~~t~~ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 0 ~\

REGION 6 1445 ROSS AVENUE, SUITE 1200

DALLAS, TEXAS 75202 - 2733 ~v Office of the Regional Administrator "\V ~'<"\f'..(

September 18, 2015 {xqo \1) . Mr. Richard A. Hyde, P .E. Executive Director f°ifECEIV;~o Texas Commission on Environmental Quality I [s~p2a 20;-: Post Office Box 13087 Austin, Texas 78711-3087 ~, J

{ECUTIVE DIRECTOR Dear Mr. Hyde:

This letter responds to the Texas Commission on Environmental Quality's proposed exceptional events flag and demonstration for the air quality concentration raw ozone data value of 128 parts per billion during hour 1300 local standard time on August 26, 2011 , at the Houston East monitor (Air Quality System numper 48-201 -1034). Your request was submitted in a letter dated September 30, 2014, after satisfying a 30-day public review requirement. The U.S. Environmental Protection Agency has completed its analysis of this submittal to ensure it meets the requirements of 40 Code of Federal Regulations (CFR) §50.14.

After completing our review of your request, we are unable to concur on the proposed exceptional event flag. We came to this conclusion after comparing the evidence offered in your demonstration against the standard set forth at 40 CFR 50.14(c)(3)(iv). Details of our review are found in the enclosure.

The determinations conveyed in this letter do not constitute final EPA action regarding any matter on which the EPA is required to provide an opportunity for public comment. In particular, this applies to determinations regarding the attainment status or classification of the area. Final actions will take place only after the EPA completes rulemaking with public notice and comments on those determinations.

We appreciate the work and effort of the TCEQ to develop its exceptional event package. If you have any questions about our review, please contact me at (214) 665-2200, or have your staff contact Ms. Frances Verhalen of my staff at (214) 665-2172.

Enclosure

cc: Mr. David Brymer Director, Air Quality Division, TCEQ

This paper is printed with vegetable-oil-based inks and is 100-percent postconsumer recycled material, chlorine-free-processed and recyclable

Technical Review ofAugust 26, 2011 Exceptional Events Demonstration Package at the Houston East (CAMS 1} monitoring site by the Texas Commission on Environmental Quality {TCEQ}, dated September 30, 2014

Introduction EPA promulgated the Exceptional Events Rule (EER) in 2007, pursuant to the 2005 amendment of the Clean Air Act (CM) Section 319. The EER added 40 CFR §50.lU}, (k), and (I); §50.14; and §51.930 to the Code of Federal ~egulations (CFR). These sections contain definitions, criteria for Environmental Protection Agency (EPA) approval, procedural requirements, and requirements for air agency demonstrations, all of which must be met before EPA can concur under the EER on the exclusion of air quality data from regulatory decisions.

As a requirement under the EER, data claimed to be due to an exceptional event must be flagged in the EPA's Air Quality System (AQS) database and an initial description of the event should be provide~ to the EPA, as well as, notice and opportunity for public input. Failure to meet the above criteria will result in non-concurrence with the flagging of the measured proposed National Ambient Air Quality Standard (NMQS) exceedance(s).

After considering the weight of evidence provided in the demonstration, the EPA will decide to concur or not to concur with each flag. Under 40 CFR §50.14(c)(3)(iv), the air agency demonstration to justify exclusion of data must provide evidence that:

• the event was caused by human activity unlikely to reoccur at a particular location or was a natural event, and

• the event was not reasonably controllable or preventable

• the event was in excess of normal historical fluctuations

• the event affects air quality

• there was a clear causal relationship

• there would have been no exceedance or violation but for the event We address several of these criteria below. A deficiency with any one part of the demonstration would

be determinative of our inability to concur.

