Technical Guidance for Demonstration of Inter-
Precursor Trading (IPT) for Ozone in the
Nonattainment New Source Review Program
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EPA-454/R-18-004
May 2018
Technical Guidance for Demonstration of Inter-Precursor Trading (IPT) for Ozone in the
Nonattainment New Source Review Program
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, NC
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Table of Contents
1 Background 2
2 03 formation in the atmosphere 2
3 Modeling systems for estimating single source 03 impacts 3
4 Model application considerations for estimating 03IPT ratio 4
4.1 Model platform 4
4.2 Episode selection 4
4.3 Model domain and receptor placement 5
4.4 Project and credit source emissions 5
4.5 Model evaluation 5
5 Approach for establishing a case-specific 03 IPT ratio 6
6 General guidance for developing a case-specific IPT ratio for 03 precursors 6
7 Area Specific 03 IPT ratios 8
8 References 9
APPENDIX A. Illustrative example of a hypothetical project and credit source 03 interprecursor trading
scenario (example 1) 12
APPENDIX B. Illustrative example of a hypothetical project and credit source 03 interprecursor trading
scenario (example 2) 20
APPENDIX C. Illustrative example of a hypothetical project and credit source 03 interprecursor trading
scenario (example 3) 30
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1 Background
The EPA's implementing regulations at 40 CFR 51.165 and part 51 Appendix S allow air agencies to
establish inter-precursor trading (IPT) provisions for ozone (03) as part of their Nonattainment New
Source Review (NNSR) programs. See 40 CFR 51.165(a)(ll)(i) and part 51 Appendix S section IV.G.5(i). 03
IPT provisions allow any new or modified major stationary source, locating in an 03 nonattainment area
to satisfy the NNSR emissions offset requirements for 03 with emissions reductions of volatile organic
compounds (VOC) or nitrogen oxides (NOx) interchangeably, subject to all statutory and regulatory
offset requirements. This guidance and the supporting documents are not final agency actions and do
not create any binding requirements on permitting authorities, permit applicants, the EPA, or the public.
Further, this guidance applies only to IPT for the NNSR1 program
The CAA recognizes that emissions of both VOC and NOx contribute to ground-level 03 and, as such, are
considered precursors for 03. In turn, the EPA's NNSR regulations identify both NOx and VOC as
precursors for 03, and generally apply the control requirements for 03 to both precursors in 03
nonattainment areas. See 40 CFR 51.165(a)(xxxvii)(c)(l). However, emissions of NOx and VOC are not
considered interchangeable for all aspects of 03 control. For example, in certain situations for purposes
of meeting the CAA's reasonable further progress requirements, the NNSR requirements for 03 in the
CAA expressly require reductions in VOC emissions. Nevertheless, in NNSR permitting situations, with an
appropriate technical demonstration, it is possible to define the relationship between emissions of VOC
and NOx to establish ratios for using NOx decreases to offset VOC increases, or vice versa, that result in
an equivalent or greater air quality benefit for 03 in a particular 03 nonattainment area.
This document provides technical guidance that can be used by both air agencies and permit applicants
to estimate facility-specific impacts on 03 for purposes of 03 IPT by comparing the equivalency of NOx
and VOC precursor emission impacts on ground-level 03. The air quality models and approaches for
estimating single source 03 impacts are consistent with those described in the most recent update to
the Guideline on Air Quality Models (U.S. Environmental Protection Agency, 2017). Further, this
document does not specifically provide guidance for inter-basin precursor trading, but may provide
useful information for developing such a demonstration. Inter-basin precursor trading demonstrations
will be reviewed on a case-by-case basis by the reviewing authority and be done in consultation with the
appropriate Regional office.
2 11 '. i« >! mation in t! i u i > i 11 '
Air pollutants formed through chemical reactions in the atmosphere are referenced as secondary
pollutants. While some very small amount of ambient 03 may result from the release of 03 emissions
from certain sources, ground-level 03 is predominantly a secondary pollutant formed through
photochemical reactions driven by emissions of NOx and VOC. 03 formation is a complicated nonlinear
process that typically requires favorable meteorological conditions in addition to VOC and NOx emissions
(Seinfeld and Pandis, 2012). Clear skies (abundant levels of solar radiation) and stagnant air masses (low
wind speeds) increase 03 formation potential (Seinfeld and Pandis, 2012).
1 It does not address guidance and policy for other programs such as general conformity, CAA § 110(1),
Economic Incentive Program (non NNSR IPT related), Motor Vehicle Emissions Budget (MVEB for conformity,
Reasonable Further Progress (RFP), Aggregate Commitments and Contingency Measures.
