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### Review of Documentation on Sacramento, CA 2008 Fire Exceptional

Events for Ozone

I. Introduction

In September 2009, the California Air Resources Board (ARB) submitted documentation to EPA in support of a request that EPA flag as exceptional various 1

- h our ozone concentrations at multiple sites in the Sacramento Regional Ozone Nonattainment Area

. ARB and Sacramento Metropolitan Air Quality Management District submitted

documentation that ozone concentrations were affected by smoke from wildfires through out northern California during June and July of 2008 ( see list of documentation reviewed at end of this document). The days covered by the documentation reviewed here

are listed in the table below . This document provides EPA Region 9 comments on

documen ts to clarify where additional analysis and/or documentation is needed to for EPA to exclude these data. It is not an EPA guidance document, nor a statement of EPA

concurrence or nonconcurrence on the events.

Monitor Day Hour O 3 (ppb)

Folsom 6/23/2008 1 3 129

Folsom 6/23/2008 14 151

Folsom 6/23/2008 15 161

Folsom 6/23/2008 16 132

Folsom 6/27/2008 15 129

Folsom 7/7/2008 15 145

Folsom 7/7/2008 16 166

Sloughhouse 7/7/2008 16 137

Sloughhouse 7/7/2008 17 148

Cool 7/7/2008 15 130

Cool 7/7/2008 16 128

Placerville 7/7/2008 18 139

Placerville 7/7/2008 19 136

Placerville 7/7/2008 20 136

Roseville 7/7/2008 14 132

Roseville 7/7/2008 15 134

Folsom 7/10/2008 11 129

Folsom 7/10/2008 12 150

Folsom 7/10/2008 13 141

Cool 7/10/2008 13 129

Placerville 7/10 /2008 17 137

Sloughhouse 7/25/2008 15 130Page 2 of 14

II. Background

Overview of the Exceptional Event Rule requirements

EPA’s Exceptional Event Rule (“EER”, 72 FR 13569, March 22, 2007) allows for ambient monitoring measurements that exceed the National Ambien t Air Quality Standards (NAAQS) to be excluded from NAAQS attainment/nonattainment decisions, if EPA determines they are caused by exceptional events (including natural events). Under the EER, a State submits documentation to EPA including a demonstration that the exceedance is due to an exceptional event. EPA has not finalized guidance to Regional Offices on evaluating the documentation. Determinations on exceptional events are made on a case by case basis by the EPA Regional Administrator, and indicated via the appropriate flag in the AQS database, generally accompanied by direct notification of the State.

Under 40 CFR 50.14 (c)(3)(iii), the State demonstration to justify data exclusion must provide evidence that:

A. The event satisfies the criteria set fo rth in 40 CFR 50.1(j) for the definition of an exceptional event, which are that the event: affects air quality; is not reasonably controllable or preventable, and is an event caused by human activity that is unlikely to recur at a particular location or a natural event;

B. There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the

area;

C. The event is associated with a measured concentration in excess of normal

histor ical fluctuations, including background; and

D. There would have been no exceedance or violation but for the event.

The demonstrations must fully meet all the above criteria to EPA’s satisfaction; failure to meet any one of the criteria will result in the n on

- concurrence of the event in question. The definition of an exceptional event provided in 40 CFR 50.1(j) also explicitly excludes stagnation of air masses or meteorological inversions, a meteorological event involving high temperatures or lack of precip itation, or pollution relating to source noncompliance. Exceptional events based on any of these conditions would not be eligible for exclusion

under the EER.

According to the EER preamble in the Federal Register (13569), generally the “affects air

qua lity” definition criterion will be satisfied by demonstration s of the “clear causalPage 3 of 14

relationship” and the “in excess of normal historical fluctuations” criteria . For wildfires, it is obvious that their emissions affect air quality in a general sense, incl uding particulate

matter and in some circumstances ozone . However, the demonstration should show that fire event had a causal relationship with each monitored exceedance of ozone in the exclusion request and that each exceedance was in excess of normal his torical fluctuations

.