(1) Providing evidence that the event was associated with a measured concentration in excess of normal historical fluctuations, including background

According to 40 CFR 50.14(c)(3)(iv)(C), the demonstration to justify data exclusion shall provide evidence

that the event was associated with a measured concentration in excess of normal historical fluctuations,

including background. This portion of the Exceptional Events Rule requires an air agency to "provide

evidence" but there is no specific statistical threshold that must be met in order to pass the test. In

reviewing the historical fluctuations using a weight of evidence approach, the EPA has observed the

following: The hourly ozone concentration recorded on August 26, 2011 at 1300 local standard time

(LST), 128 parts per billion (ppb), is not unusual or exceptional because hourly values around this

concentration or higher were recorded 3 days later on August 29, 2011 (136 ppb), and also on 2 days

just 1 year earlier in 2010 (129 ppb on July 16, 2010 and 125 ppb on August 3, 2010). Going back 5 years

there were two more high 1-hour ozone concentrations recorded at the Houston East site in 2006 (125

ppb on June 4, 2006 and 153 ppb on September 1, 2006). And going back 10 years there were multiple

1

high 1-hour ozone concentration days that exceeded 124 ppb in 2004 (3 days}, 2003 (7 days}, 2002 (4

days) and 2001 (7 days). The chart below (Figure 1) depicts the 2011 high 1-hour ozone concentration

days (i.e . days with maximum 1-hour ozone concentrations greater than 124 ppb) at the Houston East

monitoring site, including the flagged day of August 26 and also August 29 (flagged but not submitted as

a demonstration), compared to the years 2001-2013. The 2011 year was an average year (2 days above

124 ppb) for the 13-year period.

Houston East Site:# days> 124 ppb

13-year average 2013 2012

2011 flagged days 2010 2009 ...

n:, 2008 QI > 2007

2006 2005 2004 2003 2002 2001 ~~~~~~~~~~

0 2 4 6 8

# days

Figure 1. Annual number of days with maximum hourly ozone concentration greater than 124 ppb.

Peak 1-hour ozone concentrations above 124 ppb in August and September have not been uncommon

at the Houston East site over the years. Each year with high ozone concentrations depicted in the chart

above had at least 1 day with 1-hour ozone concentrations above 124 ppb occur in the August­

September time period (i.e. 1 day in 2001, 2006, and 2010; 2 days in 2002 and 2004; 3 days in 2003).

The demonstration package showed t hat the August 26, 2011 maximum hourly value was in the top 1%

of all observations. The demonstration package discussed normal historical fluctuations of ozone

concentrations at the Houston East site in Chapter 3. Following are some review comments on that chapter:

A. Section 3.5 discussed nitrogen oxides (NOx) and ozone data collected at the Houston East and

nearby sites. The text discussed the phenomenon of biomass burning leading to elevated

concentrations of NOx and NOx thereafter being transported far downwind. If this were the

case, the resulting NOx would be dominated by aged emissions or N02, not NO, which

represents fresh emissions (see, e.g., Exceptional Events Demonstration for 1-Hour Ozone

Exceedances in the Sacramento Regional Nonattainment Area Due to 2008 Wildfires, p. ?O, available at http://www.arb.ca.gov/desig/excevents/fi rem ain.pdf). The peak NOx hourly

concentration recorded ·at the Houston East site on August 26, 2011 was 122 ppb and it was

dominated by fresh emissions (N0=72% of the NOx), indicating that local NOx emissions from

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local sources wer-e significantly affecting the Houston East monitor rather than aged NO.

emissions which would be dominated by N02instead.

The demonstration package mentioned that the peak NOx hourly value of 122 ppb was very high

and in the 94th percentile. This result is unsurprising because of the very stagnant conditions

(0.2-4.1 mph resu ltant wind speed range) recorded at the Houston East site on August 26, 2011.

The demonstration package also stated that because the fires were quite distant from the

region, the plume of emissions from the fires would likely have been dispersed over a wide area.

Yet, the ozone plume that caused the 1-hour ozone exceedance at the Houston East site was

quite narrow, affecting only three monitors total in a narrow line from SE to NW from the

Houston East site to the Wayside site an hour later and finally the Aldine site another hour later

as seen in the map below (Figure 2).

·+- Flou!lon Arca I-Fir Ozone Exceedaoce Days Back Trajectories

---___..,, 100. aoowy

tQ1- 1,001r

l'°1 -l7JC "1

1 · ,~.-~--,...__ . ...._--·--·-

...... IIM).a MMle!la,y

__..., ,00-IOOYr

'°'"~ "". tsc, . na,.,, • 2:l:11 -2'00fr

• 1'li01•30CIGl'J • 3CICII . GJDl'lo . ,,o,.~ .,, . M)Ot.)100 ""

L.gend

= 11- m t ....,~kuhe.._.., ....,.. ,,f!ew o-~o.,. -......