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03 formation may be limited by either NOx or VOC emissions depending on the meteorological
conditions and the relative mix of these pollutants. When changes in ground-level 03 concentrations are
impacted by changes in NOx emissions, the 03 formation regime is termed "NOx limited". Alternatively,
the 03 formation regime is termed "VOC limited" when ambient 03 formation is sensitive to changes in
ambient VOC. The VOC-limited regime is sometimes referred to as "radical-limited" or "oxidant-limited"
because reactions involving VOCs produce peroxy radicals that can lead to 03 formation by converting
NO to N02 in the presence of sunlight. In a NOx-limited regime, 03 decreases with decreasing NOx and
has very little response to changes in VOC. The NOx-limited formation regime is more common in rural
areas of the U.S. and many urban centers tend to be VOC-limited (Seinfeld and Pandis, 2012). 03
formation regimes vary across most areas due to the different mix of NOx and VOC sources and also in
time, meaning the precursors limiting 03 formation can vary from day to day or even hour to hour in a
given area.
3 l\ 1" ii'i /sterns for est [ 1 ii'i in i i - ¦ 'j nni ¦ is
Quantifying secondary pollutant formation requires simulating chemical reactions in a realistic chemical
and physical environment. Chemical transport models (CTMs) treat atmospheric chemical and physical
processes such as chemistry, deposition, and transport. Eulerian photochemical models are three-
dimensional grid-based models that treat chemical and physical processes in each grid cell and use
Eulerian diffusion and transport processes to move chemical species to other grid cells (McMurry et al.,
2004). Photochemical models can provide a spatially and temporally dynamic and realistic chemical and
physical environment for plume growth and chemical transformation (Baker and Kelly, 2014; Zhou et al.,
2012). Publicly available and documented photochemical grid models such as the Comprehensive Air
Quality Model with Extensions (CAMx) (Ramboll ENVIRON, 2016) and the Community Multiscale Air
Quality (CMAQ) (Byun and Schere, 2006) model treat emissions, chemical transformation, transport, and
deposition using time and space variant meteorology.
When using a photochemical grid model, specific source impacts can be isolated through the use of
either source sensitivity or source apportionment approaches. The simplest source sensitivity approach
(i.e., brute-force change to emissions) would be to simulate two sets of conditions, one with all existing
emissions and one with the addition of a new source or a source of interest modified to reflect changes
in operation (Cohan and Napelenok, 2011). The difference between these model simulations provides
an estimate of the air quality change related to the change in emissions from the new or modified
source. Another source sensitivity approach to differentiate the impacts of single sources on changes in
model predicted air quality is the Decoupled Direct Method (DDM), which internally tracks the
sensitivity of the emissions from a source through all chemical and physical processes within the
modeling system (Dunker et al., 2002). Sensitivity coefficients relating source emissions to air quality
levels are estimated during the model simulation and output at the grid resolution of the host model.
Some photochemical models have been instrumented with source apportionment capability, which
enables the tracking of emissions from specific sources through chemical transformation, transport, and
deposition processes to estimate a particular source's impact on predicted air quality levels (Kwok et al.,
2015; Kwok et al., 2013). Source apportionment has been used to differentiate the impact from single
sources on model predicted 03 levels (Baker and Foley, 2011; Baker and Kelly, 2014; Baker et al., 2015).
DDM has also been used to estimate 03 impacts from specific sources (Baker and Kelly, 2014; Bergin et
al., 2008; Cohan et al., 2005; Cohan et al., 2006; Kelly et al., 2015) as well as the simpler brute-force
sensitivity approach (Baker and Kelly, 2014; Bergin et al., 2008; Kelly et al., 2015; Zhou et al., 2012).
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Limited comparison of single source impacts between models and approaches to differentiate single
source impacts (Baker and Kelly, 2014; Cohan et al., 2006; Kelly et al., 2015) has shown generally similar
downwind spatial gradients and impacts.
4 Mo i in 11 11 mi i11 r 111 ' 11 ~ . i in -in I- ¦ ¦ U' | i ¦ tio
A modeling protocol is intended to communicate the scope of the analysis and generally includes (1) the
types of analysis performed, (2) the specific steps taken in each type of analysis, (3) the rationale for the
choice of modeling system and episode(s), (4) names of organizations participating in preparing and
implementing the protocol, and (5) a complete list of model configuration options. For any IPT
demonstration, EPA recommends permit applicants first consult with the appropriate air agency and the
appropriate EPA Regional Office to develop a modeling protocol, and then conduct modeling consistent
with the protocol. Elements of a modeling protocol for these purposes are outlined in "Guidance on the
use of models for assessing the impacts of emissions from single sources on the secondarily formed
pollutants 03 and PM2.s" (U.S. Environmental Protection Agency, 2016b).
