May

1, 2014 TO: DOCKET EPA
- R09
- OAR
- 2014
- 0185 FROM: Carol Bohnenkamp SUBJECT: Review of the Modeling for the Attainment Demonstration for the Proposed Rulemaking Action on the South Coast 2012 AQMP for the One Hour Ozone Standard

**A .**  **CAA and Regulatory Requirements for 1 -**  **Hour Ozone Air Quality Modeling and EPA Guidance**  For an y ozone nonattainment area classified as serious or above, section 182(c)(2)(A) of the CAA specifically

requires the State to submit a modeled attainment demonstration based on a photochemical grid modeling evaluation or an y other anal yt ical method determined by the Administrator to be at least as effective as photochemical modeling. The following guidance documents describe the criteria that an air quality model and its application should meet to qualify for use in an ozone attainment demonstration.

 Appendix W to 40 CFR part 51, as interpreted in EPA guidance. See, e.g., Guideline for Regulatory

Application of the Urban Airshed Model, EPA
- 450/4
- 91
- 013 (July 1991);  “Guidance on Use of Modeled Results to Demonstrate Attainment of the Ozone NAAQS,” EPA
- 454/B
- 95
- 007 (June 1996);  “Guidance for the 1
- hour Ozone Nonattainment A reas that Rel y on Weight
- of
- Evidence for Attainment Demonstrations, Mid
- Course Review Guidance”(March 28, 2002);  “Guidance for Improving Weight
- of
- Evidence Through Identification of Additional Emission Reduction Not Modeled (Nov ember 1999);  “Guidance on the Use of Models and Other Anal yses for Air Quality Goals in Attainment Demonstrations for Ozone, PM 2.5 , and Regional Haze,” April 2007. These documents describe the components of the attainment demonstration, explain how the modeling and other anal yses should be conducted, and provide overall guidance on the technical anal ys es for attainment demonstrations. As with any

predictive tool, inherent uncertainties are associated with photochemical grid modeling. EPA’s guidance recognizes these limitations and provides recommended approaches for considering other analy tical evidence to help assess whether attainment of the NAAQS is likely . This process is called a weight of evidence (WOE) anal ys is. EPA’s modeling guidance (updated in 1996, 1999, and 2002) discu sses various WOE analy ses. Th e guidance recommends that all attainment demonstrations include supplemental anal ys es bey ond the recommended modeling. These supplemental anal ys es provide additional information such as data anal ys es,and emissions and air qua lity trends, which would help strengthen the conclusion based on the photochemical grid modeling. **B . 1**  **- Hour Attainment Demonstration Modeling and Weight of Evidence in the South Coast**  **2012 AQMP 1**  **. Modeling Approaches for the SCAQMD Attainment Demonstrat ion**  a. Photochemical Grid Model
. The model selected for the Final 2012 AQMP 1

– hour ozone attainment demonstration was developed using the U.S. EPA supported Community Multiscale Air Quality

(CMAQ) (version 4.7) air qualit y modeling platform with Statewide Air Pollution Research Center
- 99 ( SAPRC99) chemistry , and the Weather Research and Forecasting Model (WRF) (version 3.3) meteorological fields. The modeling s ys tem (including the photochemical model, meteorological inputs, and chemical mechanism) is consistent with the previous advice of outside peer reviewers. C MAQ is a state
- of
- the
- art air qualit y model that can simulate ozone and PM 2.5 concentrations together in a “one
- atmosphere” approach for attainment demonstrations. **Table 1: S**  **um m**  **a r**  **y of**  **F i**  **nal 2012 A**  **Q MP**  **1 -**  **hour O**  **z one**  **M od**  **e l**  **S e**  **le c**  **t i**  **on a**  **nd Mod e**  **l i**  **ng P**  **roto c**  **ol F**  **i n**  **al 2012 AQ**  **M P**  **1 -**  **H o**  **u r**  **Ozone M**  **o d**  **e l**  **in g**  **P r**  **o to**  **c ol**  1 Ozone Disp e rsion P latfo r

m: C M AQ Ch e m i str y : S AP R C99 Do m ain/ Coordinates E x p and e d S COS97 Met e o r ol o g y , Emiss i ons and Model a ppl i cat i on: L amb e rt Confo r mal G r id: 4 Km X 4 K

m O z on e : 18 la ye rs Emissions In ve ntor i es 2008 B a se yea r D a y- S p ec if

i c Emiss i ons S hipp i ng e m i ss i ons sp l it in t o 2 l a ye rs EM F AC2011 o 3
- modu l e s o Modifi e d D T IM Adjustments to fu g i t ive PM2.5 P av e d ro a d U.S. EPA with C A modifi cat i ons D a y- S p ec if

i c B i o g e n i c e m i ss i ons R e vised M e x ic an e m i ss i ons pro f i l e

