northing

108 km (-2808, 2808) (-2268, 2268) 53 43 

36 km (-1296, 2160) (-1728, 972) 97 76 

12 km (-648, 1080) (-1548, -360) 145 100 

4 km (72, 372) (-1 80, -648) 3 166 184 

Figure 3-7: MM5 Modeling Domains 

3.3.2 Model (MM5) Configuration 

Based on past TCEQ modeling efforts, the EPA’s modeling guidance (EPA, 2007), contractor 

experience, and other demonstrations including sensitivity tests and model performance evaluation, 

the MM5 was configured with parameterizations and improved input data to optimize the 

performance of the wind field (i.e., wind speed and direction). Wind speed and direction are the 
3-13 

WN program was used to 

terpolate from the 12 km domain output to the 4 km domain input. 

r 

udging. The NCEP NAM gridded output was also used for model initialization (NCEP, 2009). 

iences, MM5 community use, and features of the ozone exceedance 

pisodes being modeled. 

Table 3-3: Selected deling Schemes 

Nudging 

C s Radiation 

Land-Surface 

M 

most important parameters predicted by the meteorological model for air quality modeling 

purposes because the wind field determines the transport and dispersion of pollutants. The preprocessing of the MM5 input data followed the standard progression using the TERRAIN, 

REGRID, and INTERPF (NCAR, 2005) programs. The NESTDO

in

To improve the MM5 simulation of the meteorological parameters, in particular the wind field, the 

land use characteristics and sea surface temperatures on all domains were updated with high 

resolution satellite measurements. In addition, observed parameters are assimilated in MM5 during 

the model run through a process called Four-Dimensional Data Assimilation (FDDA), or nudging 

(Stauffer and Seaman, 1990; Stauffer et al., 1991; Stauffer and Seaman, 1994). The outer domains 

(108 km, 36 km, and 12 km) were nudged to the National Center for Environmental Prediction 

(NCEP) North American Model (NAM) gridded output for winds, temperature, and water vapor. 

The fine scale 4 km domain was observationally nudged using quality-assured upper air wind 

profiler data. MM5 default nudging strength parameters were used for both the NAM and profile

n

MM5 schemes and options typically selected for air quality applications are shown in Table 3-3: 

Selected MM5 Modeling Schemes. The selection of these schemes and options was based on 

previous modeling exper

e

 MM5 Mo

Domain Type PBL umulu Model icrophysics

108, 36, 12 km Analysis 3-D Eta Grell RRTM Noah Simple Ice 

4 km Observational Eta Grell RRTM Noah Simple Ice 

N PBL = Planetary Boundary Layer otes: 

RRTM = Rapid Radiative Transfer Model 

KE) vertical diffusivity methodology, with a minimum vertical diffusivity coefficient (K ) of 1.0. 

ature (SST) data, the nudging methodology, the 

KE methodology and the Grell cumulus scheme. 

e 

xceedance episodes, as listed in Table 3-4: 2005 and 2006 Meteorological Modeling Episodes. 

MM5 output was post-processed using the MM5CAMX utility to convert the MM5 meteorological 

fields to the Comprehensive Air Quality Model with Extensions (CAMx) grid and input format 

(Environ, 2008). The output was also processed with the Mellor-Yamada turbulent kinetic energy 

(T V

Appendix A: Meteorological Modeling for the HGB Attainment Demonstration SIP provides 

details on the development of the MM5 configuration, including the satellite-based LandUse/Land-Cover (LULC) and Sea Surface Temper

T

3.3.3 MM5 Application and Performance 

The final MM5 modeling configuration was applied to periods spanning the eight-hour ozon

e
3-14 

Table 3-4: 2005 and 2006 Meteorological Modeling Episodes 

Episode 

All Grids 

Begin Date/Time (UTC) 

Outer Grids 

End Date/Time (UTC) 

Fine Grid 

End Date/Time (UTC) 

2005ep0 May 18, 2005 06:00 June 4, 2005 06:00 June 4, 2005 06:00 

2005ep1 June 15, 2005 06:00 July 1, 2005 06:00 July 1, 2005 06:00 

2005ep2 July 25, 2005 06:00 August 9, 2005 09:00 August 9, 2005 07:00 

2006ep0 May 29, 2006 06:00 June 17, 2006 06:00 June 17, 2006 06:00 

2006ep1a August 23, 2006 07:00 

2006ep1b September 16, 2006 07:00 

2006ep1c October 1, 2006 07:00 

2006ep1d 

August 13, 2006 06:00 October 13, 2006 09:00 

October 13, 2006 07:00 

Note: UTC = Universal Time, Coordinated. 

A detailed performance evaluation for each of the 2005 and 2006 meteorological modeling 

episodes is included in Appendix A: Meteorological Modeling for the HGB Attainment 

Demonstration SIP. In addition, all performance evaluation products are available on the TCEQ 

file transfer protocol (FTP) site (TCEQ, 2009). 

As mentioned, the wind speed and direction are deemed to be the most important meteorological 

parameters input to the air quality model. The MM5 modeled wind field was evaluated by 

comparing the hourly modeled and measured wind speed and direction for all monitors in the HGB 

area. Figure 3-8: Meteorological Modeling Performance exhibits the percent of hours for which 

the average absolute difference between the modeled and measured wind speed and direction, for 

all monitors in the HGB area, was within the specified accuracy benchmarks (e.g., wind speed less 

than or equal to two meters per second: WSPD < 2 m/s). 

TexAQS II Meteorological Modeling Performance Statistics

76

82

65

76

80

67

84 83

100 100

97

100

96 96 98

78

74

80

85 83

80

69

73

98

0

10

20

30

40

50

60

70

80

90

100

2005ep0 2005ep1 2005ep2 2006ep0 2006ep1a 2006ep1b 2006ep1c 2006ep1d

Percent of Hours within Accuracy Threshold

WDIR ≤ 30 °

WSPD ≤ 2 m/s

TEMP ≤ 2 °C

Figure 3-8: Meteorological Modeling Performance

Notes: WDIR = Wind Direction 

 WSPD = Wind Speed 

 TEMP = Temperature 
3-15 

Table 3-5: Average HGB Percent Accuracy for all Meteorological Modeling Episodes provides an 

additional evaluation of MM5 predictions to stricter benchmarks (Emery et al., 2001). 

Table 3-5: Average HGB Percent Accuracy for all Meteorological Modeling Episodes 

Episode 

Wind Direction (°) 

Error ≤ 30 / 20 / 10 

Wind Speed (m/s)

Error ≤ 2 / 1 / 0.5 

Temperature (°C)

Error ≤ 2 / 1 / 0.5 

2005ep0 76 / 67 / 49 98 / 73 / 40 78 / 49 / 30 

2005ep1 82 / 71 / 40 100 / 93 / 60 74 / 50 / 28 

2005ep2 65 / 54 / 33 100 / 75 / 43 80 / 57 / 31 

2006ep0 76 / 63 / 45 97 / 72 / 38 85 / 57 / 33 

2006ep1a 80 / 67 / 43 100 / 83 / 43 83 / 61 / 39 

2006ep1b 67 / 54 / 33 96 / 63 / 26 80 / 52 / 25 

2006ep1c 84 / 76 / 57 96 / 57 / 29 69 / 33 / 16 

2006ep1d 83 / 66 / 33 98 / 75 / 42 73 / 51 / 32 

3.4 MODELING EMISSIONS 

For the stationary emission source types, which consist of point and area sources, routine emission 

inventories provided the major inputs for the emissions modeling processing. Emissions from 

mobile and biogenic sources were derived from relevant emission models. Specifically, link-based 

on-road mobile source emissions were derived from a travel demand model coupled with the EPA 

MOBILE6.2 emission factor model, and non-road mobile source emissions were derived from the 

EPA’s National Mobile Inventory Model (NMIM), or the Texas NONROAD (TexN) mobile 

source models. The on- and non-road emissions were processed to air quality model-ready using 

version three of the Emissions Processing System (EPS3; Environ, 2007). Biogenic emissions 

were derived from the Global Biosphere Emissions and Interactions System (GloBEIS) model, 

which outputs air quality model-ready emissions. 

Appendix B: Emissions Modeling for the HGB Attainment Demonstration SIP provides details on 

the development and processing of the emissions using the various EPS3 modules. The modules, 

listed in Table 3-6: EPS3 Emissions Processing Modules are used to create the chemically 

speciated, temporally (hourly) allocated, and spatially distributed emission files needed for the air 

quality model. 

Table 3-6: EPS3 Emissions Processing Modules 

EPS3 Module Description 

PREAM Prepare area and non-link based mobile sources emissions for further processing

LBASE Spatially allocate link-based mobile source emissions among grid cells 

PREPNT Group point source emissions into elevated and low-level for further processing 

CNTLEM Apply controls to model strategies, apply adjustments, etc. 

TMPRL Apply temporal profiles to hourly allocate emissions 

CHMSPL Chemically speciate emissions into nitrogen oxide (NO), nitrogen dioxide 

(NO2), CB05-VOC 

GRDEM Spatially distribute emissions by grid cell using source category surrogates 

MRGUAM Merge and adjust multiple gridded files for model-ready input 

PIGEMS Assigns PiGs and merges elevated point source files 

Notes: CB05 = the 2005 version of the Carbon Bond chemical mechanism 

 PiG = Plume-in-Grid 

Model-ready emissions were developed for the episode days listed in Table 3-7: 2005 and 2006 

Episode Days for Emissions Modeling. 
3-16 

Table 3-7: 2005 and 2006 Episode Days for Emissions Modeling 

2005 and 2006 Base Case Episodes 

Episode Code Episode Designation Episode Days 

bc05ep0 May/June 2005 May 19 through June 3, 2005 

bc05ep1 June 2005 June 17 through 30, 2005 

bc05ep2 July/August 2005 July 26 through August 8, 2005 

bc06ep0 June 2006 May 31 through June 15, 2006 

bc06aqs1 August/September 2006 August 13 through September 15, 2006 

bc06aqs2 September/October 2006 September 16 through October 11, 2006

The following sections give a brief description of the development of each type of emissions. 

3.4.1 Biogenic Emissions 

The TCEQ used Version 3.1 of the GloBEIS model to develop the biogenic emissions. It 

incorporates detailed locality-specific land-use data to generate the mix and density of vegetative 

species. In addition, solar radiation data from Geostationary Operational Environmental Satellite 

(GOES) imagery, which is used to generate the photosynthetically active solar radiation (PAR), can 

be input to the GloBEIS model. Further, the GloBEIS model can accept hourly temperature data 

generated from weather station data. 

Biogenic Emissions Landuse Data,Version 3 (BELD3; Kinnee et al., 1997), a vegetation database 

for the entire North American continent prepared specifically for creating biogenic emissions 

inventories, was used for the 36 km domain and the portion of the 12 km domain outside Texas. 

For the land-use data in the 12 km domain within Texas, the TCEQ used the Texas vegetation 

database (Wiedinmyer et al., 2001), which was derived from Texas Parks and Wildlife vegetation 

data and agricultural statistics from the National Agricultural Statistics Survey, and field surveys 

carried out in 1999. Within the 4 km nested domain, a new land-cover database from the 

University of Texas Center for Space Research (UT-CSR) was used (Feldman et al., 2007). This 

database was developed from classification of recent Landsat 7 data, Shuttle Radar Topography 

Mission and National Elevation datasets to identify wetlands, and United States Department of 

Agriculture, Common Land Unit CLU data to identify agricultural land. 

The episode-specific PAR data input to GloBEIS were obtained from the website operated by the 

Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project 

(GCIP) and GEWEX Americas Prediction Project (GAPP) located at 

http://metosrv2.umd.edu/~srb/gcip/cgi-bin/historic.cgi?auth=no. The episode-specific temperature 

data were obtained from weather stations throughout the United States, including data from the 

National Weather Service, the EPA Aerometric Information Retrieval System (AIRS) air quality 

database, the National Buoy Data Center, the Texas A&M Crop Weather Program, the Louisiana 

Agricultural Information Service, and the Texas Coastal Oceanographic Observation Network. 

GloBEIS3.1 was run for each of the modeling episode days listed in Table 3-7: 2005 and 2006 

Episode Days for Emissions Modeling. Figure 3-9: An Example of Day-Specific Biogenic 

Emissions shows the typical magnitude and distribution of biogenic VOC and NOX emissions in 

the 4 km modeling domain. 
3-17 

Biogenic VOC and NOX Emissions

August 2, 2005

Figure 3-9: An Example of Day-Specific Biogenic Emissions 

Since biogenic emissions are associated with meteorological features, the same episode dayspecific emissions were used as input for the 2006 baseline and 2018 future air quality modeling. 

3.4.2 Base Cases 

3.4.2.1 Point Sources

Point source modeling emissions were developed using data from regional inventories such as the 

Central Regional Air Planning Association/Regional Planning Organization (CENRAP/RPO) 

emissions database and EPA’s Acid Rain Database (ARD), state inventories including the State of 

Texas Air Reporting System (STARS), and local inventories including the TexAQS II Hourly 

Special Inventory (SI). Data were processed with EPS3 to generate model-ready emissions, and 

similar procedures were used to develop each base case episode. 

Outside Texas

Point source emissions data for the regions of the modeling domains outside Texas were obtained 

from a number of different sources. Emissions from point sources in the Gulf of Mexico (e.g., oil 

and gas production platforms) were obtained from the 2005 Gulf-wide Emissions Inventory 

(GWEI) provided by the Minerals Management Services (MMS) as monthly totals. The Canadian 

emissions were obtained from EPA modeling emission files developed for the 2001 Clean Air 

Interstate Rule (CAIR) base case analysis (EPA, 2005) and the Mexican emissions inventory data 

were obtained from Phase III of the Mexican National Emissions Inventory (NEI; 

http://www.epa.gov/ttn/chief/net/mexico.html). 

For all states beyond Texas, hourly NOX emissions for major electric generating units (EGUs) were 

obtained from the ARD for each episode day. Emissions for non-ARD sources in states beyond 

Texas were obtained from the 2002 CENRAP/RPO emissions database, with the exception of 
3-18 

Arkansas, Louisiana, and Oklahoma. State-specific 2005 point source annual emissions for nonARD sources were provided by Arkansas and Oklahoma. Louisiana provided their 2004 point 

source emissions, since the 2005 emissions were incomplete due to hurricane Katrina. The EPA’s 

Economic Growth Analysis System Version 5.0 (EGAS5) was used to grow these emissions to 

2005 and 2006 as appropriate for the various episodes. 

Within Texas 

Hourly NOX emissions from EGUs within Texas were obtained from the ARD for each episode day. 

Emissions from non-ARD sources were obtained from the TCEQ 2005 and 2006 STARS emissions 

inventories. The 2006 TexAQS II hourly special inventory (SI) collected August 15 through 

September 15, 2006, was used for the August/September 2006 episode (bc06aqs1). In addition, 

agricultural and forest fire emissions for the 2005 and 2006 episodes were obtained from a TCEQfunded study (Environ, 2008b), which treated fires as point sources. For the HGB area, 2005 and 

2006 event-specific tank landing loss emissions were obtained from an SI revision requested by the 

TCEQ. Highly Reactive Volatile Organic Compounds (HRVOC) (ethylene (ETH), propylene, 

butenes and 1,3-butadiene) emissions were reconciled with ambient measurements by comparing 

concentrations observed at automated gas chromatographs (auto-GCs) in the area with 

concentrations expected at those locations based on the reported inventory. See Appendix B: 

Emissions Modeling for the HGB Attainment Demonstration SIP for more details. 

Table 3-8: 2005 and 2006 Base Case Episode Point Source Modeling Emissions for HGB

summarizes the typical weekday point source emissions for the eight-county HGB area by episode. 
3-19 

Table 3-8: 2005 and 2006 Base Case Episode Point Source Modeling Emissions for HGB 

Bc05ep0 Bc05ep1 Bc05ep2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Point 

Source 

Type (tpd) (tpd) (tpd) 

ARD1 43.89 3.28 29.59 43.03 3.08 38.56 55.26 4.04 48.24

N-ARD2 147.52 224.87 95.51 147.52 224.87 95.51 147.52 224.87 95.51

Tank L3 NA 49.50 NA NA 17.80 NA NA 33.10 NA

Fires4 0.04 0.29 3.61 0.10 0.81 10.37 0.92 7.19 92.70

HRVOC5 NA 29.92 NA NA 29.92 NA NA 29.92 NA

Totals 191.45 307.86 128.71 190.65 276.48 144.44 203.70 299.12 236.45

Bc06ep0 Bc06aqs1 Bc06aqs2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Point 

Source 

Type (tpd) (tpd) (tpd) 

ARD1 46.65 2.87 39.66 40.41 2.45 29.45 48.42 2.72 36.47

N-ARD2 124.13 180.62 89.52 121.95 165.39 88.34 124.13 180.62 89.52

Tank L3 NA 17.40 NA NA 10.40 NA NA 0.30 NA

Fires4 0.04 0.27 3.46 0.13 1.05 13.47 0.04 0.30 3.72

HRVOC5 NA 21.17 NA NA 21.17 NA NA 21.17 NA

Totals 170.82 222.33 132.64 162.49 200.46 131.26 172.59 205.11 129.71

Notes: 1. ARD emissions listed are for a Wednesday in a specific episode. 

 2. Non-ARD emissions listed are for OSD weekday, OSD weekend days are slightly less. 

 3. Tank landing emissions listed are episode-specific average for days with non-zero 

emissions. 

4. Agriculture and forest fire emissions listed are episode-specific average for days with 

non-zero emissions. 

 5. HRVOC reconciled emissions listed are the amounts added through the emissions 

reconciliation procedure to those reported. 

3.4.2.2 On-Road Mobile Sources

On-road mobile source modeling emissions were developed using the EPA’s NMIM, and Highway 

Performance Monitoring System (HPMS) data and travel demand modeling (TDM) output coupled 

with the EPA MOBILE6.2 emissions model. The output from these emission modeling 

applications were processed through EPS3 to generate the air quality model-ready on-road mobile 

source emission files. 

Outside Texas 

For all of the states beyond Texas, the TCEQ used NMIM to generate average summer weekday 

mobile source emissions by county for 2005 and 2006. Average summer Friday, Saturday, and 

Sunday mobile source emissions were estimated using the weekday to Friday, Saturday, and 

Sunday ratios developed for the on-road mobile source emissions within Texas. 

Within Texas 

For the Texas counties outside of HGB and Beaumont-Port Arthur (BPA) areas, on-road emissions 

were developed by the Texas Transportation Institute (TTI) using HPMS data for 2005 and 2006, 

and the EPA’s MOBILE6.2 on-road mobile source emissions model to generate average summer 

emissions for the four day types of weekday (Monday through Thursday average), Friday, Saturday, 

and Sunday. 

For the eight-county HGB and three-county BPA areas, link-based on-road emission were 

developed by TTI using the TDM output for 2005 and 2006, and the EPA MOBILE6.2 on-road 

mobile source emissions model to generate average summer and school season on-road emission 
3-20 

for the four day types. For the 2005 and 2006 base case episodes, both the school and summer 

season day type emissions were used as appropriate. 

Table 3-9: Summary of the Development of On-Road Mobile Sources Emissions summarizes 

features of the on-road mobile emissions in the different regions of the modeling domain. 

Table 3-9: Summary of the Development of On-Road Mobile Sources Emissions 

On-Road Inventory 

Development Parameter HGB and BPA Non- HGB and BPA Non-Texas States/Counties 

VMT Source and 

Resolution TDM Roadway Links HPMS Data Sets -19 Roadways 

NMIM Database - 12 

Roadways 

Season 

Types School and Summer Summer Only 

Summer 

Only 

Day 

Types 

Weekday, Friday, 

Saturday, and Sunday 

Weekday, Friday, 

Saturday, and Sunday 

Weekday, Friday, 

Saturday, and Sunday 

Hourly VMT Mix 

By Day Type Yes Yes No 

Roadway Speed 

Distribution 

Varies by 

Hour and Link 

Varies by Hour 

and Roadway Type 

MOBILE6.2 

Default 

MOBILE6.2 Classes 28 28 12 

Temperature/Humidity 

Diesel NOX Correction Yes Yes No 

“18-Wheeler” Idling 

Emissions Separation Yes No No 

Note: VMT= Vehicle Miles Traveled 

Table 3-10: 2005 and 2006 Base Case Episode On-Road Modeling Emissions for HGB

summarizes the on-road mobile source emissions for each of the 2005 and 2006 base case episodes 

for the eight-county HGB area. 

Table 3-10: 2005 and 2006 Base Case Episode On-Road Modeling Emissions for HGB 

Bc05ep0 Bc05ep1 Bc05ep2 

NOX VOC CO NOX VOC CO NOX VOC CO 

On-Road 

Day 

Type (tpd) (tpd) (tpd) 

Weekday 233.35 110.29 1307.35 221.67 104.27 1244.93 221.67 104.27 1244.93

Friday 241.06 123.43 1457.80 223.68 113.73 1359.36 223.68 113.73 1359.36

Saturday 192.67 85.51 1099.39 180.72 80.09 1032.63 180.72 80.09 1032.63

Sunday 148.68 70.51 906.86 143.17 67.81 873.70 143.17 67.81 873.70

Bc06ep0 Bc06aqs1 Bc06aqs2 

NOX VOC CO NOX VOC CO NOX VOC CO 

On-Road 

Day 

Type (tpd) (tpd) (tpd) 

Weekday 197.28 99.39 1115.23 207.64 105.15 1171.27 207.64 105.15 1171.27

Friday 199.92 108.40 1217.36 215.43 117.70 1305.77 215.43 117.70 1305.77

Saturday 160.76 76.06 920.59 171.37 81.21 980.17 171.37 81.21 980.17

Sunday 127.68 64.42 778.75 132.59 66.99 808.41 132.59 66.99 808.41

Notes: 1. Episodes bc05ep0, bc06aqs1 and bc06aqs2 use school season emissions; episodes 

bc05ep1, bc05ep2 and bc06ep0 use summer season emissions. 

 2. VOC is reported as sum of CB05 species. 
3-21 

3.4.2.3 Non- and Off-Road Mobile Sources

Non/Off-road mobile source modeling emissions were developed using the EPA NMIM, the EPA 

NEI, TexN, and data from the TCEQ’s Texas Air Emissions Repository (TexAER). The output 

from these emission modeling applications and databases were processed through EPS3 to generate 

the air quality model-ready non- and off-road mobile source emission files. 

Outside Texas 

For all the states beyond Texas, the TCEQ used the EPA’s NMIM. NMIM generates average 

summer weekday non-road mobile source category emissions by county and was run for 2005 and 

2006. For the off-road mobile source categories (aircraft, locomotive, and marine) in the nonTexas states, the TCEQ used the EPA’s 2002 NEI with EGAS5 growth factors and national 

controls for locomotives and marine vessels to generate 2005 and 2006 average summer weekday 

off-road mobile source category emissions. Summer weekend day emissions for the non- and offroad mobile source categories were developed as part of the EPS3 processing using category 

specific weekly activity profiles. 

Within Texas 

The TCEQ used the TexN model to generate average summer weekday non-road mobile source 

category emissions by county for 2005 and 2006. County-level off-road emissions for 2005 were 

obtained from the TCEQ’s 2005 TexAER, and the 2006 county-level off-road emissions were 

estimated by adjusting the 2005 TexAER emissions with the Texas-specific Regional Economic 

Models, Inc. (REMI)-EGAS growth factors, except for the aircraft/airport emissions in the HGB 

and DFW areas. The 2005 and 2006 aircraft/airport emissions in the HGB and DFW areas were 

provided through a stakeholder process and these emissions are airport-specific rather than countylevel. Summer weekend day emissions for the non- and off-road mobile source categories were 

developed as part of the EPS3 processing using category specific weekly activity profiles. 

 

Table 3-11: 2005 and 2006 Base Case Episode Non- and Off-Road Modeling Emissions for HGB

summarizes the non- and off-road mobile source weekday emissions for each of the 2005 and 2006 

base case episodes for the eight-county HGB area. Since these are average summer weekday, the 

2005 emissions are used for each of the 2005 base case episodes and the 2006 emissions are used 

for each of the 2006 base case episodes. 

Table 3-11: 2005 and 2006 Base Case Episode Non- and Off-Road Modeling Emissions for 

HGB 

Bc05ep0 Bc05ep1 Bc05ep2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Non-Road 

Type 

(tpd) (tpd) (tpd) 

Non-Road 84.97 81.01 805.50 84.97 81.01 805.50 84.97 81.01 805.50

Airports 9.53 2.72 38.22 9.53 2.72 38.22 9.53 2.72 38.22

Locomotive 30.34 2.48 8.52 30.34 2.48 8.52 30.34 2.48 8.52

Marine 34.47 0.79 6.30 34.47 0.79 6.30 34.47 0.79 6.30

Totals 159.31 87.00 858.54 159.31 87.00 858.54 159.31 87.00 858.54

Bc06ep0 Bc06aqs1 Bc06aqs2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Non-Road 

Type 

(tpd) (tpd) (tpd) 

Non-Road 78.85 75.97 772.94 78.85 75.97 772.94 78.85 75.97 772.94

Airports 9.89 2.80 38.07 9.89 2.80 38.07 9.89 2.80 38.07

Locomotive 28.56 2.45 8.77 28.56 2.45 8.77 28.56 2.45 8.77

Marine 35.10 0.80 6.41 35.10 0.80 6.41 35.10 0.80 6.41

Totals 152.40 82.02 826.19 152.40 82.02 826.19 152.40 82.02 826.19

Note: VOC is reported as sum of CB05 species 
3-22 

3.4.2.4 Area Sources

Area source modeling emissions were developed using the EPA NEI and the TCEQ TexAER. The 

emissions information in these databases was processed through EPS3 to generate the air quality 

model-ready area source emission files. 

Outside Texas 

For all the states beyond Texas, the TCEQ used the EPA’s 2002 NEI with EGAS5 growth factors 

to generate 2005 and 2006 daily area source emissions. 

Within Texas 

The TCEQ used 2005 TexAER to generate 2005 daily area source emissions and for the 2006 daily 

area source emissions, applied the Texas-specific REMI-EGAS growth factors. 

Since these are daily emissions, the 2005 emissions are used for each of the 2005 base case 

episodes and the 2006 emissions are used for each of the 2006 base case episodes. 

3.4.2.5 Base Case Summary

Table 3-12: 2005 and 2006 Base Case Episode Anthropogenic Modeling Emissions for HGB

summarizes the typical weekday emissions in the eight-county HGB area by source type for each 

base case episode. 

Table 3-12: 2005 and 2006 Base Case Episode Anthropogenic Modeling Emissions for HGB 

Bc05ep0 Bc05ep1 Bc05ep2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Source 

Type 

(tpd) (tpd) (tpd) 

Point1 191.45 307.86 128.71 190.65 276.48 144.44 203.70 299.12 236.45 

OnRoad2

233.35 110.29 1307.35 221.67 104.27 1244.37 221.67 104.27 1244.37 

Non –

Road3

84.97 81.01 805.50 84.97 81.01 805.50 84.97 81.01 805.50 

OffRoad3, 4

74.35 5.99 53.04 74.35 5.99 53.04 74.35 5.99 53.04 

Area3 36.18 524.35 131.71 36.18 524.35 131.71 36.18 524.35 131.71 

Totals 620.30 1029.50 2426.31 607.82 992.10 2379.06 620.87 1014.74 2471.07 

Bc06ep0 Bc06aqs1 Bc06aqs2 

NOX VOC CO NOX VOC CO NOX VOC CO 

Source 

Type 

(tpd) (tpd) (tpd) 

Point1 170.82 222.33 132.64 162.49 200.46 131.26 172.59 205.11 129.71 

On-Road2 197.28 99.39 1115.23 207.64 105.15 1171.27 207.64 105.15 1171.27 

Non –Road3 78.85 75.97 772.94 78.85 75.97 772.94 78.85 75.97 772.94 

Off-Road3, 4 73.55 6.05 53.25 73.55 6.05 53.25 73.55 6.05 53.25 

Area3 36.35 528.99 134.59 36.35 528.99 134.59 36.35 528.99 134.59 

Totals 556.85 932.73 2208.65 558.88 916.62 2263.31 568.98 921.27 2261.76 

Notes: 1. Point source emissions are based on non-startup Wednesday ARD emissions and 

average non-zero tank landing emissions 

 2. On-road emissions are season- (school or summer) and year-specific emissions 

 3. Non-road, off-road and area emissions are year-specific OSD emissions 

 4. Off-road emissions consist of airport, locomotive, and marine emissions 

5. VOC is reported as sum of CB05 species 
3-23 

3.4.3 2006 Baseline 

In general, the baseline modeling emissions are based on typical ozone season emissions, whereas 

the base case modeling emissions are episode day-specific. The biogenic emissions are an 

exception in that the same episode day-specific emissions are used in the 2006 baseline and base 

cases. In addition, the 2006 baseline non- and off-road and area source modeling emissions are the 

same as used for the 2006 base case episodes, since they are based on typical ozone season 

emissions. No fire emissions were included in the 2006 baseline. 

3.4.3.1 Point Sources

For the non-ARD point sources, the 2006 baseline emissions are the same as the modeling 

emissions used for the June 2006 (bc06ep0) and the bc06aqs2 episodes. The 2006 baseline ARD 

sources EGUs emissions were estimated using the average of the 2006 third quarter hourly ARD 

emissions. The 2006 baseline tank landing emissions were estimated as the average of the tank 

landing emissions for those 2006 episode days with non-zero emissions. The HRVOC emissions 

reconciliation developed for the 2006 base cases was used for the 2006 baseline. For the Gulf of 

Mexico, Canada, and Mexico, the 2006 baseline uses the same emissions as the base cases. 

3.4.3.2 On-Road Mobile Sources

The 2006 baseline on-road mobile source emissions are the same as used for the June 2006 

(bc06ep0) base case episode. These are the summer season modeling emissions for each of the day 

types, weekday, Friday, Saturday, and Sunday. 

3.4.4 2018 Future Base and Control Strategy 

The biogenic emissions used for the 2018 future base and control strategy modeling are the same 

episode day-specific emissions used in the base cases. In addition, similar to the 2006 baseline, no 

fire emissions were included in the 2018 future base and control strategy modeling. 

3.4.4.1 Point Sources

Outside Texas

The non-ARD point source emissions data in the regions outside Texas were obtained from the 

2018 CENRAP/RPO regional haze SIP. For the Gulf, Canada, and Mexico, the 2018 emissions are 

the same as used in the 2006 baseline. The CAIR Phase 2 emission levels were used for the EGU 

2018 emissions, with an adjustment for the ozone season. The ozone season adjustment was 

developed using the ratio of the average of the 2006 third quarter hourly ARD emissions to the 

annual average ARD emissions. 

Within Texas 

Emissions for the non-ARD point sources were projected to 2018 using the larger of the Texas 

Industrial Production Index (TIPI) or Texas-specific REMI EGAS growth factors (or banked 

Emissions Reduction Credits and Discrete Emissions Reduction Credits in nonattainment areas). 

Controls pertinent to existing HGB, DFW, and BPA SIP revisions were applied to appropriate 

point source categories (e.g., Mass Emissions Cap and Trade program (MECT), HRVOC 

Emissions Cap and Trade program (HECT), and East Texas Combustion Rule). The 2018 future 

base emissions for HECT-applicable point sources in Harris County used their HECT allocations. 

The 2018 control strategy includes a 25 percent reduction (2.69 tpd) to the HECT cap for 

applicable point sources in Harris County. 

Similar to the 2018 emissions for ARD sources outside Texas, the ARD sources within Texas used 

the CAIR Phase 2 emissions adjusted to the ozone season, with the exception of ARD sources in 

the eight-county HGB area, which are subject to the MECT rule. The 2018 emissions for ARD 

sources within the HGB area used the MECT allocations adjusted to the ozone season, similar to 

the adjustment for the ARD sources in the non-HGB area. Newly-permitted ARD sources were 

limited to the CAIR 9.5 percent set-aside for growth. The 2018 tank landing emissions were the 
3-24 

same as the 2006 baseline, but the HRVOC reconciliation was reduced by the amount in Harris 

County associated with HECT applicable source categories. 

For the eight-county HGB area, the point source NOX emissions are reduced by about 5 percent 

from the 2006 baseline (172.16 tpd) to the 2018 future base (162.75 tpd) and the VOC emissions 

are increased about 48 percent from the 2006 baseline (208.34 tpd) to the 2018 future base (309.46 

tpd). The 25 percent HECT control strategy reduces the 2018 control strategy VOC emissions to 

306.75 tpd. 

3.4.4.2 On-Road Mobile Sources

Outside Texas 

The TCEQ used the EPA’s NMIM to generate average summer weekday mobile source emissions 

by county for 2018 for all of the states beyond Texas. Average summer Friday, Saturday, and 

Sunday mobile source emissions were estimated using the weekday to Friday, Saturday, and 

Sunday ratios developed for the on-road mobile source emissions within Texas. 

Within Texas 

For the Texas counties outside of the HGB and BPA areas, summer season, day type, non-link onroad emissions were developed by TTI using 2018 projected traffic data and the EPA’s 

MOBILE6.2. For the eight-county HGB and three-county BPA (Jefferson, Hardin, and Orange) 

areas, link-based on-road emissions were developed by TTI using the TDM output projected for 

2018, and the EPA’s MOBILE6.2 on-road mobile source emissions model to generate average 

summer season on-road emissions for the four day types. The 2018 control strategy includes a 1.55 

tpd Voluntary Mobile Emission Reduction Program (VMEP) NOX reduction to the on-road mobile 

sources for alternative commuting, vehicle retrofit and replacement, and traffic flow improvement 

measures. 

For the eight-county HGB area, the on-road mobile source NOX emissions are reduced by about 74 

percent from the 2006 baseline (197.28 tpd) to the 2018 future base (50.76 tpd) and the VOC 

emissions are decreased about 49 percent from the 2006 baseline (99.39 tpd) to the 2018 future 

base (50.39 tpd). The VMEP control strategies reduce the 2018 control strategy NOX emissions to 

49.21 tpd. 

3.4.4.3 Non- and Off-Road Mobile Sources

Outside Texas 

For the states outside of Texas, the TCEQ used the EPA’s NMIM to generate average summer 

weekday non-road mobile source category emissions by county for 2018. For the off-road mobile 

source categories, aircraft, locomotive, and marine, in the states beyond Texas, the TCEQ used the 

EPA’s 2002 NEI with EGAS5 growth factors and national controls for locomotives and marine 

vessels to generate 2018 average summer weekday off-road mobile source category emissions. 

Summer weekend day emissions for the non- and off-road mobile source categories were 

developed as part of the EPS3 processing using category specific weekly activity profiles. 

Within Texas 

The TCEQ used the TexN model to generate average summer weekday non-road mobile source 

category emissions by county for 2018. 2018 county-level off-road emissions were estimated by 

adjusting the 2005 TexAER emissions with the Texas-specific REMI-EGAS growth factors, except 

for the aircraft/airport emissions in the HGB and DFW areas and marine vessels in HGB and BPA. 

The 2018 aircraft/airport emissions in the HGB and DFW areas were provided through a 

stakeholder process and these emissions are airport-specific rather than county-level. The 2018 

emissions for marine vessels in HGB and BPA were developed using emission trends provided by 

the HGB and BPA Port Authorities (Starcrest, 2000). Summer weekend day emissions for the nonand off-road mobile source categories were developed as part of the EPS3 processing using 

category specific weekly activity profiles. 
3-25 

For the eight-county HGB area, the non- and off-road mobile source NOX emissions are reduced by 

about 20 percent from the 2006 baseline (152.40 tpd) to the 2018 future base (121.37 tpd) and the 

VOC emissions are decreased about 19 percent from the 2006 baseline (82.02 tpd) to the 2018 

future base (66.49 tpd). The 2018 control strategy includes 0.70 tpd NOX reduction to non-road 

VMEP measures. 

3.4.4.4 Area Sources

Outside Texas 

The TCEQ obtained emissions data used in the 2018 regional haze SIP revision that was created by 

the CENRAP/RPO for all the states beyond Texas. 

Within Texas 

The 2018 county-level area source emissions were estimated by adjusting the 2005 TexAER 

emissions with the Texas-specific REMI-EGAS growth factors, except for the flash emissions 

category. Flash emissions will be controlled in the future as a result of the Storage Vessel and 

Degassing rule (30 Texas Administrative Code (TAC) Chapter 115), so no growth was applied and 

the same emissions were used for the 2018 future base and control strategy as the 2006 baseline. 

For the eight-county HGB area, the area source NOX emissions are increased by about 16 percent 

from the 2006 baseline (36.35 tpd) to the 2018 future base (42.04 tpd) and the VOC emissions are 

increased about 23 percent from the 2006 baseline (528.99 tpd) to the 2018 future base (650.09 

tpd). 

3.4.5 2006 and 2018 Modeling Emissions Summary for HGB 

Table 3-13: Summary of 2006 Baseline and 2018 Future Base, and 2018 Control Strategy 

Anthropogenic Modeling Emissions for HGB summarizes the typical weekday anthropogenic 

emissions in the eight-county HGB area by source type for the 2006 and 2018 future base modeling 

emissions as well as the 2018 control strategy. 

Table 3-13: Summary of 2006 Baseline and 2018 Future Base, and 2018 Control Strategy 

Anthropogenic Modeling Emissions for HGB 

2006 Baseline 2018 Baseline 2018 Control Strategy 

NOX VOC CO NOX VOC CO NOX VOC CO 

Source 

Type 

(tpd) (tpd) (tpd) 

Point 172.16 208.34 126.22 162.75 309.46 182.10 162.75 306.77 182.10 

On-Road 197.28 99.39 1115.23 50.76 50.39 733.17 49.21 50.39 733.17 

Non -Road 78.85 75.97 772.94 35.65 59.56 893.84 34.95 59.56 893.84 

Off-Road 73.55 6.05 53.25 85.72 6.93 44.71 85.72 6.93 44.71 

Area 36.35 528.99 134.59 42.04 650.09 158.99 42.04 650.09 158.99 

Totals 558.19 918.74 2202.23 376.92 1076.43 2012.81 374.67 1073.74 2012.81 

Figure 3-10: 2006 Baseline and 2018 Future Base, and 2018 Control Strategy Anthropogenic NOX

and VOC Modeling Emissions for HGB graphically compares the anthropogenic NOX and VOC 

modeling emissions for the eight-county HGB area. 
3-26 

2006 Baseline and 2018 Future Anthropogenic NOX Modeling 

Emissions HGB Eight-County Area

172 163 163

197

51 48

152

121 121

36

42 42

0

100

200

300

400

500

600

2006BL 2018FY 2018CS

NOX Emissions (TPD)

Area

Non-Road

On-Road

Points

Total NOX = 557 tpd

Total NOX = 377 tpd Total NOX = 374 tpd

2006 Baseline and 2018 Future Anthropogenic VOC Modeling 

Emissions HGB Eight-County Area

208

311 308

99

50 50 82

66 66

529

650 650

0

200

400

600

800

1000

1200

2006BL 2018FY 2018CS

VOC Emissions (TPD)

Area

Non-Road

On-Road

Points

Total VOC = 918tpd

Total VOC = 1077 tpd Total VOC = 1074 tpd

Figure 3-10: 2006 Baseline and 2018 Future Base, and 2018 Control Strategy Anthropogenic 

NOX and VOC Modeling Emissions for HGB 

Notes: 2006BL = 2006 Baseline 

 2018FY = 2018 Future Year or Future Base 

 2018CS = 2018 Control Strategy 

 In the above figures, Non-Road includes the off-road emissions 

3.5 PHOTOCHEMICAL MODELING 

To ensure that a modeling study can be successfully used as technical support for an attainment 

demonstration SIP revision, the air quality model must be scientifically sound and appropriate for 

the intended application and freely accessible to all stakeholders. In a regulatory environment, it is 

crucial that oversight groups (e.g., the EPA), the regulated community, and the interested public 

have access to and also be convinced of the suitability of the model. The following three 

prerequisites were identified for selecting the air quality model to be used in the HGB attainment 

demonstration: 
3-27 

• must have a reasonably current, peer-reviewed, scientific formulation; 

• must be available at no or low cost to stakeholders; and 

• must be consistent with air quality models being used for other Texas nonattainment or 

near nonattainment areas. 

The only model to meet all three of these criteria is CAMx. The model is based on wellestablished treatments of advection, diffusion, deposition, and chemistry. Another important 

feature is that NOX emissions from large point sources can be treated with the PiG submodel, 

which helps avoid the artificial diffusion that occurs when point source emissions are introduced 

into a grid volume. The model software and the CAMx user's guide are publicly available at 

http://www.camx.com (Environ, 2009). In addition, the TCEQ has many years of experience with 

CAMx. CAMx was used for the modeling conducted in the DFW and BPA nonattainment areas, 

as well as for modeling being conducted in other areas of Texas (e.g., San Antonio). 

CAMx Version 4.53 was used for this modeling study. Some of the features in this version include 

the ability to process in parallel on multiple processors and the following probing tools for 

sensitivity analysis: 

• Process Analysis, which provides in depth details of ozone formation, showing the various 

physical and chemical processes that determine the modeled ozone concentrations at 

specified locations and times; 

• Ozone Source Apportionment Technology (OSAT), which estimates the contribution of 

emissions from multiple geographical areas and source categories to ozone formation 

(including biogenic emissions); and 

• Anthropogenic Precursor Culpability Assessment (APCA), which reallocates ozone 

apportioned to non-controllable biogenic emissions to the controllable portion of 

precursors that participated in ozone formation. 

3.5.1 Modeling Domains and Horizontal Grid Cell Size 

Figure 3-11: CAMx Modeling Domains depicts the modeling domains used in CAMx. The 

horizontal configuration of the CAMx modeling domains consist of a 2 km x 2 km grid (2 km) 

encompassing a major portion of the HGB nonattainment counties (red box), nested within a 4 km 

x 4 km grid (4 km) encompassing both the HGB and BPA counties (blue box), nested within a 12 

km x 12 km grid (12 km) covering the eastern part of Texas (green box), nested within the outer 

(black box) 36 km x 36 km grid (36km). The 36 km outer domain was selected to minimize the 

effect of boundary conditions on predicted ozone concentrations. 
3-28 

Figure 3-11: CAMx Modeling Domains 

All grids align with the grid developed by the EPA for nationwide modeling for regional haze and 

particulate matter. Choosing a grid system compatible with an existing large-scale grid system 

serves several functions, including ability to use ready-made regional inventory data directly, 

ability to integrate the TCEQ’s modeling into regional modeling projects, and promoting 

consistency among various regional and urban modeling applications in the central United States. 

A finer resolution subdomain within the 4 km HGB-BPA domain better replicates the emission 

gradients in the narrow industrial plumes emanating from the Ship Channel and surrounding areas. 
3-29 

3.5.2 Vertical Layer Structure 

The vertical configuration of the CAMx modeling domains consists of 28 layers of varying depth 

used with the 2 km and 4 km domains, and 17 layers of varying depth used with the 12 km and 36 

km horizontal domains. The unique meteorology induced by the land/sea/bay effects and the 

diverse mixture of industrial source types, which release pollutants across a wide range of 

elevations, require more vertical layers, particularly near ground level, in the fine-grid domains. 

Table 3-14: CAMx Vertical Layer Structure for 2 km and 4 km Fine Grids and Table 3-15: CAMx 

Vertical Layer Structure for Intermediate and Coarse Grids show the vertical structuring of the 28-

layered and 17-layered configurations, respectively. 

Table 3-14: CAMx Vertical Layer Structure for 2 km and 4 km Fine Grids 

CAMx Layer MM5 Layer Top (m AGL1) Center (m AGL1) Thickness (m) 

28 38 15179.1 13637.9 3082.5 

27 36 12096.6 10631.6 2930.0 

26 32 9166.6 8063.8 2205.7 

25 29 6960.9 6398.4 1125.0 

24 27 5835.9 5367 937 

23 25 4898 4502.2 791.6 

22 23 4106.4 3739.9 733 

21 21 3373.5 3199.9 347.2 

20 20 3026.3 2858.3 335.9 

19 19 2690.4 2528.3 324.3 

18 18 2366.1 2234.7 262.8 

17 17 2103.3 1975.2 256.2 

16 16 1847.2 1722.2 256.3 

15 15 1597.3 1475.3 249.9 

14 14 1353.4 1281.6 243.9 

13 13 1209.8 1139 143.6 

12 12 1068.2 998.3 141.6 

11 11 928.5 859.5 137.8 

10 10 790.6 745.2 90.9 

9 9 699.7 654.7 90.1 

8 8 609.5 564.9 89.3 

7 7 520.2 476.0 88.5 

6 6 431.7 387.8 87.8 

5 5 343.9 300.4 87.0 

4 4 256.9 213.7 86.3 

3 3 170.5 127.7 85.6 

2 2 84.9 59.4 51.0 

1 1 33.9 16.9 33.9 

Note: 1. AGL - Above ground level. 
3-30 

Table 3-15: CAMx Vertical Layer Structure for Intermediate and Coarse Grids 

CAMx Layer MM5 Layer Top (m AGL) Center (m AGL) Thickness (m) 

17 38 15179.1 12172.9 6012.5 

16 32 9166.6 7501.3 3330.7 

15 27 5835.9 4970.9 1730 

14 23 4105.9 3565.9 1080 

13 20 3025.9 2564.5 922.9 

12 17 2103 1728.1 749.8 

11 14 1353.2 1210.6 285.2 

10 12 1068.2 929.3 277.5 

9 10 790.6 700.0 181.0 

8 8 609.5 564.9 89.3 

7 7 520.2 476.0 88.5 

6 6 431.7 387.8 87.8 

5 5 343.9 300.4 87.0 

4 4 256.9 213.7 86.3 

3 3 170.5 127.7 85.6 

2 2 84.9 59.4 51.0 

1 1 33.9 16.9 33.9 

3.5.3 Model Configuration 

The TCEQ used CAMx version 4.53, which includes a number of upgrades and features from 

previous versions. The following CAMx 4.53 options were employed: 

• Parallel processing of the chemistry and transport algorithms; 

• CB05 chemical mechanism with Euler Backward Iterative (EBI) chemistry solver; 

• Piecewise Parabolic Method (PPM) advection solver; 

• Flexi-nesting to interpolate the 4 km meteorological parameters to the 2 km CAMx 

domain; and 

• PiG treatment of larger point sources of NOX using the Greatly Reduced Execution and 

Simplified Dynamics (GREASD) Lagrangian module. 

In addition to the CAMx inputs developed from the meteorological and emissions modeling, inputs 

are needed for initial and boundary conditions, spatially resolved surface characteristic parameters, 

spatially resolved albedo/haze/ozone (i.e., opacity) and photolysis rates, and a chemistry 

parameters file. 

The TCEQ contracted with Environ (Environ, 2008b) who worked with National Aeronautics and 

Space Administration (NASA) Jet Propulsion Laboratory (JPL) to derive episode-specific 

boundary conditions from the Model for Ozone and Related Chemical Tracers (MOZART) global 

air quality model. Boundary conditions were developed for each grid cell along all four edges of 

the 36 km domain (number of horizontal grid cells [69 or 67 for east-west or north-south edges, 

respectively] times the number of vertical layers [17]) for each episode hour. This work also 

produced initial conditions for each of the episodes. The TCEQ used these episode-specific initial 

and boundary conditions for this modeling study. The top-boundary conditions were set at the 

clean concentration levels as previously derived by Environ and used in the recently approved 

DFW Ozone Attainment Demonstration SIP revision (TCEQ, 2007). 

Surface characteristic parameters, including roughness, vegetative distribution, and water/land 

boundaries, are input to CAMx via a land-use file. The land-use file provides the fractional 

contribution (0 to 1) of eleven land-use categories, as defined by the United States Geological 

Survey (USGS) LULC database. For the 36 km and 12 km domains, the TCEQ used the land-use 

files developed by Environ for the DFW SIP revision approved by the EPA in 2009, which were 
3-31 

derived from the most recent USGS LULC database. For the 2 km domain and portions of the 4 

km domain, in the vicinity of HGB, the TCEQ used updated land-use files developed by Texas 

A&M University (Popescu et al., 2008), which were derived from more highly resolved LULC data 

collected by the Texas Forest Service and the UT-CSR. 

The spatially-resolved opacity and photolysis rates are input to CAMx via a photolysis rates file 

and an opacity file, which are specific to the chemistry parameters file for the CB05 mechanism, 

which is also input to CAMx. The TCEQ used episode-specific satellite data from the Total Ozone 

Mapping Spectrometer (TOMS) to prepare the photolysis rates and opacity files. 

3.5.4 Model Performance Evaluation 

The CAMx model configuration was applied to the 2005 and 2006 base cases using the episodespecific meteorological parameters and emissions. The CAMx modeling results were compared to 

the measured ozone and ozone precursor concentrations, which resulted in a number of modeling 

iterations involving improvements to the meteorological and emissions modeling and subsequent 

CAMx modeling. A detailed performance evaluation for each of the 2005 and 2006 base case 

modeling episodes is included in Appendix C: CAMx Modeling for the HGB Attainment 

Demonstration SIP. In addition, all performance evaluation products are available on the TCEQ 

FTP site (TCEQ, 2009). 

3.5.4.1 Performance Evaluations Overview

The performance evaluation of the base case modeling demonstrates the adequacy of the model to 

correctly replicate the relationship between levels of ozone and the emissions of NOX and VOC. 

The model’s ability to suitably replicate this relationship is necessary to have confidence in the 

model’s prediction of the response of ozone to various control measures. As recommended in the 

EPA modeling guidance, the TCEQ conducted two types of performance evaluations, operational 

and diagnostic. 