07116110 ,.... - O&J01/10 ,... - OOI00.!10 ,....

Oll11/10 , s.. ...,.,,, .... _ ..,,.,,, ,.... - -· ,.... _ ...,.,,, ,... - olll."12 ,... - 05/01112 ,s--- ·,... _ ..,,.,,, ,....

OOl%7M ,... O&I07/12 2 SU.

Dtieli..........llOt • IIGl l lt=::.=:=.,...._,......,.

-c-...a-::,100111t. t: -.i. lllt9ui ,...os ~ . n:itNl'.ioo'lltt.1'f-~ M)U ltppltWoo,ai ..11..o T~

Fmt Be""

0 U 5 10 15 20.....

Figure 2. Houston Area 1-Hour Ozone Exceedance Days Back Trajectories.

8. Section 3.6 discusses daily maximum ozone values at other sites in SE Texas. Notably, only in

Houston (and only at three sites in a narrow line from SE to NW as depicted on the map in

Figure 2) were 1-hour ozone exceedances recorded. The highest 1-hour ozone co ncentrations

recorded in the Beaumont area (97 ppb) and the Lake Charles, Louisiana area (90 ppb)--areas

closer to the Lower Mississippi River Valley fires discussed in the demonstration package--were

actua lly lower than those recorded in Houston, indicating t hat local Houston anthropogenic

sources, not distant fire emissions, caused the 1-hour ozone exceedances recorded at the three

Houston sites. Wind speeds in the Beaumont/Lake Charles area were also stagnant (i.e. 0.4-4.8

mph recorded at the Beaumont area Orange site #48-361-1001 from 0000 -1300 LST), but the

peak NO. hourly concentrations recorded at the Beaumont area Orange site and the Lake

Charles Westlake site were less dominated by fresh emissions (i.e. N0=38% of the NO. at

Beaumont Orange and 43% of the NO. at the Lake Charles Westlake site #22-019-0008).

3

(2) Providing a clear causal relationship between the measurement under consideration and the event claimed to have affected the air quality in the area

According to 40 CFR S0.14(c)(3)(iv)(B), the demonstration to justify data exclusion shall provide evidence

that there was a clear causal relationship between the measurement under consideration and the event

claimed to have affected the air quality in the area. To meet this regulatory element, the TCEQ must

identify both the measurement for which they are requesting exclusion and the specific event that

c.aused the identified exceedance or violation. The TCEQ identified the exceedance, but did not identify

a specific event. Rather, the demonstration states in Section 1.4 that "The TCEQ believes that this one­

hour exceedance was due to an exceptional event attributable to wildfires in the Pacific Northwest and

in the Mississippi River Valley in Northeast Louisiana, Northwest Mississippi, and Southeast Arkansas ..."

The TCEQ's demonstration contains fire counts and total acreage but does not provide sufficient

information about the fire(s) and associated fire characteristics claimed to have influenced the

monitored exceedance. The demonstration did not contain detailed information on a specific fire(s)

that may have contributed along with the specific burned acreage and distance between the fire(s) and

the monitor. Based on the EPA's review of the clear causal relationship criterion using a weight of

evidence approach, the TCEQ's demonstration package does not meet this requirement. The package

shows hourly PM-2.5 and ozone concentrations rising at the same time (Figure 4-4), but does not

contrast this behavior with a day that is not believed to be impacted by fire events. The coincident

timing of the PM-2.5 and ozone concentrations is not an unusual result because under stagnant

conditions both pollutants should rise at the same time. Also, the morning ozone concentrations at the

Houston East site are at near zero levels (Figures 3-3 and 4-4), indicating scavenging of ozone from fresh

nitrogen oxide (NO) emissions. Aged fire NOx emissions would be dominated by nitrogen dioxide (N02)

concentrations instead of NO concentrations. The graphic in Figure 3, below, starkly depicts how high

the fresh NO concentrations from local sources in Houston were on the morning of the claimed event

day (August 26, 2011) versus the mean average 25 non-event days in August, 2011 leading up to August

26, 2011. The graphic in Figure 3 also includes the preliminary diurnal NO profile from a recent

preliminary 1-hour ozone exceedance day of 130 ppb at the Houston East monitor on June 3, 2015. The

June 3, 2015 peak NO concentration traced very similarly to August 26, 2011.