1 P.VII
- 50. Appendix VII, Air Quality Management Plan, 1
- Hour Ozone Attainment Demonstration, February 2013, South Coast Air Quality Management District.Me teorology

W RF in i t i a l i z e d with N C EP data with F D D A Air Qual i ty M

od e l Performan c e Ass e ss m od e l pe r f

o rm an c e b a s e d on b oth 1
- hour stati s t i c s: No r mali z e d gross bias No r mali z e d gross e r

r o r P eak pr e diction a cc ur a c y 60 ppb thr e shold (b o th i ndic e s) 49 Cell av e ra g i n g 2008 Base Y

e ar Simulat i ons J une – Au g

ust 2008 92 d a y s o f simu l at i ons e v a luat e d P eak Episode 6/1 8
- 6/21 Future Y e ar Proj ec t i on s — D e term in i st i c Approa c h /

T ier e d RRF Approa c h 2022 b. Episode Selection. The attainment demonstration modeling focuses on 92 day s of ozone air quality observed during June through August of the base ye ar 2008. Overall, the 92 day period provides a robust description of the 2008 ozone meteorological season. During this period, there were 16 day s with measured daily

1
- hour maximum ozone concentrations of 125 ppb or higher at the Crestline monitoring site which is the monitoring site with the maximum number of exceedances. S even well defined multi
- day

ozone episodes occurred in th e Basin
. When assessed for a normalized meteorological ozone episode potential using a regression based weighting covering 30
- ye ars of data (1998
- 2010), the June 18
- 22, 2008 period was ranked in the 99th percentile. This episode contained the top four dail y Basin ozone maximum concentrations for 2008 and was selected as the focus of the attainment demonstration. c. Model Performance
. Model performance was evaluated in three zones in the South Coast Basin: the San Fernando Valley ; the eastern San Gabriel, Riverside and San Bernardino Valley s; and L os Angeles and Orange Count y.**Figure 1: Model Performance Zones in the South Coast B asin:** 

3). the San Fernando Valley ; 4). the eastern San Gabriel, Riverside and San Bernardino Valleys; and 5). Lo s Angeles and Orange County. Normalized Gross Bias, Normalized Gross Error, and Peak Prediction Accuracy were determined for each area. Normalized Gross Bias < + 15 Paired in space and time Normalized Gross Error < 35 Paired in space (+2 grid cells) and time Peak Prediction Accuracy < + 20 Unpaired in space and time Although not a requirement for determining acceptable model pe rformance, the performance statistics were compared to the EPA performance goals presented in guidance documents.**Table 2**  **: J une**  **18 -**  **22, 2008 B**  **a se**  **Y ea**  **r 1 -**  **Hour A** **v e**  **rage O**  **z one**  **P e**  **r f**  **o r**  **ma n**  **c e**  2 ( B old t y pe ind i cat e s me e t i ng stati s t i ca l pe r f o rm an c e c rit e ri a ).

* N o r m aliz e d b ias a n d n o r m al i z e d e rr o r c a lc u lated f o r h o ur s wh e r e ob s e r

v ati on s > 6 0 pp b

2 P. VII
- 57 **Da t**  **e** Z one 3 **O b**  **s er**  **v e**  **d (p**  **pb )**  **P r**  **e d**  **ic te**  **d**

**(p pb**  **) Un**  **p air**  **e d** 

**P e**  **ak Ra**  **t io**  **No r**  **m al**  **i ze**  **d**

**Bias*** **(p pb**  **) No**  **r m**  **al i**  **ze d** 

**E rr**  **o r**  ***** **(p pb**  **)** 618 87 93 1.07
- 17 **25** 619 95 109 1.15 **4 18**  620 111 99 0.89 **- 10**  **19** 621 122 107 0.87
- 19 **20** 622 123 92 0.75
- 29 **29 Da**  **t e**  Z one 4 **O b**  **s er**  **v e**  **d (p**  **pb )**  **P r**  **e d**  **ic te**  **d**