3.5.4.2 Operational Evaluations

Statistical measures including the Unpaired Peak Accuracy (UPA), the Mean Normalized Bias 

(MNB), and the Mean Normalized Gross Error (MNGE) were calculated by comparing measured 

and bi-linearly interpolated modeled ozone concentrations for all episode days and regulatory 

monitors. Graphical measures including time series and scatter plots of hourly measured and bilinearly interpolated modeled ozone and where applicable, some ozone precursors (e.g., nitric 

oxide (NO), nitrogen dioxide (NO2), ETH, and CO) concentrations were developed for each 

regulatory monitor. In addition, tile plots of modeled daily maximum eight-hour ozone 

concentrations were developed and overlaid with the measured daily maximum eight-hour ozone 

concentrations. Detailed operational evaluations for each of the 2005 and 2006 base case modeling 

episodes are included in Appendix C: CAMx Modeling for the HGB Attainment Demonstration SIP. 

Statistical Evaluations 

The statistical evaluations presented focus on the comparison of the measured and modeled eighthour ozone concentrations. Figure 3-12.a: Peak Eight-Hour Ozone Concentration, Measured 

versus Modeled for the 2005 Episode Days and Figure 3-12.b: Peak Eight-Hour Ozone 

Concentration, Measured versus Modeled for the 2006 Episode Days compare the measured and 

modeled peak eight-hour ozone concentrations for each episode day of the 2005 and 2006 base 

cases, respectively. Figure 3-13.a: Mean Normalized Gross Error (MNGE) and Bias (MNB) for 

2005 Episode Days and Figure 3-13.b: Mean Normalized Gross Error (MNGE) and Bias (MNB) 

for 2006 Episode Days show the MNGE and MNB for monitored eight-hour ozone concentrations 

greater than 40 ppb for each episode day of the 2005 and 2006 base cases, respectively. Although 

there are no recommended criteria for the eight-hour UPA, MNGE, and MNB, the one-hour levels 

recommended by the EPA (i.e., plus or minus 20 percent, 30 percent, and plus or minus 15 percent, 

respectively) were used for statistical evaluations. 
3-32 

The error bars on the daily peak measured eight-hour ozone concentrations, in Figures 3-12.a: Peak 

Eight-Hour Ozone Concentration, Measured versus Modeled for the 2005 Episode Days and 3-

12.b: Peak Eight-Hour Ozone Concentration, Measured versus Modeled for the 2006 Episode 

Days represent the plus or minus 20 percent UPA range for comparison with the daily peak 

modeled eight-hour ozone concentrations. For the 37 episode days in the 2005 base cases, only 

seven days have daily peak modeled eight-hour ozone concentrations greater than 20 percent of the 

daily peak measured eight-hour ozone concentrations. For the 50 episode days in the 2006 base 

cases only ten days have daily peak modeled eight-hour ozone concentrations outside the plus or 

minus 20 percent UPA range. 
3-33 

June 19 - 29, 2005 (bc05ep1)

0

20

40

60

80

100

120

140

160

6/19/2005

6/20/2005

6/21/2005

6/22/2005

6/23/2005

6/24/2005

6/25/2005

6/26/2005

6/27/2005

6/28/2005

6/29/2005

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

July 28 - August 8, 2005 (bc05ep2)

0

20

40

60

80

100

120

140

160

7/28/2005

7/29/2005

7/30/2005

7/31/2005

8/1/2005

8/2/2005

8/3/2005

8/4/2005

8/5/2005

8/6/2005

8/7/2005

8/8/2005

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

May 20 - June 2, 2005 (bc05ep0)

0

20

40

60

80

100

120

140

160

5/20/2005

5/21/2005

5/22/2005

5/23/2005

5/24/2005

5/25/2005

5/26/2005

5/27/2005

5/28/2005

5/29/2005

5/30/2005

5/31/2005

6/1/2005

6/2/2005

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

Figure 3-12.a: Peak Eight-Hour Ozone Concentration, Measured versus Modeled for the 

2005 Episode Days 
3-34 

June 2 - June 15, 2006 (bc06ep0)

0

20

40

60

80

100

120

140

160

6/2/2006

6/3/2006

6/4/2006

6/5/2006

6/6/2006

6/7/2006

6/8/2006

6/9/2006

6/10/2006

6/11/2006

6/12/2006

6/13/2006

6/14/2006

6/15/2006

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

August 15 - September 14, 2006 (bc06aqs1)

0

20

40

60

80

100

120

140

160

8/15/2006

8/16/2006

8/17/2006

8/18/2006

8/19/2006

8/20/2006

8/21/2006

8/22/2006

8/29/2006

8/30/2006

8/31/2006

9/1/2006

9/2/2006

9/3/2006

9/4/2006

9/5/2006

9/6/2006

9/7/2006

9/8/2006

9/12/2006

9/13/2006

9/14/2006

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

September 19 - October 11, 2006 (bc06aqs2)

0

20

40

60

80

100

120

140

160

9/19/2006

9/20/2006

9/25/2006

9/26/2006

9/27/2006

10/3/2006

10/4/2006

10/5/2006

10/6/2006

10/7/2006

10/8/2006

10/9/2006

10/10/2006

10/11/2006

Episode Day

Ozone (ppb)

Peak Measured

Reg10 Peak Modeled

Ozone NAAQS

Figure 3-12.b: Peak Eight-Hour Ozone Concentration, Measured versus Modeled for the 

2006 Episode Days 

Taking into consideration that only 17 days out of the 87 days modeled in the 2005 and 2006 base 

case episodes have daily peak modeled eight-hour ozone concentrations outside the plus or minus

20 percent UPA range, the model suitably predicts the daily peak eight-hour ozone concentrations. 
3-35 

The area depicted in Figures 3-12.a: Mean Normalized Gross Error (MNGE) and Bias (MNB) for 

2005 Episode Days and 3-12.b: Mean Normalized Gross Error (MNGE) and Bias (MNB) for 2006 

Episode Days with MNGE < 30 percent and MNB < plus or minus 15 percent represents the joint 

condition for which both the MNGE and MNB are within acceptable ranges. The episode days 

labeled in red indicate those days for which daily peak measured eight-hour ozone concentrations 

were greater than or equal to 80 ppb. 

For the 31 days of the 2005 base case episodes with daily peak measured eight-hour ozone 

concentrations greater than or equal to 80 ppb 19 days meet the joint condition of having both the 

MNGE < 30 percent and MNB < plus or minus 15 percent. The average peak monitored ozone for 

those 31 days was 93.9 ppb, and the corresponding average peak modeled ozone concentration was 

101.1 ppb. The average mean normalized bias and mean normalized gross error were 11.4 and 

19.0 percent, respectively. 

For the 36 days of the 2006 base case episodes with daily peak measured eight-hour ozone 

concentrations greater than or equal to 80 ppb, 24 days meet the joint condition of having both the 

MNGE < 30 percent and MNB < plus or minus 15 percent. The average peak monitored ozone for 

those 36 days was 96.9 ppb, and the corresponding average peak modeled ozone concentration was 

95.1 ppb. The average mean normalized bias and normalized gross error were 8.8 and 16.9 percent, 

respectively. 

Taking into consideration that 43 days out of the 67 episode days in the 2005 and 2006 base cases 

with daily peak measured eight-hour ozone concentration greater than or equal to 80 ppb meet the 

joint condition of having both the MNGE < 30 percent and MNB < plus or minus 15 percent, the 

model suitably predicts the temporal pattern of daily eight-hour ozone concentrations at the various 

monitors. 
May 20 - June 2, 2005 (bc05ep0)

3-36 

Figure 3-13.a: Mean Normalized Gross Err

2005 Episode Days

ed Gro

5/20

5/21

5/22 3

5/25

5/26

5/27

5/31 6/1

2 5/ 5/26/ 24

5/28

5/29

5/30

0

15304560

-60 -45 -30 -15 0 15 30 45 60

MNB (%)

MNGE (%)

June 19 - 29, 2005 

6/20 6

6/23 6/24

6/2

0

15304560

-60 -45 -30 -15 0 

MNB (%)

MNGE (%)

July 28 - August 8, 2005 (bc05ep2)

7/31

0

15304560

-60 -45 -30 -15 0 15 30 45 60

MNB (%)

MNGE (%) 7/28 7/29

7/30

8/1

8/2

8/3

8/5

8/6

8/7

8/8

8/4
3-37 

Figure 3-13.b: Mean Normalized Gross Err2006 Episode Days 

zed Gross Err

August 15 - September 14, 

8/30

8/31 9/1

69/7

9/

0

15304560

-60 -45 -30 -15 0 

MNB (%)

MNGE (%)

June 2 - June 15, 2006 (bc06ep0)

6/2 6/3

6/4

6/66/5 6/7

6/8 6/9

6/10

6/11

6/12

6/13

6/14

6/15

0

15304560

-60 -45 -30 -15 0 15 30 45 60

MNB (%)

MNGE (%)

September 19 - October 11, 2006 (bc06aqs2)

267

10/5 10/7 11

9/19

10/3 10/9

10/10

0

15304560

-60 -45 -30 -15 0 15 30 45 60

MNB (%)

MNGE (%)

9/20

9/29/

10/4

10/6

10/8

10/

9/25
3-38 

Graphical Evaluations 

A detailed graphical evaluation of modeling results is presented in Appendix C: CAMx Modeling 

for the HGB Attainment Demonstration SIP. A selection of graphical evaluations, organized by 

episode modeled, is presented in this section. 

For each of the 2005 and 2006 base case episodes, time series comparing hourly measured (red 

dots) and modeled (blue line) ozone concentrations are shown for three monitors in the eightcounty HGB area. The monitors presented vary by episode and were selected on the basis of 

ozone measured. Included on the time-series graphic is the modeled maximum and minimum 

hourly ozone concentration within the 7 x 7 grid cell array around the monitor (green shading). 

Additionally, time series comparing hourly measured and modeled ozone concentrations are 

shown for two or three rural monitors (GRVL and LACT, and SAGA, which was not in operation 

during bc05ep0 and bc05ep1). Figure 3-14: TexAQS II Monitoring Sites Outside HGB/BPA is a 

map of rural monitors. 

Site 

Code Site Name 

GRVL Greenville, NW of 

Dallas 

CLEB Cleburne, SW of Fort 

Worth 

LACT Livingston, NW of 

Houston 

BEVL Beeville, NW of 

Corpus Christi 

CLVL Clarksville, eastern 

TX-OK border 

NTRD 

Newton, SouthCentral TX-LA 

Border 

PLTN Palestine, Central 

East Texas 

SAGA 

San Augustine, 

Central TX-LA 

Border 

WMBA Wamba, Near 

Texarkana 

HTVL Halletsville, N of 

Victoria 

ITHS Italy, S of Dallas 

PTOC Port O'Connor, 

Middle TX Coast 

TMPL Near Temple 

Figure 3-14: TexAQS II Monitoring Sites Outside HGB/BPA 

Also included for each of the episodes are logarithmically-scaled scatter plots comparing the 

hourly measured and modeled concentrations of ozone (O3), NOX, ETH, and olefins (OLE). 

Monitor sites included in the graphical representation were the three monitors with the highest 

daily maximum monitored eight-hour ozone concentrations. If one of the top three sites did not 

also have an auto-GC, the third highest ozone monitoring site was replaced by the auto-GC site 

measuring the highest ozone. OLE is a CAMx chemical surrogate representing olefinic VOC, 

such as propylene, but excluding ethylene and certain compounds known as internal olefins such 
3-39 

 

as butenes (internal olefins are represented in CB05 by the surrogate species IOLE). Both 

ethylene and propylene are HRVOC and their emissions were adjusted in the base case modeling 

by the emissions reconciliation discussed previously in Section 3.4: Emissions Modeling. 

Included on the scatter plots is the measured versus modeled Quantile-Quantile (QQ) plot, which 

first sorts independently both the measured and modeled concentrations, then plots the sorted 

values together. QQ plot data, shown as red dots, provide a measure of how close the modeled 

and measured distributions of values are to each other. If the red dots lie close to the diagonal 

one-to-one line, the model generates the correct proportions of small, medium, and large 

concentration values. 

Tile plots of the of the daily peak modeled eight-hour ozone concentrations are shown for 

selected episode days on which several monitors measured maximum daily eight-hour ozone 

concentrations greater than 84 ppb. Included on the tile plots are the monitor locations 

represented by small circles, color coded for the measured ozone concentration. The same scale 

is used for the measured and modeled maximum daily eight-hour ozone concentrations. 

Bc05ep0: May 19 through June 3, 2005 

For the bc05ep0 episode, hourly time series are presented for the Conroe Relocated (CNR2; 

CAMS 78), Northwest Harris County (HNWA; CAMS 26), and Wallisville Road (WALV; 

CAMS 617)1

 monitors in Figure 3-15: Time Series of Hourly Ozone Concentrations for Episode 

bc05ep0 at the CNR2, HNWA, and WALV Monitors. In general, the modeled ozone 

concentrations, including the 7 x 7 cell maximum-minimum range, replicate the diurnal pattern of 

the observations. The lower ozone concentrations measured during the early morning hours, 

especially at the Conroe Relocated monitor, and the very highest ozone concentrations, for 

example, Northwest Harris County, May 27, 2005, were less well replicated. The unfavorable 

comparison between the measured and modeled hourly ozone concentrations during the early 

morning hours at the Conroe Relocated monitor is likely due to local factors, such as NOX

emissions and low wind speed meteorological conditions, which reduces the areal representation 

of the monitor to much less than the 4 km grid cell size on which the modeled concentration is 

simulated. Thus, this disparity is not necessarily an indication of poor model performance since 

local factors may create greater ozone gradients. 

 

1

 Note that CAMS 617 is a non-regulatory monitor. 
3-40 

Figure 3-15: Time Series of Hourly Ozone Concentrations for Episode bc05ep0 at the 

CNR2, HNWA, and WALV Monitors 

 Note: WALV is a non-regulatory monitor. 

Figure 3-16: Time Series of Hourly Ozone Concentrations for Episode bc05ep0 at the GRVL and 

LACT Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations, except for the latter part of the episode in the rural region represented by the 

LACT monitor, for which the modeled concentrations are relatively constant throughout the day. 

The lower ozone concentrations measured during the early morning hours on some days and not 

replicated by the model are likely due to localized emissions and meteorology limiting the areal 

representation of the monitors as described previously. Overall, modeled and measured rural 

concentrations compare favorably, and modeled rural concentrations are unlikely to cause any 

substantial predictive bias within the HGB area during this episode. 
3-41 

Figure 3-16: Time Series of Hourly Ozone Concentrations for Episode bc05ep0 at the 

GRVL and LACT Rural Monitors 
3-42 

Scatter plots for the bc05ep0 episode comparing the hourly measured and modeled concentrations 

at the Wallisville Road (CAMS 617) monitor (non-regulatory monitor) are shown in Figure 3-17: 

Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor for the bc05ep0 

Episode. The model tends to over-predict ozone at the lower measured concentrations (less than 

60 ppb), but compares favorably at the higher ozone concentrations. Conversely, the model tends 

to under-predict the NOX at the lower measured concentrations, but compares favorably at the 

higher NOX concentrations. The rank correlation QQ plot for ETH is quite favorable, although 

there is notable scatter in the individual hourly comparisons. The model tends to under-predict 

the lower and higher OLE concentrations. 

Figure 3-17: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor 

for the bc05ep0 Episode 

 Note: WALV is a non-regulatory monitor. 
3-43 

Tile plots of daily maximum eight-hour ozone concentrations for May 27, May 31, June 1, and 

June 2, 2005, are shown in Figure 3-18: Tile Plots of Daily Maximum Eight-Hour Ozone 

Concentrations for May 27 and 31 and June 1 through 2, 2005. The dots represent the monitored 

value, whereas the background color represents the modeled results. Where a dot’s color matches 

the surrounding color, the model has accurately replicated the measured ozone at that monitor. 

The model replicates the areas of highest eight-hour ozone for the selected days, with the 

exception of May 31, 2005. 

Figure 3-18: Tile Plots of Daily Maximum Eight-Hour Ozone Concentrations for May 27 

and 31 and June 1 through 2, 2005 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling adequately replicates the features that produced high ozone during this 

episode. 
3-44 

Bc05ep1: June 17 through 30, 2005 

For the bc05ep1 episode, hourly time series are presented for the Deer Park (DRPK; CAMS 35), 

Houston Croquet (HCQA; CAMS 409) and Manvel Croix Park (MACP; CAMS 84) monitors in 

Figure 3-19: Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the DRPK, 

HCQA, and MACP Monitors. In general the modeled ozone concentrations, including the 7 x 7 

cell maximum-minimum range, replicate the diurnal pattern of the observations, with the 

exception of the lower ozone concentrations measured during the early morning hours, especially 

at the Manvel Croix Park (CAMS 84) monitor. 

Figure 3-19: Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the 

DRPK, HCQA, and MACP Monitors 
3-45 

Figure 3-20: Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the GRVL and 

LACT Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations, with generally favorable comparisons during the daytime. The model does 

not replicate the lower ozone concentrations measured on some days during the early morning 

hours, likely for reasons previously discussed. Overall, modeled and measured rural 

concentrations compare favorably, and modeled rural concentrations are unlikely to cause any 

substantial predictive bias within the HGB area during this episode. 

Figure 3-20: Time Series of Hourly Ozone Concentrations for Episode bc05ep1 at the 

GRVL and LACT Rural Monitors 
3-46 

Scatter plots for the bc05ep1 episode comparing the hourly measured and modeled concentrations 

at the Deer Park (CAMS 35) monitor are shown in Figure 3-21: Scatter Plots of Hourly Ozone, 

NOX, ETH, and OLE at the DRPK Monitor for the bc05ep1 Episode. The model tends to overpredict ozone at the lower measured concentrations, but compares quite favorably at the higher 

ozone concentrations. The model tends to generally over-predict the NOX, especially at the lower 

measured concentrations. The QQ plot for ETH is quite favorable, although there is some scatter 

in the individual hourly comparisons. The model tends to under-predict the lower OLE 

concentrations and while the QQ plot shows a favorable rank correlation, there is notable scatter 

in the individual hourly comparisons. 

Figure 3-21: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc05ep1 Episode 
3-47 

Tile plots of daily maximum eight-hour ozone concentrations for June 20-23, 2005, are shown in 

Figure 3-22: Tile Plots of Daily Maximum Eight-Hour Ozone Concentrations for June 20 

through 23, 2005. The model replicates the areas of highest eight-hour ozone for the selected 

days quite favorably. 

Figure 3-22: Tile Plots of Daily Maximum Eight-Hour Ozone Concentrations for June 20 

through 23, 2005 

 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling adequately replicates the features that produced high ozone during this 

episode. 
3-48 

Bc05ep2: July 26 through August 8, 2005 

For the bc05ep2 episode, hourly time series are presented for the Houston Bayland Park (BAYP; 

CAMS 53), TCEQ Houston Regional Office (HROC; CAMS 81), and Texas City (TXCT; CAMS 

620) (non-regulatory monitor) monitors in Figure 3-23: Time Series of Hourly Ozone 

Concentrations for Episode bc05ep2 at the BAYP, HROC, and TXCT Monitors. Relatively high 

ozone concentrations were measured at these monitors on several days during this episode. In 

general, the modeled ozone concentrations, including the 7 x 7 cell maximum-minimum range, 

replicate the diurnal pattern of the observations, with the exception of the lower ozone 

concentrations measured during the early morning hours, especially at the Houston Bayland Park 

(CAMS 53) monitor. 

Figure 3-23: Time Series of Hourly Ozone Concentrations for Episode bc05ep2 at the 

BAYP, HROC, and TXCT Monitors 

 Note: TXCT is a non-regulatory monitor. 
3-49 

Figure 3-24: Time Series of Hourly Ozone Concentrations for Episode bc05ep2 at the GRVL, 

LACT, and SAGA Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations, with a tendency to over-predict the peak hourly ozone concentrations during 

the daytime. The over-prediction at these rural monitors appears to follow the same pattern as the 

over-prediction of ozone concentrations in the HGB area, especially during the latter part of the 

episode. 

Figure 3-24: Time Series of Hourly Ozone Concentrations for Episode bc05ep2 at the 

GRVL, LACT, and SAGA Rural Monitors 
3-50 

Scatter plots for the bc05ep2 episode comparing the hourly measured and modeled concentrations 

at the TXCT monitor (non-regulatory monitor) are shown in Figure 3-25: Scatter Plots of Hourly 

Ozone, NOX, ETH, and OLE at the TXCT Monitor for the bc05ep2 Episode. The model generally 

tends to over-predict ozone, especially at the lower measured concentrations. Although the QQ 

plot indicates a favorable rank correlation for the NOX, there is notable scatter in the individual 

hourly comparisons. The QQ plot for ETH indicates an even more favorable rank correlation, 

again with notable scatter in the individual hourly comparisons. The model tends to underpredict the lower and higher OLE concentrations, also with considerable scatter in the individual 

hourly comparisons. 

Figure 3-25: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the TXCT Monitor for 

the bc05ep2 Episode 

 Note: TXCT is a non-regulatory monitor. 
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Tile plots of daily maximum eight-hour ozone concentrations for July 28, August 1 through 2, 

and August 6, 2005, are shown in Figure 3-26: Tile Plot of Daily Maximum Eight-Hour Ozone 

Concentrations for July 28, August 1 through 2, and August 4, 2005. The model replicates the 

areas of highest eight-hour ozone for the selected days, although it over-predicts the daily 

maximum eight-hour ozone concentrations, especially on August 1 and 2, 2005. 

Figure 3-26: Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for July 28, 

August 1 through 2, and August 4, 2005 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling only marginally replicates the features that produced high ozone during 

this episode. 
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Bc06ep0: May 31 through June 15, 2006 

For the bc06ep0 episode, hourly time series are presented for the TCEQ Houston Regional Office 

(HROC; CAMS 81), Shell Westhollow (SHWH, CAMS 410), and Wallisville (WALV; CAMS 

617) (non-regulatory monitor) monitors in Figure 3-27: Time Series of Hourly Ozone 

Concentrations for Episode bc06ep0 at the HROC, SHWH, and WALV Monitors. Relatively high 

ozone concentrations were measured at these monitors on several days during this episode. In 

general, the modeled ozone concentrations, including the 7 x 7 cell maximum-minimum range, 

replicate the diurnal pattern of the observations, with the exception of the lower ozone 

concentrations measured during the early morning hours, especially at the Shell Westhollow 

(CAMS 410) monitor. 

Figure 3-27: Time Series of Hourly Ozone Concentrations for Episode bc06ep0 at the 

HROC, SHWH, and WALV Monitors 

 Note: WALV is a non-regulatory monitor. 
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Figure 3-28: Time Series of Hourly Ozone Concentrations for Episode bc06ep0 at the GRVL, 

LACT, and SAGA Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations, with generally favorable comparisons during the daytime. The model does 

not replicate the lower ozone concentrations measured on some days during the early morning 

hours. Overall, modeled and measured rural concentrations compare favorably, and modeled 

rural concentrations are unlikely to cause any substantial predictive bias within the HGB area 

during this episode. 

Figure 3-28: Time Series of Hourly Ozone Concentrations for Episode bc06ep0 at the 

GRVL, LACT, and SAGA Rural Monitors 
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Scatter plots for the bc06ep0 episode comparing the hourly measured and modeled concentrations 

at the Wallisville Road (CAMS 617) monitor (non-regulatory monitor) are shown in Figure 3-29: 

Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor for the bc06ep0 

Episode. The model tends to over-predict ozone at the lower measured concentrations, but 

compares more favorably at the higher concentrations. Conversely, the model tends to underpredict NOX at the lower measured concentrations, and slightly over-predict at the higher NOX

concentrations. The QQ plot for ETH indicates a somewhat favorable rank correlation, although 

the model generally tends to under-predict the ETH concentrations. The model also tends to 

under-predict the OLE concentrations. 

Figure 3-29: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the WALV Monitor 

for the bc06ep0 Episode 

 Note: WLAV is a non-regulatory monitor. 
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Tile plots of daily maximum eight-hour ozone concentrations for June 5, June 8 through 9, and 

June 14, 2006, are shown in Figure 3-30: Tile Plot of Daily Maximum Eight-Hour Ozone 

Concentrations for June 5, 8 through 9, and 14, 2006. The model replicates the areas of highest 

eight-hour ozone for the selected days, although it somewhat under-predicts the daily maximum 

eight-hour ozone concentrations. 

Figure 3-30: Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for June 5, 8 

through 9, and 14, 2006 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling adequately replicates the features that produced high ozone during this 

episode. 
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Bc06aqs1: August 13 through September 15, 2006 

For the bc06aqs1 episode, hourly time series are presented for the Houston Bayland Park (BAYP; 

CAMS 53), Houston Monroe (HSMA; CAMS 406), and Deer Park (DRPK; CAMS 35) monitors 

in Figure 3-31: Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the BAYP, 

DRPK, and HSMA Monitors. Relatively high ozone concentrations were measured at these 

monitors on several days during this episode. In general, the modeled ozone concentrations, 

including the 7 x 7 cell maximum-minimum range, replicate the diurnal pattern of the 

observations, with the exception of the very highest measured hourly ozone concentrations. 

Figure 3-31: Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the 

BAYP, DRPK, and HSMA Monitors 
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Figure 3-32: Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the GRVL, 

LACT, and SAGA Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations, with generally favorable comparisons during the daytime, with the exception 

of the region represented by the GRVL monitor on August 31 and September 1, 2006, when the 

higher measured ozone concentrations are notably under-predicted. In addition, the model tends 

to over-predict the ozone concentrations during the first segment of this episode, August 15 

through 22, 2006, in the regions represented by LACT and SAGA monitors. Again, the model 

does not replicate the lower ozone concentrations measured on some days during the early 

morning hours. Overall, modeled and measured rural concentrations compare favorably enough 

that the modeled rural concentrations are unlikely to cause any substantial predictive bias within 

the HGB area during this episode. 

Figure 3-32: Time Series of Hourly Ozone Concentrations for Episode bc06aqs1 at the 

GRVL, LACT, and SAGA Rural Monitors 
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Scatter plots for the bc06aqs1 episode comparing the hourly measured and modeled 

concentrations at the Deer Park (CAMS 35) monitor are shown in Figure 3-33: Scatter Plots of 

Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for the bc06aqs1 Episode. The model 

tends to over-predict ozone at the lower measured concentrations, but compares more favorably at 

the higher concentrations. The model tends to generally over-predict NOX concentrations. The 

QQ plot for ETH indicates a somewhat favorable rank correlation, although the model tends to 

under-predict the higher ETH concentrations. The model tends to under-predict the lower range 

of OLE concentrations and also under-predicts the very highest. 

Figure 3-33: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc06aqs1 Episode 
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Tile plots of daily maximum eight-hour ozone concentrations for August 17, August 31, 

September 1, and September 7, 2006, are shown in Figure 3-34: Tile Plot of Daily Maximum 

Eight-Hour Ozone Concentrations for August 17 and 31, and September 1 and 7, 2006. The 

model replicates the areas of highest eight-hour ozone for the selected days, although it somewhat 

under-predicts the daily maximum eight-hour ozone concentrations, except on August 17, 2006, 

when the model tends to over-predict the daily maximum eight-hour ozone concentrations. 

Figure 3-34: Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for August 17 

and 31, and September 1 and 7, 2006 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling adequately replicates the features that produced high ozone during this 

episode. 
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Bc06aqs2: September 16 through October 11, 2006 

For the bc06aqs2 episode, hourly time series are presented for the Conroe Relocated (CNR2; 

CAMS 78), Galveston (GALV; CAMS 34), and Deer Park (DRPK; CAMS 35) monitors in 

Figure 3-35: Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the CNR2, 

DRPK, and GALV Monitors. Relatively high ozone concentrations were measured at these 

monitors on several days during this episode. In general, the modeled ozone concentrations, 

including the 7 x 7 cell maximum-minimum range, replicate the diurnal pattern of the 

observations, with the exception of the lower ozone concentrations measured during the early 

morning hours, especially at the Conroe Relocated (CAMS 78) monitor. 

Figure 3-35: Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the 

CNR2, DRPK, and GALV Monitors 
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Figure 3-36: Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the GRVL, 

LACT, and SAGA Rural Monitors provides a comparison of measured and modeled hourly ozone 

concentrations at rural monitors. Modeled concentrations generally replicate the diurnal pattern 

of the observations. However, the model performance in the rural areas represented by these 

monitors varies for the different segments of the episode. For example, during the first segment, 

the model notably under-predicts the peak daytime ozone concentrations at all three monitors but 

compares more favorably with the peak daytime ozone concentrations measured during the 

middle portion of the third segment. Again, the model does not replicate the lower ozone 

concentrations measured on some days during the early morning hours. Overall, modeled and 

measured rural concentrations compare favorably enough that the modeled rural concentrations 

are unlikely to cause any substantial predictive bias within the HGB area during this episode. 

Figure 3-36: Time Series of Hourly Ozone Concentrations for Episode bc06aqs2 at the 

GRVL, LACT, and SAGA Rural Monitors 
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Scatter plots for the bc06aqs2 episode comparing the hourly measured and modeled 

concentrations at the Deer Park (CAMS 35) monitor are shown in Figure 3-37: Scatter Plots of 

Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for the bc06aqs2 Episode. As shown, 

there is a favorable comparison for the mid-range and higher ozone concentrations, with a slight 

tendency for the model to over-predict the measured concentrations. Although the QQ plot for 

NOX indicates a favorable rank correlation, the model tends to generally over-predict the NOX

concentrations. The QQ plot for ETH also indicates a favorable rank correlation, although the 

model tends to over-predict the lower concentrations and under-predict the higher ETH 

concentrations. The model tends to under-predict the lower range of OLE concentrations with 

considerable scatter in the higher concentrations. 

Figure 3-37: Scatter Plots of Hourly Ozone, NOX, ETH, and OLE at the DRPK Monitor for 

the bc06aqs2 Episode 
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Tile plots of daily maximum eight-hour ozone concentrations for September 20, September 27, 

October 6, and October 11, 2006, are shown in Figure 3-38: Tile Plot of Daily Maximum EightHour Ozone Concentrations for September 20 and 27, and October 6 and 11, 2006. The model 

replicates the areas of highest eight-hour ozone for the selected days, with the exception of 

September 20, 2006, when the model under-predicts higher levels of daily maximum eight-hour 

ozone concentrations. 

Figure 3-38: Tile Plot of Daily Maximum Eight-Hour Ozone Concentrations for September 

20 and 27, and October 6 and 11, 2006 

Overall, the graphical evaluation of model performance at key monitors on key episode days 

indicates the modeling adequately replicates the features that produced high ozone during this 

episode. 

Evaluations Based on TexAQS II Data 

Appendix C: CAMx Modeling for the HGB Attainment Demonstration SIP includes extensive 

comparisons of model predictions with observations collected by the many platforms employed 

during TexAQS II. This section provides general descriptions of the major sampling platforms 

employed and presents highlights of some of the conclusions reached based on these comparisons.

In graphics comparing TexAQS II observations with modeled output, observational data are 
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typically labeled as mixing ratios, which report moles of the pollutant per mole of ambient air. In 

practical terms, the term mixing ratio is synonymous with concentration. 

Rural Monitoring Network

The TexAQS II study included a number of additional monitoring sites, which began collecting 

data in the summer of 2005 and continued until late October, 2006. During the TexAQS II 

intensive period, August 1 through October 15, 2006, a total of nine additional ozone monitors 

had been deployed in rural areas. Two of these additional monitors were the CLVL monitor near 

the Texas Oklahoma border, which also collected NOX and total reactive nitrogen (NOY) during 

this period, and the SAGA monitor, which collected NOX in addition to ozone. The SAGA 

monitor, discussed in the previous section, was one of those deployed for TexAQS II. A full 

discussion of model performance at these and other rural monitors is provided in Appendix C: 

CAMx Modeling for the HGB Attainment Demonstration SIP. 

National Oceanic and Atmospheric Administration (NOAA) WP3-3D Orion

The NOAA WP-3D (P3) flew missions in the area between August 31 and October 13, 2006, and 

sampled many species not routinely monitored, including formaldehyde, NOY, nitric acid, and a 

suite of reactive hydrocarbons. Figure 3-39: Comparison of Modeled and P3 Observed Ozone 

(O3), August 31, 2006, 14:16 to 15:33 CST, illustrates the flight of August 31, 2006, as the 

aircraft first arrived from Florida. The top two panels compare observed and modeled ozone 

concentrations (referred to on the plots as mixing ratio) along the flight track, while the bottom 

two compare the observed and modeled concentrations as a time series and a scatter plot 

superimposed with a QQ plot. The results are consistent with Figure 3-34: Tile Plot of Daily 

Maximum Eight-Hour Ozone Concentrations for August 17 and 31, and September 1 and 7, 2006, 

which showed that the model correctly placed the highest ozone concentrations geographically, 

but did not replicate the magnitude of the highest observations at the surface. The P3 flight 

shows that at the elevation of the aircraft, around 500 meters above ground level (AGL), the 

model also replicated the position of the highest ozone concentrations, but, as above, the model 

did not replicate the high concentrations seen in western Harris County. 
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Figure 3-39: Comparison of Modeled and P3 Observed Ozone (O3), August 31, 2006, 14:16 

to 15:33 CST 

The model’s under-prediction of the highest observed ozone concentrations was common 

throughout most of the flights. A detailed discussion of model comparisons with P3 data can be 

found in Appendix C: CAMx Modeling for the HGB Attainment Demonstration SIP. Some of the 

conclusions reached are that the model usually replicated the winds observed by the P3 well and 

even in cases where it showed a directional bias, usually placed the highest ozone concentrations 

in about the right location. The model reproduced the observed NOX concentrations well, but 

over-predicted CO. Most hydrocarbon species were under-predicted by the model, even after the 

HRVOC reconciliation, as was formaldehyde on most occasions. Isoprene concentrations were 

generally modeled well, but some high modeled isoprene concentrations did not match the 

observations. 

NOAA Twin Otter Tunable Optical Profiler for Aerosol and oZone (TOPAZ)

A second NOAA aircraft, a Twin Otter, carried a downward-looking lidar tuned to ozone and 

aerosol loading called TOPAZ. Data from this instrument were valuable because they allowed 

modeled ozone to be compared with measurements vertically through up to 3,000 meters AGL. 

The instrument was flown on 13 missions between August 15 and September 13, 2006. The top 

two panels of Figure 3-40: TOPAZ-Observed and Modeled Ozone Concentrations on August 31, 

2006 compare observed and measured ozone concentrations between 255 and 377 meters AGL, 

which is the fifth vertical modeling layer. The lower plots are ozone curtains, showing ozone 

concentrations from the surface up to the aircraft elevation along the entire flight path and show 

that at around 15:00 the under-prediction carried upwards to over 1,500 meters. The TOPAZ 

concentrations near the surface are highly variable and may include contamination from surface 

features and thus, may not accurately reflect ozone concentrations within the first 200 meters. 
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Figure 3-40: TOPAZ-Observed and Modeled Ozone Concentrations on August 31, 2006 

Like the P3, the TOPAZ also showed that the model usually placed the highest ozone 

concentrations in the correct location, but generally under-predicted the observed peak 

concentrations. A comparison between the TOPAZ measurements of ozone concentration with 

those made by the P3 (the two flew together on only two days), showed relatively good 

agreement. The TOPAZ measured ozone concentrations above the mixed layer on most days that 

were notably higher than the model predicted. 

The Research Vessel (RV) Ronald H. Brown

The NOAA RV Ron Brown arrived in the HGB area on August 15, 2006, and collected data until 

its departure on September 13. The ship carried a wide array of sampling platforms onboard and 

provided extensive data collected in the Gulf of Mexico, Galveston Bay, and in the Houston Ship 

Channel. Figure 3-41: Comparison of Ozone Concentrations Observed by the RV Ron Brown 

with Modeled Concentrations, August 31, 2006, 08:00 to 16:30, compares observed and modeled 

ozone for the period from 8:00 to 16:30 on August 31. The ship sailed from Barbour’s Cut into 

the Gulf of Mexico, and then along the coast to near Freeport. This figure shows that the model 

predicted the observed concentrations of ozone very well from Barbour’s Cut to Galveston and 

then showed a brief period of over-prediction as the observed concentrations dipped between 

11:00 and 12:00. The decrease in measured ozone concentrations coincided with a period of very 

high NOX concentrations observed in the channel between Galveston Island and Bolivar 

Peninsula. The observed NOX was probably emitted by local ship traffic and likely reduced the 

ozone concentrations through titration. As the ship sailed into the Gulf of Mexico, it measured 

unusually high ozone concentrations moving onshore, which the model under-predicted. This 

under-prediction may be the result of long-range transport or of model boundary conditions that 

are too low on this day. As an alternative, the under-prediction may have resulted from air 

advected out into the Gulf of Mexico the previous day from the Houston or Beaumont areas. 
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More often, the ship encountered low ozone concentrations in the Gulf of Mexico, particularly 

under southerly wind conditions, which the model often over-predicted. 

Figure 3-41: Comparison of Ozone Concentrations Observed by the RV Ron Brown with 

Modeled Concentrations, August 31, 2006, 08:00 to 16:30 

Ozone Sondes

A number of ozone sondes, lightweight and compact balloon-borne instruments, were launched 

from the University of Houston (UH) campus southeast of downtown Houston and also from the 

deck of the RV Ron Brown in 2006. Ozone monitors attached to these balloons provide an 

opportunity to evaluate the model’s vertical ozone distribution. Figure 3-42: Comparison of 

Modeled and Observed Vertical Ozone Profiles from Two Sonde Launches at UH Campus and 

One Sonde Launch from the RV Ron Brown in the Gulf of Mexico, August 31, 2006, shows three 

vertical ozone profiles measured by sondes launched from the UH campus on August 31, 2006, 

compared with modeled concentrations on that day. The left-hand panel shows that for the 

morning (6:00 a.m.) launch from the UH campus, ozone concentrations fluctuated with altitude 

within the first 1,500 meters. This effect may not represent actual variability in concentrations, 

however, since the measurements made by the sondes launched from UH were susceptible to 

interference by sulfur dioxide (SO2); each molecule of SO2 encountered by the instrument 

effectively cancels out one molecule of ozone. Because there are numerous SO2 sources 

relatively close to the UH campus, it is very likely that the balloon may have encountered one of 

these plumes during ascent. 

Aside from the fluctuations, the model replicated ozone concentrations reasonably well up to 

around 1,200 meters. The model under-predicted ozone concentrations up to about 5,000 meters, 

but predicted concentrations fairly well above that altitude. At 12:29 p.m. (center panel), the 

model slightly over-predicted ozone concentrations near the surface, but observed ozone 

concentrations increased dramatically within the first 100 meters or so to 30 ppb greater than 
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modeled concentrations. Unlike the notches seen in the morning launch, this effect is most likely 

caused by ozone scavenging by nearby NOX sources, probably vehicular traffic. More 

significantly, after the first few meters, the model continued to under-predict observed ozone 

concentrations up to 4,000 meters. 

The right-hand panel of Figure 3-42: Comparison of Modeled and Observed Vertical Ozone 

Profiles from Two Sonde Launches at UH Campus and one Sonde Launch from the RV Ron 

Brown in the Gulf of Mexico, August 31, 2006 shows ozone concentrations observed and modeled 

for a sonde launch from the deck of the RV Ron Brown, coincident with the 12:29 p.m. launch 

from the UH. In this case, the model initially over-predicted ozone concentrations near the 

surface by 15 ppb, but within the first 100 meters or so the sonde recorded a drop in ozone 

concentrations, followed by a rapid rise. This feature is probably due to the balloon encountering 

sulfate emissions from a ship plume, possibly from a passing ship or from the Ron Brown. The 

modeled and observed profiles crossed at about 1,200 meters, and then the observations exceeded 

the model by 10 to 20 ppb up to 4,000 meters. Farther above, the observations oscillated around 

the modeled values. 

Ozone Profiles August 31, 2006

Hour 6,UH Hour 12, UH Hour 12, RHB

Figure 3-42: Comparison of Modeled and Observed Vertical Ozone Profiles from Two 

Sonde Launches at UH Campus and One Sonde Launch from the RV Ron Brown in the 

Gulf of Mexico, August 31, 2006 

Notes: TOPP = Tropospheric Ozone Pollution Project 

 RHB = Ronald H. Brown 

Moody Tower

The Moody Tower site is located atop a dormitory on the UH campus southeast of downtown 

Houston. The site is useful because it is located 60 meters AGL (in model layer 2), hence is 

insulated from some of the more localized emission sources. Much of the Moody Tower data has 

been incorporated into the standard model performance evaluation processing performed at the 
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TCEQ for surface sites, with special provisions to use modeled concentrations from layer 2 

instead of layer 1. Within this framework, the Moody Tower data offers measurements of some 

atmospheric constituents explicitly tracked in the CB05 mechanism, including nitric acid, nitrous 

acid, and formaldehyde. In addition, researchers at this site collected a wealth of information on 

radicals associated with photochemical ozone production. These data are used in conjunction 

with CAMx Chemical Process Analysis in Section 5.1: QUANTITATIVE CORROBORATIVE 

ANALYSIS of this document. 

Other TexAQS II Data

During TexAQS II, formaldehyde data were collected at two sites, Lynchburg Ferry and Houston 

Regional Monitor-3. These data have been incorporated into the TCEQ model performance 

evaluation database and are being used in routine comparisons between modeled and observed 

concentrations. 

Some additional TexAQS II data have not yet been used for model performance evaluation 

because they were not yet available in a usable form, but may be useful in the future. These data 

sources include the Houston Triangle project, the Baylor Aztec flights, the Solar Occultation Flux 

(SOF) measurements, “smart” balloon data, Differential Optical Absorption Spectroscopy 

(DOAS) observations, and satellite observations. 

3.5.4.3 Diagnostic Evaluations

Since future design values are based solely on the model’s relative response and not on the 

magnitude of its future case ozone predictions, evaluating the model’s response to emission 

changes becomes at least as important as evaluation of its ability to reproduce historically 

observed events. The EPA modeling guidance recommends several possible means of assessing 

model response to emission changes. However, most of these methods are either indirect 

(probing tools, alternative base cases, most observation-based models) or are difficult to employ 

in practice (retrospective analyses). In this section the TCEQ employs three tests to evaluate the 

model’s response to emission changes. The first of these is a sensitivity analysis designed to test 

the model’s response to a hypothetical inventory change, specifically, an increase in emissions 

from flares. The second test is a retrospective analysis that uses an existing 2000 baseline 

inventory to test the model’s ability to predict ozone design values in a previous year. The third, 

a weekday-weekend analysis, is based on observational modeling designed to assess an area’s 

VOC- or NOX-sensitivity. 

Flare Sensitivity Modeling 

The TCEQ has been evaluating flares as a potential source of underreported VOC emissions since 

TexAQS 2000. Flare monitoring requirements in the HRVOC rules in 30 TAC Chapter 115, 

Subchapter H, Division 1, were adopted in 2002 and designed to provide more accurate 

information on HRVOC and total flow rate to the flares. More recently, the TCEQ has been 

evaluating potential issues with the destruction efficiencies used to calculate emissions from 

flares. Due to the open combustion nature of flares, direct measurement of flare emissions or 

verification of flare destruction efficiencies is problematic. Remote sensing technologies such as 

differential absorption lidar (DIAL) can be used to estimate flare emissions and destruction 

efficiency. Recent work with DIAL during TexAQS II indicated destruction efficiencies on an 

actual industrial flare were less than assumed for reporting purposes. However, the use of such 

remote sensing technology is expensive and currently limited to research activities such as 

TexAQS II. Therefore, companies must still use an assumed destruction efficiency to calculate 

VOC emissions from flares. Most companies assume a flare destruction efficiency of 98 to 99 

percent, meaning the VOC emission rate is only one or two percent of the VOC mass rate sent to 

the flare. These assumptions are based on a small number of controlled studies conducted in the 

early 1980s and may not represent flare operations in real-world conditions. Furthermore, the 

chemistry that occurs within the flare flame is not well-understood in the majority of situations. 

Products of incomplete combustion may be formed and emitted from flares in addition to 
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uncombusted VOC from the material sent to the flares. Some researchers have speculated that 

flares could emit formaldehyde in sufficient quantities to significantly enhance photochemical 

reactivity in the flare plumes (Castineira and Edgar, 2006; Robinson et al., 2008). 

To study the sensitivity of the model to potential unaccounted-for flare emissions, a model run 

was conducted in which flare emissions were increased ten-fold (10X). This is equivalent to 

reducing assumed flare destruction efficiency from 99 percent to 90 percent. At the same time, 

the potential source contribution function (PSCF)-based HRVOC reconciliation was removed. 

The net effect on emissions was to replace the 23.1 tpd of ground-level HRVOC emissions with 

321.6 tpd of elevated flare VOC, of which 87.9 tpd is HRVOC. 

Figure 3-43: Comparison of P3 Measurements with Base Case and Enhanced Flare Emissions; 

observed ethylene, formaldehyde, and ozone compared to modeled concentrations using the base 

case inventory, and (right) the base case inventory with 10X flare VOC emissions, minus the 

HRVOC reconciliation compares (A) modeled ETH, (B) formaldehyde (FORM), and (C) Ozone 

concentrations with observations made on the NOAA WP-3D Orion aircraft during TexAQS II, 

inside the 2 km HGB modeling grid. In each row, the left-hand panel shows the comparison 

using the 2005-2006 base case modeling inventory, while the right-hand panel shows a similar 

comparison using the inventory with the ten-fold increase in flare VOC emissions (and 

concurrent removal of the HRVOC reconciliation discussed earlier in Section 3.4.2.1: Point 

Sources). The green dots represent actual data pairs. The red dots are plotted by matching the 

smallest observed value with the smallest modeled value, then the next smallest of each, and so 

on. The resulting QQ plot provides a means to compare the two distributions; if it lies close to 

the diagonal line, then the model is simulating the correct proportions of small, medium, and 

large concentrations of the pollutant. 
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(A)

(B)

(C)

Figure 3-43: Comparison of P3 Measurements with Base Case and Enhanced Flare 

Emissions; observed ethylene (Panel A), formaldehyde (Panel B), and ozone (Panel C) 

compared to modeled concentrations using (left) the base case inventory, and (right) the 

base case inventory with 10X flare VOC emissions, minus the HRVOC reconciliation 

The flare sensitivity markedly improves the distribution of modeled ethylene concentrations 

compared with observations and also improves modeled formaldehyde and ozone concentrations, 
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although the highest modeled ozone concentration remains at about 105 ppb compared with 

observations ranging to near 145 ppb. This discrepancy is at least partly due to the 

incommensurability of the measurements: modeled values represent averages over one hour over 

a 2 km x 2 km region (also across a vertical depth depending on model layer), while the aircraft 

measurements are essentially single points in space and time. However, the 10X flare sensitivity 

modeling degrades performance for some pollutants at the surface, as illustrated in Figure 3-44: 

Log-Log Plots of Observed vs. Modeled Ethylene at Deer Park September 19 through October 11, 

2006; with base case inventory, and base case inventory with 10X flare emissions minus the 

HRVOC reconciliation, which compares modeled and observed ozone concentrations at Deer 

Park to base case and 10X flare emissions (note that these plots use a log-log scale; blue dots 

represent observed-modeled pairs, and red dots indicate the QQ plot). 

Figure 3-44: Log-Log Plots of Observed vs. Modeled Ethylene at Deer Park September 19 

through October 11, 2006; with (Left) base case inventory, and (Right) base case inventory 

with 10X flare emissions minus the HRVOC reconciliation 

Figure 3-45: Daily Peak Modeled Eight-Hour Ozone Concentrations with Base Case Inventory 

and 10X Flare Inventory; the difference between the two plots (Flare 10X – Reg 10) is shown at 

right shows the effect of the 10X flare VOC increase on eight-hour peak ozone concentrations on 

October 6, 2006. The ozone plume, while still under-estimated, clearly matches the observed 

surface concentrations better with the 10X flare inventory (center) than the base case inventory 

(left). Observed eight-hour peak ozone concentrations are shown as small circles at the monitor 

locations. 
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Figure 3-45: Daily Peak Modeled Eight-Hour Ozone Concentrations with Base Case 

Inventory (Left) and 10X Flare Inventory (Center); the difference between the two plots 

(Flare 10X – Reg 10) is shown at right 

In addition to the 10X VOC sensitivity, the TCEQ ran a sensitivity in which only HRVOC 

emissions from flares were increased (also 10X). A third sensitivity further modified the 10X 

HRVOC sensitivity to add a formaldehyde boost equal to 10 percent of the added HRVOC 

emissions. Results of these sensitivities can be found in Appendix C: CAMx Modeling for the 

HGB Attainment Demonstration SIP. 

More work is needed to determine whether a flare adjustment is superior to the surface-level 

reconciliation currently in use. The TCEQ plans to investigate using a PSCF-based technique 

applied to flare emissions in the near future. 

Retrospective Modeling – 2000 Backcast 

The purpose of this test is to test the model in a forecast (in this case, backcast) mode, where the 

answer is known in advance. Retrospective modeling is usually difficult to implement in practice 

because of the need to create an inventory, but a 2000 inventory was already available. In this 

test, most of the 2006 baseline inventory was replaced with a baseline inventory previously 

developed for the 2000 ozone episode used in prior SIP revisions. However, the episode dayspecific biogenic emissions for the 2005 and 2006 episodes were not replaced, as is also the 

practice when modeling a future base emissions inventory. Similarly, the 2005 and 2006 

meteorology was used with the 2000 baseline emissions as is the procedure when modeling with 

the future emissions. 