4

Houston East NO Diurnal Profile Comparisons

90

.0 50 C. C.

80

70

60

40

30

20

10 ;•·

,.:

4,,

:....

. ...

o , 2 3 4 5 6 7 a g 10 11 12 13 14 15 16 11 1s 19 20 21 22 23

Hour

---•- -- 8/26/11 ---- August 1-25/2011 mean -o-- 6/3/15 prelim. data

Figure 3. Houston East site NO diurnal profile comparisons.

The EPA review observed that the back trajectories presented in the demonstration package had

omitted the last two hours before the 1-hour ozone exceedance occurred (i.e. the back trajectories

started at 1700 Coordinated Universal Time (UTC) which corresponds to 1100 LST in the central time

zone of the U.S., instead of starting at 1900 UTC which corresponds to the exceedance hour of 1300

LST). During the last two hours before the 1300 LST exceedance, the air mass slowly passed over

stationary emission sources of NOxand voe in the Houston Ship Channel (see map in Figure 2) before

reaching the Houston East monitor. In addition, the back trajectories presented in the demonstration

package are 7- day trajectories. Uncertainties in trajectory analyses increase with increasing time

backward on a trajectory path. Uncertainties associated with trajectory analyses at these long t imes and

distances limit the weight this evidence could have to demonstrate the linkage between the monitor

where the exceedance occurred and the areas 7 days upwind. Additionally, if fire emissions from

several days prior reached the monitor, it is likely that the fire emissions would be broadly distributed,

not localized over a few monitors. Also, there is no guarantee that any long-distance transported fire

emissions would mix all the way to the ground level (4 meters above ground level (agl)) where the ozone

probe is located.

Satellite pictures of thin smoke were presented in Section 4 of the demonstration package but the

image for August 26, 2011 (Figure 4-23) only shows patchy and light remnants of smoke, or clear skies,

5

over the Houston area. Further, the MODIS Aqua Satellite image for August 26, 2011 shows a clear to

thin aerosol optical depth (AOD) reading for the Houston area in Figure 4-27. And this is substantiated

by reviewing Figures 4-31, 4-35 and 4-36 for the Houston East site which shows fairly clear conditions at

the site and which shows that the aerosols depicted to the north of the site are at 2-4 km above ground

level and not at the surface. Likewise, Figure 4-34 shows the approximate location for the Houston East

site to be in clean marine air, south of where any smoke remnants are indicated. And Section 5.3 of the

demonstration package states that on August 26, 2011, ..."skies over southeast Texas were clear ..."

(3) Providing evidence that there would have been no exceedance or violation but for the event

According to 40 CFR S0.14(c)(3)(iv)(D), the demonstration to justify data exclusion shall provide evidence

that there would have been no exceedance or violation but for the event. The demonstration package

does not meet this requirement. There were no 1-hour ozone exceedances in the region (i.e. hourly

ozone values above 124 ppb) along the pathway of the incoming air masses closer to the discussed fires.

The only 1-hour ozone exceedances were recorded in Houston along a narrow plume pathway at three

Houston sites, strongly indicating that local Houston anthropogenic industrial and mobile sources, not

far away fire emissions, caused the 1-hour ozone exceedances at the three Houston sites on August 26,

2011.

The demonstration package presents an analysis of regional background ozone in Section 5.1. It is noted

that all 19 sites used in the demonstration package's regional background ozone analysis are located

near local sources or are in urban areas affected by local mobile source emissions. The 70 ppb regional

background ozone estimate for August 26, 2011 given in the demonstration package was based on the

smallest 1-hour ozone maximum concentration for the day from the 19 sites. This 70 ppb regional

background ozone estimate was the same maximum hourly ozone concentration recorded at the

Alabama-Coushatta Clean Air Status and Trends Network (CASTNET} site located about 75 miles

northeast of the Houston East site in rural Polk County, Texas. The Alabama-Coushatta site is

considered by EPA to be a good rural regional background ozone site for southeast Texas, with minimal

local anthropogenic sources of ozone precursors affecting the monitor. The Alabama-Coushatta site and

the Houston East site would have been equally influenced regionally by any distant fire emission plumes.

