An Update on EPA Attainment
Modeling Guidance for the 8Hour Ozone NAAQS
Brian Timin
EPA/OAQPS/EMAD/AQMG
November 16, 2005
1
Status of Ozone Modeling Guidance

“Guidance on the Use of Models and Other
Analyses in Attainment Demonstrations for
the 8-hour Ozone NAAQS”


Original draft released in 1999
Released “Draft Final” version on February 17th,
2005
Comments


received in March
Final version released November, 2005
Available on EPA’s website at:

http://www.epa.gov/scram001/guidance_sip.htm
2
Status of PM2.5/Regional Haze
Modeling Guidance

“Guidance for Demonstrating Attainment of Air
Quality Goals for PM2.5 and Regional Haze”


January, 2001
Available on EPA’s website at:
http://www.epa.gov/scram001/guidance/guide/draft_pm.pdf

Revised draft will be available by the end of 2005


Final version in early 2006
Plan to incorporate final version of ozone and
PM2.5 guidance into a single document
3
Final Ozone Modeling GuidanceKey Updates








Screening test/unmonitored areas
Where is the attainment test applied?
Calculation of current/baseline design values
Language concerning transport
Which future year to model?
Weight of evidence/supplemental analyses
Minimum RRF threshold
Minimum number of days to model
4
Attainment Test in Unmonitored Areas


We eliminated the “screening test” and replaced it
with an “unmonitored area analysis”.
Use “model adjusted” spatial fields to estimate
ozone concentrations in unmonitored areas.

The spatial fields can be created using software
provided by EPA. We have a work assignment in
place to create the software and plan to perform an
example analysis
5
Attainment Test in Unmonitored Areas

Policy issue:
“While it is expected that additional emissions
controls are needed to eliminate predicted violations of the monitor
based test, the same requirements may not be appropriate in
unmonitored areas...... Due to the uncertainty of the analysis, at a
minimum, it is appropriate to commit to additional deployment of
ozone monitors in areas where the unmonitored area analysis predicts
future violations...... Violations of the unmonitored area analysis
should be handled on a case by case basis. As such, additional
analyses and/or tracking requirements may be needed depending on
the nature of the problem and the uncertainty associated with the
potential violation.”
6
Where is the Attainment Test Applied?

The issue is specifically addressed within the unmonitored
area analysis.
 It is assumed that the monitored attainment test will
be applied within the nonattainment area.
 Language concerning areas outside of the NAA:
“…The unmonitored area analysis for a particular nonattainment area
is intended to address potential problems within or near that
nonattainment area. The analysis should include, at a minimum, all
nonattainment counties and counties surrounding the nonattainment
area (located within the State)…. In large States, it is possible that
unmonitored area violations may appear in counties far upwind or
downwind of the local area of interest. In those cases, the distance to
the nonattainment area and ability of the modeling to represent far
downwind areas should be evaluated on a case by case basis.””
7
Calculation of Current/Baseline Design
Values

Continue to use the 5 year “weighted” average
design values as the basis for future year
projections.



The 3 design value periods which straddle the base
emissions year are averaged (at each monitor)
Supporting analysis of 10 years of DV data shows
that the weighted DV is much more stable than a
single DV
The calculation is consistent with CAIR
8
Treatment of Transport and Downwind
Impacts

Transport within the context of section 110
(a)(2)(d) and 126 are not mentioned.


Assumed that the NOx SIP call and CAIR take care
of this issue.
Transport is only mentioned in the context of
domain selection and boundary conditions.

Modeling domains will generally be large

Will be able to evaluate transport and the effect of emissions
controls from upwind areas
9
Which Future Year to Model?

Assumed that last year of 3 year period ending in
the ozone season before the attainment year will
be modeled (model 2009 for an attainment date of
2010)

Language does not imply that an earlier modeling
year is needed due to RACM

“… Since areas are required to attain as expeditiously as
practicable and perform a RACM analysis, results of the
analysis may indicate attainment can be achieved earlier, (e.g.,
2008). In this case, the timing of implementation of control
measures should be used to determine the appropriate
projection year....... The selection of the future year(s) to model
should be discussed with the appropriate EPA Regional Office
as part of the modeling protocol development process.””
10
Weight of Evidence/Supplemental
Analyses


The guidance recommends supplemental analyses
for all attainment demonstrations.
Less emphasis on modeling (CAAAC
recommendations)


Increased weight to emissions and ambient data
trends and analyses
Weight of evidence range redefined as 82-87 ppb

85 ppb becomes less of a bright line
11
Minimum RRF Theshold


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Analysis found that the 70 ppb threshold was too
low because the model was less responsive at
predicted concentrations as low as 70 ppb (the old
threshold).
Recommend increasing the minimum threshold to
85 ppb.
This removes some bias from the results and also
makes the resulting RRF more stable.
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Minimum RRF Theshold
Example: Daily Ozone RRF vs. threshold at a monitor in Baltimore
1.05
Relative Reduction Factor (RRF)
240030014
1
240030019
240051007
240053001
0.95
240130001
240251001
240259001
0.9
245100053
Power (240030014)
Power (240051007)
0.85
Power (240030019)
0.8
60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140
2001 Base Model Value (ppb)
Number of Days to Model



The draft guidance said to model “several days”
at each monitor
The new recommended minimum is 10 days
(with an absolute minimum of 5 days)
The number of days is based on an analysis
which examined the variability of relative
reduction factors (RRF) as a function of the
number of days in the calculation.

The results show that 10 or more days provides for a
relatively stable RRF.
14
Number of Days to Model
Example: Variability of RRF as a function of the number of
days in the calculation
As the number of days in the calculation increases, the potential
variability of the RRF decreases
Threshold/Number of Days

The minimum threshold and the number of days
are combined to get a hierarchy of the number of
days and thresholds used in any possible
situation.


This will handle all cases where few days are being
modeled and/or the modeled peaks are often below
85 ppb.
The minimum threshold can be as low as 70 ppb
and the minimum number of days at each monitor
can be as few as 5.
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Threshold/Number of Days
Number of Number of
Number of
Days > 85
Days in
Threshold
Days > 70 ppb
ppb
Mean RRF < 85 ppb?
50
15
15
No
20
12
12
No
12
11
9
6
3
7
3
6
1
0
10
10
9
6
N/A
Yes
Yes
Yes
Yes
N/A
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Next Steps


Continue work on the next draft of the
PM2.5/Regional Haze guidance
Finish development of MAT/SMAT
software


Includes spatial interpolations
Modeled adjusted spatial fields
18