The nonrecurring human activity/natural event criterion will generally be satisfied by wildfires, since they are by definition (preamble 13566) natural events, or else by arson, etc. which would be the result of nonrecurring human ac tivity.

Note that lack of precipitation is excluded an exceptional event. The rule preamble (13577, footnote 15) clarifies that for high wind events, demonstration of a truly “severe drought” could provide evidence for an exceptional event.

Due to the c omplexities of ozone chemistry and its interaction with meteorology, wildfire exceptional event demonstrations for ozone will generally be more difficult than for particulate matter. An exceptional events demonstration would therefore be strengthened

if i t include s a conceptual model of the exceptional event’s ozone impact. This is a qualitative description of how emissions, chemistry, and meteorology interacted to create elevated ozone concentrations; it is a narrative that helps tie together and is supp orted by the monitored evidence and analyses, but is also in itself a form of evidence for causal relationship. Further ideas for additional specific analyses to strengthen the evidence for meeting the rule criteria will be discussed below.

Also, per 50. 14(c)(3)(i) and (iv), the documentation package must show that the public comment process was followed, and must include any p ublic comments , or a statement that

there were none received

.

Finally, under 40 CFR §51.930, a State must take “reasonable action s” to mitigate the health impact of exceptional events. These include public notification when NAAQS exceedances are expected, education on actions individuals can take to reduce exposure, and “appropriate measures” to protect public health. Documentatio n of these is not required for EPA to make determinations on particular exceptional events, but can provide useful background information, and help assure EPA and the public that the mitigation requirements of the EER are met.

Overview of wildfire effect on ozone levels

The presence of smoke from a fire does not in itself prove that ozone increased; ozone could increase or decrease, and the effect could vary by time and place. Research has shown that fire can cause ozone, but an exceptional event demonst ration should address whether it did so for the particular event under review.

The mix of pollutants emitted during a fire depends on physical and chemical details of the fuel material, and the details of the burning process. The chemical composition of a smoke plume depends on many factors, including post

- emission atmospheric reactions, dilutionPage 4 of 14

rates and chemistry of the downwind air that mixes with the plume, photolysis rates, position within the plume, altitude, and smoke temperature. All of these dep end on time of day, fuel type and combustion stage. The downwind effect of a fire plume on ozone concentration depends also on the initial vertical extent of the plume, the meteorological and chemical conditions the plume encounters, and how far downwind the measurements are made. The USDA Forest Service has published a very useful overview of the effects of fire on air quality, including a discussion of fire plume chemistry (Sandberg et al. , 2002).

Fire emissions can increase ozone. Oxides of nitrogen (NO
x ) and volatile organic compounds (VOCs) emitted by fires can lead to ozone production in the plume itself, and can add to the ozone precursor load downwind. Fires emit oxygenated VOCs, an important

source of the radicals that allow ozone levels to bu ild up. Ozone formation in fire plumes is generally limited by the availability of NO
x (Jacob et al ., 1992; Cheng et al. , 1998; Junquera et al., 2005); ozone increases can be greater once the plume reaches a NOx

- rich urban area (Wotawa and Trainer, 2000; McKeen et al ., 2002). Lower NOx emissions in rural areas (such as northern California) could result in little additional ozone formation from the fire. The amount and spatial distribution of emissions could thus be important for demonstrating increased o zone due to fires.

On the other hand, fire emissions could decrease ozone. Ozone may decrease just downwind of a fire: as for any combustion source, the NO emitted by fires consumes ozone

to form NO 2 ("titration"). The particulates emitted by fire absor b and scatter light; this decreases photolysis of NO 2 and hydrocarbons, slowing ozone formation, and may occur over a large area or just nearby on the plume’s underside. The oxygenates emitted by fires can increase or decrease ozone production depending o n initial NOx and CO concentrations relative to background (Mason et al. , 2001). During plume travel, simple dilution, chemical loss, or deposition onto surfaces of ozone, NO 2 (via HNO 3 ), and hydrocarbons may decrease ozone and precursor concentrations to levels hard to distinguish from the background. A large influx of fire plume VOC radicals could "sink" NO
x into HNO 3 and unreactive organic nitrates, lessening the amount available to form ozone. Even if a fire plume does produce ozone, the air mass con taining it may simply displace urban air containing still higher ozone concentrations, for a net decrease.