Since the model predictions of the typical future design values are based on a DVB, which is the 

average of three regulatory design values (EPA, 2007), the quantity forecast in this test is not a 

specific future year’s design value but rather the average of three years. Thus, the regulatory 

design values for 2000, 2001, and 2002 were averaged in the same manner as the 2006 DVB was 

calculated as the average of the 2006, 2007, and 2008 regulatory design values. Table 3-16: 

2000 Baseline Design Value Calculation for Retrospective Analysis shows the calculation. Only 

monitors that had at least one regulatory design value in the 2000-2002 window and also in the 

2006-2008 window were used. 
3-74 

Table 3-16: 2000 Baseline Design Value Calculation for Retrospective Analysis 

Modeling CAMS Eight-Hour DV

Site Code Number 2000 2001 2002 

2000 

Baseline DV 

BAYP 53 111 110 100 107.0 

C35C 403 101 97 93 97.0 

DRPK 35 112 108 103 107.7 

GALV 34 108 98 89 98.3 

HALC 8 111 108 107 108.7 

HCQA 409 110 104 102 105.3 

HLAA 408 96 91 83 90.0 

HNWA 26 108 105 101 104.7 

HOEA 1 102 103 101 102.0 

HROC 95 - - 95 95.0 

HSMA 406 106 93 90 96.3 

HWAA 405 105 98 89 97.3 

SHWH 410 102 104 95 100.3 

Once the model was run with the 2000 baseline emissions, RRFs were calculated. In a 

retrospective analysis, most of the RRFs are expected to be greater than 1 because ozone has 

decreased since the retrospective year. Table 3-17: 2000 Projected DVs Compared with 

Calculated DVs shows the calculated RRFs and the respective projected 2000 design values, 

compared with those listed in Table 3-16: 2000 Baseline Design Value Calculation for 

Retrospective Analysis. 

 

Table 3-17: 2000 Projected DVs Compared with Calculated DVs 

Modeling 

Site Code 

CAMS 

Number 

2006 

Baseline 

DV 

2006-to2000 

RRF 

Projected 

2000 DV 

Baseline 

2000 DV 

BAYP 53 96.7 1.11 107.0 107.0 

C35C 403 79.0 1.18 93.5 97.0 

DRPK 35 92.0 1.18 108.1 107.7 

GALV 34 83.0 1.11 92.5 98.3 

HALC 8 85.0 1.15 97.9 108.7 

HCQA 409 87.0 1.13 98.6 105.3 

HLAA 408 77.7 1.11 86.4 90.0 

HNWA 26 89.0 1.13 100.4 104.7 

HOEA 1 80.3 1.17 94.0 102.0 

HROC 95 79.7 1.15 91.6 95.0 

HSMA 406 90.3 1.16 104.8 96.3 

HWAA 405 76.3 1.14 86.9 97.3 

SHWH 410 92.3 1.11 102.9 100.3 

For two sites, Houston Bayland Park (CAMS 53) and Deer Park (CAMS 35), the projections 

were identical, or nearly identical, to the calculated baseline values. For all other sites but one, 

the model-projected 2000 DVs were lower than the calculated values, indicating that the model 
3-75 

did not respond as well to emission changes as the actual airshed for these sites. In only one case 

did the model respond notably more strongly than the airshed, Houston Monroe (CAMS 406). 

In conclusion, the modeled response generally was lower than the actual airshed’s response to 

2000-2006 emission changes. This conclusion gives confidence going forward that the model’s 

predictions are conservative, and that future ozone concentrations may be even lower than 

predicted by the model. 

Observational Modeling – Weekday/Weekend 

Weekend emissions of NOX in urban areas tend to be lower than weekday emissions because of 

fewer miles driven. The effect is most pronounced on weekend mornings, especially Sundays, 

since commuting is much lower than weekdays. In a detailed analysis presented in Appendix C: 

CAMx Modeling for the HGB Attainment Demonstration SIP an analysis using modeled 

Wednesdays, Saturdays, and Sundays is described, but the results were rather inconclusive 

because of small sample sizes (15 Wednesdays and 11 each Saturdays and Sundays). A more 

comprehensive analysis was undertaken to simulate more of each day type; in three separate runs 

each day’s modeled emissions were substituted with, Wednesday, Saturday, and Sunday 

emissions. These runs provided a total of 88 each Wednesdays, Saturdays, and Sundays. 

For comparison, 6:00 a.m. NOX concentrations were averaged for every Wednesday, Saturday, 

and Sunday between May 15 and October 15 in the years 2005 through 2008, which gives over 

100 of each day (less for some monitors because of missing data). Figure 3-46: Mean Observed 

NOX Concentrations at HGB Monitors as a Percentage of Wednesday Mean Values, May 15 

through October 15, 2005 through 2008 shows observed and modeled 6:00 a.m. NOX

concentrations at 15 sites in the HGB area. Except for anomalous behavior at Galveston Airport 

(CAMS 34), all monitors show observed and modeled NOX concentrations that decline 

monotonically from Wednesday through Saturday to Sunday. The observed concentrations 

(excluding Galveston Airport (CAMS 34)) show similar percentage declines, but the modeled 

values have much greater variability, with sites in eastern Harris County (near the Ship Channel) 

showing the slowest declines. This effect could be due to the model mixing down industrial NOX

emissions too rapidly. 

2005-8 Mean Observed 6 AM NOX Concentrations 

as a % of Wednesday

20%

40%

60%

80%

100%

120%

Wed Sat Sun

BAYP

C35C

CNR2

DRPK

GALC

HALC

HCHV

HLAA

HNWA

HOEA

HTCA

LKJK

LYNF

MACP

SBFP

Mean Modeled 6 AM NOX Concentrations 

as a % of Wednesday, all-WSS Runs

20%

40%

60%

80%

100%

120%

Wednesday Saturday Sunday

BAYP

C35C

CNR2

DRPK

GALC

HALC

HCHV

HLAA

HNWA

HOEA

HTCA

LKJK

LYNF

MACP

SBFP

Figure 3-46: Mean Observed NOX Concentrations at HGB Monitors as a Percentage of 

Wednesday Mean Values, May 15 through October 15, 2005 through 2008 

Figure 3-47: Observed and Modeled Daily Peak Eight-Hour Ozone Concentrations as a 

Percentage of Wednesdays shows observed and modeled daily peak eight-hour ozone 

concentrations as a percentage of Wednesdays for the same sites. Because the modeled episodes 

represent periods of higher-than-average ozone concentrations, the observed concentrations were 

filtered to remove values less than 40 ppb. The left-hand panel of the figure shows observed 
3-76 

concentrations trending downward for nearly all sites, but some seem to rebound on Sunday and 

exceed the respective Saturday concentrations. This effect is probably due to filtering 

concentrations below 40 ppb, which removes very low concentrations from the average. 

2005-8 Mean Observed 8-Hour Peak O3 Concentrations

as a % of Wednesday (days with min. 40 ppb 8-hour peak O3)

80%

90%

100%

110%

120%

Wed Sat Sun

BAYP

C35C

CNR2

DRPK

GALC

HALC

HCHV

HCQA

HLAA

HNWA

HOEA

HROC

HSMA

HTCA

HWAA

LKJK

MACP

SBFP

SHWH

2005-8 Mean Observed 8-Hour Peak O3 Concentrations

as a % of Wednesday (days with min. 40 ppb 8-hour peak O3)

80%

90%

100%

110%

120%

Wed Sat Sun

BAYP

C35C

CNR2

DRPK

GALC

HALC

HCHV

HCQA

HLAA

HNWA

HOEA

HROC

HSMA

HTCA

HWAA

LKJK

MACP

SBFP

SHWH

Mean Modeled 8-Hour Peak Ozone Concentrations as a % 

Of Wednesday, all-WSS Runs

80%

90%

100%

110%

120%

Wednesday Saturday Sunday

BAYP

C35C

CNR2

DRPK

GALC

HALC

HCHV

HCQA

HLAA

HNWA

HOEA

HROC

HSMA

HTCA

HWAA

LKJK

LYNF

SBFP

SHWH

Figure 3-47: Observed and Modeled Daily Peak Eight-Hour Ozone Concentrations as a 

Percentage of Wednesdays 

While the modeled concentrations are very tightly clustered in the figure, they universally decline 

from Wednesday through Saturday to Sunday, similar to the pattern shown by the observations 

(ignoring the anomalous rebound effect). The airshed and model both show sensitivity to NOX

reductions, at least for days with some ozone-forming potential. In fact, the airshed seems to 

show greater sensitivity to NOX than the model, which suggests that anticipated reductions to 

motor vehicle emissions over the next several years may be more effective than suggested by the 

model. 

3.6 BASELINE (2006) AND FUTURE CASE (2018) MODELING 

3.6.1 2006 Baseline Modeling 

The TCEQ selected 2006 as the baseline year for conducting the attainment modeling. Two 

features of the 2006 baseline year are used in the attainment modeling. First, the 2006 baseline 

year identifies the three consecutive years (2006, 2007, and 2008) with design values (DVs) that 

include the fourth high of the 2006 baseline year. These three DVs are averaged to calculate the 

baseline design value (DVB), as previously illustrated in Figure 3-1: Baseline Design Value 

Calculation Illustration. Second, typical 2006 ozone season day (OSD) emissions were 

developed, as previously summarized in Table 3-13: Summary of 2006 Baseline and 2018 Future 

Base, and 2018 Control Strategy Anthropogenic Modeling Emissions for HGB. 

The typical 2006 OSD emissions were modeled for all episode days to calculate the denominator 

of the RRF for each of the regulatory monitors. The denominator of the RRF is the average of the 

modeled maximum daily eight-hour ozone concentrations for those days with modeled 

concentrations greater than or equal to 85 ppb, within a grid cell array about each monitor. 

Figure 3-48: Near Monitoring Site Grid Cell Array Size shows a map of the 2 km subdomain 

nested in a portion of the 4 km x 4 km fine grid domain depicting the monitors, and the extent of 

7 x 7, 5 x 5, and 3 x 3 grid cell arrays based on the 2 km grid. The TCEQ has calculated RRF 

values for each of these array sizes, but used a 7 x 7 grid array about each monitor. 
3-77 

Figure 3-48: Near Monitoring Site Grid Cell Array Size 

The monitor-specific denominator of the RRF is calculated as the average of the modeled daily 

maximum eight-hour ozone concentrations above 84 ppb at that monitor. Per the EPA’s 

modeling guidance, if there are fewer than 10 days with 2006 baseline modeled concentrations 

greater than 84 ppb, then days with modeled concentrations less than or equal to 84 ppb can be 

used so the average is based on at least 10 days. Table 3-18: 2006 DVB, RRF Denominator 

(RRFD), and Number of 2006 Baseline Modeled Days Averaged summarizes the DVB and the 

denominator of the RRF for the HGB regulatory monitors. There is also one non-regulatory 

monitor, Wallisville Road (CAMS 617), which has a DVB greater than or equal to 85 ppb. 

Including non-regulatory monitors that have a DVB and a RRF denominator greater than or equal 

to 85 ppb mitigates the need to conduct an unmonitored area analysis for the area represented by 

the monitor, as required by the EPA’s modeling guidance. 
3-78 

Table 3-18: 2006 DVB, RRF Denominator (RRFD), and Number of 2006 Baseline Modeled 

Days Averaged 

Monitor 

Designation Site Code 

2006 DVB

(ppb)** 

2006 RRFD

(ppb) 

Modeled 

Days 

Averaged 

Houston East (CAMS 1) HOEA 80.3 96.662 20 

Aldine (CAMS 8) HALC 85.0 97.069 17 

Channelview (CAMS 15) HCHV 82.7 96.609 16 

Northwest Harris County 

(CAMS 26) HNWA 89.0 93.773 21 

Galveston Airport (CAMS 34) GALV 83.0 95.411 10 

Deer Park (CAMS 35) DRPK 92.0 95.032 20 

Seabrook Friendship Park 

(CAMS 45) SBFP 85.3 92.227 14 

Houston Bayland Park (CAMS 53) BAYP 96.7 96.949 28 

Conroe Relocated (CAMS 78) CNR2 83.0 91.325 10 

TCEQ Houston Regional Office 

(CAMS 81) HROC 79.7 96.776 22 

Manvel Croix Park (CAMS 84) MACP 90.7 94.912 23 

Clinton (CAMS 403) C35C 79.0 98.297 20 

Houston Monroe (CAMS 406) HSMA 90.3 95.494 25 

Croquet (CAMS 409) HCQA 87.0 96.338 26 

Shell Westhollow (CAMS 410) SHWH 92.3 101.532 22 

Houston Texas Avenue 

(CAMS 411) HTCA 79.3 97.392 23 

Lynchburg Ferry (CAMS 1015) LYNF 81.7 95.742 16 

Wallisville Road (CAMS 617)* WALV 92.0 95.091 13 

* Wallisville Road (CAMS 617) is not a regulatory monitor; 

** Values 85 ppb or greater are shown in red. 

3.6.2 Future Baseline Modeling 

Similar to the 2006 baseline modeling, the 2018 modeling was conducted for each of the episode 

days using the projected 2018 ozone season day emissions, as previously summarized in Table 3-

13: Summary of 2006 Baseline and 2018 Future Base, and 2018 Control Strategy Anthropogenic 

Modeling Emissions for HGB. Using the same days as used in the 2006 baseline modeling to 

calculate the RRFD, an RRF numerator (RRFN) was calculated as the average of the of the 2018 

modeled maximum daily eight-hour ozone concentrations within the 7 x 7 grid cell array about 

each monitor. The RRF at each monitor was calculated as the quotient of the RRFN and RRFD, 

and the 2018 future design value (DVF) at each monitor was estimated as per EPA’s modeling 

guidance, by the multiplying the 2006 DVB by the RRF. Table 3-19: Summary of 2006 Baseline 

Modeling, RRF, and Future Design Values summarizes the 2006 DVB, RRF and 2018 DVF at 

each of the regulatory monitors as well as the Wallisville Road (CAMS 617) monitor (nonregulatory monitor). 
3-79 

Table 3-19: Summary of 2006 Baseline Modeling, RRF, and Future Design Values 

Monitor 

Designation Site Code 

2006 DVB

(ppb)** RRF 

2018 DVF

(ppb) 

Houston East (CAMS 1) HOEA 80.3 0.959 77.0 

Aldine (CAMS 8) HALC 85.0 0.920 78.2 

Channelview (CAMS 15) HCHV 82.7 0.958 79.2 

Northwest Harris County 

(CAMS 26) HNWA 89.0 0.869 77.4 

Galveston Airport (CAMS 34) GALV 83.0 0.956 79.3 

Deer Park (CAMS 35) DRPK 92.0 0.958 88.2 

Seabrook Friendship Park 

(CAMS 45) SBFP 85.3 0.945 80.6 

Bayland Park (CAMS 53) BAYP 96.7 0.900 87.0 

Conroe Relocated (CAMS 78) CNR2 83.0 0.877 72.8 

Houston Regional Office (CAMS 

81) HROC 79.7 0.960 76.5 

Manvel Croix Park (CAMS 84) MACP 90.7 0.900 81.6 

Clinton (CAMS 403) C35C 79.0 0.959 78.5 

Houston Monroe (CAMS 406) HSMA 90.3 0.935 84.4 

Croquet (CAMS 409) HCQA 87.0 0.900 78.3 

Shell Westhollow (CAMS 410) SHWH 92.3 0.859 79.3 

Houston Texas Avenue (CAMS 

411) HTCA 79.3 0.942 74.7 

Lynchburg Ferry (CAMS 1015) LYNF 81.7 0.961 78.5 

Wallisville Road (CAMS 617)* WALV 92.0 0.960 88.3 

* Wallisville Road (CAMS 617) is not a regulatory monitor; 

** Values 85 ppb or greater are shown in red. 

The 2018 baseline attainment modeling projects two regulatory monitors (Houston Bayland Park 

(CAMS 53) and Deer Park (CAMS 35)) and one non-regulatory monitor (Wallisville Road 

(CAMS 617)) to have DVFs greater than 84 ppb. 

3.6.2.1 Matrix Modeling

A series of modeling sensitivities using across-the-board percentage reductions to the 2018 

baseline modeling emissions from sources in the eight-county HGB area was conducted. The 

results of the modeling were used to estimate the amount of NOX and/or VOC emissions 

reduction needed to reduce the DVFs for each of the three monitors to 85 ppb. Figure 3-49: DVF

versus NOX and/or VOC Emissions Reduction Response Curves for the BAYP, DRPK, and WALV 

Monitors graphically shows the response of the DVFs for the Houston Bayland Park (CAMS 53), 

Deer Park (CAMS 35), and WALV (non-regulatory monitor) monitors to reductions in emissions 

of NOX and/or VOC from sources in the eight-county HGB area. 
Deer Park Future Ozone Design Value 

NOx, VOC and NOx+VOC Reduc

7072747678808284868890

0 10 20 30 40 

Across-the-Board Percent Re

Future Design Value (ppb)

19.95%

7072747678808284868890

0 10 20 30 40 50 60

Across-the-Board Percent Reduction

Future Design Value (ppb)

VOC-RdctnNOx+VOC-RdctnNOx-RdctnNAAQS

% Rdctn NOx VOC 0 All 0 025 All 94 26950 All 188 538

9.59%

3-80 

Figure 3-49: DVF versus NO

X and/or VOC Emissions Reduction Response Curves for the BAYP, DRPK, and 

8.23% 43.42%

Bayland Park Future Ozone Design Value Response: 

NOx, VOC and NOx+VOC Reductions

% Rdctn NOx VOC 0 All 0 025 All 94 26950 All 188 538

14.25 37.

Wallisville Road Future Ozone Design Value 

Response: NOx, VOC and NOx+VOC Reductions

7072747678808284868890

0 10 20 30 40 50 60

Across-the-Board Percent Reduction

Future Design Value (ppb)

VOC-RdctnNOx-RdctnNOx+VOC-RdctnNAAQS

21.23%

%Rdctn NOx VOC  0 0 0 25 94 269 50 188 538

16.30%
3-81 

Table 3-20: VOC, NOX, and VOC+NOX Emissions Reductions Needed to Model Attainment

summarizes the percent and mass emissions reductions projected to be needed to model 

attainment for the Houston Bayland Park (CAMS 53), Deer Park (CAMS 35), and Wallisville 

Road (CAMS 617) (non-regulatory) monitors. 

Table 3-20: VOC, NOX, and VOC+NOX Emissions Reductions Needed to Model 

Attainment 

VOC Reductions NOX Reductions VOC + NOX Reductions 

Monitor 

Site Code Percent Mass (tpd) Percent Mass (tpd) Percent Mass (tpd) 

BAYP 43.4 467 9.59 36.2 8.23 120 

DRPK 38.0 408 20.2 75.2 14.2 207 

WALV > 50 > 538 21.2 80.0 16.3 237 

Note: WALV is a non-regulatory monitor. 

3.6.2.2 Modeling Sensitivities: Emissions Reductions within 100 and 200 km of HGB

Since the EPA allows NOX and VOC reduction credit for reasonable further progress within 200 

km and 100 km of a nonattainment area, respectively, emissions reduction modeling sensitivities 

were conducted for selected point sources of NOX and area sources of VOC in the 200 km 

adjacent to the eight-county HGB area. Figure 3-50: Map of Counties within 100 km (Red) and 

200 km (Orange) of the Eight-County HGB Area displays a map of the counties within 100 km 

and 200 km of the HGB area. 
3-82 

hese modeling sensitivities were conducted on an earlier version of the 2018 modeling 

only those counties in the eastern segment of the 200 km region (the green 

ector in Figure 3-50: Map of Counties within 100 km (Red) and 200 km (Orange) of the EightFigure 3-50: Map of Counties within 100 km (Red) and 200 km (Orange) of the EightCounty HGB Area 

T

emissions inventory. However, the sensitivity of the HGB 2018 future design values to 

reductions of NOX and VOC emissions from these outer regions is still representative for the final 

version of the 2018 modeling. 

For the counties within 200 km of the eight-county HGB area, point source NOX emission 

reductions (i.e., 25 and 50 percent) were made to selected Texas non-ARD sources including 

compressor engines, boilers, and process heaters. Compressor engines account for approximately 

47 tpd of the estimated 124 tpd of NOX emissions from the selected sources in the 2018 baseline 

modeling emissions. In addition, in a separate modeling run, a 50 percent NOX emissions 

reduction was made to 

s

County HGB Area). Compressor engines in the eastern segment account for approximately 11 

tpd of the estimated 64 tpd of NOX emissions from the selected sources in the 2018 baseline 

modeling emissions. 

Table 3-21: 200 km NOX Reduction Modeling Sensitivity summarizes the sensitivity of the 

projected DVFs for the Deer Park (CAMS 35), Houston Bayland Park (CAMS 53), and 

Wallisville Road (CAMS 617) (non-regulatory) monitors to NOX emissions reduction from the 
3-83 

ction in this region. Of 

e three monitors, the Deer Park (CAMS 35) monitor DV shows the largest sensitivity to NOX

d change rate for 50 percent NOX

emissions red segm atin

are not very sensitive to emission reductions from zed. 

Table 3-21: 2 OX od nsi

selected point sources in the 200 km region. The columns indicating change rate report the 

amount by which the DVF is reduced per 1.0 tpd of NOX emissions redu

th F

emission reductions. However, even the 0.0134 ppb per tp

uctions from the eastern ent is rather low, indic

 the sources analy

g that the HGB monitors

00 km N Reduction M eling Se tivity 

2 O 5% N X All (31 tpd) 5 O 0% N X All (62 tpd) 50% NOX East (32 tpd) 

Monitor 

Site 

Code 

DVF

Change 

(ppb) 

Change Rate 

(ppb/tpd) 

DVF

Change 

(ppb) 

Change Rate 

( ppb/tpd)

DVF

Change 

(ppb) 

Change Rate 

( ppb/tpd)

DRPK 0.23 0.0074 0.47 0.0076 0.43 0.0134 

BAYP 0.14 0.0045 0.27 0.0044 0.23 0.0072 

WALV 0.11 0.0035 0.30 0.0048 0.26 0.0081 

Note: WALV is a non-regulatory monitor. 

The TCEQ also tested the sensitivity of DVFs to reductions by 50 percent of VOC emissions from 

area sources in the counties within the 200 km region. The VOC reduction modeled was 

pproximately 273 tpd. Table 3-22: 200 km VOC Reduction Modeling Sensitivity summarizes 

AMS 35), Houston Bayland Park 

(CAMS 53), an AMS 617) monitors to VOC emission reduction from the 

area sources in 

20 OC R Modeling Sensitivity 

a

the sensitivity of the projected DVFs for the Deer Park (C

d Wallisville Road (C

the200 km region. 

Table 3-22: 0 km V eduction 

50% VOC (273 tpd) 

Monitor 

Site Code DVF Change 

(ppb) 

Change Rate 

(ppb/tpd) 

DRPK 0.09 0.0003 

BAYP 0.06 0.0002 

WALV 0.0 0.0 

Note: WALV is a non-regulatory monitor. 

3.6.2.3 Ozone Source Apportionment Tool and Anthropogenic Precursor Culpability Analysis

The TCEQ applied the OSAT and APCA CAMx tools to the 2018 baseline modeling. For both 

types of analyses, emission source groups, for example, on-road mobile, non- and off-road mobile, 

and biogenics, and source regions, HGB and non-HGB, are defined. OSAT keeps track of the 

origin of the NOX and VOC precursors creating the ozone, and ozone can then be apportioned to 

pecific sources groups and regions. APCA is similar to OSAT, but it recognizes that certain 

f every episode for 

e Houston Bayland Park (BAYP; CAMS 53), Deer Park (DRPK; CAMS 35) and Wallisville 

isodes for these three monitors are included in 

Appendix C: CAMx Modeling for the HGB Attainment Demonstration SIP. 

Table 3-23: OSAT/APCA Source Groups and Regions Defined lists all of the source groups and 

regions tracked in the OSAT and APCA analyses. 

s

sources groups, such as biogenics, are not controllable. Where OSAT would apportion ozone 

production to biogenic emissions, APCA reallocates that ozone production to the controllable or 

anthropogenic emissions that combined with the biogenic emissions to create ozone. 

Results are plotted as layered area plots for every rolling eight-hour average o

th

Road (WALV; CAMS 617) (non-regulatory) monitors. Results of one episode of the six modeled 

are presented here as an example. Plots for all ep
3-84 

Table 3-23: OSAT/APCA Source Groups and Regions Defined 

Figure Legend 

Abbreviation Description of Source Group and Region 

TOPBC Top Boundary Condition 

NTHBC North Boundary Condition 

STHBC South Boundary Condition 

ESTBC East Boundary Condition 

WSTBC West Boundary Condition 

IC Initial Condition 

Other All emission source types outside HGB, with the 

exception of elevated point sources 

Non-HGB El Points Elevated point sources outside HGB 

HGB Non-Road Non-road sources in HGB 

HGB Area Area sources in HGB 

HGB On-Road On-road sources in HGB 

HGB Low Points Low-level point sources in HGB 

HGB El Points Elevated point sources in HGB 

HGB Ships Ship emissions in HGB 

HGB HECT HECT sources in HGB 

HGB MECT MECT sources in HGB 

Biogenics Biogenic emissions from the entire modeling domain 

Figures 3-51: OSAT and APCA Results for BAYP, 3-52: OSAT and APCA Results for DRPK,

and 3-53: OSAT and APCA Results for WALV show the results of these analyses for Houston 

Bayland Park (CAMS 53), Deer Park (CAMS 35), and Wallisville Road (CAMS 617) (nonregulatory monitor), respectively. The layer corresponding to the initial model conditions 

disappears after the first few days of the episode are modeled, as expected. Layers corresponding 

to boundary conditions give an indication of wind direction on individual episode days and 

concentrations of ozone attributable to that boundary. 

Layers that correspond to HGB emission sources indicate HGB contribution to the total modeled 

ozone concentration. The other layers, Biogenics, Other, Initial and Boundary Conditions, and 

Non-HGB Elevated Points, indicate non-HGB contributions to ozone concentration. Differences 

between the depth of the biogenic layers between the OSAT and APCA plots indicate how ozone 

of biogenic origin is reallocated to anthropogenic sources in APCA. 

Lower-level local emission sources, including non-road mobile, area, on-road mobile, and lowlevel points, make a greater contribution to ozone at Houston Bayland Park (CAMS 53) than Deer 

Park (CAMS 35), although Ship Channel sources make a noticeable contribution at Houston 

Bayland Park (CAMS 53). Conversely, local elevated sources, including HGB elevated points, 

ships, HECT, and MECT, make a greater contribution at Deer Park (CAMS 35) than Houston 

Bayland Park (CAMS 53). Wallisville ozone origins are more like Deer Park (CAMS 35) than 

Houston Bayland Park (CAMS 53). 
BAYP 2018 8-Hour OSAT

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)

BAYP 2018 8-Hour APCA

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)

Figure 3-51: OSAT and APCA Results for BAYP 

3-85 
DRPK 2018 8-Hour OSAT

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)

TNSEWIOnHHHHHHHHB

DRPK 2018 8-Hour APCA

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)

TNSEWIOnHHHHHHHHB

Figure 3-52: OSAT and APCA Results for DRPK 

3-86 
3-87 

Figure 3-53: OSAT and APCA Results for WALV 

WALV 2018 8-Hour OSAT

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)

WALV 2018 8-Hour APCA

0

20406080

100120140

5/31/2006 6/1/2006 6/2/2006 6/3/2006 6/4/2006 6/5/2006 6/6/2006 6/7/2006 6/8/2006 6/9/2006 6/10/2006 6/11/2006 6/12/2006 6/13/2006 6/14/2006

Ozone (ppb)
3-88 

3.6.3 Future Case Modeling with Controls 

Proposed controls include lowering the total point source HRVOC emissions allocated by the 

HECT rule in Harris County and voluntary emission reductions of NOX and VOC from on- and 

non-road mobile sources within the eight-county HGB area. 

3.6.3.1 25 Percent HECT Cap Reduction

The modeling sensitivity for the HECT rule revision reduced current total allocated point source 

HRVOC emissions by 25 percent, 2.69 tpd. Table 3-24: HECT Modeling Sensitivity Results

shows the DVFs at the Deer Park (CAMS 35), Houston Bayland Park (CAMS 53), and Wallisville 

Road (CAMS 617) (non-regulatory) monitors for the baseline as well as those resulting from a 25 

percent reduction in the HRVOC from HECT applicable sources in Harris County. 

Table 3-24: HECT Modeling Sensitivity Results 

Monitor 

Site Code 

Baseline DVF 

(ppb) 

HECT DVF

(ppb) 

DRPK 88.14 87.90 

BAYP 86.97 86.89 

WALV 88.28 88.12 

Note: WALV is a non-regulatory monitor. 

3.6.3.2 VMEP Reductions 

Up to 3 percent of the estimated emissions needed for attainment (i.e., 75.2 tpd NOX at Deer Park 

(CAMS 35) as shown in Table 3-20: VOC, NOX and VOC+NOX Emissions Reductions Needed to 

Model Attainment) can be obtained from voluntary control measures. The Houston-Galveston 

Area Council (H-GAC; http://www.h-gac.com/taq/) has estimated that approximately 2.25 tpd of 

NOX emissions reductions from on-road (1.55 tpd) and non-road (0.70 tpd) mobile sources will 

result from the application of VMEPs, including alternative commuting, regional traffic flow and 

vehicle retrofit and replacement, as well as non-road equipment measures. The modeling 

sensitivity for VMEP was coupled with the HECT modeling sensitivity. Table 3-25: HECT and 

VMEP Modeling Sensitivity Results shows the DVFs at the Deer Park (CAMS 35), Houston 

Bayland Park (CAMS 53), and Wallisville Road (CAMS 617) (non-regulatory) monitors for the 

baseline as well as those resulting from both a 25 percent reduction in the HECT cap and a 2.25 

(1.55 on-road and 0.70 non-road) tpd VMEP reduction. 

Table 3-25: HECT and VMEP Modeling Sensitivity Results 

Monitor 

Site Code 

Baseline DVF 

(ppb) 

HECT/VMEP DVF

(ppb) 

DRPK 88.14 87.88 

BAYP 86.97 86.75 

WALV 88.28 88.09 

Note: WALV is a non-regulatory monitor. 

Applying the truncating convention for calculating DVFs, as per the EPA’s modeling guidance, 

only the Wallisville Road (CAMS 617) (non-regulatory) monitor is projected to have a DVF

greater than 87 ppb, the recommended limit for weight-of-evidence considerations. 
3-89 

3.7 MODELING ARCHIVE AND REFERENCES

3.7.1 Modeling Archive 

The TCEQ has archived all modeling documentation and modeling input/output files generated as 

part of the HGB SIP modeling analysis. Interested parties can contact the TCEQ for information 

regarding data access or project documentation. 

3.7.2 Modeling References 

Castineira and Edgar, 2006. Computational Fluid Dynamics for Simulation of Steam-Assisted 

and Air-Assisted Flare Combustion Systems, Energy & Fuels, 20: 1044-1056. 

Emery, C., E. Tai, and G. Yarwood, 2001. Enhanced Meteorological Modeling and Performance 

Evaluation for Two Texas Ozone Episodes, Final Report to the Texas Natural Resource 

Conservation Commission under TNRCC Umbrella Contract No. 582-0-31984, Environ 

International Corporation, Novato, CA. 

Environ, 2007. User’s Guide Emissions Processor, Version 3, Environ International Corporation, 

Novato, CA. 

Environ, 2008. Description from MM5CAMx README file contained in 

mm5camx.21feb08.tar.gz archive, http://www.camx.com/files/mm5camx.21feb08.tar.gz, Environ 

Holdings, Inc. 

Environ, 2008b. Boundary Conditions and Fire Emissions Modeling, Final Report to the Texas 

Commission on Environmental Quality (TCEQ), Contract No. 582-7-84005-FY08-06, Environ 

International Corporation, Novato, CA. 

Environ, 2009. User’s Guide Comprehensive Air Quality Model with Extensions (CAMx), 

Version 4.53, Environ International Corporation, Novato, CA. 

EPA, 2005. Modeling files obtained via data request from the EPA in support of the Clean Air 

Interstate Rule Notice of Data Availability Technical Support Document, as documented at 

http://www.epa.gov/cair/technical.html. 

EPA, 2007. Guidance on the Use of Models and Other Analyses for Demonstrating Attainment 

of Air Quality Goals for Ozone, PM2.5, and Regional Haze, 

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

Feldman, M.S., T. Howard, E. McDonald-Buller, G. Mullins, D.T. Allen, A. Webb, Y. Kimura, 

2007. Applications of Satellite Remote Sensing Data for Estimating Dry Deposition in Eastern 

Texas. Atmospheric Environment, 41(35): 7562-7576. 

Grell, G., J. Dudhia, and D. Stauffer, 1994. A Description of the Fifth Generation Penn 

State/NCAR Mesoscale Model (MM5), Technical Report NCAR/TN-398+STR, National Center 

of Atmospheric Research (NCAR) Tech Note. 

Kinnee et al., 1997. United States Land Use Inventory for Estimating Biogenic Ozone Precursor 

Emissions. Ecological Applications 7(1): 46-58. 

NCAR, 2005. MM5 On-line Tutorial Home Pages, http://www.mmm.ucar.edu/mm5/On-LineTutorial/teachyourself.html, NCAR, Colorado. 

NCEP, 2009. Global Energy and Water Cycle Experiment (GEWEX) Continental International 

Project (GCIP) National Centers for Environmental Prediction (NCEP) Eta Model Output, 
3-90 

Computational and Information Systems Laboratory (CISL) Research Data Archive (RDA): 

ds609.2 Home Page, http://dss.ucar.edu/datasets/ds609.2/, NCEP. 

Popescu, Sorin C., Jared Stukey, Mark Karnauch, Jeremiah Bowling, Xuesong Zhang, William 

Booth, and Nian-Wei Ku, 2008. The New Central Texas Land Use Land Cover Classification 

Project, Final Report to the TCEQ, Contract No. 582-5-64593-FY08-23, Texas A & M University, 

College Station, Texas. 

Robinson, R., T. Gardiner, and B. Lipscombe, 2008. Measurements of VOC Emissions from 

Petrochemical Industry Sites in the Houston Area Using Differential Absorption Lidar (DIAL) 

During Summer 2007, Draft. Submitted to Russell Nettles, TCEQ, by Rod Robinson, Tom 

Gardiner, and Bob Lipscombe of the National Physical Laboratory, Teddington, Middlesex UK 

TW11 0LW, February 8, 2008, pp. 86. 

Starcrest, 2000. Houston-Galveston Area Vessel Emissions Inventory, Starcrest Consulting 

Group, Houston, Texas. 

Stauffer, D. R. and N. L. Seaman, 1990. Use of Four-Dimensional Data Assimilation in a 

Limited-Area Mesoscale Model. Part I: Experiments with Synoptic-Scale Data. Monthly 

Weather Review, 118: 1250-1277. 

Stauffer, D.R. and N.L. Seaman, 1994. Multiscale four-dimensional data assimilation. Journal of 

Applied Meteorology, 33: 416-434. 

Stauffer, D. R., N. L. Seaman, and F. S. Binkowski, 1991. Use of Four-Dimensional Data 

Assimilation in a Limited-Area Mesoscale Model. Part II: Effects of Data Assimilation Within 

the Planetary Boundary Layer. Monthly Weather Review, 119: 734-754. 

TCEQ, 2007. Revisions to the State Implementation Plan (SIP) for the Control of Ozone Air 

Pollution, Dallas-Fort Worth Eight-Hour Ozone Nonattainment Area Attainment Demonstration, 

TCEQ, Austin, Texas. 

TCEQ, 2009. TCEQ Air Modeling and Data Analysis (AMDA) Section file transfer protocol 

(FTP) site, ftp://ftp.tceq.state.tx.us/. 

Wiedinmyer , C., A. Guenther, M. Estes, I.W. Strange, G. Yarwood, and D. Allen, 2001. A Land 

Use Database and Examples of Biogenic Isoprene Emission Estimates for the State of Texas, 

USA. Atmospheric Environment, 35: 6465-6477. 
4-1 

CHAPTER 4: CONTROL STRATEGIES AND REQUIRED ELEMENTS 

ntrol measures (RACM), motor vehicle emissions budgets (MVEBs), and 

ontingency measures. 

 strategies 

at were implemented for the one-hour and eight-hour ozone standards in the HGB area. 

zone Control Measures Applicable to the HGB Eight-County 

Nonattainment Area 

4.1 INTRODUCTION 

The Houston-Galveston-Brazoria (HGB) nonattainment area for the 1997 eight-hour ozone National 

Ambient Air Quality Standard (NAAQS), which consists of Brazoria, Chambers, Fort Bend, 

Galveston, Harris, Liberty, Montgomery, and Waller Counties, includes one of the most 

comprehensively controlled industrial complexes in the world. The Texas Commission on 

Environmental Quality (TCEQ) has developed stringent and innovative regulations that address 

nitrogen oxides (NOX), volatile organic compounds (VOC), and highly reactive volatile organic 

compounds (HRVOC). Despite the significant decreases in ozone design values and emissions of 

ozone precursors in the HGB area, further reductions are necessary to bring the area into attainment 

of the 1997 eight-hour standard. This chapter describes existing and proposed ozone control 

measures for the HGB area, as well as how Texas meets the following severe ozone nonattainment 

area state implementation plan (SIP) requirements: reasonably available control technology (RACT), 

reasonably available co

c

4.2 EXISTING CONTROL MEASURES 

Over several years of ozone planning in the HGB area, a broad range of control measures have been 

implemented for each emission source category. Table 4-1: Existing Ozone Control Measures

Applicable to the HGB Eight-County Nonattainment Area lists the existing ozone control

th

Table 4-1: Existing O

Measure Description Start Date(s) 

POINT SOURCE MEASURES 

NOX Mass Emissions Cap and Trade 

(MECT) Program 

n 

, and many 

ed in 

through April 1, 2007 

Overall 80 percent NOX reduction from

existing industrial sources and utility 

power plants, implemented through a 

cap and trade program. Affects utility 

boilers, gas turbines, heaters and 

furnaces, stationary internal combustio

engines, industrial boilers

other industrial sources. 

April 1, 2003, and phas

HRVOC Rules and HRVOC 

Emissions Cap and Trade (HECT) 

rogram 

s and monitoring 

d 

rogram is January 1, 

2007 

P

Affects cooling towers, process vents, 

and flares, and establishes an annual 

emissions cap with a cap and trade for 

each site in Harris County. The seven 

perimeter counties are subject to permit 

allowable limit

requirements. 

Monitoring requirements are 

January 31, 2006, and cap an

trade p

HRVOC Fugitive Rules 

er 

and third part audit 

requirements. 

More stringent leak detection and repair March 31, 2004 

(LDAR) requirements for components in

HRVOC service. Additional 

components included in LDAR program

are more stringent repair times, low

leak detection, 
4-2 

Measure Description Start Date(s) 

VOC Rules on Storage and 

egassing Operations 

es 

r 

torage 

ng 

y of 

January 1, 2009 

D

Requires controls for slotted guide pol

and more stringent controls for othe

fittings on floating roof tanks, and 

control requirements or operational 

limitations on landing floating roof 

tanks. Eliminates exemption for s

tanks for crude oil or natural gas 

condensate, and regulates flash 

emissions from these tanks. Requires 

vapors from degassing to be vented to a 

control device for a longer time period, 

and removes exemption from degassi

to control for tanks with capacit

75,000 to 1,000,000 gallons. 

NOX Emission Standards for Nitric 

Acid/Adipic Acid manufacturing anufacturing facilities 

NOX emission standards for nitric acid November 15, 1999 

and adipic acid m

in the HGB area 

Utility Electric Generation in East 

nd Central Texas s 

on sites in East and 

, 2003, through May 1, 

a 2005 

NOX control requirements 

(approximately 55%) on utility boiler

and stationary gas turbines at utility 

electric generati

Central Texas. 

May 1

VOC Control Measures 

rs 

ent 

x D: 

ontrol 

Technology Analysis). 

, 2002, and 

arlier 

Additional control technology 

requirements for batch processes, 

bakeries, and offset lithographic printe

by December 31, 2002. Examples of

additional VOC measures adopted 

earlier for RACT purposes include: 

storage, general vent gas, industrial 

wastewater, loading and unloading 

operations, general VOC LDAR, solv

using process, etc.(see Appendi

Reasonably Available C

December 31

e

AREA/NON-ROAD MEASRUES

Refueling - Stage I 

s 

 air. 

Stage I vapor recovery captures gasoline 1990 

vapors that are released when gasoline is

delivered to a storage tank. The vapor

are returned to the tank truck as the 

storage tank is being filled with fuel, 

rather than released into the ambient

Refueling - Stage II 

ing 

e 

, rather than 

Stage II vapor recovery captures 1992 

gasoline vapors when a vehicle is be

fueled at the pump. The vapors are 

returned through the pump hose to th

petroleum storage tank

released into the air. 

Federal Area/Non-Road Measures 

ards 

The United States Environmental Through 2007 

Protection Agency (EPA) has 

implemented a series of emissions limits 

for area and non-road sources. Examples 

are diesel and gasoline engine stand

for locomotives and leaf-blowers. 

Texas Emission Reduction Plan 

(TERP) 

(See also on-road TERP reductions) 

diesel engine replacement/retrofit. 

Provides grant funds for heavy-duty January 2002 

California Gasoline Engines 

engines 25 horsepower and 

California standards for non-road May 1, 2004 

gasoline 

larger. 

Stationary Diesel Engines 

 purposes between 6:00 

Prohibition on operating stationary April 1, 2002 

diesel and dual-fuel engines for testing 

and maintenance
4-3 

Measure Description Start Date(s) 

A.M. and noon. 

Natural Gas-Fired Small Boilers, its on small-scale 2002 

Process Heaters, and Water Heaters

NOX emission lim

residential and industrial boilers, process 

heaters, and water heaters equal to or 

less than 2.0 million British thermal 

units per hour. 

Minor Source NOX Controls for 

Non-MECT Sites 

s 

stationary engines and 

ded in 

esign 

NOX emission limits on boilers, proces March 31, 2005 

heaters, and 

turbines at minor sites not inclu

the MECT program (uncontrolled d

capacity to emit less than 10 tons per 

year (tpy)). 

VOC Control Measures 

ters 

nt 

December 31, 2002, and 

earlier 

Additional control technology 

requirements for batch processes, 

bakeries, and offset lithographic prin

by December 31, 2002. Examples of

additional VOC measures adopted 

earlier for RACT purposes include: 

storage, general vent gas, industrial 

wastewater, loading and unloading 

operations, general VOC LDAR, solve

using process, cutback asphalt, etc.

Texas Low Emission Diesel

(TxLED) October 31, 2005 

Requires all diesel for both on-road and

non-road use to have a lower aromatic 

content and a higher cetane number. 

Phase in began 

TxLED for Marine Fuels Adds marine distillate fuels X and A June 24, 2007 

commonly known as DMX and DMA, 

or Marine Gas Oil (MGO), into the 

definition of diesel fuels, requiring them 

to be TxLED compliant. 

Texas Low Reid Vapor Pressu

(RVP) Gasoline 

re 

om 

Requires all gasoline for both on-road 

and non-road use to have a RVP of 7.8 

pounds per square inch (psi) or less fr

May 1 through October 1 each year. 

April 2000 

Voluntary Mobile Emission

Reduction Program(VMEP) 

s Voluntary measures administered by the 

Houston-Galveston Area Council (HGAC) (see Appendix F7 of the 2004 

) 

Through 2007 

HGB Mid-Course Review SIP revision

ON-ROAD MEASRUES

Federal On-Road Measures s of 

e 

, 

The EPA has implemented a serie Phase in through 2007 

emissions limits for on-road vehicles. 

Some of these include Tier 1/2 vehicl

standards, low sulfur diesel standards

National Low Emission Vehicle 

standards, and reformulated gasoline. 

TERP 

(See also area/non-road TERP) 

Provides grant funds for heavy-duty nuary 2002 

diesel engine replacement/retrofit. 

Ja

Vehicle Inspection/ Maintenance 

(I/M) or 

 vehicles. 

May 1, 2003 

Yearly treadmill-type testing for pre1996 vehicles and computer checks f

1996 and newer

-Begin May 1, 2002, in Harris County. 

-Begin May 1, 2003, in Brazoria, Fort 

Bend, Galveston, and Montgomery 

Counties. 

May 1, 2002 

Speed Limit Reduction On roadways where speeds were 65 mph 

or higher, speed limits remain at 5 miles

per hour (mph) below what was posted

before May 1, 2002. 

September 2003 

TxLED Requires all diesel for both on-road and 

non-road use to have a lower aromatic 

content and a higher cetane number. 

Phase in began 

October 31, 2005 
4-4 

Measure Description Start Date(s) 

Texas Low RVP Gasoline 

(see also non-road Low RVP 

er 

April 2000 

Gasoline) 

Requires all gasoline for both on-road 

and non-road use to have a RVP of 7.8 

psi or less from May 1 through Octob

1 each year. 

VMEP Voluntary measures administered by the 

H-GAC (see Appendix F7 of the 2004 

sion) 

Phase in through 2007 

HGB Mid-Course Review SIP revi

Transportation Control Measures Various measures in H-GAC’s longrange transportation plans. Phase in through 2007 

OTHER

Portable Fuel Containers Rule 

See section 4.3.2 Repeal of State 

Portable Fuel Container Rule for 

additional information about this ted in 

04 

measure.

Establishes new design “no spill” 

criteria requirements for portable fuel 

containers sold, offered for sale, 

manufactured, and/or distribu

Texas. 

December 31, 20

Voluntary Energy 

Efficiency/Renewable Energy 

couraged energy efficiency and 

renewable energy projects. 

Senate Bill (SB) 5 and SB 7 from the December 2000 

80th session of the Texas Legislature 

have en

Automotive Windshield Washer VOC content limitation on automotive 

sher fluid sold, supplied, 

use in 

January 1, 1995 

Fluid windshield wa

distributed, or manufactured for 

Texas. 

4.3 UPDATES TO EXISTING MEASURES 

4.3.1 Mass Emissions Cap and Trade (MECT) Program 

The MECT program in 30 Texas Administrative Code (TAC) Chapter 101 is a market-based 

component of the SIP that provides flexibility for stationary source compliance with the emission 

on to the MECT program would ensure the integrity of the modeled HGB 

ing t

ided for a system of 

nces under existing regulations. 

specifications under 30 TAC Chapter 117, while establishing a mandatory cap for total NOX

emissions from affected source categories in the HGB ozone nonattainment area. The MECT 

program was adopted as a primary control measure of the HGB attainment demonstration for the onehour NAAQS for ozone. 

The proposed revisi

nonattainment area cap by prohibit he issuance of allowance allocations to major sources that did 

not submit the required Level of Activity Certification forms by the compliance date in 30 TAC 

§ 101.360. This proposed rule change would not reduce the current NOX cap in the HGB 

nonattainment area. 

The MECT program allocated NOX emission allowances to applicable existing facilities in the HGB 

area based on their 1997 to 1999 levels of activity. The program also prov

allocating allowances to facilities that had submitted administratively complete permit applications 

before January 2, 2001. After January 2, 2001, any applicable new or modified facilities in the HGB 

area must acquire allowances equal to their annual NOX emissions (one NOX ton per year equals one 

annual allowance) from existing facilities already participating in the program. 

The current rule does not prohibit the issuance of new allowances to existing applicable facilities that 

failed to previously participate in the MECT program; therefore, an increase of the total NOX cap in 

the HGB ozone nonattainment area may occur in certain circumsta

The proposed rulemaking would prohibit these potential future increases in the MECT program NOX

cap for maintenance of the HGB one-hour ozone attainment demonstration. Additionally, maintaining 

the integrity of the MECT program NOX cap would prevent potential adverse impacts on the 

attainment and maintenance of the 1997 eight-hour ozone NAAQS. 
4-5 

by revising the rule language to 

a

perm he required level of activity certification by the 

• facilities that were in operation prior to January 1, 1997; 

e and restricted to 10 percent or 

ss of the normal annual operating schedule. Allowing companies to use this restriction to calculate 

tely reflect the actual restriction on use of the 

September 15, 2005. The current Texas PFC 

gulations are inconsistent with the new federal standards, because they are based on the previous 

ontainers, the Federal 

FC rule is more stringent than the Texas PFC rule. 

ean Fuel Fleet Requirement 

articipation in a Clean Fuel Fleet Program (CFFP) is required by § 246 of the FCAA for 

The proposed rulemaking would maintain the NOX cap integrity 

eliminate the future allocation, after the effective date of the rule, of additional allowances to 

pplicable facilities that failed to previously participate in the MECT program and previously 

itted facilities that have failed to submit t

applicable deadlines. These facilities include: 

• new and modified facilities not in operation prior to January 1, 1997, but were included in 

a submitted New Construction or Modification Permit determined to be administratively 

complete before January 2, 2001; and 

• new and modified facilities not in operation prior to January 1, 1997, but qualified for a 

Permit by Rule and had commenced construction before January 2, 2001. 

This proposed rulemaking would also revise Chapter 101, Subchapter H, Division 3, to clarify the 

definition of “uncontrolled design capacity” as it relates to applicability of this division. The TCEQ 

has received comments from stakeholders requesting clarification of the MECT program 

applicability, specifically relating to uncontrolled designed capacity and how it differs from a 

facility’s potential to emit. The definition of “uncontrolled design capacity” would also be revised to 

allow owners or operators of emergency back-up engines at minor sources an alternative to using 

8,760 hours to calculate the uncontrolled designed capacity to emit for the engines. Emergency backup engines at minor sites are typically authorized by Permit-by-Rul

le

the uncontrolled designed capacity would more accura

engine while avoiding potentially making many minor sites needlessly subject to the MECT program 

solely because the engine is no longer exempt under Chapter 117. Because these sites would still be 

subject to the Chapter 117 minor source rules in Subchapter D, Division 1, this proposed change does 

not constitute backsliding under the Federal Clean Air Act (FCAA). 

4.3.2 Repeal of State Portable Fuel Container Rule 

The EPA adopted a federal portable fuel container (PFC) rule in the February 26, 2007, issue of the 

Federal Register (72 FR 8432) that set a national standard for gasoline, diesel, and kerosene PFCs. 