Thl)s, we consider the Alabama-Coushatta site to give a good representation of the maximum hourly

ozone concentration for August 26, 2011 which would be due to regional background conditions,

including any ozone concentrations transported long distance by fire emission plumes. Thus, any

emissions from the distant fires, if present, would have contributed to a maximum hourly ozone

concentration of just 70 ppb at the Alabama-Coushatta site. If we assume these conditions should have

also prevailed at the Houston East site, on August 26, 2011, readings would have been far below the 1-

hour ozone exceedance threshold of 125 ppb.

In the graphic below (Figure 4), we note the Alabama Coushatta ozone diurnal profile on August 26,

2011 increases uniformly about 20 ppb above an average non-event day from the first 25 days in

August, 2011. This was an expected result because of the stagnant/low wind speeds measured in the

greater Houston area on August 26, 2011. In sharp contrast to the profile for the Alabama-Coushatta

site, the ozone diurnal profile for the Houston East monitor on August 26, 2011 rises rapidly by about 80 · ·

ppb (4 times 20 ppb) to approach 130 ppb during the hours 1100 to 1300 LST. The sharp and large rise

in ozone concentration exhibited at the Houston East monitor on August 26, 2011 indicates a locally

generated reactive ozone plume passing over a monitor.

6

Ozone Diurnal Profile Comparisons

130

120

110

100

90

80

.c 70 a. a. 60

50

40

30

20

10

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Hour

___ ...__ _ Houston East 8/26/11

-- -• - - Alabama Coushatta 8/26/11 -- Alabama Coushatta August 1-25/2011 mean ----- Houston East August 1-25/2011 mean ~ Houston East 6/3/15 prelim. data

Figure 4. Houston East and Alabama-Coushatta sites Ozone Diurnal Profile Comparisons.

Th e demonstration package also presented a surrogate day ana lysis to compare to the August 26, 2011

1-hour ozone exceedance day, describing August 27, 2009 as being a day similar to August 26, 2011 in

terms of surface trajectories, sinuosity and meteorology in Sections 5.2 and 5.3. But these two days

were not similar because the average so lar radiation on August 26, 2011 was 42% higher than the

surrogate day (i.e. 0.68 Langley/min versus 0.48 Langley/min).

In addition, clear skies were present on August 26, 2011, not smoke haze. Page 5-10 states, "Skies over

southeast Texas were clear with temperatures in the mid 90 degree Fahrenheit range. The clea r skies

extended over much of the southeast United States (U.S.). Winds over southeast Texas and the Houston

area were light." The clear skies, high solar radiation, high temperatures and light w inds present on

7

August 26, 2011 would be especially conducive to ozone photochemical production and thereby result

in the 1-hour ozone exceedance concentration of 128 ppb at the Houston East site.

Section 5.4 of the demonstration package comments that local highly reactive volatile organic

compound {HRVOC) concentrations were comparable between August 26, 2011 and the surrogate day

of August 27, 2009. However, the demonstration package only discussed two sites, Clinton Drive and

HRM3, and left out data from the Deer Park site which was discussed in the earlier public comment

demonstration package {dated August 5, 2014). Figures 5-4 and 5-5 in that earlier public comment

demonstration packag~ showed higher ethylene and propylene concentrations recorded on August 26,

2011 compared to August 27, 2009 for the Clinton, HRM3 and Deer Park sites. Ethylene and propylene

are usually the HRVOC species with highest ambient concentrations; both are emitted from both

stationary industrial _sources and mobile sources. The following narrative in the earlier public comment

demonstration package {dated August 5, 2014) concedes to the potential significant impact of ethylene

concentrations on the ozone concentrations recorded at the Houston East site on August 26, 2011:

"Given wind speed and direction on August 26, 2011, it is possible that the late morning peak of 12.5

ppbC ethylene measured at the Houston Deer Park {CAMS 35) monitoring site could have influenced

ozone levels measured in the early afternoon at Houston East {CAMS 1) monitoring site." The ethylene

peak concentration of 12.5 ppbC (a very high concentration greater than the 95th percentile) was

recorded at 1100 LST, and the ethylene peaks at Clinton (about 3.5 ppbC) and HRM3 (about 7 ppbC),

also high concentrations near or above the 95th percentile, occurred an hour and 2 hours later at 1200

LST and 1300 LST. This was j~st one hour before and also during the 1300 LST 1-hour ozone exceedance

of 128 ppb ozone at the Houston East site. This sequence agrees with the back trajectories conducted at

the Houston East site starting at 1300 LST and tracing back two hours as mapped in Figure 2, above. In

addition, the "morning rush hour" peaks of ethylene and propylene concentrations at the Clinton, HRM3

and Deer Park sites were higher on August 26, 2011 compared to the surrogate day of August 27, 2009.