Given the variation and complexity within any smoke plume, demonstration of an ozone impact requires information and analysis on the source emissio ns, meteorological conditions, and ambient measurements, and should include a conceptual model of how

these interacted to affect ozone concentrations during these specific events

.

III. Review of Evidence Submitted for High Ozone in the Sacramento Regional

Nonattainment Area Due to Wildfires

A. Criteria in 40 CFR §50.1(j) definition of exceptional event

As discussed in section IIA above, these criteria are generally intrinsically met by lightning

induced wildfires, if criteria that (a) there was a “clear causal relationship” between thePage 5 of 14

measured exceedance and the wildfire emissions and (b) the measured ozone

concentration was “in excess of normal historical fluctuations” are met

.

B. Clear causal relationship

Conceptually, for showing causal relationship , a demonstration of a fire exceptional event

should include evidence that (1) the fire existed, (2) its plume followed a transport path to the area in question and pollutants from the plume did in fact arrive in the area, and (3) pollution in the plume in creased ozone, consistent with the science of ozone formation and the conceptual model of the event, as discussed above in Section II.A. The causal part of a demonstration would be far more compelling if it evaluates and rules out alternative

causes for t he elevated ozone concentration, e.g. high temperature and stagnant winds. Without that analysis, correlation of smoke and ozone may be mistaken for causation.

The documentation does not have a conceptual model of these ozone episodes or of typical

ozone formation. A conceptual model of ozone formation in the Sacramento Metropolitan area around the monitors included in the demonstration, showing the typical magnitude of

1

- hour values and the daily pattern for all the monitoring sites in the area should b e included along with a conceptual model combined with supporting data from each day and place claimed to be affected by an exceptional event to explain how ozone values differ due to the presence of a fire plume. It should also address why only certain d ays have elevated ozone, despite the presence of a fire plume over multiple days. A conceptual model would help guide selection, organization, and evaluation of the available evidence in support of

the demonstration.

1. Evidence that the Fire Event Occur red

The following information was provided to demonstrate that the fire event occurred:

FEMA CA Wildfire Incidences Map (specific fires or monitors not noted) Description of the fire season in general and some of the more well noted public

actions that e nsued (e.g. the governor issuing States of Emergency).

The document should have clearer identification of the “event” that is claimed to be exceptional and to have caused the exceedances, e.g. which fire(s) contributed when. A table listing each fire sus pected of influencing air quality along with the fire's date, size, locations and distance relative to the affected monitors would serve to help clarify which fires are the contributing event

. It would also be helpful if m aps include d the relative

location s of the source fire(s), county boundaries, and air pollution monitors

.

2. Evidence that the fire plume reached the monitor

The following information was provided to demonstrate that the fire plume reached the monitor on the specific days:Page 6 of 14

Meteorolog ical discussion of days in question including days between fires and

exceedances

NOAA Satel l ite Fire Detection Map for June 27, July 7, July 25( neither fire location

nor monitors noted)

NASA Sate l lite Images for June 27, July 7 (box noting Sacramento Regio n moves, neither fire location nor monitors noted )

Time series of PM 2.5 maximum and O 3 1

- hour maximum from June 20

– July 25 for

Roseville and Folsom monitors. Table 2 shows the mean and maximum values for the highest 24

- hour average PM 2.5 concentration m easured during June and July at Roseville for the years 1999

- 2008 (2008 mean value is not listed) Included in attachments, although not discussed, are mete o rological maps and

tables of surface observations.