4.1 h
The most recently submitted 03 attainment demonstration modeling platform considered appropriate
for the purposes of interprecursor trading demonstrations by the reviewing authority would be the best
platform for a modeling demonstrtaion. This could include the last approved SIP demonstration, a more
recent submission (even if not yet approved), or modeling not used to support a SIP demonstration but
considered representative of the current air quality in the area and of sufficient quality that is
comparable to a model platform supporting a SIP demonstration. This approach of using the most
recent SIP demonstration modeling will help support consistency and comparability between multiple
demonstrations since the same modeling platform could be used by multiple applicants. Where multiple
modeling platforms are available for a particular area, the platform that is considered to be the most
reflective of the current atmosphere in that area would best account for growth in the area and the
changing mix of sources. For instance, if an area has a SIP modeling platform with a baseline year or
2011 and projected future year of 2018 and the current year is 2018 then the projected future year may
better represent air quality in that area. For areas that do not have an existing area attainment
demonstration modeling platform, a modeling platform that represents the current air quality and
conforms to the specifications outlined for attainment demonstration modeling could be acceptable.
The specifications for area attainment demonstration model platforms (e.g., horizontal grid spacing,
vertical resolution, non-project source emission treatment, etc.) are detailed in the "Draft Modeling
Guidance for Demonstrating Attainment of Air Quality Goals for 03, PM2.5, and Regional Haze" (U.S.
Environmental Protection Agency, 2014).
4.2 le selection
Meteorology is an important factor in the formation of many secondarily formed pollutants, both
directly (e.g., ammonium nitrate formation under cool, humid conditions) and indirectly (e.g., warm
temperatures and sunlight increase photochemistry and the availability of oxidants). A time period with
meteorology generally conducive to the formation of 03 is necessary. This means that time periods with
elevated ambient 03 at the source and receptors would be most relevant for an IPT demonstration.
Since 03 formation varies, even within a given area, an 03 season or multiple well characterized 03
episodes would be appropriate for modeling single source 03 impacts to capture the variety of wind
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flows and 03 formation regimes in a given area. Where multiple 03 episode/season simulations are
necessary for a single source assessment, it is not necessary they be consecutive. Multiple 03 episodes
may be necessary when a single 03 episode does not have 03 levels above the level of the NAAQS or if
the single episode does not capture all of the typical 03 formation regimes that are known in a particular
area (U.S. Environmental Protection Agency, 2014, 2016b). Using modeled days much lower than the
NAAQS may not be totally relevant for nonattainment related demonstrations such as interprecursor
trading as the 03 formation regime may be very different at those levels and not representative of how
the atmosphere might change at higher 03 levels.
4.3 h
Model domains include locations considered "ambient air," which may be located throughout the entire
nonattainment area for the IPT demonstration. Typically, the domain for an IPT demonstration will be
consistent with an existing 03 demonstration modeling platform. Receptor placement generally would
include area just beyond beyond property owned or controlled by the project source and evenly placed
throughout the nonattainment area. When a grid-based model is used to assess 03 impacts, all grid cells
intersecting the nonattainment area would be included in the IPT analysis to ensure the demonstration
reflects impacts in the entire area.
4.4 Project and credit source emissions
Project source annual emissions reflecting the amount of Emission Reduction Credits (ERCs) would be
most appropriate for the purposes to generating offsets under the CFR 51.165. In the uncommon
situations where the project source would be emitting the vast majority of its actual emissions on a few
days in a year an alternative emission rate may be used after consultation with the reviewing authority.
Credit sources that are part of the baseline model platform scenario can be modeled based on post-
construction conditions, and reflect the decrease in emissions sought for credit. If a credit source is not
part of the baseline model platform scenario then the credit source can be modeled based on pre-
shutdown conditions, which would be an increase in emissions from the baseline scenario.
4.5 I\ I-1"-! i ^ i11 ii- 'i i
It is important to use a model evaluation approach that is universally applicable to any single source
modeling system. Modeled 03 estimates are typically compared to observation data to generate
confidence that the modeling system is representative of local and regional air quality. For 03 related
projects, model estimates of 03 are be compared with observations in both time and space (Simon et al.,
2012; U.S. Environmental Protection Agency, 2014). Model performance metrics comparing
observations and predictions are often used to summarize model performance. These metrics include,
but are not limited to, mean bias, mean error, normalized mean bias, normalized mean error, and
correlation coefficient (Simon et al., 2012). There are no specific levels of any model performance metric
that indicate "acceptable" model performance. Model performance metrics are most useful when
compared with other model applications of similar geographic areas and time of year to assess how well
the model performs (Simon et al., 2012). Model performance for chemical transport models in the
context of single source impact assessments for well characterized project sources is intended to
provide confidence in the chemical environment of the source and does not provide specific information
about the amount or directionality of possible error in modeled source impacts.
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5 A| i-I > • « ii '> i ; 1 "i • specific O3 IPX ratio
Since 03 formation can vary spatially and temporally, an IPT ratio tailored to the proposed facility's
circumstances (involving the project and credit source(s) at known locations) will best reflect the
conditions in that area. In these situations, applicants conduct modeling of the proposed source's post-
construction conditions compared with the credit source(s) used for the emissions offset. This type of
facility-specific air quality modeling is similar to a Tier 2 demonstration and procedures for using models
for this purpose are outlined in "Guidance on the Use of Models for Assessing the Impacts of Emissions
from Single Sources on the Secondarily Formed Pollutants 03 and PM2.5" (U.S. Environmental Protection
Agency, 2016b).