The rule requires all PFCs manufactured on or after January 1, 2009, to comply with the federal 

standards. The new federal PFC regulations are consistent with the revised PFC regulations adopted 

by the California Air Resources Board (CARB) on

re

PFC testing methods adopted by CARB in 2001. Therefore, the state is proposing to repeal its PFC 

regulations (rule project number 2008-032-115-EN) and to rely on the implementation of the federal 

PFC regulations to control VOC emissions from PFCs used within the state. According to an EPA 

analysis entitled, Federal Register Rule vs. Texas Register Rule Portable Fuel C

P

The repeal of the current Texas PFC regulations and reliance on the new federal PFC standards will 

not have a negative impact on the Texas SIP. The estimated emission reductions applicable to the 

implementation of the federal PFC rule in Texas are expected to be equivalent to the current Texas 

PFC rule in the early years and to provide greater reductions in the later years. 

4.3.3 Cl

P

nonattainment areas with 1980 populations greater than 250,000 that are classified as serious or above 

for ozone. In accordance with this requirement, a CFFP was instituted by rule in the HGB area 

beginning on September 1, 1998. The CFFP requires that a certain percentage of fleet purchases after 

model year 1998 be Clean Fuel Vehicles (CFV) that meet the standards set forth in § 243 of the 

FCAA. 
The most recent federal standards

4-6 

 for both light-duty and heavy-duty vehicles have eclipsed the CFV 

tandards because subsequent to September 1, 2005, any new vehicle purchase ranging from 0-26,000 

ill accomplish equal long-term reductions attributable 

 the CFFP. However, the EPA has not provided guidance on how states are to address the Clean 

t federal 

le purchases subsequent to the date of repeal would meet more stringent 

 the eight-hour ozone standard, the HGB area is required to meet the mandates of the 

CAA under §§ 172(c)(1), 182(b)(2), and 182(f). According to the EPA’s Final Rule to Implement 

 available control technology (BACT) levels 

xpected of new sources or to maximum achievable control technology (MACT) levels required for 

s

pounds gross vehicle weight rating would have either equaled or, in most cases, exceeded CFV 

standards. In a letter to manufacturers (EPA, 2005), the EPA stated that “subsequent to publishing its 

CFV regulations, EPA has promulgated new emission standards that are generally more stringent than 

or equivalent to the CFV emission standards for light-duty vehicles, light-duty trucks, and heavy-duty 

engines.” This EPA letter, dated July 21, 2005, applied to fleet purchases that began with the 2006 

model year (September 1, 2005). 

During the 79th Texas Legislature Regular Session in 2005, Senate Bill 1032 was signed into law, 

which repealed the Texas Clean Fleet Program in its entirety because the federal standards already in 

place at that time eclipsed the CFV standards referenced in the FCAA. On April 26, 2006, the TCEQ 

formally repealed the Texas Clean Fleet Program because no additional benefit could be achieved 

from new vehicle purchases under CFFP. A revision to the SIP that reflected the repeal of the Texas 

Clean Fleet Program was submitted to the EPA on May 15, 2006. EPA approval of measures that 

substitute for the initial requirement to implement CFFP is provided for in § 182(c)(4) of the FCAA 

as long as the EPA determines the substitute w

to

Fuel Fleet substitution requirement in their SIP submittals, in light of the more stringen

standards. Since new vehic

federal emission standards, cancellation of the Texas Clean Fleet Program does not necessitate action 

to substitute this program with a separate emission reduction measure containing equivalent benefits. 

Such a substitution would only be warranted when a net increase in emissions would occur due to 

repeal or cancellation of an existing program. 

4.4 REASONABLY AVAILABLE CONTROL TECHNOLOGY (RACT) ANALYSIS 

4.4.1 General Discussion 

The HGB area is currently classified as a severe nonattainment area for the 1997 eight-hour ozone 

NAAQS. Under

F

the 1997 eight-hour ozone NAAQS (40 Code of Federal Regulations (CFR) § 51.912), states 

containing areas classified as moderate nonattainment or higher must submit a SIP revision 

demonstrating that their current rules fulfill the RACT requirements for all Control Technique 

Guidelines (CTG) categories and all non-CTG major sources of NOX and VOC. The major source 

threshold for severe nonattainment areas is a potential to emit 25 tons per year (tpy) or more of either 

NOX or VOC. 

In the September 17, 1979, issue of the Federal Register (44 FR 53762) RACT is defined as the 

lowest emissions limitation that a particular source is capable of meeting by the application of control 

technology that is reasonably available considering technological and economic feasibility. RACT 

requirements for nonattainment areas classified as moderate and higher are included in the FCAA to 

assure that significant source categories at major sources of ozone precursor emissions are controlled 

to a reasonable extent, but not necessarily to best

e

major sources of hazardous air pollutants. While RACT and RACM have similar consideration 

factors like technological and economic feasibility, there is a significant distinction between RACT 

and RACM. To be considered RACM, a control measure must advance attainment of the area 

towards meeting the NAAQS for that measure (see § 172(c)(1) of the FCAA). Advancing attainment 

of the area is not a factor of consideration when evaluating RACT because the benefit of 

implementing RACT is presumed under the FCAA. 

Under the current state rules, the HGB area is subject to some of the most stringent NOX and VOC 

emission control requirements in the country, and for many source categories, the existing rules are 

more stringent than recommended RACT standards for those categories. In the final approval notice 
for the revised HGB one-hour oz

4-7 

one attainment demonstration SIP published in the September 6, 

006, issue of the Federal Register (71 FR 52676), the EPA noted that the HGB VOC rules in 30 

 the one-hour ozone attainment demonstration and 

reviously approved by the EPA. 

he TCEQ's analysis demonstrates that the current NOX rules and controls for the HGB area fulfill 

B area. 

he TCEQ has determined that RACT for the Longhorn Glass Corporation glass furnace is met 

view (NSR) permit. TCEQ Permit Number 42623 requires 

 area. Therefore, the TCEQ is 

ot implementing any rule amendments or new rules for the glass furnaces in the HGB area. 

 and economically feasible is fulfilled by the EPApproved Chapter 115 rules or other federally enforceable measures. 

The EPA issued 11 Consumer and Commercial Products CTG documents between 2006 and 2008 

with recommendations for VOC controls on a variety of consumer and commercial products. Some 

of the new CTG recommendations are updates to previously issued CTG documents and some are 

recommendations for new categories. The TCEQ evaluated these new CTG documents in this RACT 

analysis to determine if additional VOC controls were necessary to fulfill RACT requirements. The 

following is a list of the 11 CTG documents: 

2

TAC Chapter 115 and NOX rules in Chapter 117 were previously determined to meet the FCAA 

RACT requirements. Under the one-hour ozone NAAQS, the HGB area was also designated as a 

“severe” nonattainment area and the threshold for major stationary sources under the one-hour ozone 

nonattainment designation was identical to the current threshold under the eight-hour ozone 

designation. Therefore, controls to satisfy RACT for most major sources under the eight-hour ozone 

designation were implemented by the TCEQ under

p

Specified information regarding the TCEQ's NOX and VOC RACT analysis is provided in Appendix 

D: Reasonably Available Control Technology Analysis; Table D-1: State Rules Addressing RACT 

Requirements in CTG and ACT Reference Documents provides additional details on the CTG and 

Alternative Control Techniques (ACT) source categories; and Table D-2: State Rules Addressing 

RACT Requirements for Major Emission Sources in the HGB Area provides additional detail on the 

non-CTG/ACT major emission source categories. 

4.4.2 NOX RACT Determination 

T

the FCAA requirements for NOX RACT. The MECT program and accompanying Chapter 117 rules 

represent one of the most comprehensive NOX control strategies in the nation and encompass both 

RACT and beyond-RACT levels of control. Except for the EPA's Glass Furnace ACT document, the 

current EPA-approved Chapter 117 rules fulfill RACT requirements for all CTG and ACT NOX

source categories. For non-CTG/ACT major NOX emission source categories, RACT is fulfilled by 

the MECT program or by separate source-specific rules in Chapter 117 for sources that NOX controls 

are technologically and economically feasible. 

The TCEQ identified one major source glass manufacturing facility, Longhorn Glass Corporation 

(TCEQ Account No. HG-0028-R), in the 2006 point source emissions inventory for the HG

T

through the site's New Source Re

Longhorn's oxy-fired glass furnace to meet a NOX emission specification of 1.48 pounds per ton of 

glass produced. This control requirement is more stringent than the current Chapter 117 NOX

emissions specification of 4.0 pounds per ton of glass produced for glass furnaces that was approved 

by the EPA as part of the 2007 Dallas-Fort Worth eight-hour ozone attainment demonstration and is 

sufficient to satisfy RACT for the glass furnace category for the HGB

n

4.4.3 VOC RACT Determination 

The TCEQ's analysis demonstrates that the current VOC rules and controls for the HGB area satisfy 

the FCAA requirements for RACT for all CTG or ACT VOC source categories specific to any CTG 

or ACT documents issued prior to 2006. RACT for all non-CTG/ACT major VOC emission source 

categories that controls are technologically

a
4-8 

 in 2006

006

008

2008

• Miscellaneous Metal and Plastic Parts Coatings, Group IV Issued in 2008

 CTG documents are provided in 

ppendix D: Reasonably Available Control Technology Analysis. 

• Flat Wood Paneling Coatings, Group II Issued in 2006

• Flexible Packaging Printing Materials, Group II Issued

• Industrial Cleaning Solvents, Group II Issued in 2006

• Offset Lithographic and Letterpress Printing, Group II Issued in 2

• Large Appliance Coatings, Group III Issued in 2007

• Metal Furniture Coatings, Group III Issued in 2007

• Paper, Film, and Foil Coatings, Group III Issued in 2007

• Auto and Light-Duty Truck Assembly Coatings, Group IV Issued in 2

• Fiberglass Boat Manufacturing Materials, Group IV Issued in 

• Miscellaneous Industrial Adhesives, Group IV Issued in 2008

The following provides a brief summary of the TCEQ's determinations regarding these 11 CTG 

documents. Additional details regarding the evaluation of the 11

A

4.4.3.1 CTG Documents That Are Not Applicable to the HGB Area

The TCEQ provides a negative declaration for the Automobile and Light-Duty Truck Assembly 

Coatings and the Flat Wood Paneling Coatings CTG documents. The TCEQ determined that no 

sources meeting the applicability criteria recommended in these two CTG documents are located in 

the HGB area. 

4.4.3.2 CTG Documents That Do Not Represent RACT for the HGB Area

For the following three CTG documents, the TCEQ determined that the CTG recommendations either 

do not represent RACT due to economic or technological feasibility concerns or that the current 

Chapter 115 rules are equivalent or superior to the CTG-recommended controls: Fiberglass Boat 

Manufacturing Materials; Flexible Packaging Printing Materials; and Paper, Film, and Foil Coatings. 

Therefore, the TCEQ is not implementing any rule amendments or new rules associated with these 

CTG categories. 

4.4.3.3 CTG Documents That a RACT Determination Cannot Be Made at This Time

The TCEQ is not making a determination at this time whether the Industrial Cleaning Solvents or the 

Miscellaneous Industrial Adhesives CTG recommendations represent RACT for Texas. The TCEQ's 

initial assessment indicates that the EPA substantially underestimated the scope and potential impact 

of the CTG recommendations and that implementing the CTG recommendations would have 

widespread and potentially adverse impacts to small businesses and micro-businesses. The TCEQ 

will continue to evaluate these CTG documents and plans to provide small business outreach to 

engage stakeholders that could be potentially impacted by the EPA's suggested control measures. A 

RACT determination for these CTG categories will be made after adequate stakeholder input and the 

TCEQ has determined the impact to small businesses, economic and technological feasibility, and 

practical enforceability of the CTG recommendations. 

By letter dated December 8, 2008, the TCEQ requested clarification from the EPA regarding several 

issues related to the following three CTG documents: Large Appliance Coatings; Metal Furniture 

Coatings; and Miscellaneous Metal and Plastic Parts Coatings. A number of the recommended VOC 

content limits for specific coatings categories in the CTG documents are less stringent than the more 

general VOC content limits specified in the EPA's original CTG recommendations. The TCEQ 

requested clarification to assure that implementing the CTG recommendations would not be 

considered as backsliding and to be certain that the TCEQ has the appropriate information to 

determine whether the CTG recommendations actually represent RACT for Texas. As of September 

4, 2009, the EPA has not responded to the TCEQ request for clarification on the CTG 

recommendations. Therefore, the TCEQ is not making a determination at this time whether these 

CTG recommendations represent RACT for Texas until the EPA provides clarification to the issues 
4-9 

identified by the TCEQ and staff has had sufficient time to evaluate the CTG recommendations in 

context with the EPA's response. 

4.4.3.4 CTG Documents That Represent RACT for the HGB Area

The TCEQ has determined that portions of the Offset Lithographic and Letterpress Printing CTG 

recommendations represent RACT for the HGB area. Concurrent with this SIP revision, the TCEQ is 

proposing rulemaking to limit the VOC content of solvents used by offset lithographic printing 

facilities in the HGB area (Rule Project 2008-019-115-EN). The proposed rulemaking would 

implement the CTG recommendations to reduce the VOC content of the fountain solutions and 

cleaning materials. Additionally, the proposed rulemaking would expand the current rule 

applicability to include smaller sources not currently subject to the rule. The TCEQ is not 

implementing any rule amendments or new rules associated with the CTG-recommended control 

requirements for heatset presses or with the letterpress printing portion of this CTG document for the 

GB area. Additional discussion concerning the TCEQ's determination regarding the CTG 

endix D: Reasonably 

gy Analysis. 

AA as a requirement that states incorporate into their SIP all reasonably 

vailable control measures that would advance a region’s attainment date. However, regions are 

potential control strategy concepts for the RACM 

nalyses of stationary and mobile sources include both the strategies presented to stakeholders in 

March 2008 and the strategies suggested by stakeholders during the informal stakeholder comment 

process. 

H

recommendations for heatset press and letterpress printing is provided in App

Available Control Technolo

4.5 REASONABLY AVAILABLE CONTROL MEASURES ANALYSIS 

4.5.1 General Discussion 

States are required by § 172(c)(1) of the FCAA to “provide for implementation of all reasonably 

available control measures as expeditiously as practicable” and to include RACM analyses in the SIP. 

In the General Preamble for implementation of the FCAA Amendments of 1990 published in the 

April 16, 1992, issue of the Federal Register (57 FR 13498), the EPA explains that it interprets 

§ 172(c)(1) of the FC

a

obligated to adopt only those measures that are reasonably available for implementation in light of 

local circumstances. 

The TCEQ used a two-step process to identify potential control strategies for the HGB area RACM 

analysis. The TCEQ compiled a list of potential control strategy concepts based on an initial 

evaluation of the existing control strategies and existing sources of VOC and NOX in the HGB area. 

Stationary sources outside the HGB area within either a 100 kilometer (km) or 200 km range of the 

HGB area were also considered for this initial evaluation. According to the EPA's guidance, sources 

of VOC must be within 100 km of the nonattainment area and sources of NOX must be within 200 

km. The EPA allows states the option of considering control measures outside the ozone 

nonattainment area that can be shown to advance attainment; however, consideration of these sources 

is not a requirement of the FCAA. Draft lists of potential control strategy concepts for stationary and 

mobile sources were developed from this initial evaluation. The draft lists of potential control 

strategy concepts were presented to stakeholders for comment at stakeholder meetings held in the 

HGB area on March 25 and 26, 2008. The TCEQ requested comment on the potential control 

strategies and invited stakeholders to suggest any additional strategies that might help advance 

attainment of the HGB area. The final lists of 

a
Each potential control measure identified through the control strategy development process was 

evaluated to determine if the measure would meet established criteria to be considered reasonably 

available. The TCEQ used the general criteria specified by the EPA in the proposed approval of t

4-10 

he 

ew Jersey RACM published in the January 16, 2009, issue of the Federal Register (74 FR 2945): 

d and non-road emission source categories that meets the 

 

e does not cause ‘‘substantial widespread and long-term 

• The control measure can advance the attainment date by at least one year. 

eight-hour ozone 

duction benefit in terms of parts per billion (ppb) using modeling sensitivity runs. 

ted control measure was 

onsidered not RACM because reasonable controls were already in place. 

implemented earlier than January 1, 2018, the 

easure should be implemented as early as feasible. 

re to reduce the HRVOC cap for Harris County is 

cluded in Section 4.6: New Control Measures. 

impacts, or ability of the measure to advance attainment of the NAAQS. Additional information and 

N

RACM is defined by the EPA as any potential control measure for application to 

point, area, on-roa

following criteria: 

• The control measure is technologically feasible

• The control measure is economically feasible 

• The control measur

adverse impacts’’ 

• The control measure is not ‘‘absurd, unenforceable, or impracticable’’ 

The EPA did not provide guidance in the Federal Register on how to interpret the criteria "advance 

the attainment date by at least one year." Because modeling all possible year scenarios for potential 

control measures is not practical, the TCEQ evaluated whether a potential control measure would help 

the HGB area make progress toward attainment of the NAAQS based on potential 

re

The TCEQ also considered whether the control measure was similar or identical to control measures 

already in place in the HGB area. If the suggested control measure would not provide substantive and 

quantifiable benefit over the existing control measure, then the sugges

c

The control measure must be able to be implemented before and reduce emissions prior to the 

beginning of the ozone season immediately before the attainment date. The attainment date for the 

1997 eight-hour ozone NAAQS for the HGB area is June 15, 2019. Any control measures must be 

implemented and emissions reductions made no later than January 1, 2018. However, the HGB area 

must make progress toward attainment of the 1997 eight-hour ozone NAAQS as expeditiously as 

practicable. Therefore, if control measures can be 

m

4.5.2 Results of RACM Analysis 

Based on the RACM analysis, the TCEQ determined that only one potential control measure met the 

criteria to be considered RACM. A reduction in the HRVOC cap for Harris County under the HECT 

program was determined to help advance attainment of the HGB area and to meet the other RACM 

criteria. Reported HRVOC emissions from sources in the HECT program during the first two years 

of the HECT program, calendar years 2007 and 2008, averaged approximately 56 percent of the total 

allocated HRVOC allowances for Harris County. Because there is a demonstrated substantial surplus 

in the HRVOC cap, a 25 percent reduction in the cap for Harris County is technologically feasible 

and should have minimal economic impact. Modeling demonstrates that a 25 percent reduction in the 

HRVOC cap for Harris County will help the HGB area make progress toward attainment of the 1997 

eight-hour ozone NAAQS. Based on 2007-2008 emissions, a 25 percent reduction would leave a 

buffer of approximately 600 tpy, or more, in the cap that should be sufficient to account for any 

significant variations in HRVOC emissions in future years due to emission events and scheduled 

startup, shutdown, and maintenance events as well as allow for future economic growth. Additional 

discussion regarding the proposed control measu

in

All other potential control measures evaluated for both stationary and mobile sources were 

determined not to be RACM due to technological or economic feasibility, enforceability, adverse 
specific details regarding the RACM analysis f

4-11 

or the HGB area are contained in Appendix E: 

easonably Available Control Measure Analysis. 

ASURES 

R

4.6 NEW CONTROL ME

4.6.1 Stationary Sources 

4.6.1.1 HECT Cap Reduction and Allowance Reallocation

The proposed revisions to the HECT Program Cap rule would result in a 25 percent reduction in the 

total HECT allowance cap and revise the HRVOC allocation methodology. The HECT program was 

adopted by the commission as an ozone control measure for the HGB area on December 1, 2004. 

urrently, the HECT program is applicable only in Harris County. 

. See Chapter 3: PHOTOCHEMICAL MODELING for 

rther discussion regarding the modeling. 

eeded to account for the inherent variability of HRVOC emissions associated with these 

ctivities. 

pproach while contributing to the area’s attainment of the 

AAQS as expeditiously as practicable. 

olymer, plastics, and other chemical producers may have not received a 

ufficient allocation. 

 rates 

ssociated with the processes of the industry sectors with HRVOC emissions in Harris County. 

C

Photochemical modeling analysis demonstrates that a 25 percent reduction of the HECT cap on the 

total Harris County HRVOC allocation would advance attainment of the 1997 eight-hour ozone 

NAAQS by reducing the future 2018 ozone design values (DV18s) at all HGB monitors. Future 

design value calculations were based on 2006. The largest decrease in the projected DV18s (0.24 ppb) 

was at the Deer Park monitor. The average decrease for all sites was 0.11 ppb. The three HGB 

monitors projected to be exceeding the eight-hour ozone NAAQS (i.e., DV18 > 84 ppb) in the 2018 

future case modeling, also exceed in the HECT sensitivity modeling. The Wallisville monitor has the 

highest predicted DV18 (88.3 ppb) in the 2018 future case modeling, and continues to be the highest in 

the HECT sensitivity modeling (88.1 ppb)

fu

HRVOC data from the first two years indicates that the total reported actual emissions from sources 

in the HECT program are approximately 50 percent of the total HRVOC cap. Because the HRVOC 

rules in Chapter 115, Subchapter H, Divisions 1 and 2, require emissions from startup, shutdown, and 

maintenance activities be included in the HECT program, the total surplus observed in the first two 

years of the program cannot be removed. Proposing a 25 percent reduction leaves a buffer in the cap 

that is still n

a

Following the initial allocation of allowances, companies participating in the HECT program 

commented that the allocation was not equitably distributed and that some sites did not receive 

enough allocations while other sites received allocations greater than necessary. Monitoring data 

supports the assertion of an inequitable distribution of allowances. Revisions to the rule are 

anticipated to result in a more equitable a

N

The existing allocation methodology was based on the total amount, in pounds, of HRVOC produced 

as an intermediate, byproduct, or final product, or used by a process unit at each participating site. 

Analysis of the monitoring data from previous control periods indicate that refineries may have been 

over-allocated while p

s

The rule revision proposes a new allocation methodology beginning with the 2011 calendar-year 

control period based on actual emissions data with the goals of fairly and equitably distributing the 

compliance burden for HECT program participants, applying credit for controlling and reducing 

HRVOC emissions, and not rewarding or encouraging emissions from emissions events. The 

proposed revised allocation methodology is based on calculating “uncontrolled” or “precontrolled” 

emissions for facilities using reported control efficiencies based on the specifications for flares in 

Chapter 115; creating a 250 ton emission event set aside pool to encourage market trading; and 

dividing the cap into four industry-type sector pools to account for different HRVOC emission

a
The proposed rulemaking would also reduce the cap in a gradual step down fashion beginning with a 

10 percent cap reduction at the beginning of the 2014 calendar-year control period, and co

4-12 

ntinue to 

duce the cap to a total of 25 percent in annual five percent reductions from 2015 to 2017. 

Houston-Galveston-Brazoria State Implementation Plan 

repared by ENVIRON for the H-GAC).

re

4.6.2 Local Programs 

The H-GAC worked with HGB area local governments and business stakeholders to develop 

appropriate control strategies to meet the SIP requirements and to recruit stakeholders who would 

take legal responsibility for implementing these strategies through the establishment of memoranda of 

agreement. As a result, six projects were identified as Transportation Control Measures (TCMs), and 

numerous strategies were agreed upon with local governments as voluntary measures. For more 

information regarding the development of local control strategies, see Appendix F: Evaluation of 

Mobile Source Control Strategies for the 

(p

4.6.2.1 Transportation Control Measures

TCMs are transportation projects and related activities that are designed to reduce on-road mobile 

source emissions and are included as control measures in the SIP. Allowable types of TCMs are 

listed in § 7408 (Air Quality Criteria and Control Techniques) of the FCAA, and defined in the 

federal transportation conformity rule found in 40 CFR, Part 93 (Determining Conformity of Federal 

Actions to State or Federal Implementation Plans). The federal transportation conformity rule 

requires that timely implementation of TCMs be demonstrated. In general, TCMs are transportation 

related projects that attempt to reduce vehicle use, change traffic flow, or reduce congestion 

conditions. Projects that add single-occupancy-vehicle roadway capacity or are based on 

provements in vehicle technology or fuels are not considered to be TCMs. 

AC’s Technical 

dvisory Committee approved and identified funding for these local commitments. 

im

The H-GAC has identified TCMs that have been or will be implemented in the nonattainment area. 

By the start of the 2018 ozone season, these TCMs will reduce NOX emissions in the HGB area by 

.015 tons per day (tpd). Appendix G: Transportation Control Measures for the HGB Attainment 

Demonstration SIP Revision for the 1997 Eight-Hour Ozone Standard (prepared by ENVIRON for 

the H-GAC) summarizes the emission reductions by type of TCM. The H-G

A

4.6.2.2 Voluntary Mobile Emission Reduction Programs 

Voluntary mobile source measures have the potential to contribute, in a cost-effective manner, 

mission reductions needed for progress toward attainment and maintenance of the NAAQS. 

ctor activity levels or changes in vehicle and engine fleet composition were explored 

nd developed. 

gaging the public to make changes in activities 

at will result in reducing mobile source emissions. 

e

Historically, federal mobile source control strategies have focused primarily on reducing emissions 

per mile through vehicle and fuel technology improvements. Tremendous strides have been made 

resulting in new light-duty vehicle emission standards that are 70 to 90 percent less than that for the 

1970 model year. However, mobile sources continue to constitute a significant portion of ozone 

precursor emissions in the HGB area due to population and employment growth as well as an increase 

in daily vehicle miles traveled per person. Therefore, mobile source strategies that attempt to 

complement existing regulatory programs through voluntary, non-regulatory changes in local 

transportation se

a

A number of voluntary mobile source and transportation programs have already been initiated at the 

state and local levels in response to increasing interest by the public and business sectors in creating 

alternatives to traditional emission reduction strategies. Some examples include economic and 

market-based incentive programs, trip reduction programs, growth management strategies, ozone 

action programs, and targeted public outreach. These programs attempt to gain additional emissions 

reductions beyond mandatory FCAA programs by en

th
The H-GAC identified three voluntary measures that will aid in the improvement of the HGB region’s 

air quality. These measures were identified through a contract between H-GAC and ENVIRON 

International Corporation. Nineteen meetings were held with stakeholders from the region to solicit 

comments and suggestions for voluntary programs. The H-GAC’s commitment for NOX from VMEP 

is 2.25 tpd. The H-GAC, as the regional metropolitan transportation planning agency for the HGB 

area, has committed to make a good faith effort to implement the projects and/or programs outlined in 

this document and will be responsible for monitoring and reporting the emission reductions to the 

TCEQ. More information on each of the VMEP commitments can be found in Appendix H: 

Voluntary Mobile Emission Reduction Programs for the HGB Attainment Demonstrat

4-13 

ion SIP 

evision for the 1997 Eight-Hour Ozone Standard (prepared by ENVIRON for the H-GAC). 

 Eight-County HGB Area. For additional detail, see Appendix B: Emissions 

ventory Development. 

T n ight-County HGB Area 

R

4.7 Motor Vehicle Emissions Budget (MVEB) 

The MVEB refers to the maximum allowable emissions from on-road mobile sources for each 

applicable criteria pollutant or precursor as defined in the SIP. The budget must be used in 

transportation conformity analyses. Areas must demonstrate that the estimated emissions from 

transportation plans, programs, and projects do not exceed the MVEB. The attainment budget 

represents the on-road mobile source emissions that have been modeled for the attainment 

demonstration. The budget reflects all of the on-road control measures reflected in that 

demonstration. The MVEB is shown in Table 4-2: 2018 Attainment Demonstration Motor Vehicle 

Emissions Budget for the

In

able 4-2: 2018 Attainme t Demonstration MVEB for the E

Eight-County HGB Area Summer Weekday Emis tpd) sions (

NOX VOC 2018 MVEB 49.22 45.97 

4.8 MONITORING NETWORK 

States are required by 40 CFR, Part 58, Subpart B, to submit an annual monitoring network review to 

the EPA by July 1 of each year. This network review is required to provide the framework for 

establishment and maintenance of an air quality surveillance system. The annual monitoring network 

review must be made available for public inspection for at least 30 days prior to submission to the 

EPA. The review, and any comments received during the 30 day inspection period, are then 

forwarded to the EPA for final review and approval. The TCEQ posted this plan from June 1 through 

June 30, 2009. The document presented the current Texas network of ambient air Photochemical 

Assessment Monitoring Station (PAMS) monitors as well as proposed changes to the network from 

uly 1, 2009, through December 31, 2010. 

 sampling at the Deer Park 

onitor (AQS ID 48-201-1039) will continue January through December. 

J

This network review includes posting of the TCEQ's EPA-approved PAMS Network Plan which 

focuses on ozone precursors. The reclassification of the Houston ozone nonattainment area to severe 

requires one major change in the HGB area PAMS plan. The TCEQ will conduct intensive carbonyl 

sampling at the Clinton PAMS Type 2 Site (AQS ID 48-201-1035) each year. As agreed upon with 

the EPA, Region 6, the TCEQ will collect a total of 240 carbonyl samples at this site at a sampling 

frequency of eight 3-hour samples per day every three days during July-September. Carbonyl 

sampling will be terminated at the Houston Channelview site to offset this increased sampling 

schedule at the Clinton site. The 24 hour sample every sixth day carbonyl

m

4.9 CONTINGENCY PLAN 

SIP revisions for nonattainment areas are required by § 172(c)(9) of the FCAA to provide for specific 

measures to be implemented should a nonattainment area fail to meet reasonable further progress 

(RFP) requirements or attain the applicable NAAQS by the attainment date set by the EPA. These 

contingency measures are to be implemented without further action by the state or the EPA. In the 
General Preamble for implementation of the FCAA Amendments of 1990 published in the April 16, 

1992, issue of the Federal Register (57 FR 13498), the EPA interprets the contingency requirement to 

mean additional emissions reductions that are sufficient to equal up to 3 percent of the e

4-14 

missions in 

e adjusted base year inventory. These emissions reductions should be realized in the year following 

our Ozone Nonattainment Area Reasonable Further Progress 

IP revision (Project No. 2009-018-SIP-NR), which is being proposed concurrently with this 

ble Further Progress Demonstration 

alculations Spreadsheet of the HGB 1997 Eight-Hour Ozone Nonattainment Area Reasonable 

Table 4-3: 2019 Contingency n for the HGB Area 

th

the year in which the failure is identified (i.e., an RFP milestone year or attainment year). 

The adjusted base year emissions inventory is used in the RFP planning process to calculate required 

emissions reduction targets and excludes certain on-road mobile source emissions reductions from 

controls that were promulgated prior to the 1990 amendments to the FCAA. This 1997 eight-hour 

ozone attainment demonstration SIP revision also uses the adjusted base year inventory as the 

inventory from which to calculate the required 3 percent reduction for contingency. For further 

information regarding the adjusted base year inventory for the HGB area and how the area meets RFP 

requirements, see the HGB 1997 Eight-H

S

attainment demonstration SIP revision. 

A summary of the 2019 contingency analysis is provided in Table 4-3: 2019 Contingency 

Demonstration for the HGB Area. Consistent with the EPA’s NOX substitution guidance, the 3 

percent attainment demonstration contingency analysis for 2019 is based on a 2 percent reduction in 

NOX emissions (17.16 tpd) and a 1 percent reduction in VOC emissions (9.36 tpd) to be achieved 

between 2018 and 2019 (EPA, 1993). Inventory analyses were performed on the fleet turnover 

effects for the federal emission certification programs for on-road and non-road vehicles. The 

emission reductions from 2018 to 2019 were estimated for these programs. For a detailed description 

of the contingency reductions, see Appendix 1: HGB Reasona

C

Further Progress SIP revision (Project No. 2009-018-SIP-NR). 

Demonstratio

Description 

NOX VOC 

Adjusted 2018 Base Year Emissions Inventory 8 93 58.18 5.57

Percent for Contingency Calculation (total of 3 percent) 2.00 1.00

2018 to 2019 Required Contingency Reductions 17.16 9.36

Federal On-Road Mobile New Vehicle Certification Standards 3.97 2.73

Federal On-Road Reformulated Gasoline (RFG) 5.09 0.70

State I/M and Anti-Tampering Programs (Brazoria, Fort Bend, 

Galveston, Harris, and Montgomery Counties) 1.23 0.31

Federal Non-Road Mobile New Vehicle Certification Standards 3.56 1.78

Non-Road RFG Gasoline 0.00 0.03

Federal Tier I and II Locomotive Standards 0.68 0.01

Federal Tier 2 Marine Diesel Standard 0.55 0.02

Additional Contingency Measures to be Quantified before 2019 2.08 3.78

Total Contingency Reductions 17.16 9.36

Contingency Excess (+) or Shortfall (-) 0.00 0.00

Note: Emissions are represented in tons per day.

re study before emissions reductions can be quantified 

To meet the contingency requirement, the TCEQ will evaluate potential control measures to be 

implemented at the state level that require mo
4-15 

are not yet final or have not yet been implemented. Potential measures 

clude but are not limited to the following: 

Potentia

and federal measures that 

in

l State Measures

Gas Imaging "Find and Fix" Rule 

Contingency measure rule to require the use of gas imaging camera t

•

echnology for periodic 

spection of sources of VOC emissions such as storage tanks, barges, etc., that are not 

ontingency measure rule to require 

e use of gas imaging camera technology for more frequent monitoring on difficult-toto-monitor components that would normally have very long monitoring 

frequencies under traditional LDAR monitoring rules. 

Potentia

in

currently subject to leak detection monitoring programs and set reasonable time periods for 

companies to address possible problems found (e.g., leaking seals). 

• Enhanced LDAR for Difficult-to-Monitor Components C

th

monitor and unsafel Federal Measures

• International Maritime Engine Emission Standards for Oceangoing Vessels 

m 

nover. 

•

r 

E rules are part of a 

larger federal energy bill, H.R. 6, which was signed into law on December 19, 2007. The 

 in 2019. 

e in 2013. 

• EPA Proposed Rule to Reduce Air Toxics Emissions from Area Source Asphalt Refining and 

 would likely go into effect before 2019. 

• EPA Final Rule for National Volatile Organic Compound (VOC) Emission Standards for 

nd reactivity factors go into effect July 2009. 

Any measure used to meet the contingency requirement will be included in the SIP for the 1997 eighthour ozone standard in the HGB area before 2019. 

If implemented by the EPA, this measure would result in annual emissions reductions fro

fleet tur

Potential Enhanced Corporate Average Fuel Economy (CAFE) Standards for Cars and 

Trucks 

The original federal measure increased the fuel economy of vehicles starting with model yea

2011 to approximately 35 miles per gallon (mpg) in 2020. The CAF

administration is proposing to move the 35-mpg requirement to 2016. This measure would

result in fleet turnover reductions that could be available

• EPA Proposed Rule to Reduce Air Toxics from Stationary Diesel and Gas-Fired Engines 

If finalized, this rule would become effectiv

Asphalt Roofing Manufacturing Facilities 

If finalized, this rule

Aerosol Coatings 

Final rule amendments to add compounds a
4-16 

.10 REFERENCES 

PA, 1993. NO Substitution Guidance, http://www.epa.gov/ttncaaa1/t1/memoranda/noxsubst.pdf

4

E X

EPA, 2005. Clean-Fuel Vehicle Standards, no. CCD-05-12. 
5-1

CHAPTER 5: WEIGHT OF EVIDENCE 

5.1 QUANTITATIVE CORROBORATIVE ANALYSIS 

5.1.1 Introduction 

The corroborative analysis presented in this chapter demonstrates the progress that the HoustonGalveston-Brazoria (HGB) area is making towards attainment of the 1997 eight-hour ozone National 

Ambient Air Quality Standard (NAAQS) of 0.08 parts per million (ppm). The United States 

Environmental Protection Agency’s (EPA) April 2007 “Guidance on the Use of Models and Other 

Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze” 

(EPA, 2007) states that all model attainment demonstrations should include supplemental evidence that 

the conclusions derived from the basic attainment modeling are supported by other independent sources 

of information. This document will present the supplemental evidence, i.e., the corroborative analyses, 

for the current modeling demonstration. The guidance also states that a weight of evidence demonstration 

is allowed when the future design value is at or below 87.9 parts per billion (ppb). 

The first section of the quantitative corroborative analysis will discuss photochemical grid modeling. 

Modeling is one of the most important tools available for evaluating progress toward meeting air quality 

standards, but it is not a perfect tool. The first section will also discuss known issues with photochemical 

grid modeling and how the Texas Commission on Environmental Quality (TCEQ) has dealt with them. It 

also discusses overall model performance. Finally, it discusses the diagnostic analyses performed by the 

TCEQ, and the implications of those analyses on the projected attainment status. The second section of 

the quantitative corroborative analysis will discuss trends in ozone and ozone precursors observed in the 

HGB area, and examines the possible causes for those trends. The third section describes air quality 

control measures that cannot yet be adequately quantified but are nonetheless expected to yield tangible 

air quality benefits. 

5.2 Corroborative Analysis: Modeling 

Photochemical grid modeling of the HGB area is challenging, due to complex coastal wind circulation, 

complex petrochemical point sources of emissions in Brazoria, Chambers, Galveston, and Harris 

Counties, and the challenges associated with modeling a metropolitan area of over five million 

inhabitants. 

One purpose of the Texas Air Quality Study 2000 (TexAQS 2000) and the Texas Air Quality Study 2006 

(TexAQS II) field studies was to address the uncertainties that affect photochemical grid modeling and 

their regulatory applications. Insights gleaned from the TexAQS 2000 and subsequent studies have 

helped resolve some of these uncertainties. 

Several studies have tried to identify and reduce uncertainties in the HGB photochemical grid modeling. 

Foremost among these efforts are the studies that have sought to quantify underreported industrial highly 

reactive volatile organic compounds (HRVOC) emissions (Wert et al., 2003; Xie and Berkowitz, 2007; 

Yarwood et al., 2004; TCEQ, 2002, 2004, 2006; Smith and Jarvie, 2008) and to assess the sensitivities of 

ozone simulations to underreporting these emissions (TCEQ, 2002, 2004, 2006; Byun et al., 2007; Jiang 

and Fast, 2004). Other modeling efforts have tested different chemical mechanisms in the HGB area’s 

photochemical grid modeling, to study the effects of using different mechanisms on ozone model 

performance and control strategy effectiveness (Byun et al., 2005b; Faraji et al., 2008; Czader et al., 

2008). Modeling sensitivity studies have also been performed to guide selection of model parameters 

such as vertical mixing schemes, number and depth of model layers, and horizontal grid resolution 

(Kemball-Cook et al., 2005; Byun et al., 2005b; Byun et al., 2007; Bao et al., 2005). 

 
5-2

Some of the most important findings of these studies include the following. 

• Emissions inventories must be reconciled to some extent with observational data before the 

model can accurately depict the ozone formation processes in the HGB area, especially for 

HRVOC. 

• Adding HRVOC to modeling emissions inventories generally increases ozone concentrations and 

alleviates a portion of the ozone and HRVOC under-prediction problems found by every 

modeling group who has attempted to model the HGB area. 

• Reactivities of the TCEQ-defined HRVOC are high regardless of which chemical mechanism is 

used to evaluate their effects. In addition to the TCEQ list of HRVOC, formaldehyde also 

displays high reactivity. 

Mesoscale meteorological modeling is used to drive photochemical grid models, and many studies have 

examined and reduced uncertainties in these models as well. One of the most successful efforts improved 

meteorological simulations of ozone episodes by using radar profiler and other upper level wind data to 

“nudge” the meteorological modeling (Nielsen-Gammon et al., 2007; Zhang et al. 2007; Stuart et al., 

2007; Bao et al., 2005; Fast et al., 2006). Other efforts improved land cover data and land surface 

modeling (Byun et al., 2005a; Cheng et al., 2008a, 2008b) and studied the sensitivity of ozone simulations 

to solar irradiance and photolysis rates (Zamora et al., 2005; Fast et al., 2006; Pour-Biazar et al., 2007; 

Byun et al., 2007; Koo et al., 2008). 

Some of the most important findings of these meteorological modeling studies include the following. 

• Assimilation of radar profiler and other upper air wind data is essential to good meteorological 

modeling performance in the HGB area. 

• Modeling parameterizations need to be chosen carefully to alleviate the common problem of 

spurious thunderstorms and clouds. 

• Accurate simulation of cloud cover is crucial to getting photolysis rates correct in the 

photochemical grid model, and ozone predictions are very sensitive to photolysis rates. 

• An ensemble approach to meteorological and photochemical grid modeling may be warranted, 

given the sensitivity of ozone modeling to relatively small changes in meteorology. The 

ensemble approach will allow probabilistic attainment demonstrations to be produced. 

In the remainder of this section, modeling issues identified by the studies described above will be 

discussed, as well as issues raised by TexAQS 2000 research, by TexAQS II research, and by TCEQsponsored investigations. Overall performance of the photochemical grid modeling and the implications 

of the model’s ability to accurately simulate ozone episodes will also be discussed. Finally, additional 

metrics that show the effects of the proposed control strategies on ozone in the HGB area will be 

presented. 

5.2.1 Solving Modeling Problems 

For the HGB area, there are several aspects of ozone modeling that require special attention, due to their 

role in current or historical shortcomings in model performance. This section discusses some of these 

issues, and how TCEQ has attempted to resolve them in this round of modeling. 

5.2.1.1 Industrial Point Source Emission Inventory Issues 

High concentrations of light alkenes such as propylene, ethylene, 1,3-butadiene, and butenes have been 

observed in the HGB metropolitan area, and are closely associated with petrochemical industry facilities 

in eastern Harris, Galveston, Chambers, and Brazoria Counties (Ryerson et al., 2003; Daum et al., 2003; 

Daum et al., 2004; Berkowitz et al., 2004; Berkowitz et al., 2005; Kleinman et al., 2002; Kleinman et al., 

2005; Jobson et al., 2004; Karl et al., 2003; Buzcu and Fraser, 2006; Xie and Berkowitz, 2006, 2007; Kim 

et al., 2005). These compounds have been identified as highly reactive, and they play a major role in 

forming the highest concentrations of ozone observed in the HGB area (Ryerson et al., 2003; Daum et al., 

2003, 2004; Kleinman et al., 2002, 2005; Wert et al., 2003; Czader et al., 2008). Historical analyses of 

routinely collected volatile organic compounds (VOC) data indicate that these compounds are present in 
5-3

high concentrations on a routine basis in the HGB area (Hafner Main et al., 2001; Estes et al., 2002; 

Brown and Hafner Main, 2002; Brown et al., 2002; Hafner and Brown, 2003; Jolly et al., 2003; Fang and 

McDowell, 2003; Jolly, 2003; Kim et al., 2005; Buzcu and Fraser, 2006; Xie and Berkowitz, 2006, 2007). 

Consequently, the high HRVOC concentrations observed during the two field study periods in 2000 and 

2006 are not anomalously large, and the conclusions drawn from those data should be generally 

applicable to the HGB area. 

Both field studies sponsored by the TCEQ, TexAQS 2000 and TexAQS II, have indicated that there are 

substantial discrepancies in the reported emissions of HRVOC, especially ethene and propylene (Ryerson 

et al., 2003; Daum et al., 2003; Daum et al., 2004; Wert et al., 2003; Gilman et al., 2009; de Gouw et al., 

2009). The TCEQ remote sensing studies of flares, storage tanks, cooling towers, and other sources have 

shown that large quantities of VOC emissions have gone unreported (Robinson et al., 2008; Smylie et al., 

2004). In addition, solar occultation flux measurements have shown that 30-minute variations in 

industrial HRVOC emissions can be an order of magnitude or more (Mellqvist et al., 2007, 2008). 

In an attempt to better quantify underreported HRVOC for purposes of photochemical grid modeling, the 

TCEQ commissioned a study by researchers at the Pacific Northwest National Laboratory (Xie and 

Berkowitz, 2006, 2007). The researchers used historical HRVOC measurements from the extensive 

automated gas chromatograph network currently in place in the industrial areas of the HGB area. Most of 

the sites in this network went into operation during 2003. Using trajectories to link the source areas to the 

observations, the researchers were able to estimate which areas had the greatest emissions relative to other 

areas. 

For the current round of modeling, TCEQ researchers extended the methods developed by Pacific 

Northwest National Laboratory to quantitatively estimate underreported HRVOC emissions in the HGB 

area. The Potential Source Contribution Function method has measurably improved model performance 

for ozone and its precursors by reconciling the industrial point source emissions inventory with observed 

HRVOC concentrations during 2005-2006 (Smith and Jarvie, 2008). This method does not attempt to 

reproduce the temporal variations in emissions, but instead calculates a median rate of emission for each 

square kilometer of the HGB area. Since two years of data are used to estimate the medians, the metric is 

statistically robust. 

5.2.1.2 Modeling of Emissions Events

Attempts have been made to quantify temporal variations in industrial point source emissions by 

accessing emission event reports that are delivered by industry to the TCEQ (Murphy and Allen, 2005). 

Problems with the event report data include the following. 

• Emission events were self-reported by industry, and the quantities of emissions reported were not 

independently observed or verified. Facilities are allowed, by rule, to estimate emissions during 

emergency releases due to safety concerns. 

• Emission events were only reported if estimated emissions were greater than a certain threshold 

above the permitted emission level. Some facilities have very large permitted emissions levels, and 

therefore large fluctuations in emissions may occur under an authorized emission rate that are not 

included in the data set. Consequently, the frequency and magnitude of emission events in this data 

set does not reflect the actual magnitudes or frequency of emission events. 

• Emission event data for the Murphy and Allen study were collected before industry was required to 

monitor HRVOC. Therefore, most of the emission estimates are not based upon measurements of 

the events. 

• The TCEQ infrared camera studies have found numerous instances where emissions were 

emanating from locations that were not included in any emissions inventory. 

• The TCEQ flare investigations have found that flares are typically managed to reduce noise, smoke, 

and glare. Optimizing the flare to keep destruction efficiency at a maximum is a secondary 

consideration. In particular, flares used as both emergency flares and process flares have been 

observed to operate with poor combustion efficiency when operating in process flare mode 

(Robinson et al., 2008). 
5-4

• In addition, flare monitoring records only the chemicals flowing to the flare, not which species are 

actually being emitted. Combustion efficiencies are estimates of how much of the original material 

has been destroyed, and no effort is made to estimate the composition or reactivity of the 

combustion products. Circumstantial evidence from the TexAQS II and from the Study of Houston 

Atmospheric Radical Precursors (SHARP) suggests that formaldehyde may be produced during 

flare combustion, though the absolute quantity of emissions may only constitute a small part of the 

observed ambient formaldehyde (Gilman et al., 2009; De Gouw et al., 2009). The SHARP field 

campaign in April-May 2009 is investigating this hypothesis in greater depth. 

• Field studies (Mellqvist et al., 2007, 2008; de Gouw et al., 2009) and recent infrared camera and 

differential absorption lidar (DIAL) results (Robinson et al., 2008) show that the techniques used by 

industry to estimate HRVOC point source emissions are still inadequate to quantify them properly, 

because these experiments measured much higher emission fluxes than were reported. 

A number of recent modeling studies have attempted to investigate the frequency, magnitude, and impact 

of emission events upon ozone in Houston (Webster et al., 2007; Nam et al., 2006, 2008). Since these 

studies are based upon the emission event reports, they have not properly quantified the frequency or 

magnitude of the emission events, due to the problems discussed above. Therefore, the modeled impact 

of emission events described in the Webster et al. and Nam et al. studies are unlikely to accurately reflect 

the complete impact of emission events in the HGB area. Since the acquisition of properly quantified 

emissions for all industrial emission events that occur in the HGB area appears to be far in the future, the 

TCEQ has not attempted to speculate on the exact frequency or magnitude of sporadic emission events in 

this modeling exercise. 

5.2.1.3 Resolution of Photochemical Modeling Grids 

Numerous studies have investigated the effects of grid size on model behavior (Cohan et al., 2006; Esler, 

2003; Gego et al., 2005; Valari and Menut, 2008). The main interest in finer grid resolution is that higher 

resolution can increase concentrations of ozone precursors in narrow plumes, which can affect ozone 

production rate and sensitivity to VOC or nitrogen oxides (NOX) within the plumes. In a city such as 

Houston, using a higher resolution grid is sensible, given the abundance of industrial point sources, which 

can generate narrow plumes. Researchers during TexAQS 2000 determined that rapid ozone formation 

occurring within narrow industrial plumes are responsible for the highest observed ozone in the HGB 

area, and for the strong ozone gradients that can form. Strong ozone gradients can cause large increases 

in ozone concentration at monitoring sites as the plume is carried across town by winds that have shifted 

direction and are no longer parallel to the plumes. To resolve these atmospheric features, the TCEQ is 

using smaller-sized grid cells than previous modeling exercises (2 kilometer (km) × 2 km instead of 4 km 

× 4 km). In general, the TCEQ has found that smaller grid sizes can yield higher ozone production and 

can alleviate, in part, the commonly observed low bias for ozone within industrial plumes. There are 

limits to this solution, however; it is inappropriate to decrease grid size indefinitely. Parameterizations in 

both the meteorological modeling and the photochemical grid modeling are based upon the assumption 

that turbulence features within the planetary boundary layer (PBL) are much smaller than the grid size. If 

the grid size is decreased to 1 km × 1km or lower, the assumption probably no longer holds, and more 

uncertainty can be added to the modeling as a result of the finer resolution. If smaller grid sizes are 

desired, large eddy simulation modeling should be considered rather than photochemical grid modeling. 