The provided information is useful, however, the items below are additional analyses that could strengthen the evidence for this criteria, or are requests for clarification or correction of the information that has already been submitted.

a. Other useful analyses could include forward and backward traject ories (e.g. from HYSPLIT), gridded wind fields, and/or a qualitative map with overall direction arrows supplemented with wind vectors at individual meteorological sites.

b. M aps should include the relative locations of the source fire(s), county boundaries,

a nd air pollution monitors

. Data from other monitoring sites between the fire and the site claiming the exceptional event exclusion could be included to show the progression of the fire plume to the monitor or area of monitors in question. Some

of the tec hniques ARB has used in past triennial assessments of ozone transport between air basins could be useful for this (ARB, 2001).

c. Satellite photos of June 27, July 7 and July 25 show what seem to be obvious smoke plumes from individual fires in the general vi cinity on these days

. Please describe what all the NOAA and NASA satellite figures are showing ( e.g. what wavelength, corresponding to what pollutant, column v ersus surface etc.) and how this might relate to the other days not shown. Also, t here is no ind ication of the locations of monitors or specific fire names, so it is difficult to tell which fire(s) may be affecting the monitors on the dates included in this package. Distinguishing plumes from

clouds and from terrain of similar color is difficult . H owever , when labeled with locations, and related to particular exceedance dates, the photos would be useful in making the case that fire plume(s) reached the monitors. Infrared imagery to show fire locations would also be a useful supplement. Satellite p roducts such as fire detects and aerosol optical depth, and column ozone could also be useful.

d. The l ast sentence on page 6 states “On this day, PM 2.5 measurements showed...”; please clarify which day of the June 23

- 27 event this refers to.

e. The s econd full paragraph on page 7 states that lowered visibilities continued to bring smoke in to the Sacramento Region. P lease clarify sentence to indicate the

intended causal relationship.Page 7 of 14

f. Page 9 contains a reference to Auburn as one of the sites exceeding the standa rd on July 7. Further references in the document to the July 7 flags use “Cool” to denote the monitor that is exceeding. Please clarify whether these refer to the same monitor or this is a typographic error, and revise the report to have consistent termin ology.

g. P lease clarify what criterion is being supported by the PM 2.5 information in Table 2 and explain why the mean value for 2008 is not included.

h. Levoglucosan measurements at stations throughout CA are available from ARB’s Monitoring and Laboratory Divi sion (MLD). These data should be included where

available as they would strengthen support for the causal connection with biomass combustion. Support for this would also be strengthened by inclusion of PM speciation data where available from Speciation T rends Network sites in California e.g. for evidence of increased organic carbon or increased ratio of organic to

elemental carbon.

3. Evidence that the fire plume increased ozone at the monitor

Much of the document ation focuses on a relationship between fires and smoke, or fires and

PM 2.5 , rather than between fire and ozone

, the object of the request. Overall, the impression given is that there was a lot of smoke around from various fires, which, based on the literature review, could have caused exceeda nces. There is no discussion of when fires do not increase ozone, or in what circumstances one would expect a 10 ppb increase rather than a much larger increase. Without explaining why one would expect the results from other studies to be relevant, the l ink to the cause of the exceedance in these events is not clear. In summary, this review documents that fire emissions can elevate ozone, however, without a discussion to say how this occurs or how it compares to the event days in question, it is not clea r that fire emissions did elevate ozone on these days in these

locations. Also

, it is clear from the documentation that the event is the fire and its
emissions, but it is not clear if the documentation is meant to demonstrate that the

exceedance was cause d by fire emissions alone or by a combination of fire emissions plus

urban emissions.

As mentioned above, EPA strongly encourages the development of a conceptual model for typical exceedance

- day ozone formation for comparison to the event days to support the causal connection argument. Using such a model for a framework could help tie together the timing of fire, emissions, plume transport, and ozone chemistry, and explains how these exceedance days differ from typical high ozone days, or from neighboring days within the period when smoke was present and high ozone concentrations were not. Without this

framework

, it is significantly more challenging to demonstrate a causal relationship

. Therefore, graphed information should be discussed more fully in the context of a conceptual model of the events to have any weight in terms of demonstrating a causal relationship, rather than correlation alone

.