**(p pb**  **) Un**  **p air**  **e d** 

**P e**  **ak Ra**  **t io**  **No r**  **m al**  **i ze**  **d**

**Bias*** **(p pb**  **) No**  **r m**  **al i**  **ze d** 

**E rr**  **o r**  ***** **(p pb**  **)** 618 162 123 0.76
- 17 **20** 619 152 136 0.90 **- 1**  **18** 620 176 129 0.73 **- 12**  **16** 621 156 150 0.96 **- 1**  **18** 622 123 134 1.09 **10 21**  **Da t**  **e Z**  **o n**  **e 5**  **O b**  **s er**  **v e**  **d (p**  **pb )**  **P r**  **e d**  **ic te**  **d**

**(p pb**  **) Un**  **p air**  **e d** 

**P e**  **ak Ra**  **t io**  **No r**  **m al**  **i ze**  **d**

**Bias*** **(p pb**  **) No**  **r m**  **al i**  **ze d** 

**E rr**  **o r**  ***** **(p pb**  **)** 618 118 107 0.91 **0 22**  619 110 111 1.01 **11 15**  620 114 106 0.93 **0 13**  621 107 115 1.07 **4 12**  622 107 121 1.13 **13 19** The performance goals for Normalized Gross Error and Peak Prediction Accuracy were met in the eastern San Gabriel, Riverside and San Bernardino Valley s. The statistic for bias (Normalized Gross Bias) tends to be negative, indicating that the model tends to slightly under
predict ozone. Both June 18th and June 20th failed to meet the model acceptance criteria for the unpaired peak anal ys is. As a result, the attainment demonstration focused on the June 19th and 21st , day s with observed peak concentrations that closely matched the design values. Based on their anal ys is, South Coast concludes and EPA agrees that model performance is acceptable for this application. **2 . Results of SCAQMD Modeling**  Photochemical model s imulations were conducted for the base ye ar 2008 emissions, and future
ye ar 2022 baseline and controlled emissions. The ozone attainment demonstration was based on the deterministic approach outlined in the “Guidance on Use of Modeled Results to Demonstrat e Attainment of the Ozone NAAQS,” EPA
- 454/B
- 95
- 007 (June 1996.) In addition, the weight of evidence anal ys is uses the model in a relative sense, using the relative response factor (RRF) technique described in the “Guidance on the Use of Models and Other An aly ses for Air Quality Goals in Attainment Demonstrations for Ozone, PM 2.5 , and Regional Haze,” April 2007. a. Modeled Attainment The model predicted a maximum 1
- hour ozone concentration for 2022 of 125 ppb (0.125 ppm) on June 19th at Pasadena. All other predicted concentrations during the five day episode are projected to be below a concentration of 0.12 ppm . The results of the attainment demonstration for 2022 indicate that, allowing for one day per y ear above the standard, the federal 1
- hour ozone standard would be attained by 2022 at all monitors with the controlled emissions inventory . The attainment targets (410 tpd VOC and 150 tpd NOx) are based on both short
- term and long
- term control measures. With controls in p lace, it is expected that all stations in the South Coast ozone nonattainment area will meet the federal 1
- hour ozone standard in calendar y ear 2022. b. Weight of Evidence Analy sis Relative reduction factor The weight of evidence analy sis for the ozone attainment demonstration relies on the use of site
specific relative response factors (RRFs) being applied to the 2008 weighted design values. The RRFs are determined from the future ye ar controlled and the 20 08 base y ear simulations. The results of the relative response factor anal ys is supports the deterministic attainment demonstration and the level of emission reductions needed for attainment. The second element of the weight of evidence discussion utilize s the tiered RRF approach to determine station specific future ye ar design concentrations based on base y ear 2008 emissionsand 2022 controlled emissions. 3 The proposed methodology tiers the concentration threshold for accepting a simulation station day b ased on three criteria for evaluation: (1) the base ye ar daily maximum concentration absolute prediction error (calculated for a station per episode day) must be 20 percent or less; (2) the observed station concentration must be within 25 percent of the de sign value; and (3) a minimum of four station specific day s simulated must meet the error at the set concentration threshold for the RRF to be calculated. The 20 percent error criteria is the same level used in the 8
- hour ozone anal ys is and the four day mi nimum was iteratively determined to provide a measure of robustness to the RRF calculation. Basically , the four day criteria represented a balance between an analy s i s based on a higher error criteria with potentially