EPA recommends that methods used to model project and credit source impacts be consistent with
guidance provided in "Guidance on the Use of Models for Assessing the Impacts of Emissions from Single
Sources on the Secondarily Formed Pollutants: 03 and PM2 5" (U.S. Environmental Protection Agency,
2016b). Since the reactivity of specific VOCs make some more important for 03 production, VOC
emissions get speciated to match the VOC emissions expected to be released from the proposed source.
The credit sources would be modeled such that operating conditions and locations reflect the credit
sources before controls or retirement unless otherwise directed after consultation with the reviewing
authority. It would not be appropriate to model the credit source emissions and stack release at the
same location as the project source unless the project and credit sources are actually co-located in the
post-construction scenario.
If the location and stack release characteristics of the credit emissions are not known, then a
conservative approach must be taken in the technical demonstration to ensure protection of the air
quality in the area. Conservative assumptions include stack parameters (e.g., low stack height), VOC
speciation (e.g., VOC modeled as not highly reactive), and the "credit source" location, which could be
considered by modeling the credit source at multiple locations in the area. The most conservative
estimate from each of these modeled "credit sources" would represent a value most protective of an
area when developing an IPT with the project source.
In situations where mobile source emissions may be allowed as credits, EPA believes the best technical
approach would be to model those emissions using the location and emissions release characteristics of
the specific project from which the credits originated. For instance, if a project was put into place to
change roadways to significantly reduce emissions then that particular road segment would be the
source of emissions.
6 - in 1 I ¦ "i.!! 11 ¦ " 1 •. I >i i"i case-s|" • II'I r > l"i 1 ¦
precursors
The general approach for developing an IPT demonstration is similar to that outlined for area-specific
interpollutant trading for precursors of PM2.5 (Fox, 2007; McCarthy, 2011). Illustrative examples using
hypothetical sources are provided in the Appendix. Model simulations include impacts from both the
project and credit sources are estimated. These impacts could be estimated in separate simulations or in
a single simulation using source apportionment or other instrumented technique (e.g., higher-order
DDM) that allows for differentiating source impacts. Here, the approach is described using the simplest
approach where three separate scenarios would be modeled.
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1) A baseline scenario where project source is operating at pre-construction conditions and credit
source(s) reflect actual conditions (e.g., not operating or operating at pre-construction
conditions);
2) A project source scenario, which is the same as the baseline scenario except the project source
is operating at post-construction conditions; and
3) A credit source scenario, which is the same as the baseline scenario except the credit source(s)
is operating at post-construction conditions if included in the baseline scenario or operating at
pre-closure conditions if not included in the baseline scenario.
Hereafter, scenario 1 will be referred to as the "baseline scenario", scenario 2 will be referred to as the
"project source scenario" and scenario 3 will be referred to as the "credit source scenario".
In order to establish that the proposed increase in emissions is comparable to the reductions from the
credit source(s) for an 03IPT ratio, the modeled results of the project source scenario and the credit
source scenario would be compared in grid cells or receptors within the nonattainment area using
NAAQS relevant averaging times (e.g. daily maximum 8-hr average) where the model is predicting
elevated 03 (U.S. Environmental Protection Agency, 2016b). The general steps for estimating project and
credit source sensitivities over an area follow.
First, estimate the modeled maximum daily 8-hr 03 (MDA8) at each receptor for each simulation day of
each of the baseline, project source, and credit source scenarios.
Second, estimate project source impacts by subtracting the project source scenario MDA8 values for
each receptor and modeled day from the corresponding baseline scenario MDA8 values. If the credit
source was not part of the baseline scenario, then estimate the credit source impacts by subtracting the
credit source scenario MDA8 values for each receptor and modeled day from the corresponding
baseline scenario MDA8 values. If the credit source was in the baseline scenario and was modeled with
emission reductions matching the credit emissions amount, then subtract the baseline scenario MDA8
values from the credit source scenario MDA8 values at each receptor and modeled day.
Third, match the MDA8 values estimated by the baseline (step 1) and project source (step 2). Next,
match baseline (step 1) and credit source scenarios (step 2) for each receptor and model simulation day.
