1. Overview of Photochemical Modeling for Ozone Attainment Demonstrations
Air Modeling and Data Analysis Section
Air Quality Division
Chris Kite
Environmental Trade Fair
Austin, Texas
May 3, 2016
Air Quality Division

2. National Ambient Air Quality Standards
The United States (U.S.) Environmental Protection Agency (EPA) is required by the Clean Air Act to establish National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to health and the environment (
The NAAQS for ozone have changed over time:
0.08 parts per million (ppm) one-hour precursor standard established in 1971;
0.12 ppm one-hour ozone standard established in 1979;
0.08 ppm eight-hour ozone standard established in 1997;
0.075 ppm eight-hour ozone standard established in 2008;
0.070 ppm eight-hour ozone standard established in 2015; and
units of parts per billion (ppb) are often used for reporting purposes, such as 70 ppb, 75 ppb, and 84 ppb.
The air quality monitoring network operated by each state is used to determine if an area is meeting the NAAQS.

3. Why Conduct Photochemical Modeling for Ozone Attainment Demonstrations?
Serious and above ozone nonattainment areas (and multi-state Moderate nonattainment areas) are required to use photochemical grid modeling to demonstrate attainment in their State Implementation Plan (SIP).
Moderate nonattainment areas are required to use photochemical modeling as well.
An alternative approach can be used for Moderate nonattainment areas if the Administrator determines that it is at least as effective.
Model results are used to determine the amount of nitrogen oxides (NOX) and/or volatile organic compounds (VOC) emission reductions that may be needed for the area to attain the NAAQS.
EPA has specified approved models and has issued guidance, which is available on their SIP Attainment Demonstration Guidance Web page at
Two EPA guidance documents applicable to modeling ozone are currently available:
a finalized version from April 2007; and
a draft update from December 2014 that has not yet been finalized.

4. Dallas-Fort Worth (DFW) Trends in Regulatory Ozone Design Values and Population from 1991 through 2015

5. DFW Area Regulatory Ozone Design Values by Monitor from 2003 and 2015
Notes:
Regulatory ozone design value (DVR) per monitor in units of parts per billion (ppb).
Result on left in green is the 2003 DVR from 2001, 2002, and 2003 monitored data.
Result on right in purple is the 2015 DVR from 2013, 2014, and 2015 monitored data.
Red monitor is current maximum.
Blue monitor is current minimum.
NA indicates monitor was not operational from
Pilot Point
NA / 79
Denton Airport South
97 / 83
Greenville
NA / 64
Frisco
88/ 76
Eagle Mountain Lake
96 / 76
Grapevine Fairway
100 / 78
Rockwall Heath
81 / 70
Dallas North #2
86 / 75
Keller
100 / 76
Parker County
89 / 75
Dallas Hinton Street
90 / 75
Fort Worth Northwest
96 / 80
Arlington Municipal Airport
NA / 67
Dallas Executive Airport
85 / 68
Kaufman
73 / 67
Midlothian Old Fort Worth Road
NA / 68
Granbury
84 / 73
Cleburne Airport
90 / 73
Italy
NA / 66
Corsicana Airport
NA / 66

6. Wind Direction Impacts on Peak Ozone Levels in the DFW Area
Ozone Season Winds
Highest
frequency
direction of wind on high ozone days.
Ozone design values have typically been set in the north and northwest part of the DFW area and follow the typical wind pattern shown above.
The location where the design values are set generally remains the same, but the intensity has dropped over time.

7. Fourth Highest Eight-Hour Ozone Levels at Five Northwest DFW Monitors from 2001 through 2015

8. Eight-Hour Ozone Regulatory Design Values at Five Northwest DFW Monitors from 2003 through 2015
Monitored regulatory ozone design value:
three-year rolling average of the fourth highest reading per year.
Example:
The 2015 monitored design value is a truncated average of the fourth highest monitored levels from 2013, 2014, and 2015.