Also, note that if the spatial resolution of the photochemical grid modeling is reduced, then the temporal 

resolution of the meteorological and chemical processes within the model ought to be reduced, to match 

the shorter residence time of precursors in each grid cell. In other words, as the size of the box shrinks, 

the amount of time that a mass of air resides in the box also shrinks, affecting how the ozone chemistry 

plays out. While the Comprehensive Air Model with Extensions (CAMx) automatically adjusts the time 

step for chemical processes, the meteorological process time step is fixed, based upon the input data from 

the Fifth Generation Meteorological Model (MM5). While it is possible to extract meteorological output 

with higher temporal resolution, reduction of the time steps seems likely to cause unusual model 

behavior. The reduction of time steps in regulatory photochemical grid modeling has not been well 

studied. In the future, it may be desirable to use grid sizes smaller than 2 km, and shorter time steps, but 

for now, TCEQ will refrain from experimenting with finer resolutions. For this round of modeling, the 
5-5

TCEQ has reduced the size of the CAMx modeling grid cells from 4 km to 2 km through flexi-nesting, 

but has kept the size of the MM5 modeling grid cells at 4 km. 

5.2.1.4 Incommensurability and Model Performance Evaluation 

Swall and Foley (2009) discuss the problems inherent in comparing point measurements to grid cell 

values. In statistical parlance, this problem is known as incommensurability. A portion of the difference 

between point measurements and grid cell values is due solely to the fact that measurements made at a 

monitoring station do not generally represent an average of the conditions for the 2 km × 2 km grid cell in 

which it resides. The ability of a point measurement to represent the average of the entire grid cell area is 

related to how much sub-grid variation is observed in the area. If sub-grid variation is small, then the 

point measurement and the grid cell value are commensurate. If the spatial gradients of the variables of 

interest are large, the point measurements are less able to reflect the average conditions of the entire grid 

cell, and therefore they are incommensurate with the grid cell value. 

HGB area ozone often has strong spatial gradients due to the rapid ozone formation within industrial 

source plumes. In the HGB area, the worst ozone model performance is sometimes found in areas with 

the steepest ozone gradients, and the best ozone model performance is often found in areas further 

downwind, where the ozone gradients have lessened. Swall and Foley demonstrated that 

incommensurability alone is capable of degrading model performance in areas of steep gradients. They 

state in their discussion: “This means that, even if the model is performing perfectly and there is no 

observational error, we cannot expect that in a scatterplot, points representing paired modeled and 

observed values will lie on a one-to-one line. Our comparison of Gaussian and exponential correlation 

structures with the same effective range shows that this concern looms larger for correlation structures in 

which there is a rapid decrease in correlation for small distances relative to grid cell size (like the 

exponential).” While there are other causes of poor model performance as well, note that 

incommensurability is likely to be responsible for some of the differences between model output and 

point measurements. 

5.2.1.5 Ensemble Modeling 

A number of researchers have discussed the benefits of using ensembles of models to create more 

accurate forecasts (Pinder et al., 2009; Zhang et al., 2007). Pinder et al. and Zhang et al. have noted that 

probabilistic attainment demonstrations could be made using ensemble modeling and have argued that 

this approach can be more scientifically sound than a deterministic attainment demonstration. The TCEQ 

acknowledges the potential soundness of the ensemble approach but notes that the current regulatory 

framework does not easily allow for a probabilistic attainment demonstration. 

5.2.1.6 Vertical Distribution of Ozone 

Ozonesonde measurements have been made each summer in the HGB area since 2003 (Morris et al., 

2006). Findings from this study indicate that elevated free tropospheric ozone (i.e., above the PBL) in the 

HGB area is usually underestimated, and it often does not appear to mix down to the ground. Ozone in 

the lowest layers of the atmosphere often shows much more structure than the model simulates. The 

implication is that the model is mixing the lowest layers of the atmosphere more efficiently than they are 

actually mixing. The TCEQ has attempted to address these two issues. For the free tropospheric ozone, 

the TCEQ has obtained global model output for the appropriate time periods so that boundary conditions 

of free tropospheric ozone are more appropriate. Some of the discrepancies still persist; they appear to be 

related to phenomena that occur between the outermost domain boundaries and the HGB area. . For the 

PBL mixing issue, the TCEQ has improved the land cover data and sea surface temperature data in its 

latest round of modeling, in an attempt to improve the simulations of surface energy balance. In addition, 

the TCEQ has chosen the Eta PBL scheme (i.e., the Mellor-Yamada-Janjic scheme), which appears to be 

more effective at simulating PBL dynamics in the coastal regions than other available schemes. The 

TCEQ continues to investigate potential improvements for vertical mixing in the modeling. 

5.2.1.7 Photolysis Discrepancies Due to Improper Placement of Clouds 

Researchers at the University of Alabama-Huntsville performed a modeling study that examined the 

effects of modeled cloud cover on ozone performance in the HGB area, and found that some of the 
5-6

shortcomings in model performance could be corrected with better depiction of clouds (Pour-Biazar et al., 

2007). University of Houston researchers also found that their forecasts were occasionally biased due to 

poor depiction of cloud cover (Byun et al., 2007). TCEQ-funded research found that higher-order 

decoupled direct method analysis of modeling sensitivities indicated substantial sensitivity to photolysis 

rates (Koo et al., 2008). 

The TCEQ has found similar cloud cover effects in the photochemical modeling for this state 

implementation plan (SIP). The greatest discrepancies tend to involve the model under-predicting cloud 

cover, and hence, greatly over-predicting ozone on low ozone days. Modeled episode days for which 

cloud cover problems exist include: May 28, 2005; June 17, 2005; July 31, 2005; Aug 5, 2005; May 31-

June 1, 2006; Aug 15, 2006; Aug 19, 2006; Aug 22, 2006; September 12, 2006; October 10, 2006. The 

average mean normalized bias for these days is +34.6 percent, compared to an average mean normalized 

bias on exceedance days of +9.7 percent. TCEQ process analysis shows that most of the radical 

initiation, propagation and termination steps are very sensitive to photolysis rates. Hence, improvements 

in cloud placement could greatly improve ozone and precursor performance, though the greatest 

improvements will likely occur on low ozone days. 

To improve the cloud distribution, the TCEQ has followed the guidance of Texas A&M University 

(TAMU) researcher and state climatologist John Nielsen-Gammon and has utilized the Grell cumulus 

parameterization, which reduces the amount of spurious thunderstorm formation in the HGB area. 

5.2.1.8 Radical Shortage 

A number of researchers studying urban photochemistry in the HGB area and other cities have found that 

available mechanisms for simulating radical production are unable to replicate the observed radical 

formation and propagation rates (Mao et al., 2007, 2009; Chen et al., 2009). The process analysis section 

of Appendix I: Corroborative Analysis for the HGB Attainment Demonstration SIP discusses this issue in 

detail and compares TCEQ process analyses to the Mao et al. and Chen et al. work. The TCEQ modeling 

is consistent with the Mao et al. and Chen et al. findings that there is apparently something missing in the 

current mechanisms. The atmospheric chemistry community as a whole has not yet resolved the problem 

or problems with the current mechanisms. Several hypotheses for the missing radical formation 

mechanism exist, including daytime nitrous acid (HONO) production from nitric acid-aerosol interactions 

and photolysis (Ziemba et al., 2009); isoprene production of hydroxyl radical (OH) (Lelieveld et al., 

2008; North and Ghosh, 2009); formation and decomposition of electronically excited nitrogen dioxide 

(NO2

*

) (Li et al., 2008); nitryl chloride (ClNO2) chemistry (Osthoff et al., 2008; Simon et al., 2008); 

improved aromatic chemistry (Faraji et al., 2008; Hu et al., 2007); and molecular chlorine reactions 

(Chang et al., 2002; Tanaka et al., 2003; Chang and Allen, 2006; Sarwar and Bhave, 2007). Given the 

manifold hypotheses and the current lack of a definitive explanation, the TCEQ has not incorporated 

modified chemical mechanisms into its base case modeling at this time. However, the TCEQ continues to 

support investigations for improving chemical mechanisms, and is prepared to adopt an improved 

mechanism when it becomes sufficiently mature. 

5.2.2 Model Performance Evaluations: Implications of the Model Performance of the Current SIP 

Modeling 

Model performance evaluation is presented in Chapter 3, Photochemical Modeling and in its associated 

appendices. Appendix I: Corroborative Analysis for the HGB Attainment Demonstration SIP includes 

two discussions of model performance in the Chemical Process Analysis and Intensive Model 

Performance sections. In addition, Appendix I: Corroborative Analysis for the HGB Attainment 

Demonstration SIP includes a discussion of using 2005 baseline modeling to estimate future 2018 design 

values. Based upon these evaluations, the following overall conclusions can be reached. 

Ozone performance 

• The model simulates the location, spatial extent, and relative intensity of ozone relatively well on 

most of the high-ozone days. 

• The model consistently underestimates peak ozone within the highest concentration plumes. 

• Simulated ozone depicts rapid morning ozone increases (30-50 ppb) relatively well, but tends to 
5-7

miss afternoon peak concentrations. 

• Radical and ozone precursor budgets were calculated directly from observations by Mao et al. 

(2009) at the Moody Tower during TexAQS II. They observed that ozone formation in the HGB 

area is both VOC- and NOX-sensitive, with VOC-sensitive ozone formation usually occurring in 

the morning and NOX-sensitive formation occurring in the afternoon. Based upon the TCEQ’s 

process analysis, the TCEQ modeling appears to be simulating the VOC- and NOX-sensitivity of 

ozone formation at Moody Tower relatively well, because the relative radical termination rates 

generally agree with the Mao et al. data. 

• Process analysis and modeling sensitivity analyses show that peak eight-hour ozone is primarily 

NOX-sensitive in much of the domain, but can be VOC-sensitive downwind of the urban core and 

the HGB industrial areas. 

• According to TCEQ process analyses, VOC-sensitive conditions occur more often and more 

strongly in the industrial and urban core plumes. When ozone production is VOC-sensitive, 

usually more ozone is created than in NOX-sensitive conditions. 

• Chen et al. (2009) used the Moody Tower TexAQS II observations to constrain a steady-state 

photochemical box model. They used the Carbon Bond 05 chemical mechanism and several 

other chemical mechanisms to simulate the chemistry with the box model. They found that all of 

the chemical mechanisms underestimated peak daytime radical concentrations. The Carbon Bond 

05 mechanism used by the TCEQ in this modeling exercise is one of the better performing 

mechanisms, but it still doesn’t make enough radicals. The shortfall in radical production may be 

related to the shortfall in ozone production rates observed in the photochemical grid modeling. 

Note, however, that the results from Chen et al. are based upon a constrained steady-state box 

model, which assumes that the chemical system is in a photochemical steady state. It isn’t clear 

whether this assumption is valid all of the time in the HGB area. 

• Decreases in ozone production rates and other reaction rates correlate with decreases in NO2

photolysis, implying that most of the ozone formation chemistry is highly sensitive to photolysis, 

and hence, highly sensitive to cloud-cover errors. 

• Background ozone concentrations are important in accurately simulating the modeling for the 

HGB area. For most of the modeled days, the background ozone is unlikely to bias the modeling 

results in the HGB area, but during the July-August 2005 episode, excessively high background 

concentrations seem to compromise the model performance. 

• In rural areas, the model routinely over-predicts nighttime ozone and under-predicts NOX. The 

cause of this issue is unknown, but it could involve unreported NOX sources or problems with 

vertical mixing in rural areas. 

• Above the planetary boundary layer, the model sometimes underestimated ozone concentrations, 

especially in the springtime. Usually the high ozone above the PBL was not being mixed 

downward, so that this error usually did not have much effect upon the ozone concentrations in 

the HGB area. 

• Transport and mixing of urban and industrial emissions within the HGB area can apparently 

affect the ozone chemistry substantially, especially when the urban core plume and the industrial 

plumes mix together. Ozone behavior, including VOC- and NOX-sensitivity, appears to change 

when these plumes mix. The implication is that the VOC- and NOX-sensitivity of ozone 

formation in the HGB area depend somewhat on the wind direction. 

• Since ozone was sometimes overestimated during the evening hours, the model did not display 

the amount of dynamic range present in the observations. 

Ozone precursor performance

• In general, the modeling simulated ozone precursors relatively well, albeit with a large degree of 

scatter, and the peak concentrations for some species were underestimated. 

• NO2 was usually simulated in an unbiased manner, but nitric oxide (NO) was often 

underestimated for the peak concentrations, which were usually observed in the pre-dawn hours, 

i.e., during morning rush hour. 

• The highly reactive Carbon Bond 05 species ETH and OLE, which represent ethylene, propylene, 

and other alkenes, were well simulated much of the time, but the model tended to underestimate 
5-8

the peak concentrations. Concentrations of these two species were routinely overestimated at the 

Wallisville Road (CAMS 617) monitoring site. 

• The performance of isoprene, represented by the Carbon Bond 05 species ISOP, was mixed, with 

some areas showing no bias, others showing high bias, and others showing low bias. 

• Formaldehyde data were available during the TexAQS II study at three sites. For the Moody 

Tower site, the concentrations were usually well simulated, but the peak concentrations were 

underestimated. For the Lynchburg Ferry (CAMS 1015) and HRM-3 Haden Road (CAMS 603) 

sites, the performance was mediocre. The HRM-3 Haden Road (CAMS 603) observations were 

consistent with secondary formaldehyde formation as the main source of formaldehyde, but the 

diurnal patterns of the modeled concentrations were more consistent with a primary source: 

concentrations peaked in the pre-dawn hours, like NO. The aircraft data generally show that the 

model underestimated formaldehyde peaks, though the location, extent, and relative magnitude 

were well simulated, much like the ozone data. 

Meteorological performance evaluation

• The meteorological modeling was able to successfully replicate the major features of ozone 

episodes in the HGB area much of the time, including the typical veering pattern of local winds, 

stagnation and flow reversal, and the coastal oscillations associated with the Galveston Bay 

breeze and Gulf breeze. 

• Trajectory analyses and vertical wind profiles in the HGB area show that much of the time on 

high ozone days, the model transported ozone and precursors to approximately the correct areas 

at approximately the correct times. 

• The model occasionally did not generate enough cloud cover, resulting in high ozone on days 

when low ozone was observed. While the addition of the Grell cumulus parameterization and 

improved land surface characteristics data appeared to reduce the common problem of spurious 

thunderstorms, the problem has not been completely eliminated. 

• Episode days with strong stagnation were more difficult to model precisely than days for which 

the winds did not stagnate. The model sometimes simulated nighttime winds that were too brisk, 

resulting in more dilution of emissions than was actually observed. 

• Ozonesonde and radar profiler data indicate that for most episode days, the PBL over land 

appeared to be modeled with good accuracy. Over water, however, planetary boundary layer 

depth was consistently modeled less accurately. 

Model response to emission changes

• The base case modeling has been challenged with different emissions inventories in order to 

evaluate its dynamic response to emission changes (Gilliland et al., 2009). 

• Adding more VOC to the flare emissions increases peak ozone concentrations, though the 

emission changes do not completely correct the ozone underestimations. Addition of 

formaldehyde emissions to HRVOC flares increases peak ozone concentrations further. 

• Substitution of flare emissions for the standard emission reconciliation tends to improve the 

model performance by increasing ozone production close to the industrial emission sources and 

by increasing the peak ozone concentrations, without adversely affecting ozone performance at 

other times and places. 

• Modeled ozone appears to decrease slightly in response to NOX emission decreases typical of the 

changes that occur on weekends. The observed weekend effect is a slightly stronger response to 

NOX emission decreases, implying that the model may be slightly less NOX-sensitive than it 

should be. 

• Modeled ozone increases substantially in response to VOC and NOX emission increases 

commensurate with the difference between 2006 emissions and 2000 emissions in the HGB area. 

When relative response factors are calculated using 2000 as the baseline year and 2006 as the 

future year, the modeled response to emission reductions is less vigorous than the observed 

response. This finding implies that the current modeling appears to underestimate the response to 

emission controls. If the atmosphere responds to the emission reductions from 2006 to 2018 in a 

manner similar to its response to the emission reductions between 2000 and 2006, the actual 

decrease in ozone design value will be greater than the model predicts. 
5-9

• Some of the strongest model responses to emission changes occur outside the boundaries of the 

current ozone monitoring network, and sometimes outside the current nonattainment area. This 

finding suggests that the proposed controls may have a greater impact on ozone than the 

responses registered at the different monitoring sites would indicate. 

5.2.3 Model Response to Proposed Controls: Additional Ways to Measure Progress 

Table 5-1: Changes in the Area and Population Affected by an Eight-Hour Ozone Design Value Greater 

than or Equal to 85 ppb in Response to Growth and Controls shows how the area affected by high ozone 

is expected to shrink dramatically in response to the emission changes projected to occur between 2006 

and 2018. Even though peak ozone drops by only 8 percent, the area with an estimated ozone design 

value greater than the 85 ppb standard shrinks by 96 percent. The population living in those areas and 

how the changes might reduce the number of people that encounter high ozone were considered. The 

estimated number of people residing in the high ozone areas decreases by 92 percent. Note that the 

population data is from the 2000 Census and has not been grown to reflect changes in population in those 

areas in 2006 or 2018. Also note that the numbers reflect areas where people reside, i.e., their home 

addresses, not necessarily where they might be during the hours of highest ozone during the ozone season. 

However, the dramatic decrease in the area with high ozone suggests that ozone decreases arising from 

the proposed control strategies are likely to benefit many residents of the HGB area. 

Table 5-1: Changes in the Area and Population Affected by an Eight-Hour Ozone Design Value 

Greater than or Equal to 85 ppb in Response to Growth and Controls 

Run name 

Peak 

Ozone, 

ppb 

Area with 

design 

value > 85 

ppb, km2

2000 

population 

in area 

with 

design 

value > 85 

Area ×

Concentration 

(km2 × ppb) 

Population ×

ppb 

Ozone design value > 

85 ppb 

 baseline 2006.reg2 95 7,236 2,680,249 19,864 11,024,868

 future year 2018.cs05 87 296 219,285 291 197,713

Percentage decrease 

from 2006 to 2018 8% 96% 92% 99% 98%

5.2.4 Conclusion 

The photochemical grid model performed by the TCEQ for this SIP revision has been rigorously 

evaluated against observational data. While there are a number of shortcomings that this modeling has in 

common with other modeling exercises in the HGB area as discussed in Sections 5.2.1, Solving Modeling 

Problems, and 5.2.2, , Model Performance Evaluations: Implications of the Model Performance of the 

Current SIP Modeling, modeling for many of the simulated ozone days appears to behave in a manner 

consistent with most of the atmospheric phenomena of interest. Evaluation of the modeling response to 

emission changes appears to show that the modeled ozone is slightly less responsive to emission changes 

than the observed ozone. Thus, modeling of 2018 emissions with the proposed control package in place 

may overpredict the future ozone concentrations. 

 

5.3 AIR QUALITY TRENDS IN THE HGB AREA 

This section describes analyses of air quality observational data in the HGB area. Trends in ozone and its 

precursors demonstrate not only the substantial progress the HGB area has made in improving air quality 

but also the magnitude of the future challenge in attaining the ozone NAAQS. Trends are also useful to 

show how ozone is related to its precursors. Decreases in NOX and VOC demonstrate the effectiveness of 

policies to reduce emissions; however, due to its dependence on meteorological variables, ozone may not 

always exhibit trends identical to its precursors. Separating variations in meteorological factors from 

trends in ozone and its precursors can highlight whether ozone reductions are due to decreases in 
5-10

precursor emissions or are due to year-to-year variability in local meteorology (Sullivan, 2009; Camalier, 

et al., 2007). 

5.3.1 Ozone Trends 

This section examines the frequency at which the NAAQS for ozone are exceeded, with the 

understanding that the 1997 eight-hour standard of 0.08 ppm is the subject of interest for this SIP revision 

and that the one-hour standard is no longer in effect, but still a useful benchmark for understanding ozone 

behavior in the HGB area. While the NAAQS is expressed in units of ppm, this section will use the 

familiar convention of expressing concentrations in ppb. 

The trend in design values for the HGB area is seen clearly in Figure 5-1: Ozone Design Values for the 

HGB Area. While the HGB area continues to exceed both the one-hour and eight-hour ozone standards, 

one-hour ozone design values have generally decreased over the past 17 years, and eight-hour ozone 

design values have decreased over at least the past nine years. The eight-hour ozone design value in 2008 

was 91 ppb, a 24 percent decrease from the 1991 design value of 119 ppb. The 2008 value is approaching 

the 1997 eight-hour ozone NAAQS of 85 ppb. A regression analysis of design value on year estimates 

that eight-hour ozone design values decreased at the rate of 1.2 ppb per year, which is statistically 

significant at the 5 percent level (α = 0.05). If this trend were to continue at that rate, attainment of the 

1997 eight-hour standard could be reached in five years, though if the pace of recent years were 

maintained, it could occur even sooner. 

Ozone Design Values for the HGB Area

104 110 114 116 117 116 118 112 110 107 102 101 103 103

96

210

200 202

189 188

199 196

203 199

185

175 175 170 169

153 153

91

116 119

147

220

0

50

100

150

200

250

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Design Value

(ppb)

1-Hour NAAQS: 125 ppb

8-Hour NAAQS: 85 ppb

1-Hour DV

8-Hour DV

Figure 5-1: Ozone Design Values for the HGB Area 

The one-hour ozone design value in 2008 was 147 ppb, a 33 percent decrease from the 1991 design value 

of 220 ppb. Regression of one-hour design values on year shows they decreased at the rate of 3.6 ppb per 

year, which is faster than the decrease for eight-hour ozone design values; the slope is also statistically 

significant at the 5 percent level.
Table 5-2: Eight-Hour Ozone Design Values (in ppb) for Each Regulatory Monitor in the HGB Area

Monitor/CAMS # 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

2003 

2004 

Houston Bayland Park C53 111 110 100 102 101 Houston Westhollow C410 95 101 95 102 102 104 95 87 87 Park Place C416 Hous.DeerPrk2 C35/235/1001/  AFH139FP239 108 112 108 103 102 101 Manvel Croix Park C84 91 97 Northwest Harris Co. C26/A110/  X154 98 101 100 110 113 110 106 106 109 108 105 101 100 94 Houston Aldine C8/AF108/F150 119 116 104 102 103 114 116 116 108 111 108 107 100 95 Houston Monroe C406 105 102 96 93 97 102 109 112 113 106 93 90 90 95 Houston Croquet C409 117 112 103 96 104 104 117 115 118 110 104 102 99 99 Conroe Relocated C78 85 Channelview C15/C115 87 90 Houston East C1 104 103 88 86 108 106 102 103 101 100 95 Seabrook Friendship Park C45 85 94 Houston Texas Avenue C411 88 89 Lang C408 105 103 93 95 98 99 100 96 96 96 91 83 78 79 Lake Jackson C1016 Houston North Wayside C405 114 102 94 91 91 91 96 99 104 105 98 89 86 85 Lynchburg Ferry C1015 Houston Regional Office C81 95 94 88 Clinton C403/C113/C304 115 109 100 100 106 106 107 100 103 101 97 93 96 96 Galveston Airport C34/C109/C154 90 112 108 98 89 89 91 Clute C11 96 93 91 96 92 92 84 95 93 91 86 87 Texas City C10 93 82 90 89 114 102 105 91 100 98 91 83 80 Conroe C65 91 Houston Crawford C407 105 98 89 89 95 91 97 96 100 100 Houston Manchester C22 103 104 104 103 106 102 103 Houston Deer Park C18 107 96 85 89 107 116 

Note: Missing values indicate a monitor was not operating during that year or did not produce a valid year of data. Three years of valid data are required to calculate an eight-hour o

5-11
5-12

The design value in a metropolitan area is the highest design value of all of the area’s monitors’ 

individual design values. Because ozone varies spatially, it is also prudent to investigate trends at 

all monitors in an area. Table 5-2: Eight-Hour Ozone Design Values (in ppb) for Each 

Regulatory Monitor in the HGB Area and Table 5-3: One-Hour Ozone Design Values (in ppb) 

for Each Regulatory Monitor in the HGB Area contain the eight-hour and one-hour ozone design 

values at all regulatory monitors in the HGB area from 1991 to 2008. More monitors than these 

operate in the HGB area, but because the data at those monitors do not meet the EPA’s quality 

control standards, the design values at those additional monitors are not displayed here. These 

non-regulatory monitors are discussed in Section 5.2.2: Model Performance Evaluations: 

Implications of the Model Performance of the Current SIP Modeling. 
5-13

Table 5-3: One-Hour Ozone Design Values (in ppb) for Each Regulatory Monitor in the HGB Area 

Monitor/CAMS # 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

2003 

2004 

Houston Bayland Park C53 189 185 173 154 163 148 1Houston Westhollow C410 164 155 164 155 165 150 150 141 141 128 1Park Place C416 Hous.DeerPrk2 C35/235/1001/  AFH139FP239 147 164 203 185 182 168 161 157 1Manvel Croix Park C84 143 132 142 1Northwest Harris Co. C26/A110/  X154 160 160 166 173 172 172 165 164 163 161 157 154 156 148 1Houston Aldine C8/AF108/X150 220 190 197 197 189 173 189 187 187 180 166 166 143 136 1Houston Monroe C406 170 170 155 147 154 161 174 196 196 170 143 151 141 141 1Houston Croquet C409 200 200 178 152 167 167 168 168 167 167 160 157 150 141 1Conroe Relocated C78 119 137 128 1Channelview C15/C115 154 141 140 1Houston East C1 210 200 200 202 177 182 182 198 180 180 171 171 165 1Seabrook Friendship Park C45 132 135 135 1Houston Texas Avenue C411 146 172 157 1Lang C408 200 183 158 159 159 159 158 155 155 175 175 149 128 128 1Lake Jackson C1016 119 1Houston North Wayside C405 210 190 173 173 155 143 155 158 189 190 168 153 131 138 1Lynchburg Ferry C1015 157 1Houston Regional Office C81 185 178 175 170 1Clinton C403/C113/C304 210 210 176 158 173 173 173 161 183 199 176 157 175 158 1Galveston Airport C34/C109/C154 170 170 176 168 164 133 123 129 1Galveston 99th St. C1034 Clute C11 150 150 132 129 144 144 148 134 154 161 154 136 133 136 Texas City C10 150 150 163 163 184 182 182 146 175 172 139 121 116 116 1Conroe C65 145 145 140 Houston Crawford C407 220 190 165 165 165 166 172 172 164 173 173 194 Houston Manchester C22 190 190 180 160 172 170 175 173 176 Houston Deer Park C18 160 160 150 157 188 188 199 163 San Jacinto Monument C166/C245 143 124 124 Note: Missing values indicate a monitor was not operating during that year or did not produce a valid year of data. Only one year of valid data is required to calculate a one-hour oz

that have a one-hour ozone design value may not have an eight-hour ozone design value. 
5-14

Figure 5-2: Eight-Hour Ozone Design Value Statistics for All Monitors in the HGB Area and 

Figure 5-3: One-Hour Ozone Design Value Statistics for All Monitors in the HGB Area display 

three summary statistics for the eight-hour and one-hour design values, respectively: the 

maximum, median, and minimum design values computed across all monitors in the HGB area. 

These figures facilitate assessment of the range of design values observed within a year, as well 

as how these distributions change over time. From these figures, it appears that neither eighthour nor one-hour design values exhibited a noticeable trend until about 1999, after which both 

began falling steadily. Before 2002, no monitors in the HGB area met either standard; since then, 

the area has seen a steady increase in the number of monitors attaining both standards. By 2008, 

over half of the monitors in the area had attained both standards, as median ozone design values 

fell below the NAAQS that year. 

Eight-Hour Ozone Design Value Statistics in the HGB Area

0

20

40

60

80

100

120

140

199119921993199419951996199719981999200020012002200320042005200620072008

Design Value 

(ppb)

8-Hour NAAQS: 85 ppb

MAX

Median

MIN 

Figure 5-2: Eight-Hour Ozone Design Value Statistics for All Monitors in the HGB Area 
5-15

One-Hour Ozone Design Value Statistics in the HGB Area

0

50

100

150

200

250

199119921993199419951996199719981999200020012002200320042005200620072008

Design Value 

(ppb)

1-Hour NAAQS: 125 ppb

MAX

Median

MIN 

Figure 5-3: One-Hour Ozone Design Value Statistics for All Monitors in the HGB Area 

Ozone trends can also be investigated by looking at the number of days an exceedance of the 

ozone NAAQS was recorded, termed an exceedance day. An exceedance day for the 1997 eighthour ozone NAAQS is any day that any monitor in the area measures an eight-hour average 

ozone concentration greater than or equal to 85 ppb over any eight-hour period. An exceedance 

day for the one-hour ozone NAAQS is any day that any monitor in the area measures a one-hour 

average ozone concentration greater than or equal to 125 ppb for at least one hour. Previous 

research (Savanich, unpublished, 2006) by the TCEQ has shown that, until 2006, the number of 

exceedance days was positively correlated with the number of monitors in a particular area. As 

the number of monitors increases, so does the number of exceedance days recorded, at least until 

the area has been saturated with monitors or until ozone concentrations truly decrease. Because 

of this correlation, when examining exceedance-day trends, the number of monitors must always 

be considered. Thus, it is especially noteworthy that Figure 5-4: Number of Monitors and Ozone 

Exceedance Days in the HGB Area shows that, despite an increase in the number of monitors, the 

number of exceedance days for both one-hour and 1997 eight-hour ozone NAAQS has decreased, 

a decrease that is especially pronounced over the past three years. Since 1999, the number of 

1997 eight-hour and one-hour ozone exceedance days occurring in the HGB area has fallen 83 

percent and 96 percent, respectively. In just the last three years, the number of 1997 eight-hour 

and one-hour ozone exceedance days has fallen 76 percent and 92 percent, respectively. 
5-16

Number of Monitors and Ozone Exceedance Days 

in the HGB Area

39

34

52 54

48

54

45

36

41

44 45

32

20

11

28 28 30

26

35

49

34

28

23

27

30

26

17

6

39

73

64

32

45

56

2

37

0

20

40

60

80

100

199119921993199419951996199719981999200020012002200320042005200620072008

Days

0

5

10

15

20

25

Monitors

One-Hour Exceedances

Eight-Hour Exceedances

number of monitors

Figure 5-4: Number of Monitors and Ozone Exceedance Days in the HGB Area 

Results for individual monitors, displayed in Figure 5-5: Number of 1997 Eight-Hour Ozone 

Exceedance Days by Monitor and Figure 5-6: Number of One-Hour Ozone Exceedance Days by 

Monitor support the conclusion that the number of exceedance days at individual monitors also 

appears to be decreasing. Figure 5-5: Number of 1997 Eight-Hour Ozone Exceedance Days by 

Monitor highlights two monitors, Houston Aldine (CAMS 8) (red line) and Houston Bayland 

Park (CAMS 53) (blue line), that recorded the most 1997 eight-hour ozone NAAQS exceedances 

in the past. Since recent peaks in 1999 (at Houston Bayland Park (CAMS 53)) and in 2000 

(Houston Aldine (CAMS 8)), neither monitor, in any year, has come within 60 percent of these 

peaks; in 2008 both monitors experienced at least an 85 percent reduction from the recent peaks. 

While results for other monitors are less impressive, overall, the trend in ozone exceedance days 

at monitors throughout the HGB area is clearly downward. Due to the large number of monitors 

in the HGB area, data from Figure 5-5: Number of 1997 Eight-Hour Ozone Exceedance Days by 

Monitor and Figure 5-6: Number of One-Hour Ozone Exceedance Days by Monitor are 

presented in Table 5-4: Number of Days with a 1997 Eight-Hour Ozone Exceedance and Table 5-

5: Number of Days with a One-Hour Ozone Exceedance for detailed inspection. 
5-17

Eight-Hour Ozone Exceedance Days in the HGB Area 

0

5

10

15

20

25

30

35

40

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Days

Manvel Croix Park Lake Jackson

Galveston Airport Galveston 99th St.

Houston Aldine Channelview

NW Harris Co. North Wayside

Lang Croquet

Bayland Park Monroe

Westhollow Hou. Reg. Office

Texas Avenue Park Place

Lynchburg Ferry Houston East

Clinton Deer Park 2

Seabrook Conroe Relocated

Figure 5-5: Number of 1997 Eight-Hour Ozone Exceedance Days by Monitor 

One-Hour Ozone Exceedance Days in the HGB Area

0

5

10

15

20

25

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Days

Manvel Croix Park Lake Jackson

Galveston Airport Galveston 99th St.

Houston Aldine Channelview

NW Harris Co. North Wayside

Lang Croquet

Bayland Park Monroe

Westhollow Hou. Reg. Office

Texas Avenue Park Place

Lynchburg Ferry Houston East

Clinton Deer Park 2

Seabrook Conroe Relocated

Figure 5-6: Number of One-Hour Ozone Exceedance Days by Monitor 

The progress achieved in recent years in reducing eight-hour and one-hour ozone concentrations 

in the HGB area is evident in Table 5-4: Number of Days with a 1997 Eight-Hour Ozone 

Exceedance and Table 5-5: Number of Days with a One-Hour Ozone Exceedance. The number of 

times the monitors in the HGB area registered daily peak eight-hour ozone ≥ 85 ppb fell from a 
5-18

high of 340 occurrences in 1995, to 39 occurrences in 2007, to 19 occurrences in 2008. Prior to 

2007, that number was never below 90. The number of monitors recording at least one 

exceedance of the 1997 eight-hour ozone standard has fallen by half, from a maximum of 23 

monitors in 2003 to only 12 in 2008. 

A similar pattern is apparent with the number of exceedances of the one-hour ozone NAAQS 

presented in Table 5-5: Number of Days with a One-Hour Ozone Exceedance. The table shows 

that the total number of one-hour ozone NAAQS exceedance occurrences fell from a high of 165 

in 1995 to just three in 2008. Prior to 2005, the number of one-hour exceedances was never 

below 50. The three exceedances in 2008 occurred at only two monitors. As recently as 2006, a 

total of 15 monitors recorded at least one exceedance. This significant progress has occurred in a 

fairly short amount of time in an area well known for its air quality challenges. 
5-19

Table 5-4: Number of Days with a 1997 Eight-Hour Ozone Exceedance Monitor 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

2003 

Houston Bayland Park C53 17 31 19 17 11 16 Houston Westhollow C410 4 36 8 16 11 17 11 8 3 3 Park Place C416 Hou.DeerPrk2 C35/235/1001/AFHP139FP239 18 9 26 20 10 8 18 Manvel Croix Park C84 5 8 14 Northwest Harris Co. C26/A110/X154 3 14 12 21 34 13 12 23 25 7 11 9 11 Houston Aldine C8/AF108/X150 15 17 11 19 38 16 25 23 22 29 15 7 11 Houston Monroe C406 13 10 7 7 22 5 28 12 21 12 3 7 8 Houston Croquet C409 23 9 9 8 36 8 28 19 31 15 9 10 10 Conroe Relocated C78 1 3 7 Channelview C15/C115 1 5 10 Houston East C1 9 10 2 0 0 13 16 12 13 15 10 6 15 Seabrook Friendship Park C45 2 4 8 Houston Texas Avenue C411 5 2 9 Lang C408 5 10 8 10 18 8 5 11 5 8 2 3 1 Lake Jackson C1016 3 Houston North Wayside C405 9 8 5 5 26 8 9 12 24 14 5 2 9 Lynchburg Ferry C1015 14 Houston Regional Office C81 11 11 5 9 Clinton C403/C113/C304 16 11 7 6 21 7 14 11 22 11 6 7 10 Galveston Airport C34/C109/C154 18 13 23 5 3 4 12 Clute C11 8 10 6 5 15 3 4 5 9 2 3 6 3 Conroe C65 4 17 6 Houston Crawford C407 5 6 7 4 15 3 16 10 11 8 0 Houston Manchester C22 19 10 8 10 27 5 18 Houston Deer Park C18 8 4 3 18 27 12 Texas City C10 6 1 9 7 25 1 10 10 11 6 1 3 3 San Jacinto Monument C166/C245 0 5 1 Galveston 99th St. C10 34 Number of Monitors in Operation 13 13 13 14 14 14 15 15 16 17 23 21 23 2Note: Monitors with exceedance days do not necessarily have a complete year of ozone data; therefore, there may be years where a monitor has ozone exceedance days but no ozon
5-20

Table 5-5: Number of Days with a One-Hour Ozone Exceedance Monitor 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

2003 

Houston Bayland Park C53 12 18 8 10 3 6 Houston Westhollow C410 3 20 3 8 5 12 5 6 2 2 Park Place C416 Hou.DeerPrk2 C35/C235/1001/AFH139/FP239 13 7 14 13 6 5 7 Manvel Croix Park C84 1 2 1 Northwest Harris Co. C26/A110/C154 1 9 10 14 9 7 4 9 9 5 6 4 2 Houston Aldine C8/AF108/X150 9 8 7 12 11 15 12 12 8 16 8 1 6 Houston Monroe C406 8 6 3 3 11 2 15 8 10 5 5 5 3 Houston Croquet C409 16 5 5 4 21 3 14 12 14 6 4 5 4 Conroe Relocated C78 0 1 2 Channelview C15/C115 1 5 6 Houston East C1 6 6 2 0 0 12 13 8 10 11 7 4 7 Seabrook Friendship Park C45 3 4 5 Houston Texas Avenue C411 5 0 8 Lang C408 5 6 6 6 9 4 6 8 4 6 3 2 2 Lake Jackson C1016 1 Houston North Wayside C405 5 6 3 4 4 5 5 8 7 11 1 1 5 Lynchburg Ferry C1015 9 Houston Regional Office C81 6 7 3 5 Clinton C403/C113/C304 13 8 7 4 15 6 8 7 13 8 7 3 6 Galveston Airport C34/C109/C154 5 7 7 4 0 0 3 Galveston 99th St. C1034 Clute C11 3 3 2 0 6 1 3 1 4 2 0 2 1 Texas City C10 4 1 7 2 14 0 3 3 7 3 0 0 1 Conroe C65 1 5 2 Houston Crawford C407 5 4 5 3 9 4 11 12 5 8 0 Houston Manchester C1029 11 7 7 7 18 4 10 Houston Deer Park C18 6 2 1 6 18 4 San Jacinto Monument C166/C245 0 2 0 Number of Monitors in Operation 13 13 13 14 14 14 15 15 16 17 23 21 23 
5-21

The ozone season spans the entire year in the HGB area; the period of elevated ozone 

concentrations, however, varies from year to year. Figure 5-7: 1997 Eight-Hour Ozone 

Exceedance Days in the HGB Area shows the frequency of, and variation in, the number of 1997 

eight-hour ozone NAAQS exceedance days in the HGB area by month and year. While the 

duration and intensity of the ozone season does vary from year to year, in the past few years the 

HGB area has experienced fewer ozone exceedance days over fewer months. The darker areas in 

the figure show that peak ozone season in the HGB area typically occurs from August to 

September, with a smaller, secondary peak occurring earlier, roughly in June. 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

200620072008

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Eight-Hour Ozone Exceedance Days in the HGB Area

1 - 3

15 - 17 17 - 19 13 - 15

11 - 13

9 - 11

7 - 9

5 - 7

3 - 5

Figure 5-7: 1997 Eight-Hour Ozone Exceedance Days in the HGB Area 

In summary, the number and intensity of ozone exceedances in the HGB area has been dropping, 

especially since 2000, with 2007 and 2008 demonstrating the largest of these decreases. 

5.3.2 Ozone Trends at Regulatory and Non-Regulatory Monitors 

Twenty-three monitors in the HGB area, listed in Table 5-6: Eight-Hour Ozone Design Values at 

Regulatory and Non-Regulatory Monitors and Table 5-7: One-Hour Ozone Design Values at 

Regulatory and Non-Regulatory Monitors report ozone concentrations following EPA 

certification protocols and are used for attainment determinations for regulatory purposes. 

However, since 2003, over 20 additional monitors have become operational in the HGB area that 

measure ozone concentrations following protocols that have not been certified to EPA standards. 

Usually, this means fewer calibrations and/or zero and span checks. These non-regulatory 

monitors are located throughout the HGB area. The locations were chosen with the aim of 

ensuring that all episodes of elevated ozone and precursors are observed. The additional 

monitoring sites also help to describe the spatial extent and distribution of high ozone more fully 

than the regulatory monitors alone. While the non-regulatory monitors are not acceptable for 

making regulatory determinations, they help describe the spatial patterns of ozone more 

completely and thus provide a broader perspective on trends in ozone concentrations across the 

HGB area. 
5-22

Table 5-6: Eight-Hour Ozone Design Values at Regulatory and Non-Regulatory Monitors 

AIRS Site Name 2003 2004 2005 2006 2007 2008

ppb ppb ppb ppb ppb ppb 

Regulatory Monitors 

 482010055 Houston Bayland Park C53 102 101 103 103 96 91

 482010066 Houston Westhollow C410 87 87 89 96 92 89 

 482010416 Park Place C416 89 

 482011039 Houston Deer Park 2 C35/139 102 101 100 96 93 87 

 480391004 Manvel Croix Park C84 91 97 97 96 91 85 

 482010029 Northwest Harris Co. C26/A110/C154 100 94 93 91 91 85 

 482010024 Houston Aldine C8/AF108/X150 100 95 92 88 84 83 

 482010062 Houston Monroe C406 90 95 97 99 91 81 

 482010051 Houston Croquet C409 99 99 98 94 87 80 

 483390078 Conroe Relocated C78 85 86 85 84 80 

 482010026 Channelview C15/C115 87 90 89 85 83 80 

 482011034 Houston East C1 100 95 87 83 78 80 

 482011050 Seabrook Friendship Park C45 85 94 92 90 86 79 

 482010075 Houston Texas Avenue C411 88 89 88 84 78 76 

 482010047 Lang C408 78 79 79 80 77 76 

 480391016 Lake Jackson C1016 79 79 76 76 

 482010046 Houston North Wayside C405 86 85 82 78 76 75 

 482011015 Lynchburg Ferry C1015 96 89 82 74 

 482010070 Houston Regional Office C81 94 88 88 84 81 74 

 482011035 Clinton C403/C113/C304 96 96 95 85 79 73 

 481670014 Galveston Airport C34/C109/C154 89 91 87 83 71 

 480391003 Clute C11 87 

 481671002 Texas City C10 80 

Non-Regulatory Monitors 

 482010554 West Houston C554 102 99 94 

 482010558 Tom Bass C558 104 100 93 

 482010559 Katy Park C559 98 96 92 

 482010562 Bunker Hill Village C652 81 96 91 

 482010617 Wallisville Road C617 96 93 93 90 

 482010561 Meyer Park C561 90 89 84 

 482010557 Mercer Arboretum C557 88 88 84 

 482010560 Atascocita C560 88 86 83 

 482010556 La Porte Sylvan Beach C556 90 87 82 

 482010552 Baytown Wetlands Center C552 87 89 86 81 

 480390619 Mustang Bayou C619 93 89 84 81 

 482010572 Clear Lake High School C572 83 88 84 81 

 482010803 HRM-3 Haden Road C603 92 88 84 80 

 482010553 Crosby Library C553 87 86 84 80 

 481670056 Texas City 34th St, C620 89 90 84 79 

 482010570 Clear Brook High School C570 89 92 84 78 

 480390618 Danciger C618 80 83 80 78 

 482010555 Kingwood Library C555 82 81 77 

 482010551 Sheldon C551 92 85 80 76 

 481670571 Clear Creek High School C571 83 84 

Source: Leading Environmental Analysis and Display System (LEADS). 

Monitors are sorted in descending order of 2008 design values, then 2007, 2006, etc. The annual maximum of each series is noted in 

boldface type. Because of the way design values are computed, some monitors in some years may have one-hour but not eight-hour

design values. 

Table 5-7: One-Hour Ozone Design Values at Regulatory and Non-Regulatory Monitors 
5-23

AIRS Site Name 2003 2004 2005 2006 2007 2008

ppb ppb ppb ppb ppb ppb

Regulatory Monitors 

 482010055 Houston Bayland Park C53 163 148 148 143 142 139

 482010066 Houston Westhollow C410 141 128 126 131 127 126

 482010416 Park Place C416 136 136 136

 482011039 Houston Deer Park 2 C35/C139 161 157 153 150 150 147

 480391004 Manvel Croix Park C84 132 142 134 138 128 128

 482010029 Northwest Harris Co. C26/A110/C154 156 148 131 127 127 126

 482010024 Houston Aldine C8/AF108/X150 143 136 139 125 122 122

 482010062 Houston Monroe C406 141 141 131 133 131 117

 482010051 Houston Croquet C409 150 141 136 131 126 117

 483390078 Conroe Relocated C78 137 128 128 128 124 116

 482010026 Channelview C15/C115 141 140 135 134 128 120

 482011034 Houston East C1 171 165 154 137 119 119

 482011050 Seabrook Friendship Park C45 135 135 153 153 153 119

 482010075 Houston Texas Avenue C411 172 157 157 127 110 110

 482010047 Lang C408 128 128 127 126 108 108

 480391016 Lake Jackson C1016 119 113 105 99 101

 482010046 Houston North Wayside C405 131 138 138 118 100 102

 482011015 Lynchburg Ferry C1015 157 157 152 149 117

 482010070 Houston Regional Office C81 175 170 169 135 131 119

 482011035 Clinton C403/C113/C304 175 158 158 124 121 111

 481670014 Galveston Airport C34/C109/C154 123 129 129 117 104 97

 481671034 Galveston 99th St. C1034 115 115

 480391003 Clute C11 133 136

 481671002 Texas City C10 116 116 124 

Non-Regulatory Monitors 

 482010554 West Houston C554 141 141 146 145 131

 482010558 Tom Bass C558 145 145 146 146 138

 482010559 Katy Park C559 127 143 143 135 129

 482010562 Bunker Hill Village C562 135 137 135 132

 482010617 Wallisville Road C617 147 145 138 139 134

 482010561 Meyer Park C561 139 133 127 111

 482010557 Mercer Arboretum C557 108 118 121 121 121

 482010560 Atascosita C560 137 137 125 120

 482010556 La Porte Sylvan Beach C556 148 149 149 133

 482010552 Baytown Wetlands Center C552 138 138 133 129 129

 480390619 Mustang Bayou C619 134 130 127 112 107

 482010572 Clear Lake High School C572 145 141 140 119 114

 482010803 HRM-3 Haden Road C603 161 161 144 135 127 122

 482010553 Crosby Library C553 141 147 141 126 123

 481670056 Texas City 34th St C620 143 139 136 119 114

 482010570 Clear Brook High School C570 140 140 135 117 109

 480390618 Danciger C618 121 120 111 108 108

 482010555 Kingwood Library C555 130 123 122 108

 482010551 Sheldon C551 153 153 150 130 125 123

 481670571 Clear Creek High School C571 138 138 138 119 99

 480710013 Smith Point Hawkins Camp C96 143 143 133

 482010808 HRM-8 LaPorte C608 149

 482010804 HRM-4 Sheldon Rd. C604 128

480710900 HRM-10 Mont Belvieu C610 119
5-24

 482010807 HRM-7 W Baytown C607 113

Source: LEADS (Leading Environmental Analysis and Display System). 

The annual maximum of each series is noted in boldface type. Because of the way design values are computed, some monitors in 

some years may have one-hour but not eight-hour design values 

Figure 5-8: Distributions of Eight-Hour Ozone Design Values at Regulatory and Non-Regulatory 

Monitors in the HGB Area compares eight-hour ozone design values at regulatory and nonregulatory monitors in the HGB area from 2003 to 2008. This period was chosen because many 

non-regulatory monitors only became operational, or had complete data, in 2003 and later years. 

The distributions of eight-hour ozone design values dropped for both types of monitors over the 

six-year period, though the interquartile range, a measure of spread between high and low values, 

did not narrow noticeably for either. Annual median fourth high eight-hour ozone design values 

fell from 90 ppb in 2003 to 80 ppb in 2008 at regulatory monitors, a drop of 11.1 percent. The 

median at non-regulatory monitors fell from 89 ppb to 81 ppb over the period, a 9.0 percent drop. 

While medians and other moments from the distributions all dropped over the period, the annual 

maximum eight-hour ozone design value is most relevant, as this value is the current standard 

used for regulatory attainment determinations. The annual maximum eight-hour ozone design 

value measured at regulatory monitors fell from 102 ppb in 2003 to 91 ppb in 2008, a drop of 

10.4 percent. The annual maximum at non-regulatory monitors fell from 96 ppb in 2005, when 

three-year design values were first computable, to 94 ppb in 2008, a drop of 2.1 percent. Note, 

however, that maximum eight-hour design values at non-regulatory monitors in 2006 and 2007 

were higher than in 2008, 104 ppb and 100 ppb respectively, presumably because those years are 

strongly influenced by the fourth high value observed at Wallisville Road (CAMS 617) in 2006 

(111 ppb). Even though this 2006 fourth high value continued to influence the 2008 design value, 

when averaged with the 2008 fourth high value of 85 ppb, the three-year average dropped to 94 

ppb, a 6 percent decline in a single year. 

81

86

89 89

80

84

87

91

94

90

94

100

104

96

91

96

103 103

101 102

70

75

80

85

90

95

100

105

110

2003 2004 2005 2006 2007 2008 2003 2004 2005 2006 2007 2008

90th percentile

regulatory monitors non-regulatory monitors

maximum

75th percentile

median

25th percentile

10th percentile

ppb

no data no data

Figure 5-8: Distributions of Eight-Hour Ozone Design Values at Regulatory and NonRegulatory Monitors in the HGB Area 
5-25

The ozone design values computed for the non-regulatory monitors are within the range of design 

values computed for the regulatory monitors. This finding suggests that both sets of monitors 

observe the same ozone behavior. 

Figure 5-9: Distributions of One-Hour Ozone Design Values at Regulatory and Non-Regulatory 

Monitors in the HGB Area compares one-hour ozone design values at regulatory and nonregulatory monitors in the HGB area from 2003 to 2008. This period was chosen because many 

non-regulatory monitors became operational or had complete data in 2003 and later years. The 

one-hour design value is computed as the fourth highest one-hour value observed among all 

values during each rolling three calendar-year period. The distributions of one-hour ozone design 

values dropped for both types of monitors over the six-year period and the spread between high 

and low values narrowed for both. Annual median fourth high one-hour ozone design values fell 

from 141 ppb in 2003 to 118 ppb in 2008 at regulatory monitors, a drop of 16.3 percent. The 

median at non-regulatory monitors fell from 149 ppb to 122 ppb over the period, an 18.1 percent 

drop. 