Fourth, remove receptor-day pairings where either the project source or credit source impacts are
negative (i.e., a disbenefit to air quality). Situations in which the increased emissions from the project or
credit source result in a negative contribution are not included in the calculation of an 03 IPT ratio. Next,
remove receptor-day pairings where source contribution is < 1 ppt. Additionally, receptor-day pairings
where the baseline modeled MDA8 is less than a specific value may be removed where appropriate and
technically justified (e.g. 65 ppb or other episode-specific/appropriate value to emphasize impacts on
days where the model predicts relatively elevated 03 levels). A lower threshold may be necessary in
some situations where there are few modeled days in the area at that level which means a slightly lower
threshold may be needed to develop a robust respresentation of impacts. If modeled 03 levels are low
throughout the episode then that episode is not appropriate for this type of demonstration. Selecting
modeled receptor-days with elevated 03 is important for NNSR demonstrations since the relationship
between the project and credit source is most relevant for 03 levels closer to the level of the NAAQS.
Using modeled days where levels are half or lower than the NAAQS for instance may not be relevant
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because the 03 formation regime may be very different at those levels and not representative of how
the atmosphere might change at higher 03 levels.
Fifth, for each modeled day, sum the project source contributions over all receptors (grid cells) meeting
the criteria in step 4 of this process. Then sum the credit source contributions over all receptors (grid
cells) meeting the criteria in step 4 of this process. Since emissions sensitivity will vary spatially, it would
not be fully protective of the air quality in a given area to only consider impacts at monitor locations.
Sixth, sum the daily impacts over all days in the episode or modeling period for both the project and
credit sources. The ratio of the episode or modeling period summed impacts represents the relative
impacts of the project and credit sources on 03 in that particular area. It is unlikely that the impacts will
be exactly the same (i.e., a 1-to-l relationship) so this ratio provides information about how much
additional (or less) credit emissions may be needed to offset the change in project source emissions.
Before selecting a specific 03IPT value, conduct quality assurance of the resulting ratio and evaluate the
appropriateness given the nature of 03 precursor emissions sources and chemical formation in the area
of interest. This evaluation will likely require area-specific emissions inventory information and observed
ambient data for 03 and 03 precursors. One way to provide confidence in the modeled impacts would be
to qualitatively determine whether the impacts conform to the conceptual understanding of the NOx
and/or VOC limited formation across the area. This means that in an area that is NOx limited the
introduction of VOC emissions would not lead to as much 03 formation as the introduction of new NOx
emissions and vice versa in VOC limited areas. Another option for quality assurance may be comparison
with other single source modeling done for that area or similar areas to support Tier 1 PSD
demonstration tools (U.S. Environmental Protection Agency, 2016a).
A narrative that shows that the increased emissions sought by the applicant for the project source will
not adversely impact a particular population in the area either through indirect chemical reactions
forming 03 disproportionally in that area or that increased exposure to the precursor itself or toxic
components (e.g., formaldehyde) will not lead to adverse health effects in the area is an important
element of an IPT demonstration. For example, a hypothetical situation where a new refinery or paint
coating facility in an urban core area seeking NOx credits to offset increased VOC emissions. This result
may not cause violations of the 03 NAAQS, but may result in increased exposure to air toxics in the
urban core area.
If there are questions about applying these steps, air agencies can contact their Regional Office for
further technical consultation.
7 /1 s « j cific ! < 11 i i .
The previous section (Section 6 above) provided guidance on developing case-specific IPT ratios for 03
precursors. This section provides an approach for generating area-specific, i.e., "default" 03 IPT ratios,
which involves an analysis of the existing technically credible 03 attainment demonstration (or similar
quality) modeling data, emission inventory data, and ambient monitor data to determine whether an
area or sub-sections in an area could be characterized as either NOx or VOC limited for 03 formation.
Ambient data would typically include co-located NOx and VOC measurements to determine the
relationship between these 03 precursors for an area. In addition to considering ambient and modeling
data, emissions information is considered useful when determining whether an area's 03 formation is
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N0X or VOC limited. This determination may be easier for smaller metropolitan areas that do not have
large NOx emissions sources (e.g. industrial point sources, transportation, etc.) and that do have large
regional VOC sources (e.g., biogenic VOC) or large highly reactive VOC sources.
This section provides information about how NOx and VOC single-source impacts on downwind 03 could
be used to estimate an IPT ratio protective for a given area. Depending on the size of the nonattainment
area, the prescribed area within which offsets need to be obtained may be smaller than the total
nonattainment area, i.e., a defined sub-area, in order for emissions precursors to have a similar impact
on 03. However, even if there is some variation in impacts within an entire nonattainment area, the
ratio would be developed to be conservative enough to address any IPT used anywhere in the area as an
alternative to generating sub-area ratios.