9. Photochemical Modeling Steps to Demonstrate Attainment of the Ozone Standard
Attainment of the ppb eight-hour ozone standard for a moderate nonattainment area like DFW will be determined by the average of the fourth-highest ozone readings per year from for each regulatory monitor, which will result from:
background ozone levels and precursor emissions entering the area;
local and regional meteorological conditions that will occur; and
the magnitude, spatial distribution, and temporal distribution of NOX and VOC emissions.
Photochemical modeling is a computer tool used to predict future ozone levels based on the projected level of precursor emissions. Basic steps:
Episode: Select a representative historical ozone episode, with preference given to full cycles with transition from low to high and back to low ozone days.
Base Case: Develop modeling inputs for this episode that include meteorological fields, biogenic emissions, anthropogenic emissions, boundary conditions, initial conditions, etc.
Performance: Evaluate performance of the episode by comparing with historically monitored data.
Baseline Case: Run the base case meteorology and biogenic emissions with daily average inputs. For example, the base case has specific EGU emission measurements by day; the baseline has a seasonal representative average day instead.
Future Case: Develop daily average anthropogenic emission inputs for the future year accounting for expected growth and benefits of known federal, state, and local rules.
Attainment Test: For each ozone monitor, obtain a future design value (DVF) by applying the future/baseline modeled ozone ratio to a baseline design value (DVB), which is an average of the regulatory design value (DVR) over a three-year period.

10. Days at DFW Regulatory Monitors per Month from 1991 through 2014 with Ozone Levels Above 75/84 ppb

11. DFW Maximum Monitored Eight-Hour Ozone May 31 through July 2, 2006 Episode

12. DFW Maximum Monitored Eight-Hour Ozone August 13 through September 15, 2006 Episode

13. Episode Days Greater than 75 ppb Episode Days Less than 75 ppb
48-Hour Back Trajectories from Denton Airport South Monitor: May 31 through July 2, 2006
Episode Days Greater than 75 ppb
Episode Days Less than 75 ppb

14. Episode Days Greater than 75 ppb Episode Days Less than 75 ppb
48-Hour Back Trajectories from Denton Airport South Monitor: August 13 through September 15, 2006
Episode Days Greater than 75 ppb
Episode Days Less than 75 ppb

15. Street View of Denton Airport South Ozone Monitor

16. 29 4x4 kilometer (km) Grid Cell “Boxes” from 0 to 18,233 meters Above Ground Level (AGL)

17. Roughly 1,750 Surface Level 4 km Grid Cells (35x50) Needed to Cover Greater DFW Area
Notes:
Red dots indicate the location of each Continuous Air Monitoring Stations (CAMS) located throughout the DFW area.

18. North American Regional Domains for Texas Air Quality Modeling Efforts
Grid Size
Number of Cells
in X Direction
Number
of Cells
in Y
Direction
4 km
191
218
12 km
149
110
36 km
148
112
Modeling
Domain
Grid Size
Number of
Surface
Cells
Number of Cells in
29 Layers
4 km
41,368
1,207,502
12 km
16,390
475,310
36 km
16,576
480,704

19. Base Case Episode Development in Ten Time-Consuming and Not-So-Easy Steps
Description 1
Develop or update existing conceptual model. 2
Select a time period to model. 3
Develop meteorological inputs and run the mesoscale model. 4
Develop inputs for and run the biogenics model. 5
Develop anthropogenic emission inputs for area, on-road, non-road, oil and gas, off-road, and point source categories plus Canada and Mexico portions of domain. 6
Process emissions to obtain speciated and temporally allocated inputs by grid cell. 7
Develop initial conditions, boundary conditions, and land cover fractions. 8
Aggregate all inputs and run the photochemical model. 9
Evaluate performance by comparing modeled output to observations. 10
Investigate problems, update input with new data, and redo steps 3-9 (ongoing).

20. 2006 Summer Weekday Anthropogenic NOX Emissions Texas 4 km Domain – June 14 Episode Day
Area Total =
4,524 NOX tpd

21. 2006 Summer Weekday Anthropogenic NOX Emissions Texas 12 km Domain – June 14 Episode Day
Area Total =
11,494 NOX tpd

22. 2006 Summer Weekday NOX Emission Estimates for North American 36 km Domain – June 14 Episode Day
Area Total =
61,454 NOX tpd