Using this conceptual model and other analyses (see attachment for suggestions) , the

documentation for these e vents should discuss the following:Page 8 of 14

h ow the exceedance day s differ meteorologically from a typical day in general or from a typical day with elevated ozone

, meteorological factors that may partly explain the higher ozone, e.g. the day being

warmer or mor e stagnant than typical

, the timing of the plume generation relative to the timing of elevated ozone levels at specific monitoring stations , and how spatial and temporal patterns of ozone and its precursors differed between the exceedance days and typica l high ozone days . There is some comparison to an average (not a typical) diurnal temporal profile (e.g. Graph 5), but no analysis of why the profile takes the shape it does, and why it is different than neighboring days

that are also smoke

- affected.

The submitted documentation for this exceptional event request include s the following to
demonstrate that ozone increased at the monitor due to wildfire emissions :

g raphical comparisons of the diurnal pattern of PM 2.5 1

- hour maximum and ozone

1

- hour maximum for June 20

- July 25 for Roseville and Folsom monitors and

d iscussion of previous research

.

Graphical comparisons of the diurnal pattern of ozone concentration during the exceptional event request days and the average of the top five ozone days from 2005

- 2007 (see graphs 8

- 12) were included in the discussion of “ in excess of historical fluctuations

. ” EPA notes that similar plots may be more useful in supporting the clear causal relationship criteria. Additional suggestions about these plots are given in section C below. The following is a list of comments and clarification requests about the information presented to satisfy the criteria of the causal link between fire emissions and ozone exceedances at

these monitors on these dates.

a. Pages 6

- 13 indicate the correlation of the flagged days between the presence of smoke plumes from the fire with elevated PM 2.5 concentrations throughout the region and measured O 3 exceedances at the monitors that were flagged. (e.g. page 11, 12). To draw conclusions about cau sal relationship, comparisons could be made

to data from days not c laimed to be affected by fire, both historically and in the same year as the fire. Otherwise there is difficult to know whether the ozone diurnal pattern often looks like this, independent of fires (or conversely, whether PM 2.5 often looks like this, without being followed by ozone ).

b. It is not clear wh ich criteri on the argument on page 7 regarding the rate of O 3 concentration change is intended to support. In addition, a rguments based on h ow fast ozone changes is not convincing without comparisons to the normal or largest change at that site historically, during the same season or meteorological conditions.

c. Please clarify what evidence was presented to support the statement on page 12

that “Without the additional emissions from the wildfires, ozone concentrations

would not have exceeded the 1

- hour standard in the Sacramento Valley

. “ Likewise,

t he causal argument for July 25 was supported by a statement on page 12 that

met eorological condit ions and PM 2.5 concentrations indicate “that some wildfirePage 9 of 14

emissions were probably present” and that observations of haze at the airport indicates the presence of wildfire emissions. Both of these statements require greater substantiati on. d. Pages 11 & 13 indicate a contribution from urban (anthropogenic) emissions not

addressed later. Please include discussions of the contribution from anthropogenic precursors in your conceptual model framework.

e. The l ast sentence on pg 13 states that “Each of these ozone violations can be attributed to ozone precursor emissions from the wildfires.” This statement has not been supported

, since t here is no d iscussion (even qualitative) about how fire

emissions resulted in elevated ozone or violations.

f. Page 14 states that the design value for some of these sites had been decreasing in previous years and therefore would have been below the standard in 2008 if not for the fires. To make this argument more convincing, it should include a more thorough examination of why the tren d was expected to continue. This would require an analysis that at a minimum includes an evaluation of the emissions inventory for ozone precursors and a comparison of meteorology for this year versus previous years.

g. Pg 15 states that the impact of the wildfire is indicated by elevated PM 2.5 levels.