While medians and other moments from the distributions all dropped over the period, the annual 

maximum one-hour ozone design value is most relevant, as this design value would be compared 

to the one-hour ozone NAAQS to determine attainment, were the one-hour standard still in force. 

The annual maximum one-hour ozone design value measured at regulatory monitors fell from 

175 ppb in 2003 to 147 ppb in 2008, a drop of 16.0 percent. The annual maximum at nonregulatory monitors fell from 161 ppb to 138 ppb over the period, or 14.3 percent. Note that the 

eight-hour design value does not change when the data from the non-regulatory monitors are 

added to the calculation. 

122

126

137

140 141

149

118

127

131

136

141 141

138

150 149 149

161 161

147

153 153

170 169

175

100

110

120

130

140

150

160

170

180

2003 2004 2005 2006 2007 2008 2003 2004 2005 2006 2007 2008

90th percentile

regulatory monitors non-regulatory monitors

75th percentile

median

25th percentile

10th percentile

maximum

ppb

# of monitors: 

 21 22 21 21 22 22 5 15 20 21 21 21 

Figure 5-9: Distributions of One-Hour Ozone Design Values at Regulatory and NonRegulatory Monitors in the HGB Area 
5-26

Figure 5-10: 1997 Eight-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory 

Monitors, 2003 through 2008 presents the number of days per year from 2003 through 2008 that 

the 1997 eight-hour ozone NAAQS was exceeded in the HGB area at regulatory monitors and at 

all monitors, both regulatory and non-regulatory. Since 2005, the combined network has 

recorded a total of 19 additional exceedances of the 1997 eight-hour ozone standard that would 

not have been captured by the regulatory network, i.e., about four to five per year. This result 

confirms earlier findings that suggest as the monitoring network has expanded, fewer episodes of 

elevated ozone concentrations are likely to elude detection. 

54

48

37

26

12

43

50

41

31

16

51

44

0

10

20

30

40

50

60

2003 2004 2005 2006 2007 2008

Number of regulatory monitors operating: 

 21 22 21 21 22 22 

Number of non-regulatory monitors operating: 

 5 15 20 21 21 21 

Figure 5-10: 1997 Eight-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory 

Monitors, 2003 through 2008 

Figure 5-11: One-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory Monitors, 

2003 through 2008 presents the number of days per year from 2003 through 2008 that the onehour ozone NAAQS was exceeded in the HGB area at regulatory monitors and at all monitors, 

both regulatory and non-regulatory. Both series initially increased, then fell at similar rates 

throughout the period, suggesting that the two sets of monitors measure broadly similar 

phenomena. During the first half of the period, non-regulatory monitors measured from five to 

nine additional exceedance days that were not detected by regulatory monitors. However, in the 

second half of the period, that gap dropped to only two to three additional days, indicating that 

non-regulatory monitors are detecting fewer and fewer events not detected by regulatory 

monitors. This result confirms earlier findings that suggest that, as the monitoring network has 

expanded, fewer episodes of elevated ozone concentrations are likely to elude detection. 
5-27

37

31 32

28

18

34

9

3

33

20

6

10

0

10

20

30

40

2003 2004 2005 2006 2007 2008

exceedance days at regulatory

and unique non-regulatory 

monitors

exceedance days at

regulatory monitors

Number of regulatory monitors operating: 

 21 22 21 21 22 22 

Number of non-regulatory monitors operating: 

 5 15 20 21 21 21 

Figure 5-11: One-Hour Ozone Exceedance Days at Regulatory and Non-Regulatory 

Monitors, 2003 through 2008 

Table 5-8: Exceedance Days at Regulatory and Non-Regulatory Monitors, 2003 through 

2008 

 One-Hour Ozone 

 Exceedance days Number of monitors

 regulatory non-regulatory regulatory non-regulatory 

Year monitors monitors total monitors monitors total

 # # # # # # 

2003 31 2 33 21 5 35 

2004 32 5 37 22 15 37 

2005 28 6 34 21 20 41 

2006 18 2 20 21 21 42 

2007 9 1 10 22 21 43 

2008 3 3 6 22 21 43

Source: Leading Environmental Analysis and Display System (LEADS). 
5-28

Table 5-9: Monitors Recording the Annual Maximum One-Hour Ozone Design Value 

Regulatory monitors Non-regulatory monitors

year site name value site name value

 ppb ppb 

2003 Houston Bayland Park C53 163 HRM-3 Haden Road C603 161 

2004 Houston Deer Park 2 C35/139 157 HRM-3 Haden Road C603 161 

2005 Houston Deer Park 2 C35/139 153 Sheldon C551 150 

2006 Houston Deer Park 2 C35/139 150 La Porte Sylvan Beach C556 149 

2007 Houston Deer Park 2 C35/139 150 La Porte Sylvan Beach C556 149 

2008 Houston Deer Park 2 C35/139 147 Tom Bass C558 138

Source: Leading Environmental Analysis and Display System (LEADS). 

Another way to see the ozone trend in the HGB area is to examine how the spatial distributions of 

ozone have changed over the years. Figure 5-12: Eight-Hour Ozone Design Values for 2000, 

2005, and 2008 shows the spatial distribution of eight-hour ozone design values in the HGB area, 

for regulatory monitors only, and the changes that have occurred from 2000 to 2005 to 2008. In 

2000, local peaks in design value were at Houston Aldine (CAMS 8), Houston Bayland Park 

(CAMS 53), and Deer Park (CAMS 35/139), and all three peaks were 110 ppb or higher. 

By 2005, eight-hour ozone design values had dropped across the region. While the highest 

concentrations still occurred at Houston Bayland Park (CAMS 53) and Deer Park (CAMS 

35/139), they were no longer observed in the Houston Aldine (CAMS 8) area. Further, the 2005 

peaks are much lower, between 100 and 103 ppb. The lowest eight-hour ozone concentration is 

still observed at Lang (CAMS 408), but low ozone also occurs to the northeast at Houston North 

Wayside (CAMS 405), to the north at Conroe (CAMS 65) or Conroe Relocated (CAMS 78), and 

to the south at Galveston Airport (CAMS 34/CAMS 109/CAMS 154). The minimum eight-hour 

ozone concentration in 2005 is below the 1997 NAAQS. 

In 2008, eight-hour ozone design values dropped even further. Ozone concentrations are 

substantially lower across a large part of the HGB area, with the kriging model predicting design 

values below the 1997 eight-hour ozone NAAQS at many locations. Maximum eight-hour ozone 

concentrations are now considerably lower, between 89 ppb and 91 ppb. The highest 

measurements occurred at Houston Bayland Park (CAMS 53) and Deer Park (CAMS 35/139), 

and also at a new monitor, Park Place (CAMS 416), which measured ozone in the same range as 

Houston Bayland Park (CAMS 53) and Deer Park (CAMS 35/139). The eight-hour ozone 

concentrations in 2008 are lower throughout the HGB area, with a local ozone minimum located 

in the urban core area surrounding the Lang (CAMS 408), Houston North Wayside (CAMS 405), 

Houston Texas Avenue (CAMS 411), Clinton (CAMS 403/CAMS 113/CAMS 304), and the 

TCEQ Houston Regional Office (CAMS 81) monitors. 

Notice that while the overall concentrations of eight-hour ozone are lower, the areas that 

experience the highest and lowest ozone remain the same. Spatial interpolation shows that high 

ozone concentrations continue to occur south of downtown Houston, and stretch from the 

Houston Ship Channel in the east to west Houston, near Houston Bayland Park (CAMS 53). The 

lowest ozone values are found to the south along the coast, at the northern edge of the 

nonattainment area towards Conroe (CAMS 65), and to the northwest of downtown Houston, at 

Lang (CAMS 408). 
5-29

Figure 5-12: Eight-Hour Ozone Design Values for 2000, 2005, and 2008 
5-30

The kriging method can also be employed to investigate the geographic origins of high ozone 

concentrations. Studies during the TexAQS 2000 field study reported that the highest ozone in 

the HGB area occurs in plumes emanating from industrial areas (Daum et al., 2004; Kleinman et 

al., 2005; Ryerson et al., 2003; Berkowitz et al., 2005; Banta et al., 2005). As these plumes are 

transported across the region, they can be tracked by the high ozone concentrations recorded at 

successive downwind monitors as the day progresses. An analysis of the time of day of 

maximum ozone at each monitoring site can confirm or challenge conclusions of the field study 

about these origins by revealing spatial patterns of ozone formation and movement. 

Yet another way to examine the ozone behavior in the HGB area is to investigate the time of day 

that ozone peaks, on average, in each part of the monitoring network. Daily maximum ozone 

concentrations were divided into two groups: days with values exceeding the 1997 eight-hour 

ozone NAAQS, and days not exceeding the 1997 eight-hour ozone NAAQS. The time of day 

when peak ozone was recorded at each monitor was determined for each day, then averaged 

across the two groupings of days. Only monitors that report data to the EPA were included. 

Days were restricted to March through November to exclude months when few or no exceedance 

days occur in the HGB area. 

Maps of the time of peak ozone in the HGB area, averaged from March through November 1998-

2008, are found in Figure 5-13: Time of Day of Peak Hourly Ozone on Low and High Ozone 

Days. The left map shows that on days with low eight-hour ozone values, daily maximum values 

are recorded in the Galveston area early in the day, between 11:30 a.m. and 11:45 a.m. Inland 

monitors record their highest daily values at progressively later times of day, as monitors are 

located farther inland from the Gulf Coast. On low ozone days, the earliest ozone maxima occur 

near the coast, and the latest occur in the Conroe area between 2:00 p.m. and 2:15 p.m. This 

pattern of ozone concentrations is consistent with the occurrence of the sea breeze, which often 

dominates local weather during the summer in the absence of strong synoptic-scale weather 

influences. After the plume is carried past a monitor, ozone levels often drop, reflecting the 

cleaner maritime air behind the sea breeze front. 

By contrast, the right map of the daily pattern on high eight-hour ozone days looks quite different. 

Daily maximum ozone concentrations are observed earliest in the industrial areas, and 

successively later at sites that are progressively farther away from these areas. This pattern 

indicates that high ozone forms first in the industrial areas, and is transported outward to urban, 

suburban, and rural sites later in the day. Maximum ozone occurs latest at Lake Jackson (CAMS 

1016), Clute (CAMS 11), Northwest Harris Co. (CAMS 26), Conroe (CAMS 65) and Conroe 

Relocated (CAMS 78), the sites at the greatest distance from the industrial area. 

The time of day of maximum ozone on high eight-hour ozone days represents a composite 

pattern: high ozone formed in industrial areas is carried by winds to Conroe (CAMS 65) and 

Conroe Relocated (CAMS 78) on some days, to Lake Jackson (CAMS 1016) on other days, and 

to western Houston on other days. Combined with the earlier spatial design value analysis, the 

patterns of peak ozone appear to show that the highest ozone concentrations are formed in the 

vicinity of the heavily industrialized areas of metropolitan Houston and are then transported 

throughout the area. 
5-31

Figure 5-13: Time of Day of Peak Hourly Ozone on Low and High Ozone Days 
5-32

5.3.3 Trends in the Strength of Observed Ozone Gradients in the HGB Area 

Rapid ozone increases have been observed at HGB area monitoring sites for many years, but the 

phenomenon was not sufficiently explained until the TexAQS 2000 study. Researchers from 

Brookhaven National Laboratory and National Oceanic and Atmospheric Administration 

(NOAA) Aeronomy Laboratory were able to establish that the rapid ozone increases were due to 

strong spatial ozone gradients that arose when ozone formed very rapidly in industrial plumes. 

The rapid ozone formation observed by Daum et al. (2003, 2004) allowed ozone to build up in the 

plumes before ozone and its precursors could disperse. Shifting winds due to the coastal 

oscillation or bay/Gulf breeze phenomena pushed the strong ozone gradients over the monitoring 

sites, resulting in observations of rapid ozone increases (Banta et al., 2005). The rapid ozone 

formation occurs when industrial HRVOC reacts with co-emitted NOX (Ryerson et al., 2003; 

Wert et al., 2003). The following analysis examines whether the strength of these ozone 

gradients has lessened, as measured by the magnitude of one-hour changes in ozone observed at 

monitoring sites. 

One-hour changes in ozone concentrations examined for each hour during the ozone season (May 

through October) at each site for each year. The maximum daily peak change in ozone 

concentration was chosen for each day, and various statistical measures were calculated from 

those values. Not all sites were included in this analysis: only those with long operating histories 

were included. 

Figure 5-14: Trends in the Strength of Ozone Gradients Measured in the HGB Area from 1995 

through 2008 shows how the daily maximum one-hour change in ozone has changed since 1995 

in the HGB area. While at the mean and median levels the change is slight, the steepest observed 

ozone gradients have been reduced dramatically since 1995, decreasing by about 40 percent. 
5-33

32

27

30

28

32

27 28

26

30

27 28

25 24

21 29

22

26

23

29

22

24

21

26

23

25 25

22 20

62

57

65 66

62 63

55

62

58

53 52

44

48

38

0

10

20

30

40

50

60

70

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Peak 1-hr delta ozone, ppb/hr

Mean

Median

95th percentile

32

27

30

28

32

62

57

65 66

62 63

55

62

58

53 52

44

48

38

27 28

26

30

27 28

25 24

21 29

22

26

23

29

22

24

21

26

23

25 25

22 20

0

10

20

30

40

50

60

70

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Peak 1-hr delta ozone, ppb/hr

95th percentile

Mean

Median

Figure 5-14: Trends in the Strength of Ozone Gradients Measured in the HGB Area from 

1995 through 2008 

Figure 5-15: The Number of Occurrences of One-Hour Increases in Ozone Greater Than 40 

ppb/hr in the HGB Area for the Subset of Monitors with Long Historical Records shows that the 

number of strong ozone gradients observed by monitoring sites in the HGB area has also 

decreased substantially since the 1990s, matching the general trends in decreasing ozone 

concentrations. The intensity of ozone gradients has decreased, and the frequency of strong ozone 

gradient observations has also decreased, which strongly suggests that ozone is forming less 

rapidly in the HGB area than in previous years. This change in ozone behavior is consistent with 

decreasing reactivity of VOC emitted in the HGB area. Note that the intensity of ozone gradients 

can depend upon meteorological factors as well as chemical factors. This analysis has not 

examined the importance of meteorological factors upon the observed trends. Subsequent 

sections will discuss trends in HRVOC concentrations. 
5-34

y = -5.6593x + 92.659

R2 = 0.6093

0

20

40

60

80

100

120

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Number of observed strong ozone gradients

Figure 5-15: The Number of Occurrences of One-Hour Increases in Ozone Greater Than 

40 ppb/hr in the HGB Area for the Subset of Monitors with Long Historical Records 

5.3.4 The Impact of Hurricane Ike on Ozone Observations in the HGB Area 

The HGB area typically records high ozone values each year in September. Sometimes, these 

values help determine the area-wide design value for that year. The HGB eight-hour ozone 

design value has been declining recently and was particularly low in 2008 (91 ppb). September 

2008 was not typical for the HGB area. Hurricane Ike, a strong Category 2 hurricane, struck the 

Texas coast near Galveston Bay on September 13, 2008. Most monitors in the area were shut 

down and emissions patterns were substantially altered. 

Hurricane Ike struck the Texas coast near Galveston Bay on September 13, 2008. Before the 

hurricane struck, the evacuation of Galveston Island and the surrounding areas created enormous 

traffic jams. After the storm passed, there was far less automobile traffic than normal for several 

weeks. In preparation for the storm, many of the local petrochemical facilities shut down their 

operations, generating unknown quantities of emissions in the process, and after the storm, their 

operations were atypical for an extended period. Rescue operations, tree cutting and burning, 

lack of electrical power, unusual traffic patterns, and abnormal industrial operations were among 

the atypical conditions that occurred before, during, and after the hurricane. The exact effect of 

the emission changes on ozone concentrations is unknown, due to the number of ozone 

monitoring sites disabled indirectly or directly by Hurricane Ike. Monitors in the HGB area 

ceased operations for as little as one day, and as long as 69 days at a site that was severely 

damaged by storm surge. Key monitors that typically record the area design values were down 

for as much as 16 days, e.g., Houston Bayland Park (CAMS 53) (see Table 5-10: List of the 

Number of Days HGB Ozone Regulatory and Non-Regulatory Monitors were Not Operating 

Before and After the Landfall of Hurricane Ike). 
5-35

Table 5-10: List of the Number of Days HGB Ozone Regulatory and Non-Regulatory 

Monitors were Not Operating Before and After the Landfall of Hurricane Ike 

Monitor 

First Date 

Monitor Did Not 

Report Data 

Restart 

Date 

Days 

Down 

Houston Bayland Park C53/A146 9/13/2008 9/29/2008 16 

Houston Westhollow C410 9/12/2008 9/30/2008 18 

Park Place C416 9/12/2008 9/15/2008 3 

Houston Deer Park 2 C35/C139 9/12/2008 9/22/2008 10 

Manvel Croix Park C84 9/12/2008 9/21/2008 9 

Northwest Harris Co. C26/A110/X150 9/13/2008 9/14/2008 1 

Houston Aldine C8/AF108/X150 9/13/2008 9/15/2008 2 

Houston Monroe C406 9/12/2008 9/19/2008 7 

Houston Croquet C409 9/12/2008 9/26/2008 14 

Conroe Relocated C78/A321 9/13/2008 9/17/2008 4 

Channelview C15/AH115 9/13/2008 9/16/2008 3 

Houston East C1/G316 9/13/2008 9/29/2008 16 

Seabrook Friendship Park C45 9/13/2008 9/16/2008 3 

Houston Texas Avenue C411 9/12/2008 9/16/2008 4 

Lake Jackson C1016 9/12/2008 9/16/2008 4 

Lang C408 9/12/2008 9/18/2008 6 

Houston North Wayside C405 9/12/2008 9/15/2008 3 

Lynchburg Ferry C1015/A165 9/12/2008 10/16/2008 34 

Houston Regional Office C81 9/13/2008 9/20/2008 7 

Clinton C403/C304/AH113 9/12/2008 9/30/2008 18 

West Houston C554 9/13/2008 9/14/2008 1 

Tom Bass C558 9/13/2008 9/18/2008 5 

Wallisville Road C617 9/12/2008 9/17/2008 5 

Meyer Park C561 9/13/2008 9/15/2008 2 

Atascocita C560 9/14/2008 9/23/2008 9 

La Porte Sylvan Beach C556 9/12/2008 11/6/2008 55 

Baytown Wetlands Center C552 9/12/2008 10/31/2008 48 

Mustang Bayou C619 9/12/2008 9/26/2008 14 

Clear Lake High School C572 9/13/2008 9/14/2008 1 

HRM-3 Haden Road C617 9/12/2008 9/22/2008 10 

Crosby Library C553 9/13/2008 9/20/2008 7 

Texas City 34th St. C620 9/12/2008 9/18/2008 6 

Dacinger C618 9/12/2008 9/19/2008 7 

Kingwood Library C555 9/13/2008 9/14/2008 1 

Mercer Arboretum C557 9/22/2008 10/8/2008 16 

Sheldon C551 9/12/2008 9/22/2008 10 

Clear Creek High School C571 9/13/2008 9/15/2008 2 

Galveston 99th St. C1034/A320/X183 9/12/2008 11/20/2008 69 

Pasadena AAMS C672 9/12/2008 9/22/2008 10 

Hurricane Ike’s greatest impact occurred during the second half of September and the first half of 

October. August and September are typically the months when the HGB area records the most 

number of days that exceed the ozone standard. For 2000 through 2008, 21 percent of the 266 

observed 85 ppb exceedance days in the HGB area were recorded in September (Figure 5-16: 

Number of Days that Exceeded the 1997 Eight-Hour Ozone NAAQS by Month from 2000 through 

2008). 
5-36

3

20

26

49

32

54 55

22

5

0

10

20

30

40

50

60

Mar Apr May Jun Jul Aug Sep Oct Nov

Number 

of Days

Figure 5-16: Number of Days that Exceeded the 1997 Eight-Hour Ozone NAAQS by Month 

from 2000 through 2008 

Figure 5-17: Frequency of Daily Peak Eight-Hour Ozone Values for All Ozone Monitoring Sites 

in Texas, September 2006 and Figure 5-18: Frequency of Daily Peak Eight-Hour Ozone Values 

for All Ozone Monitoring Sites in Texas, September 2008 show peak eight-hour ozone at all 

Texas monitoring sites in September 2006, which was unaffected by tropical systems and in 

September 2008, the month in which Hurricane Ike struck. In 2008, the number of monitors in 

operation dropped substantially just before the hurricane made landfall, as they were shut down 

by the TCEQ. The monitors came back on-line gradually, as electrical power was restored, and 

storm damage was repaired. Ozone concentrations immediately before and after Ike were fairly 

low. 

The purpose of this analysis is to examine how the ozone behavior in September and October 

2008 deviated from the 2000 through 2007 average, and thus to ascertain whether the lower 

design value observed in 2008 was due primarily to the effects of Hurricane Ike. 
5-37

0

20

40

60

80

100

120

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Sept 2006 date

Site Count

below 15 ppb

15 to 29 ppb

30 to 44 ppb

45 to 59 ppb

60 to 74 ppb

75 to 84 ppb

85 ppb or above

Figure 5-17: Frequency of Daily Peak Eight-Hour Ozone Values for All Ozone Monitoring 

Sites in Texas, September 2006 

0

20

40

60

80

100

120

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Sept 2008 date

Site Count

below 15 ppb

15 to 29 ppb

30 to 44 ppb

45 to 59 ppb

60 to 74 ppb

75 to 84 ppb

85 ppb or above

Figure 5-18: Frequency of Daily Peak Eight-Hour Ozone Values for All Ozone Monitoring 

Sites in Texas, September 2008 

5.3.4.1 Approach

One approach to estimate the influence of Hurricane Ike on the HGB area’s ozone design value is 

to estimate what the eight-hour ozone design value might have been in 2008 if Hurricane Ike had 

not occurred. This estimate is derived from historical data collected during 2000-2007. 

Removing calendar days affected by Hurricane Ike and replacing them with averages derived 

from historical data yields a re-calculated fourth-highest eight-hour ozone concentration for each 

monitor. The actual fourth-high is then divided by the re-calculated fourth-high to obtain an 
5-38

adjustment ratio or an Ike Adjustment Factor (IAF). This ratio is expected to be greater than one, 

and can be used to adjust 2008 ozone data to non-hurricane conditions. The IAF can be 

calculated as an area-wide average IAF or as a monitor-specific IAF. An area-wide average IAF 

is computed as the average of all IAFs from all monitors in the region, applied to all 2008 data. 

The monitor-specific IAF was applied only to the monitor in question. After the data were 

adjusted with IAFs, an IAF-corrected design value was calculated and compared to the current 

unadjusted ozone design value to determine the influence of Hurricane Ike. 

The days affected by Hurricane Ike are not easy to identify. As stated before, many unusual 

activities occurred in the HGB area before the arrival of Hurricane Ike, and many others occurred 

in the aftermath. For example, many industrial facilities shut down operations before the storm 

arrived, releasing emissions that they usually would not release. After the hurricane, electrical 

power was not available in parts of the HGB area for two or more weeks. Given the difficulties 

in establishing the exact period of Hurricane Ike’s influence, alternative IAFs were calculated by 

removing three different time periods from the historical ozone data. The first period considered 

for exclusion was a two-week period from September 11 through September 25, 2008, which 

includes days immediately before and after the hurricane. Two other periods considered for 

exclusion were a one-month period from September 6 through October 5, 2008, and a one-month 

period after the storm (September 13 through October 12, 2008). All data used in this analysis 

were obtained from the TCEQ-LEADS system, and are eight-hour ozone averages. The HGB 

area eight-hour ozone design value was obtained from the EPA. 

5.3.4.2 Results

Table 5-11: Alternative Fourth-High Daily Peak Eight-Hour Ozone Concentration Calculations 

Using Different Ike Adjustment Factors (IAFs) shows results of the six different methods for 

estimating the fourth-high daily peak eight-hour ozone concentration for each monitoring site. 

The table shows that the expected fourth high is greater than the observed at most sites, regardless 

of which method is used to calculate the expected fourth high. This indicates that the atypical 

conditions experienced during and after Hurricane Ike during September and October in 2008 did 

have an effect on the monitored values, but the effect was no greater than 4 ppb on the fourthhigh daily maximum ozone concentration. 
5-39

Table 5-11: Alternative Fourth-High Daily Peak Eight-Hour Ozone Concentration 

Calculations Using Different Ike Adjustment Factors (IAFs) 

Monitoring site 

2008 

observed 

fourth 

high 

9/11-

9/26 

average 

IAF 

9/11-

9/26 

monitorspecific 

IAF 

9/6-

10/5 

average 

IAF 

9/6-10/5 

monitorspecific 

IAF 

9/13-

10/12 

average 

IAF 

9/13-

10/12 

monitorspecific 

IAF 

ppb ppb ppb ppb ppb ppb ppb 

Houston Aldine C8 /AF108/X150 83 85 86 87 86 86 86 

Houston Bayland Park C53 83 85 84 87 86 86 85 

Channelview C15/C115 76 78 77 79 78 79 78 

Houston Croquet C409 76 78 78 79 80 79 79 

Houston Deer Park C18 76 78 78 79 79 79 78 

Lake Jackson C1016 76 78 77 79 80 79 78 

Northwest Harris Co. C26/A110/C154 76 78 78 79 81 79 80 

Manvel Croix Park C84 75 77 77 78 81 78 78 

Conroe C65 73 75 74 76 75 76 75 

Houston East C1 73 75 74 76 76 76 76 

Houston Monroe C406 71 73 73 74 75 74 74 

Seabrook Friendship Park C45 71 73 75 74 75 74 75 

Houston North Wayside C405 70 72 70 73 71 73 71 

Houston Texas Avenue C411 70 72 71 73 73 73 73 

Lang C408 70 72 73 73 75 73 74 

Clinton C403/C113/C304 69 71 70 72 72 71 72 

Houston Westhollow C410 69 71 70 72 71 71 71 

Houston Regional Office C81 68 70 69 71 71 70 70 

Lynchburg Ferry C1015 65 66 65 68 66 67 66 

This table compares the observed 2008 fourth-high at each monitor to the expected fourth high, as 

calculated by six different methods. 

The attainment status of an area is not based upon fourth-high ozone concentrations, but upon 

design values. Table 5-12: Observed and Expected Design Values, Recalculated to Account for 

Hurricane Ike shows the observed 2008 design value, and the expected design values, as 

calculated with the six different methods described above. As Table 5-12: Observed and 

Expected Design Values, Recalculated to Account for Hurricane Ike shows, the effect upon the 

design value for the HGB area is at most 1 ppb, and for two of the alternatives there is no effect. 

This analysis is robust, because six different methods of estimating the effect of the hurricane on 

ozone design value have given substantially the same answer: the 2008 eight-hour ozone design 

value was not different from the expected design value, based upon comparisons with historical 

data. Therefore, based upon the historical analysis, the effect of Hurricane Ike upon the eighthour ozone design value in the HGB area was apparently minimal. 

Table 5-12: Observed and Expected Design Values, Recalculated to Account for Hurricane 

Ike 

Observed Design Value: 91 ppb 2-weeks 

9/11-9/25 

1-month 

9/13-10/12 

1-month 

9/6-10/5 

Estimated Design Value after applying area-wide 

average Ike Adjustment Factor 91 ppb 92 ppb 92 ppb 

Estimated Design Value after applying monitorspecific Ike Adjustment Factor 92 ppb 91 ppb 92 ppb 
5-40

5.3.5 NOX Trends 

Nitrogen oxides, or NOX, are a variable mixture of NO and NO2 and are critical precursors to 

ozone formation. NOX is primarily created by fossil fuel combustion, lightning, biomass burning, 

and microbial action in the soil. 

Previous analyses performed using aircraft measurements and emission inventories obtained 

during TexAQS 2000 and TexAQS II indicate that NOX emissions in the Houston Ship Channel 

area have decreased between 2000 and 2006 (Cowling et al., 2007). Furthermore, aircraft data 

obtained during the two field studies were in agreement with data measured by continuous 

emission monitoring systems (CEMS) located at the facilities. Analyses done by the Rapid 

Science Synthesis Team of the 2005-2006 Texas Air Quality Study (TexAQS II) indicate that 

NOX emissions at several electric generating units (EGUs) have decreased by factors ranging 

from two to four between 2000 and 2006 (Cowling et al., 2007). These reductions were seen at 

EGUs that implemented NOX control features, such as selective catalytic reduction (SCR), 

between 2000 and 2006, which suggests these control strategies are working. The two field 

studies effectively describe the emissions during two short time windows, six years apart. To 

complement these analyses, the TCEQ has performed a more comprehensive investigation of 

long-term trends in NOX concentrations. 

Daily peak one-hour NOX from all monitors in the HGB area from 1991 through 2008 is plotted 

in Figure 5-19: Daily Peak Hourly NOX in the HGB Area. The increasing density of NOX data 

points shows that the number of NOX monitors in the HGB area has greatly increased since 1991. 

Annual 90th percentile and annual average NOX values are also plotted in the figure. Both of 

these measures have decreased markedly over the 1991 to 2008 period, falling 64 percent and 68 

percent, respectively. Even more remarkable may be the 53 percent and 48 percent declines since 

1999. 
5-41

 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 20Date of 90th percentile: 

 Oct Dec Dec Oct Nov Dec Nov Feb Nov Sep Apr Dec Dec Apr D

 22 15 25 30 22 12 19 24 12 5 27 15 19 28 Figure 5-19: Daily Peak Hourly NOX in the HGB Area 
5-42

Table 5-13: NOX Values in the HGB Area by Year shows the degree of decrease in NOX 

concentrations from 1991 through 2008 and 1999 through 2008. 

Table 5-13: NOX Values in the HGB Area by Year 

 annual annual 

 maximum average 

year NOX NOX

 ppb ppb 

1991 880 110 

1992 780 110 

1993 622 103 

1994 523 99 

1995 524 99 

1996 773 98 

1997 521 75 

1998 520 67 

1999 696 75 

2000 641 57 

2001 629 66 

2002 678 52 

2003 809 53 

2004 509 49 

2005 609 49 

2006 593 49 

2007 461 48 

2008 409 35 

overall decrease through 2008 since: 

1991 -53.5% -67.7% 

1999 -41.2% -53.0% 

annual decrease through 2008 since: 

1991 -4.4% -6.4% 

1999 -5.7% -8.0% 

Annual decreases are computed as compound annual rates. 

Though highly variable from season to season, daily peak hourly NOX also shows a general 

decreasing trend since 1991. Maximum NOX concentrations have decreased overall by 41 

percent since 1999, an average of roughly 32 ppb per year, or nearly 6 percent per year. The 

drop since the 1991 high of 880 ppb is 54 percent or greater than 4 percent annually. 

Average daily peak hourly NOX has dropped even more precipitously, falling 53 percent, or 8 

percent per year, from 75 ppb to 35 ppb, since 1999. Since 1991, average hourly NOX has 

dropped 68 percent, or over 6 percent per year, from the series high of 110 ppb. Notice that in 

2008, both the NO2 design value and maximum daily peak NOX recorded the lowest values of any 

previous year back to 1991. 
5-43

While the highest NOX values occur in the winter, the NOX values during the summer months, 

when ozone production is the highest, are of particular interest. Trends in median hourly NOX

concentrations at individual monitors in the HGB area from May through October, 1998 to 2008, 

are shown in Figure 5-20: Median NOX Concentrations in the HGB Area. Four monitors of 

particular interest, Houston Texas Avenue (CAMS 411), Lang (CAMS 408), Clinton (CAMS 

403/CAMS 113/CAMS 304), and Houston Bayland Park (CAMS 53), are highlighted. Sites with 

less than 75 percent complete data for a year were not plotted for that year; for example, Clinton 

(CAMS 403/CAMS 113/CAMS 304) had less than 75 percent complete data in 2008 and 

therefore was not plotted. 

Median NOX Concentrations in the HGB Area 

(May through October)

0

5

10

15

20

25

19981999200020012002200320042005200620072008

NOX

(ppb) Conroe

Deer Park

Lynchburg Ferry

Manvel Croix

NW Harris Co.

Park Place

Texas Ave

Houston East Clinton

Lang

Galveston Airport Lake Jackson

Aldine

Seabrook

Channelview

Bayland Park

Figure 5-20: Median NOX Concentrations in the HGB Area 

Median NOX values tend to vary from year to year, but most monitors show overall decreases in 

median NOX since 1998. Monitors that show the smallest decreases or show no change are at 

sites that have traditionally had lower NOX concentrations. Some of the largest median NOX

concentrations were measured at the Lang (CAMS 408) monitor (in close proximity to Highway 

290), and at the Houston Texas Avenue (CAMS 411) monitor (in downtown Houston). These 

monitors are both near major roadways; their similar trends suggest they may be measuring 

decreases in NOX emissions from mobile sources. Monitors at Galveston Airport (CAMS 

34/C109/C154), Seabrook Friendship Park (CAMS 45), and Lake Jackson (CAMS 1016) 

measured the lowest median NOX concentrations. 

Sites recording among the highest ozone design values, for example, Houston Bayland Park 

(CAMS 53) and Park Place (CAMS 416), are not necessarily the sites with the highest median 

NOX concentrations. The previous section showed that Houston Bayland Park (CAMS 53) has 

the highest eight-hour ozone design value in the HGB area of 91 ppb, yet it has a lower median 

NOX concentration than many other sites in the area. This observation is consistent with the 

behavior expected from ozone chemistry; in addition to being an ozone precursor, NO also reacts 

directly with ozone and in areas with high NO emissions, can destroy more ozone than it creates. 
5-44

Downwind from the high emission areas, however, ozone destroyed by reaction with NO can reform. 

The largest decreases since 1998 (Table 5-14: Median and 90th Percentile Hourly NOX Values) 

were observed at monitors primarily influenced by mobile source emissions, rather than industrial 

sources. Clinton (CAMS 403/CAMS 113/CAMS 304) and Houston East (CAMS 1), which are 

located near both industrial sources and highways, have seen larger decreases in median NOX

values than in 90th percentile values since 1998. At Houston East (CAMS 1), the 90th percentile 

value decreased 34 percent, while the median decreased 42 percent between 1998 and 2008. The 

Clinton (CAMS 403/CAMS 113/CAMS 304) monitor experienced a drop of 16 percent in the 90th

percentile, with a 21 percent decrease in the median between 1998 and 2007 (2008 was not used 

due to incomplete data), though these measures have increased in recent years. 

Table 5-14: Median and 90th Percentile Hourly NOX Values 

 median 90th percentile 

% change % change 

monitor 1998 2007 2008 1998-2008* 1998 2007 2008 1998-2008*

ppb ppb ppb % ppb ppb ppb % 

monitors with decreasing trends

 Houston Bayland Park C53 8 8 3 -63 33 30 19 -42 

 Northwest Harris Co. C26/ 10 5 4 -60 21 12 12 -43 

 A110/C154 

 Lang C408 21 16 11 -48 65 48 35 -46 

 Houston East C1 19 15 11 -42 56 46 37 -34 

 Clinton C403/C113/C304*

 24 19 - -21 56 47 - -16 

monitors with increasing trends

 Houston Aldine C8/AF108/X150 3 10 9 200 30 32 30 0 

 Houston Deer Park C18 3 5 5 67 25 21 18 -28 

monitors with indeterminate trends

 Channelview C15/C115 - 9 8 - 24 20 

 Conroe C65 - 4 4 - 10 10 

 Galveston Airport 

 C34/C109/C154 0 - - 1 - - 

 Houston Texas Avenue C411 - 17 14 - 53 37 

 Lake Jackson C1016 - 2 2 - 7 6 

 Lynchburg Ferry C1015 - 11 - - 33 - 

 Manvel Croix Park C84 - 5 4 - 17 15 

 Park Place C416 - 11 8 - 47 32 

 Seabrook Friendship Park C45 - 4 3 - 12 12 

* Percentage changes computed from 1998 to 2007 for years missing 2008 data, due to 

incomplete data. 

Monitors are sorted in increasing order by percentage change in median values. Monitors with 

indeterminate trends began operating after 1998. 

While several monitors recorded large decreases from 2007 to 2008, most others observed only 

minimal changes over that same period. These large disparities in patterns of ambient NOX

concentrations across the region are appropriate for further investigation, suggesting that larger 

decreases are not due solely to variations in meteorological conditions, which would be expected 
5-45

to influence all monitors similarly, though not identically. The differences seem to be related to 

the relative magnitudes of the overall concentrations. Sites with the highest concentrations, 

which tend to be urban sites, showed the greatest decrease. More rural sites like Lake Jackson 

(CAMS 1016), Conroe (CAMS 65), and Conroe Relocated (CAMS 78) may reflect slight 

changes in background values, while more urban sites may reflect actual emission changes. 

Similar to ozone, NOX concentrations in the HGB area appear to be decreasing over time, in large 

measure the result of the comprehensive suite of NOX-targeted controls implemented since 2000. 

Stringent point source NOX standards have been adopted along with numerous factors affecting 

mobile source NOX emissions. 

5.3.6 Ambient VOC Concentrations 

The other major class of compounds that are ozone precursors are VOC. TexAQS 2000 

researchers identified a specific subset of VOC that were closely associated with rapid and 

efficient ozone formation, i.e., light alkenes (Ryerson et al., 2003; Daum et al., 2003, 2004; 

Jobson et al., 2004). The TCEQ examined the historical data for these compounds, and decided 

to regulate several light alkenes emitted by industry that were particularly reactive, and that often 

had particularly high concentrations: ethylene, propylene, 1,3-butadiene, and butenes. 

Since the mid-1990s, the TCEQ has collected 40-minute measurements, on an hourly basis, of 45 

VOC compounds using automated gas chromatograph (auto-GC) instruments. Initially, 

measurements were collected at just one site (Clinton (CAMS 403/CAMS 113/CAMS 304)), but 

in subsequent years, auto-GC monitors have been added to new sites (see Figure 5-21: Houston 

Ship Channel Auto-GC Monitors and 2006 Reported Point Source HRVOC Emissions Points and 

Plant Boundaries). Currently, eight sites, listed in Table 5-15: Auto-GC Monitors in the Houston 

Ship Channel Area, along or near the Houston Ship Channel, along with three in Brazoria County 

and one in Texas City, are collecting VOC measurements with auto-GCs. 
5-46

Figure 5-21: Houston Ship Channel Auto-GC Monitors and 2006 Reported Point Source 

HRVOC Emissions Points and Plant Boundaries 

Ambient concentrations of the TCEQ-defined HRVOC (ethylene, propylene, 1,3-butadiene, 1-

butene, c-2-butene, and t-2-butene) were analyzed from 1995 to 2008. 

Table 5-15: Auto-GC Monitors in the Houston Ship Channel Area 

 start 

site name CAMS AIRS code latitude longitude city date 

Channelview C15/C115 482010026 29.8025 -95.1256 Channelview 8/3/2001 

Houston Milby Park A169 482010069 29.7062 -95.2611 Houston 2/19/2005 

HRM-3 Haden Road C603 482010803 29.7483 -95.1811 Houston 8/20/2001 

Lynchburg Ferry C1015 482011015 29.7646 -95.0780 Houston 5/24/2003 

Clinton C403/113/304 482011035 29.7337 -95.2576 Houston 7/1/1995 

HousDeerPrk2 C35/139 482011039 29.6700 -95.1285 Deer Park 1/5/1997 

Cesar Chavez C1020/175 482016000 29.6844 -95.2536 Houston 4/13/2004 

Wallisville Road C617 482010617 29.8214 -94.99 Baytown 6/5/2003 

Trends at each of the eight Houston Ship Channel monitors were examined. Data from the four 

other auto-GC monitors were analyzed only for trend slope and possible statistical significance of 

trends. Daily geometric means were computed from valid ambient hourly measurements for days 

with at least 18 valid hours of data. A geometric mean was calculated by taking the natural 

logarithm of each of the measurements, averaging these logs, then calculating the antilog of this 

mean log value. The geometric mean is a preferable statistic to median or arithmetic (ordinary) 

mean for evaluating the central tendency of data when the data are skewed, that is, when the data 

are not symmetrically, or normally, distributed, but clustered around extreme high or low values. 

It is more robust than an ordinary average, meaning its value is not greatly influenced by one or a 

few very high or very low values. Many distributions of pollutant measurements in the HGB area 

are skewed. Monthly geometric means were also computed with a 75 percent data completeness 

criterion for valid days in a month. 

Figure 5-22: Monthly Geometric Mean Ethylene Concentrations at the Eight Houston Ship 

Channel Monitors, July 1995 through December 2008 shows monthly geometric mean ethylene 

concentrations, ordered according to the monitor location from west to east. Grey bars denote the 

range of values from the 25th through 75th percentile concentrations, for all monitors. Noteworthy 

in this figure is the frequency of extremely high values recorded during the 1990s at Clinton 

(CAMS 403/CAMS 113/CAMS 304), at the western end of the Houston Ship Channel, and Deer 

Park (CAMS 35/139), in south central Houston Ship Channel. These were the only monitors 

operating during the early years of this period; this pattern suggests that high ethylene 

concentrations were not restricted to certain areas of the Houston Ship Channel, but were 

somewhat geographically widespread. 
5-47

Figure 5-22: Monthly Geometric Mean Ethylene Concentrations at the Eight Houston Ship 

Channel Monitors, July 1995 through December 2008 

For four consecutive years, July 1995 through July 1999, valid monthly geometric mean 

concentrations at Clinton (CAMS 403/CAMS 113/CAMS 304) exceeded the 75th percentile of the 

multi-decade series. Deer Park (CAMS 35/139) also exhibited high concentrations in the first 

several years, including the highest mean value for any complete month, 10.2 parts per billion, 

carbon (ppbC) in March 2001. By contrast, few monthly mean concentrations exceeded the 75th

percentile in the most recent four years, 2005 through 2008. 

Though measured ethylene and propylene concentrations show a large degree of variability at all 

auto-GC monitors, downward trends are apparent at seven of the eight; only Wallisville Road 
5-48

(CAMS 617) appears to show no decrease. A statistical trend analysis, described below, provides 

further insight into this. 

Peak monthly geometric mean ethylene concentrations at all monitors, 6.9 ppbC and 8.4 ppbC in 

2003 and 2004 respectively, decreased to 5.6 ppbC in 2005, 4.9 ppbC in 2006, and 4.5 ppbC in 

2007, before climbing to 5.1 ppbC in 2008. This decline in ambient ethylene concentrations 

suggests that ethylene emissions in the Houston Ship Channel are declining, though meteorology 

could be responsible for some or all of the decline in geometric mean concentrations. 

Similar to Figure 5-22: Monthly Geometric Mean Ethylene Concentrations at the Eight Houston 

Ship Channel Monitors, July 1995 through December 2008, Figure 5-23: Monthly Geometric 

Mean Propylene Concentrations at the Eight Houston Ship Channel Monitors, July 1995 through 

December 2008 displays monthly geometric mean concentrations of propylene for the eight 

Houston Ship Channel area auto-GC monitors. Again, Clinton (CAMS 403/CAMS 113/CAMS 

304) and Deer Park (CAMS 35/139) show higher concentrations in earlier years compared to 

recent ones; however, the magnitude of concentrations at the two monitors are dissimilar, unlike 

ethylene, suggesting elevated propylene concentrations are more geographically limited than 

elevated ethylene concentrations. Two other eastern Houston Ship Channel monitors, 

Channelview (CAMS 15/CAMS 115) and Lynchburg Ferry (CAMS 1015), report concentrations 

well above the 75th percentile in 2003, and to a lesser extent in 2004 and subsequent years, 

suggesting there are greater propylene emissions in the eastern Houston Ship Channel than the 

western Houston Ship Channel. However, the relatively fast reactivity of propylene, compared to 

ethylene, may explain part or all of the low concentrations seen in the western Houston Ship 

Channel. 

Similar analyses were performed for 1, 3-butadiene and the isomers of butene; however, trends in 

these pollutants can be difficult to interpret, as their relatively low concentrations are frequently 

within accepted measurement uncertainty. Further work is needed before trend estimation for 

these compounds can be considered accurate. 

Though still variable from month to month, pervasive decreases in the ambient concentrations of 

ethylene and propylene suggest that overall industrial emissions of these compounds have 

decreased considerably since 1995. This finding agrees with early reports from TexAQS II that 

ethylene emissions along the Houston Ship Channel have decreased approximately 40 percent 

from 2000 to 2006. 
5-49

Figure 5-23: Monthly Geometric Mean Propylene Concentrations at the Eight Houston 

Ship Channel Monitors, July 1995 through December 2008 

A preliminary analysis was performed to verify whether decreases observed were statistically 

significant. Ordinary least squares regression lines were fit to the monthly geometric mean 

ethylene and propylene concentrations, using an index of month, where the first recorded month 

was given a value of zero. Results of these fits are reported in Table 5-16: Parameter Estimates 

of Monthly Geometric Mean Concentrations Trends. In 23 of the 24 regressions, concentrations 

decreased across the respective study periods, with correlation coefficient (R2

) values ranging 

from 0.045 to 0.549. Eight of 12 monitors recorded statistically significant decreases for 

ethylene, including six of eight Houston Ship Channel monitors. All 12 monitors recorded 

statistically significant decreases for propylene. However, caution must be exercised when 
5-50

interpreting these results. First, some of the computed R2 values are very low, confirming there is 

a substantial degree of variation in the measured values, with only a portion of it explained by a 

simple linear model. Further statistical testing and verification, such as testing for and correcting 

possible autocorrelation, is necessary to fully validate these models. 

Table 5-16: Parameter Estimates of Monthly Geometric Mean Concentrations Trends 

 ethylene propylene 

monitoring site N slope intercept R2

 N slope intercept R2

Houston Ship Channel-area auto-GC monitors: 

 Cesar Chavez C1020/175 52 -0.019*

 2.74 0.09 52 -0.025* 2.86 0.16 

 Channelview C15/C115 62 -0.017*

 3.85 0.22 62 -0.039* 4.64 0.49 

 Clinton C403/C113/C304 60 -0.032*

 4.75 0.44 62 -0.018* 3.85 0.36 

 Deer Park C35/139 54 -0.033*

 4.12 0.25 65 -0.026* 4.09 0.22 

 HRM-3 Haden Road C603 56 -0.051*

 5.37 0.55 55 -0.026* 3.82 0.42 

 Houston Milby Park A169 39 -0.011 1.88 0.06 39 -0.021*

 2.05 0.20 

 Lynchburg Ferry C1015 56 -0.029*

 3.41 0.24 56 -0.059* 4.89 0.42 

 Wallisville Road C617 55 -0.002 1.79 0.00 55 -0.017*

 2.08 0.17 

Non-Houston Ship Channel-area auto-GC monitors: 

 Mustang Bayou C619 53 -0.008*

 0.72 0.20 53 -0.006* 0.83 0.13 

 Danciger C618 56 -0.003 0.57 0.05 56 -0.006*

 0.78 0.16 

 Lake Jackson C1016 50 -0.006 1.00 0.05 50 -0.007*

 0.77 0.18 

 Texas City 34th St. C620 59 -0.027*

 2.43 0.50 59 -0.020* 2.19 0.37

*Significant at the 5 percent (0.05) level. Significance levels for intercepts are not reported. 

Parameter estimates from ordinary least squares fits of monthly geometric mean concentrations of 

ethylene and propylene on an index of month, by monitoring site and compound. 

5.3.7 Geographic Patterns in Ambient HRVOC Concentrations Near the Houston Ship 

Channel 

The next analysis showed that, for some HRVOC, geographic patterns are apparent. Wind speed 

and wind direction measurements, collected in tandem with HRVOC concentrations at the 

Houston Ship Channel auto-GC monitors, were used not only to identify these patterns, but to 

track their changes over time. Radar plots of geometric mean concentrations of ethylene and 

propylene, by wind direction, were plotted, superimposed on maps of the Houston Ship Channel, 

and displayed in Figure 5-24: Geometric Mean Ethylene Concentration at Western Houston Ship 

Channel Monitors through Figure 5-27: Geometric Mean Propylene Concentration at Western 

Houston Ship Channel Monitors. 

These plots consist of jagged rings encircling a monitor. Each ring around a particular monitor 

represents the geometric mean concentration of the subject HRVOC at each of the 360 degrees 

surrounding the monitor, for a particular year. The distance from the origin to any point on the 

ring is proportional to the concentration of HRVOC arriving at the monitor from that direction. 

For example, Figure 5-25: Geometric Mean Ethylene Concentrations at Eastern Houston Ship 

Channel Monitors shows that in 2003 at Deer Park (CAMS 35/139), the highest mean ethylene 

concentration, 16 ppbC, occurred when winds were blowing from the northeast, suggesting there 

may be large ethylene emissions sources upwind of Deer Park (CAMS 35/139) in that direction. 

To help interpret these graphs, it is useful to describe a couple of hypothetical scenarios. In the 

first one, if HRVOC did not vary when winds arrived from different directions, i.e., the same 

concentrations were observed regardless of the wind direction, the ring would be a smooth circle. 
5-51

Conversely, in the second scenario, if HRVOC were detected only when winds arrived from a 

single direction, the ring would simply be an elongated spike pointing in that direction. 

In Figures 5-24: Geometric Mean Ethylene Concentration at Western Houston Ship Channel 

Monitors through 5-27: Geometric Mean Propylene Concentration at Western Houston Ship 

Channel Monitors, for the Houston Ship Channel monitors, a strong directional association with 

mean concentration is typical. The directional spikes seen in these rings are referred to as “lobes” 

in this section. 