Since emissions sensitivities typically vary across an area, an area-specific 03 IPT ratio would be most
protective for an area when based on refined modeling that follows the approach outlined for a NNSR
credit demonstration in this guidance. However, rather than modeling a specific post-construction
scenario for existing project source facilities, the approach for this purpose involves modeling multiple
hypothetical sources with varying emission rates and stack release characteristics typical of sources in
the area or region. These sources would need to be located in different parts of the area to account for
differences in sensitivities that may be possible when considering air quality impacts of sources located
in different parts of the area. The overall approach for hypothetical source impact assessment would be
generally similar to that provided for a tier 1 demonstration tool such as MERPs (U.S. Environmental
Protection Agency, 2016a). Choices made for the number, placement, and type (emission levels and
stack release characteristics) of hypothetical sources are important and EPA recommends selection be
done in consultation with the permitting authority. Multiple hypothetical sources would be modeled in a
particular area and the impacts from each would be compared then the most conservative ratio selected
as the default ratio for that area.
8
Baker, K.R., Foley, K.M., 2011. A nonlinear regression model estimating single source concentrations of
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Pollution Research 7, 122-133.
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offsets. Memorandum to EPA docket # EPA-HQ-OAR-2003-0062
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analysis in a photochemical model. Atmospheric Environment 80, 398-407.
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performance statistics published between 2006 and 2012. Atmospheric Environment 61, 124-139.
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Air Quality Goals for Ozone, PM2.5, and Regional Haze.
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precursors (MERPs) as a tier 1 demonstration tool for permit related programs.
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from single sources on secondarily formed pollutants ozone and PM2.5. EPA 454/R-16-005.
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APPENDIX A. Illustrative example of a hypothetical project and credit
source O3 interprecursor trading scenario (example 1)
The following example is intended only to provide an illustrative example of how model results for
specific sources could be used in the framework provided in this guidance document toward estimating
equivalency in terms of 03 formation to inform an IPX ratio.
Multiple hypothetical sources were modeled for a high 03 period in the northeast U.S. during July 2011.
This hypothetical example considers source 4 the project source and source 2 the credit source (see
Figure 1 left panel). The project source is seeking to offset 500 tpy of NOx emissions with 500 tpy of VOC
emissions from the credit source. MDA8 03 impacts from both the project and credit source were
estimated for each day of the July 2011 episode using the CMAQ model applied with 4 km sized grid
cells and 35 layers to resolve the vertical atmosphere from the surface to the tropopause. The extent of
the 4 km model domain and area of interest for this hypothetical demonstration are shown in Figure 1
(right panel).
4 kin model domain (4NYPA2)
Figure 1, Hypothetical sources used in this analysis (4 and 2). The model domain and hypothetical
area of interest (shown in orange) in the right panel.
12
-------
Daily absolute impacts for the project source are shown in Figure 2 and credit source in Figure 3.
Source 4 500 TPY NOX - July 14. 2011
Source 4 500 TPY NOX - July 2, 201
Source 4 500 TPY NOX - July 6, 201
Source 4 500 TPY NOX
Source 4 500 TPY NOX-July 12, 2011
Source 4 500 TPY NOX - July 9.2011
Source 4 500 TPY NOX - July 11. 2011
Figure 2. MDA8 03 impacts for source 4 (project source) for 500 tpy of NOX.
MDA8 03
1700 1800 1S00 2000
MDA8 03
1700 1800 1900 2000
MDA8 03
1700 1800 1800 2000
MDA8 03
MDA8 03
1800 1900
MDA8 03
1800 1900
MDA8 03
MDA8 03
MDA8 03
1700 1800 1900 2000
MDA8 03
1700 1800 1900 2000
MDA8 03
MDA8 03
1800 1900
MDA8 03
MDA8 03
MDA8 03
13
-------
MDA8 03
MDA8 03
MDA8 03
MDA8 03
Source 4 5QD TPY NOX - July 24, 2011
Source 4 500 TRY NOX - July 22.2011
MDA8 03
MDA8 03
MDA8 03
MDA8 03
0.08
8
0.06
8
0.04 w
0.02 8
0.00
0.08
8
0.06
8
0.04
Source 4 500 TPY NOX - July 27.2011
MDA8 03
MDA8 03
MDA8 03
MDA8 03
0.08
0.06
0.04 N
0.02 |
0.10 8
0.08
0.06
0.04 ™
0.02 |
0.00
Source 4 500 TPY NOX - July
ppb
1700
1900
2000
14
-------
Figure 3. MDA8 03 impacts for source 2 (credit source) 500 tpy of VOC.
MDA8 03
Source 2 500 TPY VOC - July 1. 2011
\\
,flY?