While the elevated PM 2.5 levels (along with other evidence) may indicate the presence of the primary fire emissions (or elevated secondary aerosol formation

from fire emissions ), this is indicative of t he fir e impact on PM 2.5 concentrations

measured at those sites . Without further discussion this concept does not indicate anything about the impact of the fire on ozone (as compared to PM 2.5 )

concentrations measured at those sites , as this criterion requires

. h. T he Nicolov 2008 citation is a presentation at a workshop and not a widely available (or peer reviewed) document and thus should be used with caution or eliminated

. Also, a statement that “biomass burning can significantly increase surface ozone

concen trat ions” does not provide a convincing causal link between fire and ozone concentrations for any other event without a discussion of when one would expect the fire to increase ozone or not, and which case is more relevant to the cases under

examination.

i. Plot s 1

- 2 do not sufficiently demonstrate a direct correlation between PM 2.5 and O 3 ,

nor a causal link. I ncluding a time lag between the two would potentially be more illustrative. This could be informed by the conceptual model of how ARB expects hourly PM 2. 5 maxima to relate to hourly O 3 maxima, and why. Nevertheless, there are times with high PM 2.5 without high ozone and high O 3 without high PM 2.5 , making the correlation less than convincing

. The presence of correlation does not indicate causation, partic ularly in the absence of a conceptual model of what is causing the correlation. j. The discussion of high PM 2.5 concentrations and related Table 2 on page 16 is not linked with ozone, so does not support a clear causal relationship

. k. Page 1 of the “Exceptional Event Justification” attachment states that “As a result, ozone precursors originating from these fires increased the Sacramento region’s ozone concentration causing violations of the 1

- hour ozone NAAQS...” This

statement is not supported, as there is no c ausality discussed. For example, a re thePage 10 of 14

precursors higher on these days than any other , or do they exhibit different spatial or temporal patterns?

The demonstration should be comparing similar meteorological conditions, for example, times during which t he air parcel is coming from the same locations, during strong, low inversions and passing through Sacramento to outlying monitor. Comparing and contrasting the exceedance days with similar days, typical high ozone days, and other non

exceeding nearby mon itors may help strengthen the evidence that the fire as an exceptional cause of the ozone exceedance and other scenarios.

Comparisons are sometimes made between the exceedance day and the average of other days, which is less meaningful than comparison to t ypical ozone exceedance days or days with similar meteorology, or to the envelope of a range of other days.

C. Concentrations in excess of normal historical fluctuations

The following information was submitted to demonstrate this criterion: Bar g raphs showing number of days in each 1

- hour maximum ozone concentration

bin for the 2008 ozone seasons compared to a historical data set (2005

- 2007 ozone seasons) for each monitor. The event days in question are noted as is the

concentration bin that is 3 abov e the mean of the historical data set. Diurnal plots of 1

- hour ozone concentrations for the exceptional event days and for the average of the top five days in 2005

- 2007. A plot of 1

- hour ozone maxima at Folsom and Sloughhouse from June 20

– July 25

Concent ration maps of 1 hour ozone maxima throughout the Sacramento Metropolitan area on the day before and day of event for two events (6/23 and 7/7)

The following lists our concerns about whether this criterion was met, some requests for clarifications and sug gestions for further analyses.

a. 40 CFR Part 51, Appendix W, 8.3.1.2 indicates 5 years of data is the minimum period needed to adequately represent the variability in ambient pollution concentrations

. Therefore, a data set comprised of 5 years may strength en the argument that it encompasses the expected range of variability

. Also, c omparisons to the historical data set may be more convincing if data reflected the same met eorological

condition s

. b. The text states that concentrations on the event days are grea ter than 3 standard deviations (above the mean of the historical data set, presumably) . S ince

concent ration data typically has a log normal distribution, this could be translated into a statement about the likelihood of the observed concentrations, given t he underlying historical distribution. Adding an analysis to include a discussion of this type of likelihood may add to the argument of why or how these concentrations are

“in excess of normal historical fluctuations”.

c. The 3σ line on g raphs 3

- 7 ( see pages 17

- 19) is at times lower than historical data

that are not flagged , with no discussion of why those historical should not bePage 11 of 14

considered for this criterion: Folsom: July 27; Sloughhouse: July 9, 25; Placerville: June 26 ; Cool: June 23 and 27, July 1. This evidence would also be strengthened by this type of discussion for the other points either on the 3 line or in the same

concentr ation “ bin ” as historical data.