23. Changes in DFW Area NOX and VOC Emission Estimates by Source Category from 2006 to 2018

24. 2006 10-County DFW Area Summary of Anthropogenic Emissions
Source Category
NOX Emissions
(tpd)
VOC Emissions
On-Road
284.27
116.50
Non-Road
98.06
64.69
Off-Road – Locomotives
29.02
1.72
Off-Road – Airports
12.78
4.46
Area Sources
290.46
Oil and Gas – Production
61.84
43.72
Oil and Gas – Drill Rigs
18.23
1.16
Point – Oil and Gas
11.53
21.82
Point – Electric Utilities
9.63
1.03
Point – Cement Kilns
22.08
1.94
Point – Other
14.31
25.65
10-County DFW Area Total
591.72
573.15

25. 2018 10-County DFW Area Summary of Anthropogenic Emissions
Source Category
NOX Emissions
(tpd)
VOC Emissions
On-Road
119.69
62.20
Non-Road
42.13
33.02
Off-Road – Locomotives
17.86
0.89
Off-Road – Airports
13.06
3.55
Area Sources
30.76
284.94
Oil and Gas – Production
8.31
24.24
Oil and Gas – Drill Rigs
2.82
0.21
Point – Oil and Gas
16.37
26.02
Point – Electric Utilities
16.91
4.44
Point – Cement Kilns
17.64
0.78
Point – Other
6.62
20.43
10-County DFW Area Total
292.17
460.72

26. Arlington Municipal Airport Dallas Executive Airport
2018 Future Ozone Design Value (DVF) per DFW Area Monitor: Results for All Days and Top 10 Days Attainment Tests
Notes:
Result on left in green is the 2018 DVF based on the all days test.
Results on right in purple is the 2018 DVF based on the top 10 days test.
Monitor in red indicates the maximum projected DVF.
Monitor in blue indicates the minimum projected DVF.
Monitors in orange began operation after 2006.
Pilot Point
66 / 65
Denton Airport South
76 / 75
Greenville
62 / 62
Frisco
73 / 72
Eagle Mountain Lake
75 / 74
Grapevine Fairway
75 / 73
Rockwall Heath
65 / 65
Dallas North #2
71 / 70
Keller
75 / 73
Parker County
71 / 71
Dallas Hinton Street
68 / 67
Fort Worth Northwest
73 / 72
Arlington Municipal Airport
69 / 68
Dallas Executive Airport
70 / 70
Kaufman
62 / 62
Midlothian
OFW – 62 / 62
Tower – 67 / 66
Granbury
67 / 67
Cleburne Airport
70 / 68
Italy
Activated in 2007
Corsicana Airport
Activated in 2009

27. Key Provisions and Differences Between April 2007 and December 2014 EPA Modeling Guidance Documents
EPA Guidance on the Use of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, April 2007:
Section 2.3 (page 17): “The results of corroboratory analyses may be used in a weight of evidence determination to show that attainment is likely despite modeled results which may be inconclusive.”
Table 2.1 (page 17): ppb is the weight of evidence range for the 84 ppb standard, which equates to a ppb weight of evidence range for the 75 ppb standard.
Section 2.4 (page 18): “We recommend a modeled attainment test in which model predictions are used in a relative rather than absolute sense.”
Sections 2, 3, and 4 (pages 15-42): Include all episode days in the baseline modeled above a specific threshold (e.g., 75 ppb) in the relative response factor (RRF) attainment test.
EPA Draft Modeling Guidance for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, December 2014:
Section (page 190): “A fully-evaluated, high-quality modeling analysis that projects future design values that are close to the National Ambient Air Quality Standards (NAAQS).”
Section 4.0 (page 95): “The recommended test uses model estimates in a relative rather than absolute sense to estimate future year design values.”
Section (page 100): “Model response to decreasing emissions is generally most stable when the base ozone predictions are highest.”
Section (page 100): “On days with high ozone concentrations, there is a relatively high percentage of locally generated ozone compared to days with low base case concentrations.”
Section (page 101): “Use of the highest 10 days in the mean RRF calculation yields a slightly better estimate of the actual observed ozone change than the previous guidance approach.”