0.10 |
0.08
1
- 0.06
0-04 8
- 0.02 S
- 0.00
ppb ®
MDA8 03
Source 2 500 TPY VOC - July 2. 2011
1 -J
0.10 |
0.08
I
0.06
8
0.04 N
0.02 8
0.00
MDA8 03
Source 2 500 TPY VOC - July 3. 2011
/
I- 0.00
ppb c
MDA8 03
Source 2 500 TPY VOC - July 4. 2011
-m
1700 1800
1700 1800 1900 2000
1900 2COO
1700 1800
MDA8 03
Source 2 500 TPY VOC - July 5. 2011
m
rbW /
\ A
0.04
0,02 S
MDA8 03
Source 2 500 TPY VOC - July 6. 2011
MDA8 03
Source 2 500 TPY VOC - July 7. 2011
>n
1900 2000
1700 1800 1900 2000
MDA8 03
Source 2 500 TPY VOC - July 13, 2011
1l\
0 10 |
- 0.08
i
0.06
§
- 0.04
I- 0.00
ppb
MDA8 03
Source 2 500 TPY VOC - July 14, 2011
&
MDA8 03
Source 2 500 TPY VOC - July 15. 2011
0.-I0 |
- 0.08
S
- 0.06
- 0.04 ~
MDA8 03
Source 2 500 TPY VOC - July 16. 2011
f
fi\v
?AIH
—i 1 1
1700 1800 1900
1700 1800 1900 2000
1700 1800 19CO
1700 1800 1900 2000
15
-------
MDA8 03
Source 2 500 TPY VOC - July 17, 2011
MDA8 03
Source 2 500 TPY VOC - July 18, 2011
- 0.06
- 0.04
0.02 S
MDA8 03
Source 2 500 TPY VOC - July 19. 2011
MDA8 03
Source 2 500 TPY VOC - July 20,2011
0.10 | _
- 0.06
- 0.06
- 0.04
- 0.00
1700 1600
MDA8 03
Source 2 500 TPY VOC - July 21. 2011
A :% Jl ,
MDA8 03
Source 2 500 TPY VOC - July 22, 2011
1700 1800
- 0.10 g
V/f
y i
J&\\
3
MDA8 03
Source 2 500 TPY VOC - July 24, 2011
1700 1600 1900
1700 1600 1900
- 0.10 g
D.02 § -
I- 0.00
ppb
1900 2000
MDA8 03
Source 2 500 TPY VOC - July 25.2011
MDA8 03 MDA8 03 MDA8 03
Source 2 500 TPY VOC - July 26, 2011 Source 2 500 TPY VOC - July 27, 2011 Source 2 500 TPY VOC - July 28.2011
0.10
- 0.10 |
- 0.04
0,02 S
- 0.02
- 0.02
1700 1800 1900 2CO0
1700 1800
1700 1800 1900 2000
MDA8 03
Source 2 500 TPY VOC - July 29. 2011
- 0.06
1700 1800 1900 2000
16
-------
Figure 4 shows the ratio of MDA8 03 project to credit source impacts where multiple conditions are
satisfied. First, only impacts greater than 1 ppt are shown; second, only impacts are shown where the
baseline bulk model 03 prediction was greater than 60 ppb; third, only impacts are shown where the
grid cell intersects the area of interest (shown in Figure 1 as the orange colored cells).
Figure 4. Ratio of project source to credit source impacts where multiple conditions are satisfied.
MDA8 03
Sourca 2 500 TPY VOC - Julv 1.2011
MDA8 03
source 2 500 TPY VOC - Julv 2. 2011
MDA8 03
Source 2 500 TPY VOC - Julv 3.2011
MDA8 03
Source 2 500 TPY VOC - Julv 4.2011
8 -
8 -
8 "
- 3
§ ¦
8 -
- 3
8 ¦
8 ¦
- 3
8 -
- 3
8 -
I -
8 -
1 "
- 0
g ¦
1.
- 0
8 ¦
1 -
- 0
- 0
MDA8 03
Source 2 500 TPV VOC - July 5.2011
MDA8 03
Source 2 500 TPY VOC - Julv 6.2011
'
MDA8 03
Source 2 500 TPY VOC - July 7,2011
MDA8 03
Source 2 500 TPY VOC - Julv 8,2011
8 -
8 ¦
8 -
8 -
•<*
- 4
8 -
- 3
8 -
- 2
8 -
8 ¦
8 -
- 3
8 -
- 2
8 -
8 ¦
8 -
- 3
8 •
- 2
8 -
8 -
- 3
- 2
"
MDA8 03
Source 2 500 TPY VOC July 9,2011
MDA8 03
Source 2 500 TPY VOC - July 10.2011
MDA8 03
Source 2 500 TPY VOC - Julv 11.2011
MDA8 03
Source 2 500 TPY VOC - July 12.2011
S -
S ¦
g -
§ -
t
8 -
- 3
8 "
- 2
a .
8 ¦
I -
- 3
8 ¦
- 2
8 -
8 -
- 4
8 -
- 3
- 2
8 -
8 ¦
- 3
- 2
MDA8 03
Source 2 500 TPY VOC - July 13,2011
MDA8 03
Source 2 500 TPY VOC - July 14.2011
MDA8 03
Source 2 500 TPY VOC - July 15.2011
MDA8 03
Source 2 500 TPY VOC - July 16. 2011
§ -
I -
8 ¦
- 3
1 "
I ¦
- 3
I '
8 ¦
- 3
.Jd
- 3
S -
1 -
- 0
S -
8 "
- 0
Ll-ci j
- 0
. « « «.