d. Graphs 8

- 13 (diurnal plots of 1

- hour ozone concentrations for the exceptional event days and for the average of the top five days in 2005

- 2007) are analys e s that may be useful with some changes to supporting the clear causal relationship requirement. The evidence presented in those graphs could better satisfy E ER criteria with the following additions/changes :
i. There should be a discussion of the diurnal pattern on a normal, no n

- fire

affected, high ozone day

. ii. Comparing a single day to a five day average may be misleading since the average inherently smoothes out any variability in the variable of interest

– in this case the diurnal shape of the ozone concentration and timing of the peak

level of O 3 at a certain location. It is possible that comparing it to the range of top 5 days would be more illustrative.

iii. If av ailable, f

ive years of data would be more representative of historical

fluctuations

. iv. There should be a description of h ow is this is evaluated for days with incomplete data , e.g. 2008 data at Placerville.

e. P lease explain the reason for incomplete data at Pl acerville on the days requested for exceptional event exclusion as seen in Graph 11.

f. C larify the conclusion intended by the correlation of 1

- hour maximum ozone concentration between Folsom and Sloughhouse (graph 13 and accompanying text on page 23). As pr esented this correlation does not clearly demonstrat e that any of the requirements of the exceptional event rule are met.

g. Figures 6

- 7 (Concentration maps of 1 hour ozone maxima throughout the Sacramento Metropolitan area on the day before and day of event for two events (6/23 and 7/7) ) and corresponding discussion does not support “ in excess of

normal historical fluctuations ” without a discussion of how fast O 3 concentrations or extent can/has built up in this valley before. If revised, this evidence may b e more useful in demonstrating the “ clear causal relationship ” or the “ but

- for ” criteria.

h. The conclusions stated in the first paragraph on page 24 that the ozone concentrations on June 23 and July 7 are atypical need more clarification (atypical in

what wa y ? ) and justification (what evidence is being used to support what claim ? )

.

D. No exceedance but for the event

In order to demonstrate that there would have been no ozone exceedance but for the wildfire event, the District provided a regression analysis that empirically calculates the expected maximum 1

- hour ozone concentration in a county on a given day. The regression model for each county contains different meteorological variables and account for 55 to 79% of the variability in 1

- hour ozone and is b ased on 1997

- 2003 data.

Other relevant information that may support this requirement include qualitative causal arguments, using the conceptual model framework, documenting how the event days werePage 12 of 14

expected to be different than observed. It would also be possible to apply a photochemical model to this event, as was done for 2007 California wildfires (Pfister, 2008). This work was cited in the documentation ( page 5 ) as evidence that fire can produce ozone, but such modeling was not used to show that ozone was produced in the 2008 fires. Note that under the BlueSky modeling framework ( http://www.airfire.org/bluesky/ ), Sonoma Technology runs the CMAQ photochemical model twice daily for th e entire U.S., including estimates of fire emissions partly derived f rom satellite data.

The following lists our recommendations for the information that was p resented, as well as requests for clarifications.

a. Smoke contribution is estimated as the difference between the measured value and empirically calculated data from the regression model. Please address the assumption that smoke is the only variable that contributes to the difference between a forecasted day and the observed exceedance day.

b. There should be a discussion of the uncertainty or confidence limits in the mo del

results

. Please include a quantitative estimate of the uncertainty in the concentration calculated by the regression equations and confirm whether or not some of the higher estimates (particularly 118 ppb) are distinguishable from an

exceedance.

c. Ple ase also discuss whether it is reasonable to still use these models derived from

1997

- 2003 data and how well this model is predicting non

- fire impacted days in

2008. Does a regression model based on data from more recent years produce

similar results? A re there reasons one would expect the regression results to change (or not) as the ozone formation regime changes in the area due to emission reductions or changes ?

d. Please clarify if the study investigated the influence of artifacts of regression analysis, such as serial correlation, on the results.

e. Please discuss the spatial resolution of estimates from regression models. T he equations were formed using county

- wide data. Please explain more clearly how you use this information to derive a concentration at a certain site.