Figure 5-24: Geometric Mean Ethylene Concentration at Western Houston Ship Channel 

Monitors 

Sources of ethylene (blue circles) and propylene (brown circles) are also depicted on the map of 

the respective compound, with sizes proportional to values reported in the 2006 TCEQ point 

source emissions inventory. Valid hourly measurements from 2002 through 2008 were used; 

hours with hourly wind speed measurements less than two miles per hour (mph) were discarded, 

due to considerable error in wind direction measurements at low wind speeds. 

While a compound’s concentration for a particular wind direction at a particular monitor is 

proportional to the distance from the monitor to the ring at that direction, the scale differs across 

monitors. For example, peak 2003 ethylene concentration (see Figure 5-25: Geometric Mean 

Ethylene Concentrations at Eastern Houston Ship Channel Monitors) at Lynchburg Ferry 

(CAMS 1015) is 24 ppbC, and 15 ppbC at Wallisville Road (CAMS 617), yet the length from 

each monitor to its respective peak (tip of sharp “point”) is approximately the same. For this 

reason, peak concentration at each monitor, for each pollutant, is labeled. 
5-52

Figure 5-25: Geometric Mean Ethylene Concentrations at Eastern Houston Ship Channel 

Monitors 

Figure 5-24: Geometric Mean Ethylene Concentration at Western Houston Ship Channel 

Monitors shows mean ethylene concentrations at the three western-most Houston Ship Channel 

auto-GC monitors. Sources of ethylene having the greatest impact on these monitors are all 

located east of the monitors, because the greatest peaks for each monitor point in this direction for 

all the years. The plot also shows trends across time at each monitor. At Clinton (CAMS 

403/CAMS 113/CAMS 304), peak ethylene occurred in 2003 from almost due east, as seen in the 

lobe labeled “14 ppbC.” Following 2003 and 2004, peak concentrations from that direction have 

been somewhat lower. Also, the lobes pointing south observed in 2003 and 2004 are markedly 

smaller in 2005 and subsequent years. An olefins production plant located in the Houston Milby 

Park (A169) area shut down in 2005; its emissions may have been responsible for those lobes. 

The plot shows mean ethylene concentrations for the Cesar Chavez (CAMS 1020/175) and 

Houston Milby Park (A169) monitors, which started operation in 2004 and 2005, respectively. 

While these monitors measured peak concentrations in different years, both monitors have peaks 

pointing in the direction of the Houston Milby Park (A169) olefins plant while it was in 

operation; Houston Milby Park (A169) observed a large lobe to the southeast in 2005, and Cesar 

Chavez (CAMS 1020/175) observed a notable lobe to the north in 2004 and 2005. This provides 

a stronger indication, when combined with the Clinton (CAMS 403/CAMS 113/CAMS 304) peak 

to the south, of the influence of emissions from that plant on local concentrations. 

Figure 5-25: Geometric Mean Ethylene Concentrations at Eastern Houston Ship Channel 

Monitors shows mean ethylene concentrations at the five auto-GC monitors located in the eastern 

part of the Houston Ship Channel. Variation in mean concentrations by direction is even more 

pronounced here than in the western portion of the Houston Ship Channel. The pattern in mean 

concentrations at Lynchburg Ferry (CAMS 1015) suggests there is a large source of ethylene 

emissions south-southeast of the monitor, near Battleground Road and Highway 225, and that 

emissions from this area have decreased. 
5-53

Table 5-17: Geometric Mean Ethylene for Key Wind Direction Lobes at Eastern Houston Ship 

Channel Monitors shows that this lobe’s mean 2003 concentration of 24.3 ppbC has halved in 

recent years. 

Table 5-17: Geometric Mean Ethylene for Key Wind Direction Lobes at Eastern Houston 

Ship Channel Monitors 

 principal 

Monitor direction(s) 2003 2004 2005 2006 2007 2008

 ppbC ppbC ppbC ppbC ppbC ppbC 

lobes pointing to the same sources in the central Houston Ship Channel area: 

HRM 3 ESE 24.8 18.0 15.6 5.0 4.7 5.2 

Channelview C15/C115 SW 8.9 8.9 5.6 4.3 3.6 4.1 

lobes pointing to the same sources in the eastern Houston Ship Channel area: 

Hous.DeerPrk2 C35/139 NE 16.6 missing 12.1 10.7 11.1 13.0

Lynchburg Ferry C1015 SSE 24.3 17.7 14.5 10.8 14.0 12.6 

Channelview C15/C115 SE 12.5 11.9 6.6 6.9 7.1 6.8 

Wallisville Road C617 SW 15.0 9.8 8.4 11.1 9.9 12.8 

lobes pointing in other directions: 

Channelview C15/C115 N 10.5 9.0 3.7 6.3 7.9 6.9 

Wallisville Road C617 ENE 9.7 11.5 9.6 10.8 9.2 11.6

Annual maxima are noted in boldface type. 

The pattern observed at Deer Park (CAMS 35/139) may provide additional evidence of suspected 

emission decreases in the same source area. The northeast lobe in Table 5-17: Geometric Mean 

Ethylene for Key Wind Direction Lobes at Eastern Houston Ship Channel Monitors has dropped 

from a high of 16.6 ppbC in 2003 to a range of about 11 to 13 ppbC in recent years. Similarly, 

the southeast lobe at Channelview (CAMS 15/CAMS 115), which points yet again to the same 

source area, peaked at 12.5 ppbC in 2003, dropped to 11.9 ppbC in 2004, and has not exceeded 

7.1 ppbC since. While this monitor is farther from this source region than are the other two 

monitors, and therefore is more likely to be impacted by other emissions sources, consistent 

decreases observed at these three monitors across the six-year span of available data suggest 

ethylene emissions have decreased in the subject source region. 

HRM-3 Haden Road (CAMS 603) shows a peak of 24.8 ppbC to the southeast in 2003, which fell 

to 18 ppbC in 2004, then further to 15.6 ppbC in 2005. The mean concentration has dropped 

since then, not exceeding 5.2 ppbC. The magnitude of the decrease over 2006 to 2008, as 

compared to 2005 and earlier years, suggests a shut down of one or more major process units, or 

even entire plants, somewhere southeast of this monitor, or implementation of HRVOC rules. 

Peaks at the Wallisville Road (CAMS 617) monitor point southwest, toward the east Houston 

Ship Channel, and east-northeast, in the direction of the Mont Belvieu industrial area, where there 

is considerable ethylene and propylene storage in underground salt caverns. Table 5-17: 

Geometric Mean Ethylene for Key Wind Direction Lobes at Eastern Houston Ship Channel 

Monitors shows that ethylene originating to the southwest decreased from the six-year peak in 

2003 (15 ppbC), to a range from 9.9 to 11.1 ppbC, before rising slightly to 12.8 ppbC in 2008. In 

contrast, the east-northeast lobe at this monitor shows relatively unvarying mean concentrations 
5-54

across the entire six-year period, ranging from 9.2 to 11.6 ppbC, with the six-year peak occurring 

in 2008. 

These conclusions for five monitors and eight directional lobes show a nearly consistent pattern 

across these monitors. Seven of eight lobes witnessed their highest mean concentration in 2003. 

Within one or two years of this peak, concentrations at all seven had dropped, from 27 to 65 

percent, and have leveled off since; mean concentrations have not varied appreciably from 2006 

to 2008. These findings suggest ethylene emissions from source areas close to these monitors, 

especially Battleground Road, Highway 225 in La Porte, and the petrochemical complex north of 

the Channelview (CAMS 15/CAMS 115) monitor, have decreased considerably in recent years. 

These observations suggest that the new TCEQ regulations specifically targeting HRVOC 

emissions and requiring full compliance by 2006 are proving effective in controlling point source 

HRVOC emissions. However, the trends shown here have not been corrected for meteorological 

variations. 

Results for the lobe pointing east-northeast from the Wallisville Road (CAMS 617) monitor 

disagree with some key findings at other lobes. The Wallisville Road (CAMS 617) east-northeast 

lobe, unique among the eight, experienced an increase in mean concentration from 2003 (9.7 

ppbC) to 2004 (11.5 ppbC). While 2006 to 2008 mean concentrations at Wallisville Road (CAMS 

617), like those of other monitors and lobes, changed relatively little, mean concentrations of the 

east-northeast Wallisville Road (CAMS 617) lobe changed relatively little across the entire sixyear period. The absence of recent decreases at this lobe compared to earlier years suggests that 

meteorology may not have caused high concentrations seen at most other lobes in earlier years. 

Figure 5-26: Geometric Mean Propylene Concentration at Eastern Houston Ship Channel 

Monitors displays monthly geometric mean concentrations of propylene in the same area of the 

eastern Houston Ship Channel. Table 5-18: Geometric Mean Propylene Concentrations for Key 

Wind Directions at Eastern Houston Ship Channel Monitors lists mean propylene concentrations 

across the study period, for each monitor and lobe. Similarities with ethylene are evident. For 

propylene, all seven lobes measured their highest concentrations in 2003 or 2004; five of the 

seven had their two lowest annual concentrations in 2007 and 2008. All seven lobes had 

concentrations in 2007 and 2008 that were 40 percent or more lower than their respective six-year 

peaks. 
5-55

Figure 5-26: Geometric Mean Propylene Concentration at Eastern Houston Ship Channel 

Monitors 

These results suggest that the propylene emissions in the source regions near the monitors have 

dropped considerably in the six-year study period, and that the HRVOC regulations may be 

responsible for the decreases. As seen with ethylene, patterns in geometric mean propylene 

concentrations at the east-northeast Wallisville Road (CAMS 617) lobe differed considerably 

from the other seven. Propylene concentrations varied relatively little across the six-year period, 

suggesting that, like ethylene, Mont Belvieu propylene emissions have changed little or not at all, 

on average, across the study period. 

Figure 5-27: Geometric Mean Propylene Concentration at Western Houston Ship Channel 

Monitors shows mean propylene concentrations by wind direction at the three western Houston 

Ship Channel monitors. Patterns depicted here exhibit strong similarities to those seen with 

ethylene in this area: the largest propylene source areas are to the east, and judging from the 

disappearance of strong peaks from 2006 onward, emissions from the now-defunct olefins plant 

located in the Houston Milby Park (A169) area were probably affecting these monitors. 
5-56

Figure 5-27: Geometric Mean Propylene Concentration at Western Houston Ship Channel 

Monitors 

Table 5-18: Geometric Mean Propylene Concentrations for Key Wind Directions at Eastern 

Houston Ship Channel Monitors lists mean propylene concentrations across the study period, for 

each monitor and lobe. 

Table 5-18: Geometric Mean Propylene Concentrations for Key Wind Directions at 

Eastern Houston Ship Channel Monitors 

 principal 

Monitor direction(s) 2003 2004 2005 2006 2007 2008

 ppbC ppbC ppbC ppbC ppbC ppbC 

lobes pointing to the same source in the eastern Houston Ship Channel area: 

HRM-3 Haden Road C603 SE 17.1 20.5 15.2 12.4 7.8 7.0 

Hous.DeerPrk2 C35/139 NE 50.0 30.3 25.4 21.2 19.6 18.6 

Lynchburg Ferry C1015 S 82.8 75.4 51.5 46.2 31.5 26.3

Channelview C15/C115 SE 30.1 19.0 11.7 13.8 11.7 8.2 

Wallisville Road C617 SW 35.6 27.3 22.3 18.4 14.5 21.3 

lobes pointing to other sources: 

Lynchburg Ferry C1015 SW 68.7 33.9 13.7 18.8 9.9 6.8 

Channelview C15/C115 N 11.3 7.7 3.0 5.5 8.1 5.2 

Wallisville Road C617 ENE 9.0 12.2 9.7 12.3 9.7 11.2

Annual maxima are noted in boldface type. 
5-57

5.3.8 Ambient Total VOC Concentrations 

Considerable research has focused on patterns and trends in HRVOC concentrations in the HGB 

area (Hafner Main et al. 2001; Brown and Hafner Main, 2002; Jolly et al., 2003; Fang and 

McDowell, 2003). Less examined are patterns for other, less-reactive VOC. This section 

presents a detailed examination of patterns in total VOC concentrations in the HGB area, using 

concentrations of total nonmethane hydrocarbons (TNMHC) as a measure of total VOC. Each 

TNMHC measurement corresponds to the sum of all chromatogram peaks (identified and 

unidentified) from the start to the end of sample collection. TNMHC is a useful measure of total 

VOC because it has been calculated in a consistent manner over the entire study period, unlike 

other parameters, such as the sum of Photochemical Assessment Monitoring Stations (PAMS) 

target compounds, whose constituents have changed periodically. 

Similar to the first HRVOC analysis presented in this section, geometric mean TNMHC 

concentrations, by monitor, year, and month, were calculated for valid months for all available 

data from each of the 12 HGB monitors. Further analysis of the four non-Houston Ship Channelarea monitors has not been completed at this time. 

Figure 5-28: Monthly Geometric Mean TNMHC Concentrations, July 1995 through December 

2008 shows, for each of the eight Houston Ship Channel monitors, monthly geometric mean 

TNMHC concentration for all months with complete data, between the start of monitoring and 

December 2008. Monitors are sorted according to their location from west (top) to east (bottom); 

the grey bars denote the 25th through 75th percentile concentrations (85 ppbC and 149 ppbC 

respectively) of all valid months across all monitors. 

As with ethylene and propylene, the two monitors with data before 2001, Clinton (CAMS 

403/CAMS 113/CAMS 304) and Deer Park (CAMS 35/139), recorded their highest monthly 

geometric mean values before 2001. Both monitors exhibited overall decreases across their 

respective data collection periods. A statistical analysis of possible trends, using ordinary least 

squares regression, is presented in Table 5-19: Parameter Estimates of Monthly Geometric Mean 

TNMHC Concentration Trends Houston Ship Channel Area Auto-GC Monitors. This statistical 

model indicates that all 12 monitors had decreasing monthly mean concentrations, from the 

beginning to the end of each monitor’s respective data range. As well, this model indicates that 

eight of the 12 monitors’ decreases were statistically significant at the 95 percent confidence 

level. 
5-58

Figure 5-28: Monthly Geometric Mean TNMHC Concentrations, July 1995 through 

December 2008 
5-59

Table 5-19: Parameter Estimates of Monthly Geometric Mean TNMHC Concentration 

Trends Houston Ship Channel Area Auto-GC Monitors 

Sitename 

Slope of 

Trend Intercept 

Degrees of 

Freedom R squared 

Cesar Chavez C1020/175 -0.61 132 47 0.07 

Channelview C15/C115 -0.37* 153 49 0.10 

Clinton C403/C113/C304 -0.63* 225 78 0.46 

Hous.DeerPrk2 C35/139 -0.55* 148 80 0.31 

Houston Milby Park A169 -0.33 99 33 0.03 

HRM-3 Haden Road 

C603 -1.22* 173 47 0.52 

Lynchburg Ferry C1015 -1.14* 156 47 0.27 

Wallisville Road C617 -0.31* 79 49 0.11 

Non-Houston Ship Channel-area auto-GC monitors 

Sitename 

Slope of 

Trend Intercept 

Degrees of 

Freedom R squared 

Danciger C618 -0.22* 44 47 0.12 

Lake Jackson C1016 -0.18 34 43 0.04 

Mustang Bayou C619 -0.11 61 43 0.01 

Texas City 34th St. C620 -0.95* 102 57 0.46 

*Significant at the 5 percent (0.05) level. Significance levels for intercepts are not reported. 

Parameter estimates from ordinary least squares fits of monthly geometric mean concentrations of 

TNMHC on an index of month, by monitoring site. 

Figure 5-29: 90th Percentile TNMHC Concentration in the HGB Area presents 90th percentile 

TNMHC concentrations at each auto-GC monitor. The area-wide 90th percentile TNMHC 

concentrations and the 90th percentile TNMHC at most of the individual monitors are decreasing. 

Smaller decreases are evident at Wallisville Road (CAMS 617), Channelview (CAMS 15/CAMS 

115), Lake Jackson (CAMS 1016), Mustang Bayou (CAMS 619), and Danciger (CAMS 618), 

while larger decreases are observed primarily at monitors closer to the Houston Ship Channel. 

Monitors in Brazoria County (Danciger (CAMS 618), Lake Jackson (CAMS 1016), and Mustang 

Bayou (CAMS 619)) and Galveston County (Texas City 34th St. (CAMS 620)) tend to report 

lower 90th percentile TNMHC than monitors located in Harris County. In the past, Clinton 

(CAMS 403/CAMS 113/CAMS 304) has recorded the highest TNMHC concentrations, but since 

2006 Clinton has decreased at a faster rate and Channelview (CAMS 15/CAMS 115) has 

recorded the highest concentrations. 
5-60

90th Percentile TNMHC Concentration in the HGB Area

0

100

200

300

400

500

600

700

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Concentration 

(ppbC)

Mustang

Milby Park

HRM-3

Cesar Chavez

Clinton

Channelview

Deer Park

Lynchburg

Danciger

Lake Jackson

Texas City

Wallisville

Figure 5-29: 90th Percentile TNMHC Concentration in the HGB Area 

5.3.9 Meteorologically Adjusted Ozone Trends 

Ozone formation is dependent not only on its precursors (NOX and VOC), but also on 

meteorological variables. While trends in ozone design values have been decreasing, design 

value trends must be examined to determine if the values are decreasing due to emission controls 

or if they are decreasing simply because of meteorological conditions in the area in the past 

several years. To determine whether control strategies have been effective, meteorological 

influences must be removed from ozone trends. Analysis done by Sullivan (2009) used a 

generalized linear model to account for meteorological influences in ozone trends. The following 

discussion is based upon Sullivan (2009), who used a modified version of the Camalier et al. 

(2007) technique for removing the meteorological influences from the ozone trends. 

Before meteorological influences can be removed from ozone trends, the meteorological factors 

that are most important to ozone formation must first be identified. Various correlations and 

factor analyses were used to identify the most important meteorological variables for ozone 

formation in the HGB area. Data from the Omnibus Meteorological Database (METDAT) 

maintained by the EPA was compared to ozone data obtained from surface monitors in the HGB 

area. Because the set of observed ozone levels can be influenced by the number of monitors in an 

area, Sullivan (2009) used a consistent set of ozone monitors in the HGB area. These monitors 

are listed in Table 5-20: Area Ozone Monitoring Sites with Long-Term Data. Most contain a 

consistent set of data from 1990 to 2007. Data from monitors that were moved a short distance 

during the period from 1990 to 2007 were combined with data from monitors in nearby locations, 

for example, data at Clute (CAMS 11) were combined with data from Lake Jackson (CAMS 

1016). 
5-61

Table 5-20: Area Ozone Monitoring Sites with Long-Term Data 

AQS Number Site Name 

482011039 Hous.DeerPrk2 C35/139 

482011035 Clinton C403/C113/C304 

482011034 Houston East C1 

482010075 Houston Texas Avenue C411 

482010062 Houston Monroe C406 

482010051 Houston Croquet C409 

482010047 Lang C408 

482010046 Houston North Wayside C405 

482010029 Northwest Harris Co. C26/A110/C154 

482010024 Houston Aldine C8/AF108/X150 

480391016 Lake Jackson C1016 (and Clute C11) 

Source: Sullivan, 2009. 

Figure 5-30: Actual Mean Eight-Hour Ozone Concentrations (Blue Line) and Mean Eight-Hour 

Predicted Concentrations with the Non-Meteorological Trend Removed (Red Line), which was 

reproduced from Sullivan (2009), displays two time series. The values in blue represent the 

observed mean daily maximum eight-hour ozone concentrations; values in red represent the daily 

peak ozone based purely on the meteorological variations, with the non-meteorological factors 

removed. In other words, the statistical model described above has been used to re-create the 

ozone time series with only the meteorology taken into account. 

For 2006 and 2007, the statistical model predicts that the observed mean daily peak eight-hour 

ozone should have been higher than observed, based upon the conduciveness of the meteorology 

toward ozone formation. In other words, based on the weather, ozone concentrations should have 

been higher in 2006 and 2007. Subtracting the meteorologically-based eight-hour ozone 

estimates from the actual eight-hour ozone results in a trend with the meteorological effects 

removed (Figure 5-31: Residual Meteorologically Adjusted Eight-Hour Ozone Concentrations 

Trend). This trend represents how the sum of anthropogenic factors, model error, and 

undiagnosed meteorological factors have changed from 1996 to 2007. Figure 5-31: Residual 

Meteorologically Adjusted Eight-Hour Ozone Concentrations Trend, which was reproduced from 

Sullivan et al., 2009, represents the trend in peak daily maximum ozone with the meteorological 

factors removed. The meteorologically-adjusted ozone trend is clearly downward. Since the 

meteorological variations have been removed, this downward trend shows the effect of emission 

reductions in the HGB area. Statistical results of this analysis are listed in Table 5-21: Summary 

Statistics for Meteorologically Adjusted Ozone Trends from 1996 to 2007. The slope of -0.86 

shows that eight-hour ozone trends in the HGB area are decreasing and that they are significant 

(p-value = 0.00). 
5-62

Figure 5-30: Actual Mean Eight-Hour Ozone Concentrations (Blue Line) and Mean EightHour Predicted Concentrations with the Non-Meteorological Trend Removed (Red Line) 

Figure 5-31: Residual Meteorologically Adjusted Eight-Hour Ozone Concentrations Trend 
5-63

Table 5-21: Summary Statistics for Meteorologically Adjusted Ozone Trends from 1996 to 

2007 

Parameter Value 

Intercept 6.438 

Slope -0.86*

 t-statistic -4.20 

p-value 0.00 

Lag 1 Coefficient -0.20 

 t-statistic -0.63 

* Value is statistically significant. (Sullivan et al., 2009) 

The analysis from Sullivan (2009) shows that, after adjusting for meteorology, concentrations of 

ozone has declined substantially in the HGB area. All else held equal, daily maximum eight-hour 

ozone concentrations in the HGB area should be around 9 ppb lower in 2007 compared to 1996. 

5.3.10 Background Ozone Concentrations: Transport of Ozone into the HGB Area 

Estimating the levels of ozone transported into the HGB area is important in order to identify so 

that the amount of locally produced ozone. Several researchers have previously investigated the 

background ozone concentrations in Texas and the transport winds that are associated with them. 

Nielsen-Gammon et al. (2005) investigated background ozone from 1998-2003 in the HGB area 

and obtained the following insights (paraphrased from Nielsen-Gammon et al., 2005): 

• The seasonal variability in eight-hour maximum ozone in eastern Texas is primarily 

associated with background ozone. Local contributions tend to be highest during the 

summer when background ozone reaches a minimum. 

• The late spring peak in eight-hour maximum ozone in eastern Texas is primarily 

associated with “tropospheric background” ozone. This ozone maximum has been 

observed at rural sites elsewhere and is associated with variations in the lifetime of 

ozone, the concentrations of NOx, and enhanced transport from the stratosphere. 

• The midsummer minimum in background ozone in eastern Texas leads to a minimum in 

eight-hour peak ozone that is strongest in southeastern Texas and barely noticeable in 

northeastern Texas. The primary cause of the summertime minimum is a decline in the 

tropospheric background ozone. Although the relatively clean southerly flow is 

weakening during this period, most air parcel paths remain maritime in nature. 

• When easterly and northeasterly winds become more frequent in late summer, 

background ozone and total ozone in eastern Texas begin rising. Winds are also less 

steady than in the middle of summer, so continental transport becomes increasingly 

frequent. 

Langford et al. (2009) showed that the techniques used by Nielsen-Gammon et al. (2005) yielded 

results consistent with a different technique of estimating background, except on some occasions 

when the Galveston Airport (CAMS 34/CAMS 109/CAMS 154) site was chosen as the 

background site. Langford et al. showed that the Galveston site is the site most strongly affected 

by the Gulf breeze, and that on some days, the maritime air from the Gulf does not affect the 

Houston area, even though this air affects Galveston. Hardesty et al. (2007) have shown that 

during the TexAQS II study in August through September 2006, background ozone in southeast 

Texas averaged about 50 ppb, with background concentrations lower near the coast, and higher in 

northeast Texas. On one day, September 8, 2006, the background ozone entering Texas from east 

was 85-90 ppb. The results of these studies have shown that background ozone entering 

southeast Texas can have a large effect on the total observed eight-hour ozone concentrations. To 

investigate the role of background ozone for the most recent years, the TCEQ commissioned a 

study of background ozone and its relationship to larger-scale wind patterns. Below is a 

description of this work. 
5-64

Sullivan (2009) used 72-hour back trajectories calculated with the Hybrid Single Particle 

Lagrangian Integrated Trajectory (HYSPLIT) algorithm, using data from the Ecosystem 

Dynamics and the Atmosphere Section (EDAS) meteorological model to estimate the amount of 

ozone entering into the HGB area. A total of 1,456 backward trajectories were run starting at 

12:00 Central Standard Time in central Houston, at 300 meters above ground level, during the 

peak of ozone season in the HGB area (May 1 through October 31, 2000 to 2007). Analysis of 

multiple trajectories can distinguish between source areas, or paths, that lead to higher than 

average, or lower than average ozone concentrations (Sullivan et al., 2009). A clustering 

algorithm was used to group multiple trajectories based on trajectory size and shape. Six 

identified clusters appear in Figure 5-32: Six Clusters Found Using HYSPLIT Backward 

Trajectory Clustering Algorithm, which was reproduced from Sullivan, 2009. Forty backward 

trajectories that did not end up in any of the six clusters, illustrated in Figure 5-33: Cluster 0 

Backward Trajectories, reproduced from Sullivan (2009), were grouped and assigned a cluster 

number of zero. All but one of the back trajectories in cluster zero originate from the south and 

that these trajectories appear to extend beyond the EDAS modeling domain, which is the only 

difference between cluster zero and cluster two. 
5-65

Figure 5-32: Six Clusters Found Using HYSPLIT Backward Trajectory Clustering Algorithm 

z 

<D 

(j) 

(\J 

co 

Cluster 1 of 6 - Standard 

217 backward trajectories ending at various times 

EDAS Meteorological Data 

Cluster 4 of 6 - Standard 

314 backward trajectories ending at various times 

EDAS Meteorological Data 

:J 

0 

(/) 

Cluster 2 of 6 - Standard 

512 backward trajectories ending at various times 

EDAS Meteorological Data 

·f················.f .... 

Cluster 5 of 6 - Standard 

167 backward trajectories ending at various times 

EDAS Meteorological Data 

z 

49 backw

157 backw

<D 1::'--..;-- -l 

1"-

oi (\J 

co 
5-66

Figure 5-32: Six Clusters Found Using HYSPLIT Backward Trajectory Clustering Algorithm

shows that cluster one and cluster two represent days in which winds originated from the Gulf of 

Mexico; these trajectories typically represent cleaner air coming from the Gulf of Mexico and 

hence lower observed ozone concentrations in the HGB area. Cluster three represents long 

trajectories, which come into the HGB area from the north as far away as Canada. This type of 

trajectory can also bring clean air from northern states and Canada into the HGB area. Cluster 

four represents stagnant air conditions, a frequent cause of ozone accumulation. Cluster five 

shows trajectories that originate from the northeast, in the Ohio River Valley, that bring polluted 

air from more populated areas into the HGB area. Cluster six illustrates trajectories from the east, 

some of which cross over Louisiana and the Beaumont-Port Arthur (BPA) area and some of 

which cross over the Gulf of Mexico. The mean centerline from each of the six clusters is shown 

in Figure 5-34: Means of Six 60-Hour Backward Trajectory Clusters. Trajectories were 

compared to ozone concentrations in the HGB area to quantify how these trajectories are related 

to ozone in the HGB area. 

Figure 5-33: Cluster 0 Backward Trajectories 
5-67

Figure 5-34: Means of Six 60-Hour Backward Trajectory Clusters 

Twelve ozone sites, shown in Figure 5-35: Sites Used in Ozone Area Maximum and Background 

Determination, that had near continuous operation from 2000 to 2007 in the HGB area were 

selected to compare with trajectory clusters. In an effort to use measurements from a consistent, 

long-term set of monitors, data from sites that were shut down were combined with data from 

sites that began collecting data near the sites that were taken off-line. Sites where data were 

combined are Lake Jackson (CAMS 1016) and Clute (CAMS 11), and Galveston Airport (CAMS 

34/CAMS 109/CAMS 154) and Galveston Airport 99th St. (CAMS 1034). Sites were selected 

based on locations as either a site upwind or downwind of the HGB area. Northwest Harris 

County (CAMS 26), the Lake Jackson (CAMS 1016) / Clute (CAMS 11) combined site pair, and 

the Galveston Airport (CAMS 34/CAMS 109/CAMS 154)/ Galveston 99th St. (CAMS 1034) 

combined site pair generally represent sites measuring background ozone concentrations. Sites 

on the downwind side of downtown Houston and the Houston Ship Channel generally represent 

sites measuring maximum ozone concentrations in the HGB area. Maximum peak and minimum 

peak eight-hour ozone concentrations from the twelve monitors were found for each day, then 

merged with the cluster classification from each day. Following Nielson-Gammon et al. (2005), 

that minimum peak eight-hour average ozone concentration was used to represent the 

“background” ozone level in the HGB Area. 
5-68

Figure 5-35: Sites Used in Ozone Area Maximum and Background Determination 

Table 5-22: Ozone Statistics for HYSPLIT Back Trajectory Clusters summarizes average 

maximum and average minimum, or background, ozone concentrations for each cluster. Average 

maximum peak daily eight-hour ozone among the clusters ranges from 40.6 ppb to 73.3 ppb, 

while average minimum peak daily eight-hour ozone, considered a proxy for background ozone 

concentrations, ranges from 21.4 ppb to 45.1 ppb. The difference between these two means can 

be used as a surrogate for locally produced ozone. Cluster four and cluster five, which represent 

the short fetch and the northeast fetch, have the highest average maximum ozone concentrations, 

71.6 ppb and 73.3 ppb, respectively, and the highest average background, 40.8 ppb and 45.1 ppb. 

These two clusters also exhibit some of the largest average differences or local contributions. 

Cluster zero, the far southeast cluster, cluster one, the east southeast cluster, and cluster two, the 

southeast cluster, exhibited some of the lowest average background and average peak ozone; 

these clusters are expected to have a lower background ozone due to their origins over the Gulf of 

Mexico. 
5-69

Table 5-22: Ozone Statistics for HYSPLIT Back Trajectory Clusters 

 Average Average Average 

 Number maximum minimum difference, 

 of back peak daily peak daily minimum 

 trajec- eight-hour eight-hour and maximum 

Cluster Fetch tories ozone ozone ozone*

 # ppb ppb ppb 

 5 NE 166 73.3 45.1 28.1 

 4 Short 312 71.6 40.8 30.8 

 6 East 151 61.1 35.6 25.5 

 3 North 49 59.1 37.2 21.9 

 2 SE 506 48.5 24.8 23.7 

 0 far SE 40 45.0 23.8 21.1 

 1 ESE 217 40.6 21.4 19.1

*

 May not sum due to rounding. Note: Data is May through October, 2000 to 2007. Fetch 

represents the main direction of the cluster, count is the number of back trajectories in each 

cluster, average minimum peak daily eight-hour ozone is taken as the background ozone 

concentration. Clusters are sorted in descending order by average maximum peak daily eight-hour 

ozone. 

The 95 percent confidence intervals for the mean eight-hour ozone maximum for each cluster are 

shown in Table 5-23: Average Maximum Ozone and 95 Percent Confidence Intervals. Two 

standard errors were used for the confidence intervals in each row. The confidence intervals in 

the table show that differences between means are statistically significant for most of the pairwise comparison. This is shown graphically in Figure 5-36: Average Maximum Ozone and 95 

Percent Confidence Intervals. Fetches originating from the northeast and east, as well as the 

“short” fetch, have the highest average peak daily ozone values, and they are tightly clustered. 

Clusters originating from the north and far southeast have noticeably wider confidence intervals, 

indicating more variability, but with lower average peak daily ozone concentrations than the 

northeast and east clusters. 

Table 5-23: Average Maximum Ozone and 95 Percent Confidence Intervals 

 Average Average Average 

 Cluster maximum maximum maximum 

 ranked by peak daily + 2 - 2 

 maximum eight-hour standard standard 

 average Fetch Count ozone errors errors 

 # ppb ppb ppb 

 5 NE 166 73.3 76.7 69.8 

 4 Short 312 71.6 74.3 68.9 

 6 East 151 61.1 64.5 57.8 

 3 North 49 59.1 65.2 53.0 

 2 SE 506 48.5 50.3 46.6 

 0 far SE 40 45.0 51.5 38.4 

 1 ESE 217 40.6 42.7 38.5 

Note: Confidence intervals were constructed using two standard errors. Clusters are sorted in 

descending order by average maximum peak daily eight-hour ozone. Confidence intervals for 

differences between the area ozone maximums generally do not overlap beyond one or two rows. 

Although many of the selected sites were intended to represent background and maximum ozone 

in the HGB area, note that on many days true background ozone concentrations may be observed 
5-70

farther away, in more rural areas, and the true maximum ozone concentration may also be 

underestimated. Despite uncertainty in estimates of true background and maximum ozone 

concentrations, the large number of observations used in this analysis, as well as evidence 

presented earlier, provide clear evidence that ozone in the HGB area is affected by transport of 

ozone from external sources. 

0

20

40

60

80

NE Short East North SE far SE ESE

ppb

average maximum peak ozone

upper bound of 95% confidence interval

lower bound of 95% confidence interval

Figure 5-36: Average Maximum Ozone and 95 Percent Confidence Intervals 

Figure 5-37: Relationship Between Minimum and Maximum Ozone Concentrations, recreated 

from Sullivan (2009), shows there is a significant linear relationship between mean HGB area 

minimum and maximum eight-hour average ozone concentrations by trajectory cluster (p-value < 

0.01). The dark red points and estimated regression line represent the relationship between mean 

maximum ozone and mean minimum (background) ozone concentrations by cluster. The olive 

points and estimated regression line represent the relationship between “local contribution” 

(difference between maximum and minimum) and mean minimum ozone concentrations by 

cluster. The relationship between maximum and minimum ozone by cluster suggests that 

trajectory direction is a factor determining severity of both HGB area maximum and background 

ozone concentrations (Sullivan, 2009). The estimated slope parameter (β = 1.36) of the ordinary 

least squares regression of average minimum ozone concentration against average maximum 

ozone concentration shows that maximum ozone concentration increases at a greater rate with 

trajectory direction when compared to minimum ozone. 
5-71

O3max = 1.36 O3min + 12.76

R2 = 0.96

O3(max-min) = 0.36 O3min + 12.67

R2 = 0.65

10

30

50

70

10 30 50 70

1

0

2

3

4 5

6

ppb

ppb

 ESE

far SE 

SE 

 north

short NE

east 

Figure 5-37: Relationship Between Minimum and Maximum Ozone Concentrations 

Figure 5-37: Relationship Between Minimum and Maximum Ozone Concentrations also shows 

that the difference between mean HGB area maximum and minimum ozone concentrations is also 

roughly linear with area minimum, but with a lower slope (β=0.36) and lesser statistical 

significance (p-value=0.03) (Sullivan, 2009). The linear relationship between the difference and 

mean HGB area minimum ozone suggests the transport direction also affects local ozone 

production. The slower air movement of cluster four, which is the “short” cluster, allows greater 

accumulation in the area under lower local surface wind speeds. Winds originating from the 

directions of cluster six, the “east” cluster, and cluster five, the “northeast” cluster, help to move 

surface air along the area around the Houston Ship Channel and across the downtown Houston 

area, which, as noted, contain large amounts of ozone precursors. Overall, this analysis shows 

that directions of back trajectories can account for up to 24 ppb of variation in background ozone 

concentrations, and up to 35 ppb of variation in maximum ozone concentrations. 

5.3.11 Transport and Surface Wind Trajectories 

While still incomplete, a preliminary analysis of upper level, or transport, wind trajectories was 

conducted to confirm and extend findings from the previously discussed directional analysis. 

Additional HYSPLIT modeling of 48-hour back trajectories at 1,500 meters altitude for May 

through August, 2000 to 2008, was used to detect difference in trajectories across years that may 

have influenced ozone concentrations in the HGB area. 

A simple visual inspection of the densities of distributions of trajectory end points presented in 

Figure 5-38: Distributions of End Points from HYSPLIT 48-Hour Back Trajectories shows that 

upper level wind patterns for 2008, a year which had relatively low ozone concentrations, do not 

noticeably differ from patterns in other years. Of the years analyzed, the pattern for 2000, a year 

with relatively high levels of ozone, is perhaps the most similar to 2008. The spatial distribution 

is similar among years and wind speeds are also similar. Higher wind speeds are evident in 2004 

and 2005, as implied by trajectories with longer fetches. The implication is that the wind patterns 
5-72

observed during 2008 were not responsible for the lower ozone concentrations observed, since 

high ozone was observed during other years that had wind patterns similar to 2008. 

Figure 5-38: Distributions of End Points from HYSPLIT 48-Hour Back Trajectories 

5.3.12 Background Ozone in Texas 

Research on the meteorology of the HGB area has found that the highest background ozone 

transported into the HGB area predominately originates from the north and northeast (NielsonGammon et al., 2005). In the present analysis, two techniques are used to examine background 

ozone concentrations in Texas since 2000. The first technique examines the trend in ozone 

concentrations at four sites that can be considered background sites under certain flow conditions. 

The second technique examines ozone concentrations associated with different patterns of longterm backward trajectories. 

Identifying appropriate background ozone monitoring sites from which to ascertain trends is 

complicated by local ozone, complex wind patterns, and natural variability in background ozone 

itself. To estimate background ozone, Nielson-Gammon et al. evaluated all monitors in the 

region to identify those that could be considered to be recording background ozone values. They 

proposed a modification of a TCEQ procedure to identify such sites. 

The TCEQ procedure involves determining the direction of transport winds, then selecting a rural 

monitor upwind of the area in that direction. Nielson-Gammon et al. simply select as the 

background value the lowest of the peak eight-hour ozone values from all monitors. Unlike the 
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Nielson-Gammon procedure, which used gridded output of a meteorological model, this analysis 

follows the TCEQ approach using direct measurements of surface winds and tracking background 

ozone concentrations over time at selected monitors. Modifying the Nielson-Gammon procedure, 

the approach presented here identifies the 90th percentile values recorded at the selected monitors 

and examines the distribution of daily maximum ozone concentrations over time to determine 

whether these supposed background concentrations have increased or decreased. Both the 

Nielson-Gammon method and the TCEQ method may not strictly estimate background ozone, as 

defined above, because they do not remove any potential recirculation of pollutants generated via 

local emissions. Also, background ozone alone may not tell the complete story, since ozone 

precursors, which can react with each other and with local emissions to produce ozone, may also 

be present in transported air. 

Four candidate monitors were selected for this analysis and are listed in Table 5-24: Monitors 

Selected for Background Transport Analysis. Two monitors, West Orange (CAMS 9) and 

Mauriceville (CAMS 642/CAMS 311/CAMS 665), are located east of the HGB area, adjacent to 

the Texas-Louisiana border, east of the BPA area; one, Karnack (CAMS 85), is located in 

northeast Texas near the Texas-Louisiana-Arkansas border and the Tyler-Longview-Marshall 

(TLM) area; and one, Hamshire (CAMS 64/CAMS 654), is located east of the HGB area, 

between the HGB area and the BPA area. Each of these monitors was selected for specific 

purposes. West Orange (CAMS 9) and Mauriceville (CAMS 642/CAMS 311/CAMS 665) were 

chosen because they are as close as possible to the Texas border and, thus, are useful for isolating 

background ozone being transported into the state from the east. Karnack (CAMS 85), in 

northeast Texas, is also very near the Texas border, and was selected to provide an assessment of 

background ozone transport from more northerly regions. The final site, Hamshire (CAMS 

64/CAMS 654), was selected to aid stratification of background ozone being transported into the 

HGB area into a component originating outside the state, and a component contributed by the 

BPA area. 

Table 5-24: Monitors Selected for Background Transport Analysis 

Monitor metro area location years CAMS code 

West Orange BPA TX-LA border 2000-2008 C9/A141 

Mauriceville BPA TX-LA border 2000-2008 C642/C311/C665 

Karnack TLM TX-LA-AR border 2001-2008 C85/AFHP303 

Hamshire HGB between BPA and HGB 2000-2008 C64/C654 

Source: TCEQ/LEADS database. Data with wind speeds less than 3 miles per hour were 

excluded to minimize influences from periods of stagnation which may result in over estimation 

of background concentrations. 

To isolate ozone being transported into the state, measurements at the selected monitors were 

restricted by wind direction. The West Orange (CAMS 9) monitor is located less than 3 miles 

from the Louisiana border but is near several industrial sites. Only ozone measurements taken 

when winds originated from directions ranging from 30° to 90° (Figure 5-39: Mauriceville 

C642/C311/C665) and West Orange (C9) Monitors) were considered, to minimize possible 

influence from these sources. Thirty degrees corresponds to a north-northeast direction and 90o

 is 

due east. The Mauriceville (CAMS 642/CAMS 311/CAMS 665) monitor is located ten miles 

from the Louisiana border, north of the West Orange (CAMS 9) monitor. This site may have 

some minor influence from relatively small NOX and VOC sources. Data from this monitor was 

restricted to wind directions originating from 30° to 90°, similarly to West Orange (CAMS 9), to 

minimize any possible influence of nearby point sources. 

The Karnack (CAMS 85) monitor in the TLM area is located eight miles from the TexasLouisiana border, and roughly 20 miles from Arkansas. Measurements from Karnack (CAMS 

85) were restricted to wind directions originating from 30° to 135° (Figure 5-40: Karnack 

C85Monitor), that is, from north-northeast clockwise to southeast. Though this site is not near 
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the HGB area, it records large influxes of continental air transported from the Midwestern United 

States into Texas, which ultimately may raise background ozone concentrations throughout the 

state. Also, estimates of background ozone concentrations from Karnack (CAMS 85) can be 

compared to background estimates from West Orange (CAMS 9) and Mauriceville (CAMS 

642/CAMS 311/CAMS 665), which is useful for corroborating estimates at these two sites, and 

determining the range of background ozone entering the state. 

The final site under consideration is Hamshire (CAMS 64/CAMS 654), located between the HGB 

area and the BPA area. Ozone measurements from this site can be used to estimate background 

ozone concentrations transported to the HGB area when winds are from the east. These 

background ozone measurements are a combination of pollution transported into Texas, as well as 

the contribution of pollution from the BPA area. To avoid undue influence of nearby industrial 

sites, similar to Karnack (CAMS 85), data from Hamshire (CAMS 64/CAMS 654) are restricted 

to measurements obtained when winds originate from directions ranging from 30° to 135°. For 

the four monitors, monthly 10th, 25th, 50th, 75th and 90th percentiles of hourly ozone 

concentrations were calculated for the spring and summer ozone season, May through September, 

2000 through 2008, except Karnack (CAMS 85) which only has data since 2001. These values 

are plotted in Figure 5-42: Selected Statistics for the West Orange C9 Monitor, Figure 5-43: 

Selected Statistics for the Mauriceville C642/C311/C665 Monitor, Figure 5-44: Selected 

Statistics for the Karnack C85 Monitor, and Figure 5-45: Selected Statistics for the Hamshire 

C64/C654 Monitor. Ninetieth percentile values are reported in Table 5-25: Range of Monthly 

90th Percentile Daily Peak Hourly Ozone Concentrations for Subject Wind Directions. 
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Figure 5-39: Mauriceville C642/C311/C65 and West Orange C9/A141 Monitors 

Figure 5-40: Karnack C85 Monitor 

Figure 5-41: Hamshire C64/C654 Monitor
West Orange

0

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note: data shown is May - September only

median

90th

75th25th10th

 2000 2001 2002 2003 2004 2005 2006 2007 2008

Figure 5-42: Selected Statistics for the West Orange C9 Monitor 

Mauriceville

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 2000 2001 2002 2003 2004 2005 2006 200

Figure 5-43: Selected Statistics for the MaurC642/C311/C665 Monitor 

Karnack

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median

th

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 2000 2001 2002 2003 2004 2005 2006 2007 2008

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Figure 5-44: Selected Statistics for the Karnack C85 Monitor 

Hamshire

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 2000 2001 2002 2003 2004 2005 2006 2

Figure 5-45: Selected Statistics for the HamMonitor 

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Table 5-25: Range of Monthly 90th Percentile Daily Peak Hourly Ozone Concentrations for 

Subject Wind Directions 

 Hamshire Karnack Mauriceville West Orange 

C64/C654 C85 C642/C311/C665 C9 

year min max min max min max min max 

 ppb ppb ppb ppb ppb ppb ppb ppb 

2000 38 74 . . 56 81 43 83

2001 50 71 . 54 45 69 57 68 

2002 51 62 58 84 40 68 53 69 

2003 30 68 60 64 39 61 38 66 

2004 43 71 39 66 30 61 41 66 

2005 55 79 62 75 43 76 52 75 

2006 45 76 42 78 32 63 43 75 

2007 37 62 55 67 40 62 47 69

2008 40 62 . 65 47 70 50 60 

9-year period 30 79 39 84 30 81 38 83 

Note: Though data has been restricted by wind direction to mitigate influences 

from nearby pollution sources, there may be unknown influences that are 

unaccounted for. Maximum values for each year are highlighted in boldface 

type. 

To statistically verify whether a trend across time exists in the data, an index of date was fit to the 

daily peak values using ordinary least squares regression. Additional regressions were performed 

using an index of month against the selected percentiles of the monthly distributions. The 

resulting parameter estimates from these models revealed no statistically significant trend at the 5 

percent significance level; however, the data likely suffer from autocorrelation, a problem 

common to time series data. Time series data are often not independent, but correlated with 

themselves across time, which complicates formal statistical estimation by biasing parameter 

estimates. 

Rather than performing the procedures necessary to detect, measure, and correct for 

autocorrelation, a careful visual inspection of time series plots, presented in Figure 5-42: Selected 

Statistics for the West Orange C9 Monitor through Figure 5-45: Selected Statistics for the 

Hamshire C64/C654 Monitor, satisfies that no time trend is perceptible. These four figures plot 

the five selected percentiles of the monthly distributions at each monitor. While no trend is 

detectable, what is apparent is that ozone concentrations measured at these monitors, which have 

been restricted in such a way as to proxy background levels, vary substantially. Background 

ozone at these monitors varies as much as 35 ppb, due to meteorological effects and ozone 

dynamics occurring in upwind regions. 

Notable in Figure 5-45: Selected Statistics for the Hamshire C64/C654 Monitor, hourly ozone 

concentrations at Hamshire (CAMS 64/CAMS 654) behave similarly to West Orange (CAMS 9) 

and Karnack (CAMS 85), in that there is no observable or statistically significant trend of the 

median or 90th percentile values. The 90th percentile value at Hamshire (CAMS 64/CAMS 654), 

considering directionally restricted data for May to September, 2000 through 2008, is 59 ppb. 

This value is in the range of values computed by Nielson-Gammon using different procedures; 

however, the 90th percentile can exceed 80 ppb at any of the sites, and even exceeded 90 ppb at 

Mauriceville (CAMS 642/CAMS 311/CAMS 665) in 2000. TexAQS II also found background 
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ozone concentrations that exceed the 1997 eight-hour ozone NAAQS (TexAQS II Rapid Science 

Synthesis Team 2006). 

Over the 2000 through 2008 period, the maximum 90th percentile one-hour ozone concentrations 

at West Orange (CAMS 9) and Mauriceville (CAMS 642/CAMS 311/CAMS 665) are 79 and 92, 

respectively. The maximum 90th percentile for Karnack (CAMS 85) over the 2001 through 2008 

period is 81. Karnack (CAMS 85) appears to consistently measure a higher background than 

either West Orange (CAMS 9) or Mauriceville (CAMS 642/CAMS 311/CAMS 665). These 

results are consistent with estimates reported by Nielson-Gammon, et al. (2005), which also 

found higher background ozone concentrations during the ozone season in northeast Texas than 

in the HGB area. 

Regression analysis was used to determine whether the 90th percentile values at West Orange 

(CAMS 9) and Mauriceville (CAMS 642/CAMS 311/CAMS 665) track one another, which 

suggests they are measuring roughly equivalent phenomena. The resulting R2

 of 0.78, which is 

significant at a probability level less than 0.1 percent (Table 5-26: Parameter Estimates for 

Regression of West Orange C9 on Mauriceville C642/C311/C665, indicates very strong 

correlation between measurements at the two sites. The scatter plot of the data is illustrated in 

Figure 5-46: Scatter-plot of 90th Percentile Hourly Values at West Orange C9 and Mauriceville 

C642/C311/C665. The values in the scatter plot are from May through September, 2000 to 2008. 

The scatter plot supports the contention that these two monitors are measuring roughly the same 

phenomena, under wind-restricted regimes. 

Table 5-26: Parameter Estimates for Regression of West Orange C9 on Mauriceville 

C642/C311/C665 

intercept slope 

β estimate 4.95706 1.01251 

Std. Error 0.55480 0.01421 

t-statistic 8.935 71.278 

 Pr(>|t|) <2e-16 <2e-16 

 R2

 0.78 
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Figure 5-46: Scatter-plot of 90th Percentile Hourly Values at West Orange C9 and 

Mauriceville C642/C311/C665 

In summary, none of the four sites used for estimating background ozone concentrations recorded 

a statistically significant trend. The Karnack (CAMS 85) monitoring site recorded the highest 

90th percentile measurement of the four background sites, with 90th percentile ozone 

concentrations reaching as high as 63 ppb. Since it is farthest from the HGB area, however, the 

HGB area may not be strongly affected by the ozone observed at this site, at least not on the same 

day. 

