Modeling Guidance and Examples for Commonly Asked Questions

(Part II)

Reece Parker and Justin Cherry, P.E.Air Permits Division

Texas Commission on Environmental QualityAdvanced Air Permitting Seminar 2014

What Is Ozone?

Good• Stratospheric Ozone

O2sunlight O + O

O + O2 O3

Bad• Ground-level Ozonesunlight

VOC + NOx O3 (and other products)

Ground-level Ozone Is:

• The main component of smog.

• Not emitted directly in the air but forms when emissions of precursors, including NOx and VOCs “cook” in the sun:

– Emissions from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are the major man-made sources of NOx

and VOCs.

• Mainly a summertime pollutant because sunlight and hot weather accelerate its formation.

Ozone levels can be high in both urban and rural areas, often due to transport of emissions of ozone precursors.

2008 Ground-level Ozone Standards

• Primary and secondary 8-hr ozone standards:

75 ppb*

*based on the 3-yr average of the annual fourth highest daily maximum

8-hr ozone concentration

Type of Application

Non-Attainment Review?

PSD Increment:• SO2

• PM10

Property Line:• SO2

• H2S

Health Effects:• Benzene

PSD Review?• SO2

• PM10

Property Line:• SO2

• H2S

Health Effects:• Benzene

Non-attainment vs. Attainment

Non-attainment Review

• Provide full documentation and details to reduce review time and mitigate potential issues

• Protocol document should resemble AQA without modeling results

Final product? Not exactly...

Ozone Impact Analysis not required.

Emissions offsets to improve air quality

PSD Review

• If project is major by itself or a major modification, a protocol is required:– For all criteria pollutants with an increase– Must be sent to EPA Region 6 for review– May include protocol for state-only requirements

• Items to include in protocol are listed in protocol checklist

• Consider all the items in the protocol check list before you start on your protocol document

An ozone impacts analysis is required when a project emits:

100 tpy or more of VOCs

and/or

100 tpy or more of NOx

Ozone Impacts Analysis

• Obtain representative monitoring data

• Determine whether the project area is VOC-limited or NOx-limited*

• Quantitative demonstration

• Qualitative demonstration

*Based on TCEQ’s own SIP photochemical modeling, most of the urban and rural areas of Texas are NOx-limited.

Quantitative Demonstration

• Photochemical modeling: Comprehensive Air Quality Model with extensions

(CAMx)

• Screening approach using AERMOD: Demonstration based on comments by EPA for NOx-

limited areas

Quantitative Demonstration (Cont.)

• Screening approach using AERMOD:

Conservative analysis based on NOx modeling:

– Determine if the project is NOx-limited or VOC-limited

– If VOC-limited, determine GLCmax at a distance of 10-11 km

– Assume 90% conversion of NOx to NO2

– Assume 3 ozone molecules per NOx molecule

– Add result to the representative monitored concentration

– Compare to the standard

Example of Quantitative Demonstration

Determine a representative monitor concentration

Project Location

Example (Cont.)

Determine a representative monitor concentration

Monitor Location

3-yr avg of 4th highest daily maximum 8-hr conc.

69 ppb

Example (Cont.)

Determine GLCmax 10-11 km from project sources

Example (Cont.)

Model Output

Converting model result to ppb:

2.96 µg/m3 x (100 ppb)/(188 µg/m3) = 1.57 ppb

Example (Cont.)

• Assume 90% conversion of NOX to NO2:

1.57 ppb x 0.9 = 1.413 ppb

• Assume 3 molecules ozone per molecule NOX:

3 x 1.413 ppb = 4.24 ppb

• Add result to monitored concentration:

69 ppb + 4.24 ppb = 73.24 ppb

• Compare to standard:

73.24 ppb < 75 ppb

Qualitative Demonstration

• Assessment of current air quality:– Ozone trends

– NOX trends

– VOC trends

• Analysis of the project’s potential ozone impact – Selection of Existing Photochemical Modeling Analyses:– Modeling simulation (Did photochemical modeling follow EPA

guidance?)