f. Please discuss whether the actual observed meteorological variables from each day could be used as input for the predictive formula, instead of the four predictions of meteorological variables, and whether one would expect this to reduce the uncertainty of the results.

g. The July 9 day at Sloughhouse does not meet the criteria used for other days, but it is still argued that it satisfies the “ but

- for ” argument. The estimated contribution from smoke ranges from

- 4.3 to 10.7 ppb

, m eaning tha t the concentration could

have been from 117.3 to 132.3. This is not clearly below the NAAQS. The discussion

continues and states that contributions calculated for nearby counties were larger

– therefore proving that the exceedance at this monitor was caus ed by the fire. This argument is unsubstantiated, especially given that these regression equations are done separately for each county and have different variables in them and therefore would not necessarily be comparable

. h. The argument that July 9, 2010 at Sloughhouse is one of the highest days, and

therefore satisfies the “ but

- for ” argument is not substantive . There are historicalPage 13 of 14

days that are higher and not flagged, as well as ten other days above the NAAQS

from 2005

- 2008. In addition, each criteria m ust be satisfied independently

, acknowledging that they may interrelate

. i. The existing documentation does not contain enough information to allow a full understanding of the results presented. It is not clear how this derived quantity

estimated smoke contri bution (page 3 of Ex. Event Justification) is used in comparison to the contribution as calculated as the difference between the observed and predicted value.

E. Evidence of Public Notice and Comment

D ocumentation included the public notice , including the proof of publication in six

newspaper s, which informed the public that documentation for this exceptional event

request was available for review

. The District included the two public comments they

received and their response to comments

.

I V. Other n otes and clarifications

1. There should be clearer identification in figures and elsewhere of event

- affected days and data as opposed to unaffected days, and in general labeling in figures should be improved. For example, Figure 1 and Figure 3 differ on whe re the box representing Sacramento is located.

2. Please include a map of the monitoring stations in the area, both stations that are included in the exceptional event request and others nearby.

3. Page 25 refers to information submitted in the 8

- hour O 3 except ional event package.

This information was not reviewed. If this information is relevant to the 1

- hour ozone exceptional event demo n stration , please submit it as a part of that package so

that it can be included in the administrative record for this review

.

4. Please refer to the discussion above to revise the outline of the rule requirements given on page 26. For example, t he bulleted items in the paragraph that starts "A clear causal relationship was demonstrated..." are not logical subpoints to the first sentence. They are assertions about other parts of the EE criteria. Also "significantly influenced" is not an element of the EE criteria.

V. Documents reviewed

" Exceptional Events Demonstration for High Ozone in the Sacramento Regional

Nonattainment A rea Due to Wildfires” Sacramento Metropolitan Air Quality Management District and California Air Resources Board dated July 8, 2009 and associated cover letter from Karen Magliano (CARB) to Joseph Lapka (EPA) dated September 17, 2009.

This documentation a lso included the following attachments:Page 14 of 14

Attachment 1 to ARB submittal (9/17/2009) Cover letter from Bridget Tollstrup, Program Coordination Division Manager, Sacramento Metropolitan Air Quality Management District, to Gayle Sweigert, California Air Resour ces Board, June 15, 2009 and attachments. The attachments are as follows: Exceptional Event Justification Appendnix A

– Regression Tool Development Documentation Appendix B

– Table of Estimated Smoke Contributions Appendix C

– Media and Public Advisories , Health Statements

Attachment 2 to ARB submittal (9/17/2009) This attachment provides an in

- depth discussion of the weather pattern for the three events: 1) June 23

- 27, 2008, 2) July 7, 9 and 10, 2008, and 3) July 25, 2008, The figures used to support the discussion include satellite images and aerosol optical depth , various meteorological surface observations and time series plots of ozone

, PM 2.5 , temperature, wind speed and direction.

Also included in Attachment 2 was a cover letter from Bridget Tollstrup to Gayle Sweigert, dated September 9, 2009, that included pu blic notices of the exceptional event package, proof of publication of these notices, written public comments and the District’s responses

to the comments.