5.3.13 Air Quality Trends Conclusions 

Ozone concentrations have decreased dramatically in the HGB area since the 1990s. 

Examination of trends in one-hour ozone, eight-hour ozone, the number of exceedances, the 

spatial distribution of ozone, the seasonal distribution of ozone, and the strength of ozone 

gradients all show substantial downward trends. The causes of the trends were investigated by 

examining the meteorological variations that have occurred over the years, by evaluating the local 

changes in ozone precursor concentrations, and by examining trends in background ozone. The 

analyses found that the interannual meteorological variations cannot explain the observed 

decreases in ozone, and that the ozone precursors are on statistically significant downward trends. 

In addition, the analyses have found that background ozone has not dropped substantially since 

2000, suggesting that the significant ozone reductions in the HGB area are due to local emission 

controls, not due to background ozone decreases. 

5.4 QUALITATIVE CORROBORATIVE ANALYSIS 

5.4.1 Introduction 

Because photochemical modeling is an evaluation tool and not an absolute prediction of future 

ozone concentrations, additional data must be considered in order to draw conclusions about the 

validity of the final predicted design value and whether the attainment demonstration satisfies the 

requirements of the Federal Clean Air Act (FCAA). The EPA’s “Guidance on the Use of Models 
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and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and 

Regional Haze,” referenced as modeling guidance in Chapter 3, Photochemical Modeling

acknowledges that many issues cannot be accurately quantified and therefore cannot be properly 

included in the photochemical modeling demonstration. The qualitative corroborative analysis 

contains information regarding federal preemption issues and analysis of additional measures that 

were not included in the modeling. 

5.4.2 Federal Preemption Issues 

The TCEQ has limited authority to regulate certain components of the emissions inventory. The 

federal government has jurisdiction over on-road and non-road vehicles, ships, locomotives, and 

aircraft, among other sources. Since states cannot control sources that are under federal 

jurisdiction or located in other states, the state is limited in its ability to impose controls on all of 

the sources that contribute to ozone formation in a nonattainment area. 

5.4.2.1 Federal Assignment

While these categories have been addressed through expeditiously implemented state incentive 

programs such as the Low Income Vehicle Repair Assistance, Retrofit, and Accelerated Vehicle 

Retirement Program (LIRAP) and the Texas Emissions Reduction Plan (TERP), future reductions 

are dependent on the prompt implementation of new federal engine and fuel standards for on-road 

and non-road vehicles, ships, locomotives, and aircraft. 

5.4.3 Additional Measures 

5.4.3.1 New International Marine Diesel Engine and Marine Fuel Standards for Oceangoing 

Vessels and Emissions Control Areas

In October 2008, the United States ratified the International Maritime Organization's (IMO) 

adoption of the amendments to Annex VI of the International Convention for the Prevention of 

Pollution from Ships (MARPOL) for new international marine diesel engine and marine fuel 

standards for oceangoing vessels (OGV). The new Annex VI Tier II and Tier III emission 

standards will apply to diesel engines with a power rating above 130 kilowatts (kW) (i.e., 175 

horsepower) installed on marine vessels constructed on or after January 1, 2011 (Tier II), and 

January 1, 2016 (Tier III), or diesel engines above 130 kW that undergo a major conversion on or 

after those dates. The revised MARPOL Annex VI will become effective on July 1, 2010. 

In March 2009, the United States submitted a request to the IMO for the creation of an emissions 

control area (ECA) around the nation's coastlines. If the ECA is granted, all marine diesel fuels 

used by OGV in the ECA will be limited to a maximum sulfur content of 1,000 ppm beginning 

January 1, 2015, and all new engines on OGV operating in these areas must use emission controls 

that achieve an 80 percent reduction in NOX emissions beginning January 1, 2016. Table 5-27: 

New MARPOL Annex VI Emission Standards for Marine Diesel Engines lists the new emission 

standards for marine diesel engines with greater than 30 liter per cylinder displacement. 
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Table 5-27: New MARPOL Annex VI Emission Standards for Marine Diesel Engines 

New MARPOL Annex VI emission standards for marine diesel engines 

with >30 liter per cylinder displacement 

NOX Emission Standards (g/kW–hr) Engine Speed (n) Tier 1 Tier 2 Tier 3 

N < 130 revolutions 

per minute (rpm) 17.0 14.4 3.4 

2000 > n ≥ 130 rpm 45.0 × n-0.20 44.0 × n-0.23 9.0 × n-0.20

N ≥ 2000 rpm 9.8 7.7 2.0 

Applicable to engines 

installed in vessels 

constructed on: 

01/01/2000 – 

12/31/2010 

01/01/2011 - 

12/31/2015 

01/01/2016 and 

thereafter 

Note: NOX emission standards presented in grams per kilowatt hour. 

In the August 28, 2009, issue of the Federal Register (74 FR 44442), the EPA proposed 

rulemaking to adopt new federal Tier 2 and Tier 3 engine standards for new marine engines above 

30 liters per cylinder displacement (i.e., Category 3 marine diesel engines) that are consistent 

with the new MARPOL Annex VI NOX emission standards shown in Table 5-27: New MARPOL 

Annex VI Emission Standards for Marine Diesel Engines. The EPA's proposed new Category 3 

marine diesel engine standards also include new standards limiting the emissions of hydrocarbons 

and carbon monoxide from new Tier 2 and later Category 3 engines to 2.0 g/kW-hr and 5.0 

g/kW-hr, respectfully. 

The EPA regulations for marine diesel fuel and new marine engines less than 30 liters per 

cylinder displacement and the new MARPOL Annex VI standards for marine residual fuels and 

new marine diesel engines above 30 liters per cylinder displacement will apply to all OGV 

flagged and registered in the United States. The EPA's proposed new regulations for new 

Category 3 marine engines and new sulfur limits for marine diesel fuel will also apply to all OGV 

flagged and registered in the United States. In addition, the new MARPOL Annex VI standards 

will apply to all new marine diesel engines and fuels on foreign marine vessels that operate near 

United States coasts and ports. 

The new marine diesel engine and fuel standards will provide a 96 percent reduction in sulfur in 

marine diesel fuels, as well as an 85 percent reduction in particulate matter emissions and an 80 

percent reduction in NOX emissions, when compared to current standards (EPA, 2009a, 

http://www.epa.gov/otaq/oceanvessels.htm#emissioncontrol). The cumulative effects of these 

new marine diesel engine and fuels standards will result in a 0.5 to 1.0 ppb reduction of ozone in 

the ambient air of the HGB ozone nonattainment area by 2020 (EPA, 2009b). 

5.4.3.2 SmartWay Transport Partnership and the Blue Skyways Collaborative

Among its various efforts to improve air quality in Texas, the TCEQ is currently promoting two 

voluntary programs in cooperation with the EPA: the SmartWay Transport Partnership and the 

Blue Skyways Collaborative. 

The SmartWay Transport Partnership is a voluntary EPA program for the freight transport 

industry that promotes strategies and technologies to help improve fleet efficiency while also 

reducing air emissions. Fleets participating in the SmartWay Transport Partnership commit to 

implementing voluntary measures over three years, providing the EPA with annual updates of 

their progress throughout that period. 

SmartWay carriers typically commit to integrating fuel-saving strategies and technologies into 

their fleet including: improved aerodynamics, single-wide tires, lighter wheels and rims, idle 

reduction, automatic tire inflation systems, driver training, and advanced powertrain technologies. 
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Rolling resistance is estimated by the EPA to account for as much as 13 percent of a heavy-duty 

vehicle’s fuel consumption. By reducing rolling resistance, as well as vehicle weight, the EPA 

believes that single-wide tires will help to improve fuel economy and reduce NOX emissions by 

an average of 5 percent. Aerodynamic drag accounts for most of a long-haul truck’s energy 

losses at highway speeds. As a result, the EPA estimates that improving the aerodynamics of 

both a long-haul truck and its trailer can help to improve fuel economy and reduce NOX

emissions by another 5 percent. 

The extended periods of idling typically associated with long-haul trucks consume an average of 

one gallon of fuel per hour, while generating associated emissions. New technologies such as 

auxiliary power units (APU) and truck stop electrification (TSE) systems reduce vehicle idling by 

providing power for air conditioning, heating, and onboard electrical accessories, even when the 

vehicle is not in operation. The EPA estimates that, assuming typical idling levels, idling 

reduction technologies such as APU and TSE can reduce NOX emissions by approximately 10 

percent. 

The transient nature of freight transportation makes it difficult to isolate emissions reductions to a 

certain region or even a certain state. As a result, any estimates of the impact of these 

technologies will largely rely on estimates of accumulated reductions based on estimated levels of 

overall fleet integration. These estimates are possible through ongoing research, and in 

conjunction with the more than 2,000 companies nationwide already committed as SmartWay 

partners, the EPA has identified a variety of technologies and the potential fuel savings and 

emissions reductions from those technologies. There are 87 Texas companies that are currently 

SmartWay partners. 

The Blue Skyways Collaborative is a related effort, spearheaded by the EPA Region 6 office in 

Dallas, Texas and the Region 7 office in Kansas City, Missouri. 

Partnering with the EPA Region 6 and Region 7 through this effort are the environmental and 

energy agencies from the 10 states along the Interstate Highway 35 (IH-35) corridor, including 

Texas, New Mexico, Louisiana, Arkansas, Oklahoma, Kansas, Missouri, Nebraska, Iowa, and 

Minnesota. In implementing the Blue Skyways Collaborative, the EPA and the participating 

states recognize that because air quality is often a regional concern, greater reductions are 

possible through cooperative efforts as opposed to individual efforts initiated independently in 

each state. 

The primary objective of the Blue Skyways Collaborative is to improve air quality in these states 

by promoting innovative technologies in a variety of sectors. In addition to promoting reduction 

strategies through the SmartWay Partnership for freight transportation via air, water, and rail, 

Blue Skyways also focuses on promoting emissions reduction strategies for other on-road 

sources, non-road sources, and highway fueling and idling reduction infrastructure, while also 

promoting renewable, efficient, and alternative energy sources. 

To achieve these objectives, the collaborative develops partnerships among international, federal, 

state, and local governments, as well as non-profit organizations, environmental groups, and 

private industries. These partnerships work together in projects along the key transportation 

corridors by sharing emission reduction technologies and leveraging financial resources from a 

variety of sources. 
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5.4.3.3 Control of VOC Emissions from Flash Emissions

When the TCEQ and its research partners began the second Texas air quality study, TexAQS II, 

in May 2005, one of the study’s primary goals was to identify VOC emission sources that have 

been historically underestimated, unreported, or underreported in the TCEQ emissions inventory 

and could potentially be contributing to a discrepancy between measured and reported emissions. 

TexAQS II remote sensing VOC project results indicate that certain types of storage tank 

emissions, including flash, generally have been underestimated, unreported, or underreported in 

the emission inventory. Flash emissions occur when a liquid with entrained gases goes from a 

high pressure to a low pressure. As the pressure on the liquid drops, some of the lighter VOC 

dissolved in the liquid are released or flashed. Compounds that are liquids at the initial pressure 

may transform from a liquid into a vapor and are also released from the liquid. As these gases are 

released, some of the heavier compounds in the liquids may become entrained in these gases and 

are emitted with the lighter VOC. 

In May 2007, the commission adopted rule amendments to 30 Texas Administrative Code (TAC) 

Chapter 115, Subchapter B, Division 1 that revised the requirements for VOC storage tanks 

located in the HGB ozone nonattainment area. The revised requirements were developed to 

reduce VOC emissions that result from uncontrolled flash emissions at upstream oil and gas 

exploration and production sites and other sources of tank emissions. At the time of the rule 

proposal, the amount of flash emissions from minor sources was unknown. 

A method for quantifying flash emissions became available around the same time. Houston 

Advanced Research Center Project 51C, conducted in 2006, quantified emission rates from 

heater-treaters (separators) and storage tank batteries, including flash and condensate tanks, 

associated with the upstream oil and gas industry in the Dallas-Fort Worth and HGB ozone 

nonattainment areas, and Jefferson County. In April 2007, the TCEQ used the results of this 

study to determine the flash emissions from the oil and gas production industry. However, the 

flash emissions were not included in the 2005 area source periodic emissions inventory (PEI) 

because there was not sufficient time to incorporate the emissions before the 2005 area source 

PEI was submitted to the EPA in May 2007. However, the updated 2005 area source emissions 

inventory is being used for this SIP revision. More information on this study can be found at: 

http://www.harc.edu/Projects/AirQuality/Projects/Projects/H051C. 

The rule amendments adopted in May 2007 resulted in actual reductions to flash emissions but no 

credit is claimed in this SIP revision. Crude and condensate storage tanks at upstream oil and gas 

exploration and production sites or midstream pipeline breakout stations with uncontrolled flash 

emissions greater than 25 tons per year (tpy) are controlled under the rule. Since the method of 

calculating the emissions was based on county-level production, it is unknown at this time how 

many sites were over 25 tpy and were required to put on controls. Also unknown is how much 

flash emissions were already controlled due to economic reasons. Because of the unknown total 

effect of this rule, the reduction in flash emissions cannot be quantified at this time and is not 

included in the modeling for this SIP revision. These amendments to Chapter 115 are described 

in more detail in the preamble of the adopted rule (Project Number 2006-038-115-EN). 

5.4.3.4 Energy Efficiency and Renewable Energy (EE/RE) Measures

Energy efficiency efforts are typically programs that reduce the amount of electricity and natural 

gas consumed by residential, commercial, industrial, and municipal energy consumers. Examples 

of energy efficiency include increasing insulation in homes, installing compact fluorescent light 

bulbs, and replacing motors and pumps with high efficiency units. Renewable energy efforts 

include programs that generate energy from resources that are replenished or are otherwise not 

consumed as with traditional fuel-based energy production. Examples of renewable energy 

include wind energy and solar energy projects. 
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The Texas Legislature has enacted a number of EE/RE measures and programs. The following is 

a summary of Texas EE/RE legislation since 1999. 

• 76th Texas Legislature, 1999 

o Senate Bill (SB) 7 (Regular Session) 

o House Bill (HB) 2492 (Regular Session) 

o HB 2960 (Regular Session) 

• 77th Texas Legislature, 2001 

o SB 5 (Regular Session) 

o HB 2277 (Regular Session) 

o HB 2278 (Regular Session) 

o HB 2845 (Regular Session) 

• 78th Texas Legislature, 2003 

o HB1365 (Regular Session) 

• 79th Texas Legislature, 2005 

o SB 20 (First Call Session) 

o HB 2129 (Regular Session) 

o HB 2481 (Regular Session) 

• 80th Texas Legislature, 2007 

o HB 66 (Regular Session) 

o HB 3070 (Regular Session) 

o HB 3693 (Regular Session) 

o SB 12 (Regular Session) 

SB 5, 77th Texas Legislature, 2001, set goals for political subdivisions in affected counties to 

implement measures to reduce energy consumption from existing facilities by 5 percent each year 

for five years from January 1, 2002 through January 1, 2006. In 2007, the 80th Texas Legislature 

passed SB 12, which extended the timeline set in SB 5 through 2007 and made the 5 percent each 

year a goal instead of a requirement. The State Energy Conservation Office (SECO) is charged 

with tracking the implementation of SB 5 and SB 12. Also during the 77th Texas Legislature, the 

Energy Systems Laboratory (ESL), part of the Texas Engineering Experiment Station, Texas 

A&M University System, was mandated to provide an annual report on EE/RE efforts in the state 

as part of the Texas Emissions Reduction Plan (TERP) under Texas Health and Safety Code 

(THSC), § 388.003(e). HB 2129, 79th Texas Legislature, 2005, directed the ESL to collaborate 

with the TCEQ to develop a methodology for computing emission reductions attributable to use 

of renewable energy and for the ESL to quantify annually such emission reductions. HB 2129 

directed the Texas Environmental Research Consortium to use the Texas Engineering Experiment 

Station to develop this methodology. With the TCEQ’s guidance, the ESL produces an annual 

report detailing these efforts (Statewide Air Emissions Calculations from Energy Efficiency, Wind 

and Renewables). The report: 

• analyzes power production from wind and other renewable energy sources; 

• provides quantification of energy savings and NOX reductions resulting from the 

installation of wind and other renewable energy sources; 

• describes methodologies developed to quantify energy savings and NOX reductions from 

energy efficiency, wind and other renewable energy initiatives; and 

• provides degradation analysis for future predictions of power production of wind farms. 

The ESL documents methods used to develop estimates of energy savings and NOX emissions 

reductions resulting from reductions in natural gas consumption and displaced power from 

conventional electric generation facilities. The ESL used the EPA’s Emissions and Generation 

Resource Integrated Database to spatially allocate energy use and emission reductions among 

electric generation facilities. The THSC, § 389.002 and § 389.003 contain requirements that the 

Public Utility Commission of Texas (PUCT), SECO, and the ESL report to the TCEQ all 
5-85

emission reductions resulting from EE/RE projects in Texas. The ESL analyzed the following 

areas/programs: 

Renewable Energies 

The 79th Texas Legislature, 2005, amended SB 5 through SB 20, HB 2129, and HB 2481 to add, 

among other initiatives, the following renewable energy initiatives, which require: 5,880 

megawatts of generating capacity from renewable energy by 2015; the TCEQ to develop a 

methodology for calculating emission reductions from renewable energy initiatives and 

associated credits; the ESL to assist the TCEQ in quantifying emissions reductions from EE/RE 

programs; and the PUCT to establish a target of 10,000 megawatts of installed renewable 

technologies by 2025. 

Residential Building Codes and Programs 

The THSC, Chapter 388, Texas Building Energy Performance Standards, as adopted by the 77th 

Texas Legislature, 2001, states in § 388.003(a) that single-family residential construction must 

meet the energy efficiency performance standards established in the energy efficiency chapter of 

the International Residential Code. The Furnace Pilot Light Program includes energy savings 

accomplished by retrofitting existing furnaces. Also included are Seasonal Energy Efficiency 

Ratio (SEER) 13 upgrades to single-family and multi-family buildings. In January 2006, federal 

regulations mandated that the minimum efficiency for residential air conditioners be increased 

from SEER 10 to SEER 13. 

Commercial Building Codes 

The THSC, Chapter 388, Texas Building Energy Performance Standards, as adopted by the 77th 

Texas Legislature, 2001, states in § 388.003(b) that all other residential, commercial, and 

industrial construction must meet the energy efficiency performance standards established in the 

energy efficiency chapter of the International Energy Conservation Code. 

Federal Facilities EE/RE Projects 

Federal facilities are required to reduce energy use by Presidential Executive Order 13123 and the 

Energy Policy Act of 2005 (Public Law 109-58 EPACT20065). The ESL compiled energy 

reductions data for the federal EE/RE projects in Texas. 

Political Subdivisions Projects 

SECO funds loans for energy-efficiency projects for state agencies, institutions of higher 

education, school districts, county hospitals, and local governments. Political subdivisions in 

nonattainment and affected counties are required by SB 5 to report EE/RE projects to SECO. 

These projects are typically building systems retrofits, nonbuilding lighting projects, and other 

mechanical and electrical systems retrofits such as municipal water and waste water treatment 

systems. 

Electric Utility Sponsored Programs 

Utilities are required by SB 7, 76th Texas Legislature, 1999, and SB 5, 77th Texas Legislature, 

2001, to report these projects to the PUCT. See THSC, § 386.205 and Texas Utilities Code, 

§ 39.905. These projects are typically air conditioner replacements, ventilation duct tightening, 

and commercial and industrial equipment replacement. 

In addition to the programs discussed and analyzed in the ESL report, local governments may 

have enacted measures beyond what has been reported to SECO and the PUCT. The TCEQ 

encourages local political subdivisions to promote EE/RE measures in their respective 

communities and to ensure these measures are fully reported to SECO and the PUCT. 

HB 3693, 80th Texas Legislature, 2007, amended the Texas Education Code, Texas Government 

Code, THSC, and Texas Utilities Code. The bill: 
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• requires state agencies, universities and local governments to adopt energy efficiency 

programs; 

• provides additional incentives for electric utilities to expand energy conservation and 

efficiency programs; 

• includes municipal-owned utilities and cooperatives in efficiency programs; 

• increases incentives and provides consumer education to improve efficiency programs; 

and 

• supports other programs such as revision of building codes and research into alternative 

technology and renewable energies. 

Emissions reductions as a result of the above programs were not explicitly included in the 

photochemical modeling because local efficiency efforts may not result in local emissions 

reductions or may be offset by increased demand in electricity. The complex nature of the 

electrical grid also makes accurately quantifying emission reductions from EE/RE projects 

difficult. At any given time, it is impossible to determine exactly where on the electrical grid 

electricity comes from for any certain electrical user. The electricity for a user could be from a 

power plant in west Texas, a nearby attainment county or from within the nonattainment area. If 

electrical demand is reduced in the HGB area due to these kinds of measures, then emission 

reductions from power generation facilities may occur in any number of locations around the 

state. 

5.4.3.5 Clean Air Interstate Rule (CAIR)

The EPA projects that CAIR regional controls will improve air quality in the HGB area, as well 

as most of Texas, according to EPA’s Texas CAIR Web page, http://www.epa.gov/cair/tx.html. 

Under CAIR, 28 eastern states (plus the District of Columbia) are required to comply with a cap 

on sulfur dioxide (SO2) and NOX for EGU emissions. The definition of an EGU for the CAIR 

program is approximately the same definition as that for an FCAA Title IV Acid Rain unit (i.e., 

larger than 25 megawatt (MW) and more than one-third of its generation going to the public grid 

for sale). CAIR is a cap and trade program, with each of the CAIR-applicable states given a 

calculated NOX budget and a calculated SO2 budget by the EPA. The EPA modeled all of these 

states in order to test the effectiveness of controls. A result of EPA’s CAIR modeling was that 

Texas “significantly contributed” to the nonattainment of the particulate matter of 2.5 microns 

and less (PM2.5) standard of two counties in Illinois, therefore, Texas was included in CAIR for 

the transport of PM2.5. Texas is not covered under the CAIR program for 1997 eight-hour ozone 

standard contribution. 

CAIR is implemented in two phases: for NOX, Phase I covers the years 2009 through 2014 and 

Phase II is for the years 2015 and later; for SO2, Phase I covers the years 2010 through 2014 and 

Phase II is for the years 2015 and later. The Phase I NOX budget calculated and assigned to Texas 

was 181,014 tons per year, and the Phase II NOX budget was 150,845. Because 2018 is the HGB 

ozone attainment year, this SIP revision incorporates CAIR Phase II (post 2014 step-down of 

CAIR) which provides for a Texas state-wide NOX budget of 150,845 tons per year, or 413.3 tons 

per day. 

See Appendix B: Emissions Modeling for the HGB Attainment Demonstration SIP, Section 

2.3.1.2.1 for the procedural details that the TCEQ used to simulate CAIR Phase II in Texas and 

the regional states. 

On July 11, 2008, the United States Court of Appeals District of Columbia Circuit (Court) (No. 

05-1244) vacated CAIR and the CAIR Federal Implementation Plan (FIP). On December 23, 

2008, the Court issued a revised opinion to remand, without vacating, CAIR to the EPA. 

Therefore, CAIR will remain in effect while the EPA analyzes data and conducts rulemaking to 
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modify the program to comply with the Court’s July 2008 opinion. The Court declined to impose 

a schedule by which the EPA must complete the rulemaking, but reminded the EPA that the 

Court does “. . . not intend to grant an indefinite stay of the effectiveness of this Court’s 

decision.” For more information on the ruling, see EPA’s CAIR Web page, 

http://www.epa.gov/cair/, or the TCEQ CAIR/CAMR Web page, 

http://www.tceq.state.tx.us/implementation/air/sip/caircamr.html. 

Any future EPA revision to the CAIR program to comply with the court’s ruling may result in 

additional reductions. 

5.4.3.6 Texas Emission Reduction Plan (TERP)

The TERP program was created in 2001 by the 77th Texas Legislature to provide grants to offset 

the incremental costs associated with reducing NOX emissions from high-emitting internal 

combustion engines. To date the TERP program has funded over $700 million in grants for 

projects in Texas ozone nonattainment and near-nonattainment areas. Over $300 million of that 

amount has been awarded to projects in the HGB area since 2001, which will help reduce more 

than 66,000 tons of NOX emissions. Of that $300 million, $5 million was awarded to the H-GAC 

through a third-party grant to administer additional grants in the HGB area. 

Additional funds are expected to be awarded to the HGB area in subsequent grant application 

periods that will result in further NOX reductions. HB 1796, 81st Texas Legislature, 2009, 

extended the TERP program beyond its current 2013 date to 2019, which will result in continued 

reductions in the significant emissions source categories of on-road and non-road engines. 

5.4.3.7 Low Income Vehicle Repair Assistance, Retrofit, and Accelerated Vehicle Retirement 

Program (LIRAP)

SB 12, 80th Texas Legislature, 2007, enhanced LIRAP to expand participation by increasing the 

income eligibility to 300 percent of the federal poverty rate and increasing the amount of 

assistance toward the replacement of a retired vehicle. The program, known as AirCheckTexas 

Drive a Clean Machine (DACM), provides $3,500 for hybrids of the current or previous model 

year; $3,000 for cars of the current or three model years; and, $3,000 for trucks of the current or 

previous two model years. The retired vehicle must be 10 years or older or have failed an 

emissions test. In the HGB area, DACM is available to vehicle owners in five counties: 

Brazoria, Fort Bend, Galveston, Harris, and Montgomery. Between December 2007 and May 31, 

2009, LIRAP/DACM has retired and replaced 9,330 vehicles at a cost of $28,370,520. An 

additional 3,949 vehicles have had emissions-related repairs at a cost of $2,136,602. The total 

repair and retirement/replacement funding for the HGB area since December 2007 is 

$30,507,122. 

5.4.3.8 Clean School Bus Program

HB 3469, 79th Texas Legislature, 2005, established the Clean School Bus Program. The new 

program is codified in THSC, Chapter 390 and implemented through 30 TAC §§ 114.640 – 

114.648. 

The program is based on the EPA guidance documents, Improving Air Quality with Economic 

Incentive Programs (EPA-452/R-01-001) and Diesel Retrofits: Quantifying and Using Their 

Benefits in SIPs and Conformity (EPA-420-B-06-005). Under the economic incentive program 

guidance, the TCEQ is using the financial mechanism option, which is described as subsidies 

targeted at promoting pollution-reducing activities or products. 

The Clean School Bus Program was established to provide monetary incentives for school 

districts in the state for reducing emissions of diesel exhaust in school buses. Eligible 

technologies include those approved by the EPA, certified by the California Air Resources Board, 

or those that the executive director finds will bring about significant emissions reductions. Some 
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of the technologies eligible for funding under the program reduce NOX emissions. However, the 

technologies mainly reduce particulate matter and reduce only negligible amounts of NOX. The 

80th Texas Legislature, 2007, provided funding for the Clean School Bus Program. 

As of May 2009, the TCEQ Clean School Bus grant program has allocated $13.8 million in grants 

for nearly 5,000 school buses in Texas. In addition, through Supplemental Environmental 

Projects (SEPs), the TCEQ has also allocated over $3.5 million to third-party SEP receivers for 

the same kind of school bus retrofits. 

5.4.3.9 81st Texas Legislature, 2009

HB 432 requires state agencies that purchase passenger vehicles or other ground transportation 

vehicles for general use to ensure that not less than 25 percent of new vehicles purchased during a 

biennium meet or exceed EPA’s Tier II, Bin 3 emission standards. This bill also limits the 

purchase of state agency passenger vehicles or other ground transportation vehicles purchased for 

general use to only those vehicles that use compressed natural gas, liquefied natural gas, liquefied 

petroleum gas, methanol or methanol/gasoline blends of 85 percent or greater, ethanol or 

ethanol/gasoline blends of 85 percent or greater, biodiesel or biodiesel/diesel blends of 20 percent 

or greater, or electricity, including electricity to power a plug-in hybrid motor vehicle. 

HB 1796 establishes a New Technology Implementation Grants (NTIG) program for facilities 

and stationary sources under TERP, requires the current New Technology Research and 

Development under TERP to be administered by the TCEQ, and extends the TERP to August 31, 

2019. See Section 5.4.3.6, Texas Emission Reduction Plan (TERP), for additional information. 

SB 1759 establishes a Texas Clean Fleet Program to be administered by the TCEQ, funding it 

with 5 percent of the 87.5 percent of the Emission Reduction Incentives Grant within TERP. The 

Texas Clean Fleet Program will provide grants to encourage large fleets to replace dieselpowered fleet vehicles with hybrid vehicles or alternative fuel-powered vehicles. 

5.4.3.10 American Waterways Operators Tank Barge Emissions Best Management Practices

Using infrared gas imaging technology in field studies conducted in the summer of 2005, the 

TCEQ detected inadvertent VOC emissions from tank barges operating in the HGB area. The 

Louisiana Department of Environmental Quality (LDEQ) also detected inadvertent emissions 

from tank barges in similar field studies conducted in the same time period. In response to these 

field studies, the American Waterways Operators (AWO) voluntarily developed industry Best 

Management Practices (BMP) to reduce VOC emissions from tank barges. The BMP includes 

procedures to reduce VOC emissions from equipment and operations on tank barges. The 

recommendations are a combination of inspection, corrective action, preventative maintenance, 

operational, procedural, and training practices. 

The BMP was reviewed by the Chemical Transportation Advisory Committee (CTAC), United 

States Coast Guard, LDEQ, and TCEQ. The BMP was distributed to AWO members in 2006 for 

implementation on a voluntary basis. In 2009, AWO reconvened the Tank Barge Emissions 

Working Group to review the BMP and make further improvements to the document. The 

improved BMP will be sent to CTAC, the Coast Guard, LDEQ, and TCEQ for review once it has 

been finalized by industry. While the BMP is a voluntary measure and does not impose an 

enforceable commitment on AWO members, the implementation of the BMP, where applicable, 

may contribute to reducing inadvertent VOC emissions from barges during dock operations and 

during transit, which will help improve the air quality in the HGB area. A copy of the 2006 BMP 

document is provided in Appendix J: Recommendations for Best Management Practices to 

Control and Reduce Inadvertent Cargo Vapor Emissions in the Tank Barge Community. 
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5.4.3.11 Local Initiative Projects

SB 12, 80th Texas Legislature, 2007, allowed the use of unexpended LIRAP funds to be used for 

Local Initiative Projects. These projects provide funding to LIRAP-participating counties for 

implementation of air quality improvement strategies through local projects and initiatives. Local 

Initiative Projects may include: 

• expand and enhance the repair and replacement program; 

• develop and implement programs to remotely determine vehicle emissions and notify the 

vehicle’s operator; 

• develop and implement projects for coordinating with local law enforcement officials to 

reduce the use of counterfeit state inspection stickers; 

• develop and implement programs to enhance transportation system improvements; or 

• develop and implement new air control strategies designed to assist local areas in complying 

with state and federal air quality rules and regulations. 

5.4.3.12 Other Local Programs

The Houston-Galveston Area Council submitted the following programs, which were not 

committed to as Transportation Control Measures or Voluntary Mobile Emission Reduction 

Program measures, but may be implemented locally in the HGB area. For a detailed analysis of 

these programs, see Appendix F: Evaluation of Mobile Source Control Strategies for the 

Houston-Galveston-Brazoria State Implementation Plan (prepared by ENVIRON for the 

Houston-Galveston Area Council). 

Scrappage and Buy-Back Plan 

This measure would build on the existing LIRAP, implemented as part of the AirCheckTexas 

Vehicle Emissions Testing program, by increasing the number of on-road light-duty gasoline 

vehicles scrapped. The plan would also make separate funds available to help with the purchase 

of new on-road heavy-duty diesel vehicles (HDDV) to replace old, highly polluting vehicles. 

Pay-As-You-Drive Insurance 

Pay-As-You-Drive Vehicle Insurance, also called Distance-Based Vehicle Insurance and 

Mileage-Based Insurance, is a program that allows a vehicle’s insurance premiums to be based 

directly on how many miles the vehicle is driven during the policy term. Currently, vehicle 

insurance is structured where high-mileage drivers are, in essence, subsidized by low-mileage 

drivers since all drivers are charged the same premiums after accounting for driving history 

related to collisions and traffic violations. 

Limitations on Idling of Heavy-Duty Vehicles; Creation of Regional Government Idling 

Restrictions 

Idling of vehicles is inherently an inefficient operation that can produce unwanted air pollutants. 

Idling also occurs during normal driving and other operations such as when the engine powers 

necessary accessories, known as power take-off, including man-lifts or concrete tumblers. It is 

not possible to eliminate all idling, but idle reduction programs are typically low in cost and may 

result in a net savings to the owner/operator of the vehicle while also reducing air emissions. 

Encourage/Mandate Livable Centers

The EPA developed the Smart Growth Implementation Assistance (SGIA) program in response to 

communities' requests for help achieving their development goals. Through this program, the 

EPA provides technical assistance from private-sector experts to help communities find the best 

tools and resources for planning growth in ways that sustain environmental and economic 

progress and create a high quality of life. The Gulf Coast Institute, Main Street Coalition, and 

Texas A&M partnered to apply for and received an SGIA grant in 2006. While the City of 

Houston is not participating in the SGIA program at this time, the area has expressed interest in 

evaluating the potential effects of these measures on travel activity and emissions. 
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Enhanced Enforcement of Smoking Vehicles

This measure would encourage local law enforcement officers to enforce existing smoking 

vehicle laws and enable the emissions inspection status of smoking vehicles to be checked. 

Owners of smoking vehicles displaying a valid inspection sticker would be fined. Smoking 

vehicles not having a valid inspection sticker would be impounded if the sticker were found to be 

fraudulent. 

Limitation on Idling of Heavy-Duty Construction Equipment 

Idling is an inefficient use of equipment in general and generates unnecessary emissions. Idling 

however cannot be avoided in all cases, such as during normal work, when work is performed 

intermittently, and when the time to restart the engine would be considered a significant delay. 

This measure would seek to limit excessive idling when equipment is not required immediately. 

Suggested periods for limiting idling could be as little as 15 minutes maximum. Many on-road 

trucks have factory-installed engine shutdown systems that automatically shut down the engine 

after a set period, or devices could be added to existing equipment. To implement this measure, 

engine shutdown systems could be employed with idle timers set to a period that would not cause 

typical operational problems. Operator training could provide significant idle reduction perhaps 

beyond engine shutdown systems. 

5.5 CONCLUSIONS 

The TCEQ has employed several sophisticated technical tools to evaluate the past and present 

causes and effects of high ozone in the HGB area in an effort to predict the area’s future air 

quality. Photochemical grid modeling has been performed and its performance has been 

rigorously evaluated. Historical trends in ozone and ozone precursor concentrations and their 

causes have been investigated exhaustively. The following conclusions can be reached from 

these evaluations. 

First, the photochemical grid modeling performs relatively well. Problems observed with the 

modeling are those that are known to exist in all photochemical modeling exercises. In spite of 

the known shortcomings, the model can be used carefully to predict ozone concentrations. The 

photochemical grid modeling predicts that the control strategy package chosen by the TCEQ can 

lower the ozone design values in the HGB area down to a value very near the 0.08 ppm eighthour ozone standard. The dynamic model evaluations show that the model response to emission 

decreases is less than the response observed in the atmosphere, suggesting that the proposed 

emission controls are more likely to yield attainment of the eight-hour 0.08 ppm ozone standard 

than the absolute modeled design values indicate. 

Second, the ozone trend analyses show that ozone has decreased significantly since the late 

1990s. Meteorological variations alone cannot explain the significant downward trend. 

Decreases in background ozone cannot explain the downward trend either. Significant decreases 

in ozone precursors, however, coincide with the decreases in ozone, indicating that the ozone 

decreases observed in the HGB area are due to local emission controls. 

Third, many additional air quality improvement measures are being adopted in the HGB area that 

cannot be included in the photochemical modeling analysis because they cannot be accurately 

quantified. These additional measures can provide additional assurance that the HGB area is on 

the path toward attainment. 

Based upon the photochemical grid modeling results and these corroborative analyses, the weight 

of evidence indicates that the HGB area will attain the 1997 eight-hour ozone standard by June 

15, 2019. 
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radical initiated chemistry, Final Report. TCEQ tracking number 2008-93, Grant Activity No. 

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S. Brown, 2008. High levels of nitryl chloride in the polluted subtropical marine boundary layer. 

Nature Geoscience doi: 10.1038/ngeo177, published online April 6. 

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probabilistic estimates of surface ozone concentration using an ensemble of model configurations 

and direct sensitivity calculations, Environ. Sci. Technol., Article ASAP, March 3, doi: 

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S. Haines, B. Dornblaser, and R. Cameron, 2007. Correcting photolysis rates on the basis of 

satellite observed clouds, J. Geophys. Res., 112, D10302, doi:10.1029/2006JD007422. 

Robinson, R., T. Gardiner, and B. Lipscombe, 2008. Measurements of VOC emissions from 

petrochemical industry sites in the Houston area using Differential Absorption Lidar (DIAL) 

during summer 2007, Draft. Submitted to Russell Nettles, TCEQ, by Rod Robinson, Tom 

Gardiner, and Bob Lipscombe of the National Physical Laboratory, Teddington, Middlesex UK 

TW11 0LW, February 8, 86 pp. 

Ryerson, T. B., M. Trainer, W. M. Angevine, C. A. Brock, R. W. Dissly, F. C. Fehsenfeld, G. J. 

Frost, P. D. Goldan, J. S. Holloway, G. Huebler, R. O. Jakoubek, W. C. Kuster, J. A. Neuman, D. 

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Flocke, A. Fried, W. T. Potter, S. Schauffler, V. Stroud, A. J. Weinheimer, B. P. Wert, and C. 

Wiedinmyer, R. J. Alvarez, R. M. Banta, L. S. Darby, and C. J. Senff, 2003. Effect of 

petrochemical industrial emissions of reactive alkenes and NOX on tropospheric ozone formation 

in Houston, Texas. J. of Geophysical Research, 108:4249, doi:10.1029/2002JD003070. 

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over the Eastern United States. J. Appl. Meteor. Climatol., 46:1009–1019. 

Savanich, K., 2006. Ozone Exceedance Days as a Function of the Number of Monitors. 

Unpublished analysis for TCEQ, February. 

Simon H., Y. Kimura, G. McGaughey, D. T. Allen, S. S. Brown, H. D. Osthoff, J. M. Roberts, D. 

Byun, and D. Lee, 2009. Modeling the impact of ClNO 2 on ozone formation in the Houston 

area, J. Geophys. Res., 114, D00F03, doi:10.1029/2008JD010732. 

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assimilation and targeted observation of a chemical tracer in a sea breeze model, Atmos. 

Environ., 41:3082-3094. 

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6-1 

CHAPTER 6: ONGOING AND FUTURE INITIATIVES

6.1 INTRODUCTION 

The Texas Commission on Environmental Quality (TCEQ) is committed to improving the air 

quality in the Houston-Galveston-Brazoria (HGB) area and continues to work toward identifying 

and reducing ozone precursors. Texas is investing resources into technological research and 

development for advancing pollution control technology, improving the science for ozone 

modeling and analysis, and refining quantification of volatile organic compound (VOC) 

emissions. Refining quantification of VOC emissions benefits SIP planning by improving 

understanding of ozone formation. Additionally, the TCEQ is working with the United States 

Environmental Protection Agency (EPA), local area leaders, and the scientific community to 

identify new measures for reducing ozone precursors. This chapter describes ongoing technical 

work that will be beneficial to improving air quality in Texas and the HGB area. 

6.2 ONGOING WORK 

6.2.1 Flare Task Force 

In November 2008, the TCEQ formed an agency-wide task force to comprehensively evaluate all 

aspects of flares in Texas. The Flare Task Force is evaluating how flares factor into air quality 

challenges with an emphasis on air toxics and ozone. Some of the specific issues under 

evaluation include: different factors affecting flare performance, such as waste gas flow rates, 

turndown ratio, and waste gas to steam assist ratios; the adequacy of existing monitoring 

requirements for flares; and alternatives to flaring routine emissions. A stakeholder group 

associated with the Flare Task Force has been formed to solicit comment on these issues related 

to flares. A report for executive management is planned that will include options, considerations, 

and recommendations for improving our understanding and regulation of flares with the goal of 

improving air quality. Additional information about the Flare Task Force is available at the 

stakeholder Web site: 

http://www.tceq.state.tx.us/implementation/air/rules/flare_stakeholder.html. 

6.2.2 Technologies for Detecting VOC 

6.2.2.1 Optical Gas Imaging Technology

Optical gas imaging technology offers a unique technological advancement in pollution detection 

capability and has proved to be highly effective in the detection of VOC emissions. An optical 

gas imaging system is a useful tool that assists the agency in actions such as facility 

investigations, reconnaissance investigations, mobile monitoring, and special projects. This 

technology is also useful in identifying sources of VOC emissions that are underestimated, 

underreported, unreported, or previously unregulated. The system also has the potential to 

advance leak detection and repair (LDAR) work practices and enable monitoring of components 

that are difficult to monitor with traditional LDAR methods. However, the commission has 

technical and enforcement concerns associated with the potential regulatory implementation of 

this technology. A standardized method or performance specification is necessary to ensure 

consistent and reliable application of optical gas imaging instrumentation. Methods and 

specifications are also necessary to set minimum standards of performance to evaluate different 

potential technologies. 

The TCEQ uses the optical gas imaging technology as a screening tool in the following areas: 

offsite surveillance to identify potential sources of contaminants in response to ambient or other 

monitoring results; identification of sites, or areas with a specific site, where a focused 

investigation may be conducted; identification of potential source control strategies or to assist in 

an assessment of existing strategies; and identification of sources for emissions inventory issues. 

6.2.2.2 Open Path Sensing Technology

Open path sensing technology allows specific pollutants to be monitored over a given distance 

(10 meters up to several kilometers) and generally provides very rapid measurements. Some of 

these techniques, such as solar occulation flux (SOF), differential absorption lidar (DIAL), and 
6-2 

imaging differential optical absorption spectroscopy (I-DOAS) provide specific capabilities that 

include the ability to monitor air pollutants not only at ground level but also along a given path 

length in the sky, which allows measurements of specific elevated sources such as flares, vents, 

and storage tanks. This information coupled with meteorological measurements and modeling 

tools are capable, in some cases, of providing emission estimates not otherwise available. These 

data can be helpful in evaluating actual emissions from specific sources. These measurement 

techniques also have limitations or challenges that include the following. 

• They are non-separatory techniques, i.e., do not physically isolate the chemical or 

chemicals of interest from other constituents, and as such are more prone to interference. 

• They normally measure a path length average concentration or number of molecules and 

as such do not provide a specific concentration at any given point and can thus be 

difficult to compare with standards or guideline concentrations. 

• They are difficult to assess from a data quality standpoint because they are an open path 

technology and thus have limitations for enforcement or compliance-related purposes. 

• They are complex instrumentation with limited commercial availability that requires a 

highly experienced operator and data analyst to obtain quality data. In some cases, such 

as SOF and DIAL, there may be only a few operational instruments and qualified 

personnel in the world, which limits the ability of Texas to either acquire and operate the 

instrumentation or contract operation on anything but a sporadic basis. 

6.2.2.3 DIAL Remote Sensing Technology

The TCEQ continued to advance the science of determining emissions from industrial sources by 

performing a five-week emissions monitoring study in the Texas City area during the summer of 

2007. For the first time, a regulatory agency in the United States used a mobile DIAL remote 

sensing technology to measure emissions from industrial sources. The study, funded by the EPA 

and the TCEQ, focused on gathering data from industrial sources that are difficult to measure 

using conventional sampling techniques. The resulting scientific data and future studies will help 

guide future research efforts and may result in additional control measures, refined emissions 

models for common sources, and improved emissions inventories. 

The TCEQ contracted with the National Physical Laboratory (NPL), based in the United 

Kingdom, to perform DIAL measurements on industrial emissions sources located in a refinery 

and a storage terminal near Houston during 2007. 

Measurements focused on those industrial sources that are difficult to measure using conventional 

sampling techniques. Specifically, the study involved: 

• identifying potentially under-reported industrial emissions sources; 

• conducting remote sensing measurements of these sources; 

• collecting process and operational data from these sources; and 

• comparing emissions determined using conventional EPA-approved determination methods 

to the remote sensing measurements. 

The NPL submitted a draft report in February 2008, which is expected to be finalized in fall 2009. 

An independent third party is currently comparing remote sensing measurements to 

conventionally determined emissions. Although these results are still being analyzed, preliminary 

total VOC measurements indicate that flare emissions may be underreported when emissions are 

determined using conventional material balance calculation methods. Additionally, preliminary 

results as well as other research indicate flare destruction and removal efficiency (DRE) may be 

reduced during certain operating conditions, such as combusting small volumes of waste gas and 

during flare air- or steam-assist operations. 

These preliminary results indicate the need to conduct a study that determines the relationship 

between flare design, operation, and DRE. 
6-3 

6.2.2.4 Helicopter-Mounted DIAL Imaging System

The TCEQ completed field work in June 2009 to demonstrate the capabilities of a helicoptermounted DIAL. The study’s major focus will be using the DIAL to locate sources of benzene 

emissions from industrial facilities in the Houston Ship Channel area. The DIAL system used 

was developed to detect methane leaks during flyovers of gas pipelines. The system uses the 

infrared absorption of methane to detect leaks. The system has been used extensively and 

successfully to find pipeline leaks in concentrations as low as 1.7 parts per million (ppm) of 

methane. Instrument sensitivity has been shown in the laboratory to be approximately 100 ppm 

for benzene. However, with tuning and adjustments during flight measurements, the benzene 

sensitivity could be as low as 10 ppm. While the primary purpose of this project will be to 

determine the capabilities of a helicopter-mounted DIAL, results from this project could also be 

used to determine potentially unreported or underreported sources of benzene. Successful 

location of benzene sources in the surveyed areas may show the potential benefit of a full-scale 

survey of the entire Houston Ship Channel as well as other industrial areas. A final report is due 

to the agency by August 2009 and the agency final evaluation of the technology should be 

completed by the fall of 2009. 

6.2.2.5 Flare Study

The purpose of the flare study is to measure flare emissions and collect required process and 

operational data in a controlled laboratory environment to determine the relationship between 

flare design, operation, and DRE. Direct measurement techniques of flare emissions, 

conceptually similar to those employed by the EPA flare studies in the 1980s, as well as remote 

sensing measurement techniques will be employed in the laboratory environment. Analysis of 

collected process and operational data will allow comparisons between traditional flare material 

balance emissions determinations, process stream measurements, and the emissions rates and 

concentrations measured by the direct and remote sensing technologies. 

The TCEQ anticipates that the results of the laboratory tests will be broadly applicable, since 

these measurements will be conducted under controlled conditions. The TCEQ also anticipates 

that the tests will provide insight to operational conditions that may impact flare VOC DRE and 

flare combustion efficiency, such as assist rates or waste gas volumetric flow rates. 

The primary study objectives include: 

• assessing the potential impact of waste stream flow rate turndown on flare DRE and 

combustion efficiency; 

• assessing the potential impact of steam/air assist on flare DRE and combustion efficiency 

at various operating conditions, including low flow rate conditions; 

• assessing whether flares operating over the range of requirements stated in 40 Code of 

Federal Regulations § 60.18 achieve the assumed hydrocarbon DRE of 98 percent at 

varying flow-rate turndown and assist ratios as well as variable waste stream heat 

content; and 

• identifying and quantifying the hydrocarbon species in flare plumes currently visualized 

with passive infrared cameras. 

Field tests should be conducted during the November 2009 to March 2010 time frame, depending 

on approval of the final test plan and the availability of a test facility. A final report is expected 

during the summer of 2010. 

6.2.2.6 Study of Houston Atmospheric Radical Precursors (SHARP) 

An extensive field study of ozone precursors and formation was conducted in the HGB area in 

April, May, and June 2009 using cutting-edge measurement technology. Approximately $2 

million of air quality research funds for this project were provided by the state legislature. The 

goal of the SHARP study is to investigate the: 
6-4 

• contribution of direct emissions of formaldehyde and nitrous acid from flares, stacks, and 

other point and mobile sources; 

• importance of secondary formation of formaldehyde from the ozonolysis of olefins; 

• identification of formation pathways of nitrous acid; 

• ambient levels of nitryl chloride and potential impact as a ozone precursor; and 

• spring and early summer ozone formation mechanisms in the HGB area. 

The data from this study will be analyzed in 2009 and 2010 and used to better understand HGB 

area emissions and chemistry, enhance model inputs and mechanisms, and aid in the evaluation of 

control strategy development. 

6.3 FUTURE INITIATIVES 

6.3.1 Mid-Course Review (MCR) 

The commission is soliciting comments on whether it is appropriate to perform a 1997 eight-hour 

ozone standard MCR analysis for the HGB area, and, if so, what elements should be contained in 

the analysis. The commission is also seeking input on the appropriate date to submit the MCR.

6.3.2 2008 Ozone National Ambient Air Quality Standard (NAAQS) 

On March 12, 2008, the EPA strengthened its NAAQS for ground-level ozone from 0.08 parts per 

million (ppm) to 0.075 ppm. Governor Rick Perry submitted the state's 

recommendation regarding boundaries and designations under the federal 2008 eight-hour ozone 

standard to the EPA on March 10, 2009. The HGB area (Brazoria, Chambers, Fort Bend, 

Galveston, Harris, Liberty, Montgomery, and Waller Counties) was included in the governor’s 

recommended nonattainment areas. Continued efforts to reduce ozone precursors will be 

necessary to address this new ozone standard. 
Appendices are located at: 

http://www.tceq.state.tx.us/implementation/air/sip/hgb.html 

For persons who do not have access to the Internet, please contact: 

Lola Brown 

Air Quality Planning Section 

Texas Commission on Environmental Quality 

Phone: (512) 239-0348