Finally, Figure 4 above, includes the ozone diurnal profile for the June 3, 2015 preliminary 130 ppb 1-

hour ozone exceedance day at the Houston East monitor, and this profile is very similar to the Houston

East August 26, 2011 ozone diurnal profile. For June 3, 2015, national fire activity was minimal with no

large fires reported in the Northwest or Lower Mississippi River Valley as depicted in Figure 5. The June

3, 2015 ozone exceedance day was similar to the August 26, 2011 ozone exceedance day in terms of

very low wind speeds recorded {0.2-1.8 mph resultant wind speed range), high maximum temperature

{91 deg. F peak temperature), and high solar radiation {0.78 Langley/min average).

8

Current Large Incidents June 04, 2015

1'0

• WOdRre • IMT1

,o • WUdRre • IMT2

Q'rs> HI {>

• WOdfire • Other

• WOdffre • NIMO . ·~..:­

l'R •

0 WHITEFISH LAKE 1 E) SPRING 0 MUD LAKE COMPLEX

E) SEVENTY MILE O GUADALUPE

Figure 5. Map of National Fires for June 4, 2015.

(4) Meeting the Definition of an Exceptional Event

According to 40 Code of Federal Regulations (CFR) S0.14(c)(3)(iv)(A), the demonstration to justify data

exclusion shall provide evidence that the event satisfies the criteria set forth in 40 CFR 50.lU). That is,

the event must affect air quality, must not be reasonably controllable or preventable, and must be an

event caused by human activity that is unlikely to recur at a particular location or a natura l event. The

definition of Exceptional event in 40 CFR 50.lU) also states that an exceptional event does not include stagnation of air masses or high temperatures alone.

The exceptional events demonstration package for August 26, 2011 at the Houston East (CAMS 1)

monitoring site fails to provide sufficient documentation meeting the definition of an exceptional event.

The exceptional event definition was not met because the event did not affect air quality, given that the

clear causal relationship and "but for" parts were not demonstrated. The dominant impact on air

quality at the Houston East monitor for the hour be.ginning at 1300 local standard time (LST) on August

26, 2011 was local anthropogenic emissions reacting photo-chemically with clear skies/ 90 degree

ambient conditions from close-by stationary industrial sources and mobile sources, not wildfires in

southeastern and northwestern U.S. States. These local anthropogenic emissions from close-by

9

stationary industrial sources and mobile sources in Houston, which are significant in abundance, are

released daily on a recurring basis. The TCEQ exceptional event package describes the Houston area as

follows in Chapter 1- Introduction: ..." A population over 6.2 million, one of the largest concentrations of

petrochemical refining and chemical production activities in the United States {U.S.), and plentiful

biogenic emissions from large tracts of oak forests all provide a complex mix of sources that can

contribute to exceedances of the ozone National Ambient Air Quality Standard {NMQS)...Elevated

ozone levels usually form in the HGB {Houston, Galveston, Brazoria) area under the persistent hot,

sunny, and relatively stagnant conditions associated with high pressure in the Gulf of Mexico during the

summer, in the presence of emissions from the mobile, area, and industrial sources in the area...the

large cluster of petrochemical industries and other sources in the Houston Ship Channel emit nitrogen

oxides (NOx) along with a variety of volatile organic compounds {VOC) precursors not typically found in

other urban areas ...The Houston East {CAMS 1) monitoring site is located east of downtown Houston

and n~ar a major interstate highway, Interstate 610 loop and major industrial sources." Adding to this,

recorded hourly resultant wind speeds at the Houston East site for August 26, 2011 from 0000-1300 LST

were all stagnant, ranging from only 0.2 - 4.1 miles per hour (mph). Under stagnant wind speeds local

emissions dominate the available emissions for o·zone production. Stagnant wind speeds and high

temperatures (the maximum temperature reached from 0000-1300 LST on August 26, 2011 was 98 degrees F) promote efficient photochemical production of ozone which often results in elevated

ambient ozone concentrations. And, as noted above, Section 40 CFR 50.lU) states that an exceptional

event does not include stagnation of air masses or high temperatures alone.