– Source characterization

– Meteorological parameters and regional transport

Example Qualitative DemonstrationOzone Trends BPA Area

BPA Area Ozone Design Values for all Monitoring Sites (1992-2013)0.105

0.100

0.095

0.090

0.085

0.080

0.075

0.070

0.065

0.060

Site ID: 482450009Site ID: 482450101Site ID: 4824510351997 8-hr Ozone NAAQS

2008 NAAQS Threshold

2008 8-hr Ozone NAAQS 1997 NAAQS Threshold

Site ID: 482450011Site ID: 482450102Site ID: 483611001

Site ID: 482450022Site ID: 482450628Site ID: 483611100

8-hr

Ozo

ne D

esig

n Va

lue

(ppm

)

Example (Cont.)

NOx Trends (BPA Area)

Summary of NOx Emissions Data in BPA Area (tons per day)

0

50

100

150

200

250

NO

x Em

issi

ons

(ton

s pe

r day

)

Nonroad

NonroadNonroad

Onroad

Area

PointPoint Point

Point

AreaArea

Area

OnroadOnroad

Onroad Nonroad

2005 NEI 2008 NEI 2011 NEI

Example (Cont.)NOx Trends (BPA Area)

Maximum BPA Area Annual Average NOX Concentration (1998-2013)

14.0

16.0

Annu

al N

Ox C

once

ntra

tion

(ppb

)

12.0

10.0

8.0

6.0

4.0

2.0

0.0

Example (Cont.)VOC Trends (BPA Area)

Summary of VOC Point and Area Emissions Data in BPA Area (tons per day)

Example (Cont.)VOC Trends (BPA Area)

Annual Average Level of Ethylene Measured in the BPA Area (1997-2013)

14.0

12.0

10.0

8.0

6.0

4.0

2.0

0.0

Annu

al A

vera

ge M

easu

rem

ents

(ppb

)

Ethylene Emissions

Range of Measured Annual Averages

Median of Measured Annual Averages

Year

Example (Cont.)VOC Trends (BPA Area)

Annual Average Level of Propylene Measured in the BPA Area (1996-2013)An

nual

Ave

rage

Mea

sure

men

ts (p

pb)

3.0

1.0

10.0

8.0

6.0

4.0

2.0

0.0

Propylene Emissions

Range of Measured Annual Averages

Median of Measured Annual Averages9.0

7.0

5.0

Year

Example (Cont.)Source Characterization

• Photochemical Modeling Project:– 24 Natural Gas-fired

Refrigeration Compressor Turbines

– 4 Acid Gas Vents– 1 Marine Flare– 2 Wet Gas Flares– 2 Dry Gas Flares– 2 Natural Gas-fired

Generator Turbines– 2 Emergency

Generators

• Proposed Project:– 6 Natural Gas-fired

Refrigeration Compressor Turbines

– 1 LNG Storage LP Flare– 1 Wet/Dry Gas Ground

Flare– 1 Auxiliary Boiler– 4 Thermal Oxidizers– 7 Diesel Generators– 1 Natural Gas-fired

Essential Generator– 1 Blowdown Vent

Example (Cont.)

Source Characterization

Photochemical ModelingPTE NOx Emissions

2,665.29 tpyPSD Increment:• SO2

• PM10

Property Line:• SO2

• H2S

Health Effects:• Benzene

Proposed ProjectPTE NOx Emissions

681.46 tpyPSD Increment:• SO2

• PM10

Property Line:• SO2

• H2S

Health Effects:• Benzene

Photochemical modeling approx. 4X more NOx than proposed project.

Example (Cont.)Meteorological Parameters and Regional Transport

BPA Area

Surface Pressure (HPA) Relative Humidity (%)

Example (Cont.)Meteorological Parameters and Regional Transport

BPA Area

Surface Roughness (m) Temperature (oC)

Example (Cont.)Meteorological Parameters and Regional Transport

BPA Area

Wind Vectors (knts) Wind Velocity (knts)

Example (Cont.)

Model Results

Photochemical modeling results in the BPA Area based on 4X as much NOx is between 0.1-0.5 ppb.

Questions?

Contact Information

• Justin Cherry, P.E.– Air Dispersion Modeling Team

– (512) 239-0955

– justin.cherry@tceq.texas.gov

• Reece Parker– Air Dispersion Modeling Team

– (512) 239-1348

– reece.parker@tceq.texas.gov

Air Permits Division

(512) 239-0955justin.cherry@tceq.texas.gov

Justin Cherry

Air Permits Division

Reece Parker

(512) 239-1348

reece.parker@tceq.texas.gov