28. Monitor Specific Ozone Design Values – Regulatory versus Baseline
Regulatory design value (DVR) for the monitor:
Fourth highest ozone reading per year averaged (and truncated) over the three previous years.
The 2006 DVR is based on the fourth-highest reading from 2004, 2005, and 2006.
Baseline design value (DVB) for the monitor:
Average of the DVR from the year of the ozone episode plus the two subsequent years.
The 2006 DVB is an average of the 2006 DVR, 2007 DVR, and 2008 DVR.
The 2006 DVB for the Denton Airport South ozone monitor is ppb:
Calendar
Year
DVR
Fourth Highest Ozone Reading per Year
2004
2005
2006
2007
2008 95 92 94
100 89 91 84

29. Ozone Attainment Test Differences - All Days versus Top 10 Days Methodologies
To reduce uncertainty associated with model predictions, use of absolute modeled differences by individual grid cell and/or episode day should be avoided.
Instead, the relative change in modeled ozone concentrations across several days from two scenarios (e.g., baseline and future year) should be applied to real-world monitored values.
To calculate the RRF for the ozone attainment test:
EPA modeling guidance from April 2007 specifies averaging the results for all episode days in the baseline modeled above the standard, such as 75 ppb.
EPA draft modeling guidance from December 2014 specifies averaging the results for the 10 episode days in the baseline with the highest modeled levels.
Example calculations for the Denton Airport South Monitor:
Description
All Days Test
Top 10 Days Test
2006 Baseline Design Value (DVB)
93.33 ppb
(remains the same for both tests)
Episode Days in Calculation
36 days out of 67 in episode
(modeled above 75 ppb in baseline)
10 days out of 67 in episode
(highest modeled in baseline)
RRF
2018 Future Design Value (DVF)
76.72 ppb
75.23 ppb
2018 Rounded/Truncated DVF
76 ppb
75 ppb

30. Friday June 9 Episode Day Friday June 9 Episode Day
Sample RRF Calculation for Attainment Test June 9 Episode Day at Denton Airport South
The highest eight-hour ozone level measured during 2006 at the Denton Airport South monitor was 106 ppb on Friday June 9.
RRF calculation for June 9 episode day at Denton Airport South:
From the baseline modeled output, identify the maximum eight-hour ozone level in a 3x3 grid cell array centered around the monitor: ppb
From the same 3x3 array, identify the maximum from the future case modeled output: ppb
Divide the future case maximum by the baseline maximum to obtain the RRF: ÷ =
April 2007 guidance for all days test specifies use of the maximum array value in the future case.
December 2014 draft guidance for top 10 days test specifies use of specific grid cell value in the future case that had the maximum in the baseline.
Friday June 9 Episode Day
2006 Baseline
108.10
103.92
100.39
111.38
107.21
102.40
112.99
110.35
105.68
2006 Maximum =
Friday June 9 Episode Day
2018 Future Case
85.54
82.58
80.24
88.29
84.90
81.95
89.80
87.57
83.91
2018 Maximum = 89.80

31. 2006 Baseline and 2018 Future Case Modeled Ozone at Denton Airport South Monitor
Episode Date
2006 Ozone
2018 Ozone
RRF
6/9
112.99
89.80
0.7948
8/23
111.72
89.36
0.7999
6/29
105.05
84.61
0.8054
8/19
101.65
80.57
0.7926
8/21
101.16
77.78
0.7689
9/1
100.98
83.88
0.8307
8/18
100.46
77.47
0.7712
6/30
99.75
80.45
0.8065
6/28
95.83
80.60
0.8411
6/15
95.23
81.59
0.8568
Top 10 Day Average
102.48
82.61
0.8061

32. Web Page Address / FTP Directory
Electronic File Availability for Ozone Modeling and Emissions Inventory Development
Description
Web Page Address / FTP Directory
TCEQ Ozone Modeling Files Web Page
2006 Episode
2012 Episode
TCEQ On-Road FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/Mobile_EI/
TCEQ Non-Road FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/Nonroad_EI/
TCEQ Off-Road FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/Offroad_EI/
TCEQ Area Source FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/Area_EI/
TCEQ Oil and Gas FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/Oil_Gas_EI/
TCEQ Point Source FTP Directory
ftp://amdaftp.tceq.texas.gov/pub/TX/ei/2006/fy2017/point/
Texas Air Emissions Repository (TexAER)
TCEQ Air Quality Research and
Contract Projects Web Page

33. Questions?
Chris Kite