The exceptional event package from TCEQ did not provide sufficient evidence that the event was not

reasonably control.lable or preventable, or was an event caused by human activity unlikely to recur at a

particular location or a natural event. Some deficiency here arises from the failure to outline specific

fire locations that TCEQ believed contributed to the event. The evidence is also deficient to allow a

conclusion that potentially contributing sources were "reasonably controlled" at the time of the event.

(5) Schedule and Procedural Requirements

A specific schedule and procedural requirements an air agency must follow to request data

exclusion is identified in 40 CFR 50.14. The table below outlines the EPA's evaluation of these

requirements.

Schedules and Procedural ·Criteria

Reference Criterion Met?

Did the State provide public notification of the event?

40 CFR 50.14{c){l){i) Yes

Were flags and initial description placed on the data by July 1, 2012?

40 CFR 50.14{c){2){iii) Yes

Was the demonstration submitted by September 30, 2014?

40 CFR 50.14{c){3){i) Yes

Was the public input process followed and documented?

40 CFR 50.14{c){3){v) Yes

. 10

{6) Conclusion

In summary, the demonstration package fails to meet several of the necessary statutory and regulatory

criteria for an exceptional event. Specifically, the demonstration package fails to demonstrate a "clear

causal relationship" between the event and elevated ozone levels and it fails to demonstrate that the

exceedance would not have occurred "but for'' the emissions from the distant fires.

The demonstration package points to elevated particulate matter (PM) levels in Houston, back

trajectories, and satellite evidence in an attempt to show that the plume from the wildfires reached the

Houston area. While this evidence indicates the plume from the fires may have reached the Houston

area, it is not sufficiently conclusive and does not adequately provide evidence that the emissions from

the fire reached the Houston area in levels that could significantly influence ozone levels. The

increased PM levels are more likely attributable to the stagnation the Houston area experienced on that

day. Moreover, the back trajectories are attenuated and uncertain due to the long distances involved,

and satellite evidence does not clearly show the plume at the monitor in question.

The TeEQ also points to elevated levels of NOx as evidence that the plume reached the area and could

influence ozone levels, but elevated levels of NOx would be expected during a stagnation event, and 72%

of this NOx was "fresh" NOx that was evidently generated in the Houston area.

Even if the plume from a wildfire reached the Houston area, the demonstration package does not

adequately shQw that the ozone levels on the day in question would not have exceeded the standard

"but for'' emissions from the wildfires. Evidence of a "clear causal relationship" is deficient. For this

demonstration, the TeEQ proposed a surrogate day with similar meteorological conditions that was not

influenced by wildfires to show that the ozone levels were impacted by the wildfire event. Given the

complexity and number of variables that can impact ozone levels in Houston, finding an appropriate

surrogate day to allow for direct comparison requires careful consideration.

In this case, the surrogate day was different from the event day in key ways that likely resulted in lower

ozone on the surrogate day. In particular, solar radiation on the surrogate day was 42% lower than on

the event day, significantly lowering the sunlight available to drive the photochemical reaction. In

addition, concentrations of ethylene and propylene were much lower at monitors in the area of the

violations on the surrogate day. This could indicate that there were different operations at industrial

sources resulting in different release rates, or that mixing heights (a measure of how well pollution can

disperse vertically) on the days were different enough to cause the concentrations to be lower. In any

case, these highly reactive voes were not the product of the distant wildfires but were locally

generated. They are termed highly reactive voes because of their significant impacts on ozone

formation, and their presence in higher concentrations than the surrogate day-would be expected to

drive higher ozone concentrations.

In conclusion, the TeEQ's demonstration package does not show a clear causal connection between the

event and the monitored exceedance, and that the exceedance would not have occurred "but for'' the

wild fires. Related to these shortcomings, the demonstration is also unable to show that the event

"affected air quality'' at the time of the exceedance. Because the TeEQ's demonstration has not

11

satisfied several necessary criteria, following careful consideration of the weight of the available

evidence, the EPA is unable to concur with TCEQ's request to exclude ozone data on August 26, 2011

from 1300 LST. This non-concurrence does not constitute final EPA action regarding use of this data

when determining the attainment status of the area. A final action will arise only after EPA completes

notice and comment-on such a determination.

12