more day s included at a higher concentr ation threshold vs. a limited set of better simulated station day s with lower prediction error. Table VII
- 5
- 9 lists the impacted stations and the threshold concentration used for the RRF calculation. Also listed in Table VII
- 5
- 9 are the base year average p ercentage prediction bias and error for those day s included in the future y ear projection. Overall, the base year tendency is towards under prediction.

3 P. VII
- 75Air Quality Data Trends The most recent ambient air quality data that we have reviewed indicate tha t the area is on track to attain the 1
- hour ozone standard b y 2022. The 1
- hour ozone design value has d ecreased from 23.4 expected exceedence day s 2000
- 2002 to 5.5 expected exceedence days in 2010
- 2012. The peak 1
- hour concentration has d ecreased from 0.1 69 ppb in 2002 to 0.147 ppb in 2012. The peak levels have decreased at all monitors throughout the South Coast Basin.

**Figure 3: South Coast Air Basin One hour Ozone Trends from 1990 to 2013**

**– at**  **Maximum Monitoring Site.** 0 20 40 60 80 100 120 140

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350**3 -** **Y e** **a r** **A v** **e r** **a g** **e E** **x p** **e c** **t e** **d E** **x c** **e e** **d a** **n c** **e s** **1 -** **H o** **u r** **O z** **o n** **e C** **o n** **c e** **n t** **r a** **t i** **o n** **( p** **p m** **)** 

### South Coast **Air Basin: 1 -**  **Hour Ozone** 

Max 1-Hour Ozone Concentration 1-Hour NAAQS (Level) 1-Hour Design Value (Expected Exceedance) 1-hour NAAQS (Form)**Figure 4**  **: South Coast Air Basin One hour Ozone Trends from 1990 to 2013** 

**– at All** 

**Monitors. c. EPA’s Evaluation and Proposed Conclusion on the Modeling Demonstration** 

Our evaluation of the air quality modeling anal ys es and supporting information provided in the South Coast 2 012 AQMP addressing 1
- hour ozone indicate that the South Coast area will attain the 1
- hour ozone standard by its attainment y ear of 2022. The appropriate episode day s that represent day s conducive to ozone formation in the South Coast Air Basin were select ed. The modeling platform, including photochemical model, domain, number of vertical lay ers, and initial and boundary

conditions most appropriate for the South Co a st Air Basin, and other factors are appropriate. Finall y, the performance of the selected m odeling platform on each of the modeled episode day s meets the performance criteria specified in EPA guidance. The modeling predicts attainment at all of the twent y ozone monitoring stations. In addition to the attainment demonstration provided in the South Coast 2012 AQMP , we have considered supplemental technical information, including ambient air quality monitoring data, which was not available at the time the attainment modeling was performed by SCAQMD. The modeling shows significant reductions in ozone from the base pe riod.**References:**

Appendix VII , Air Quality Management Plan , 1
- Hour Ozone Attainment Demonstration , February 2013 , South Coast Air Quality Management District
. Guideline for Regulatory Application of the Urban Airshed Model, EPA
- 450/4
- 91
- 013 (July 19 91)
. Guidance on Use of Modeled Results to Demonstrate Attainment of the Ozone NAAQS, EPA
454/B
- 95
- 007 (June 1996)
. Guidance for the 1
- hour Ozone Nonattainment Areas that Rel y on Weight
- of
- Evidence for Attainment Demonstrations, Mid
- Course Review Guidanc e (March 28, 2002)
. Guidance for Improving Weight
- of
- Evidence Through Identification of Additional Emission Reduction Not Modeled (Nov ember 99).