* - « « «
•
- - - - -
» „ „»
17
-------
MDA8 03
[500 TPY VOC - July 21.2011
MDA8 03
Source 2 500 TPY VOC - ..
MDA8 03
) TPY VOC -July 25,
MDA8 03
: 500 TPY VOC-.
MDA8 03
Source 2 500 TPY VOC July 29. 2011
Daily metrics relating MDA8 project and credit source impacts are shown in Table 1. These impacts are
based on episode days and grid cells meeting multiple criteria. First, only impacts greater than 1 ppt are
shown; second, only impacts are shown where the baseline bulk model 03 prediction was greater than
60 ppb; third, only impacts are shown where the grid cell intersects the area of interest (shown in Figure
1 as the orange colored cells). For each day, the ratio is provided of the sum of project source impacts
divided by the sum of credit source impacts over all cells meeting the criteria detailed above. The
number of cells meeting the criteria is also provided along with that value being expressed as the
percentage of all cells in the area of interest (the total number of ceils examined for this analysis). The
number of cells used in the analysis varies due to varying 03 production in the area of interest from day
to day during this period of time. At the bottom of Table 1, the ratio represents the ratio of episode total
impacts and is not the average of the daily ratios.
18
-------
Table 1. Project and credit source daily impacts, number of cells used, and the percentage of cells used
in the area of interest.
Episode Day
Sum of
Project
Source
MDA8 03
Impacts
(ppb)
Sum of
Credit
Source
MDA8 03
Impacts
(ppb)
Ratio of
project to
credit source
impacts
Number of
cells used for
project
source
impact sum
Project
source
impacted
cells divided
by total cells
in area of
interest x
100
Number of
cells used
for credit
source
impact sum
Credit source
impacted
cells divided
by total cells
in area of
interest x 100
1
0
1.35
0
1
0.1
88
8.7
2
0
1.23
0
0
0
57
5.6
3
0.51
0.37
1.4
26
2.6
33
3.2
4
0
3.19
0
1
0.1
64
6.3
5
0.53
2.8
0.2
50
4.9
93
9.2
6
0.19
0.13
1.5
21
2.1
20
2
7
1.72
0.15
11.5
39
3.8
28
2.8
8
0.12
1.22
0.1
46
4.5
190
18.7
9
0.12
1.09
0.1
14
1.4
61
6
10
3.44
0.77
4.5
310
30.5
196
19.3
11
0.48
0.18
2.7
20
2
28
2.8
12
0.25
0.07
3.6
6
0.6
5
0.5
13
0
0.19
0
0
0
9
0.9
14
0.05
0.34
0.1
12
1.2
21
2.1
15
0
0.26
0
0
0
31
3.1
16
0.43
0.07
6.1
21
2.1
21
2.1
17
0.09
0
Inf
2
0.2
0
0
18
0.16
0.06
2.7
16
1.6
16
1.6
19
3.55
10.09
0.4
119
11.7
241
23.7
20
2.53
3.14
0.8
828
81.5
401
39.5
21
0.34
0.21
1.6
21
2.1
30
3
22
1.33
0.06
22.2
26
2.6
19
1.9
23
1.04
0.07
14.9
33
3.2
26
2.6
24
6.18
2.61
2.4
249
24.5
225
22.1
25
2
1.06
1.9
757
74.5
178
17.5
26
0.66
1.29
0.5
16
1.6
105
10.3
27
0
1.39
0
0
0
93
9.2
28
0.16
1.66
0.1
64
6.3
90
8.9
29
0.52
0.32
1.6
30
3
27
2.7
Sum
26.4
35.37
0.746
19
-------
APPENDIX B. Illustrative example of a hypothetical project and credit
source O3 interprecursor trading scenario (example 2)
The following example is intended only to provide an illustrative example of how model results for
specific sources could be used in the framework provided in this guidance document toward estimating
equivalency in terms of 03 formation to inform an IPX ratio.
Multiple hypothetical sources were modeled for a high 03 period in the northeast U.S. during July 2011.
This hypothetical example considers source 9 the project source and source 1 the credit source (see
Figure 1 left panel). The project source is seeking to offset 500 tpy of NOx emissions with 500 tpy of VOC
emissions from the credit source. MDA8 03 impacts from both the project and credit source were
estimated for each day of the July 2011 episode using the CMAQ model applied with 4 km sized grid
cells and 35 layers resolved the vertical atmosphere from the surface to the tropopause. The extent of
the 4 km model domain and area of interest for this hypothetical demonstration are shown in Figure 1
(right panel).
4 km model domain (4NYPA2)
Figure 1, Hypothetical sources used in this analysis (9 and 1) the model domain and hypothetical area
of interest shown in orange).
Daily absolute impacts for the project source are shown in Figure 2 and credit source in Figure 3. Source
impacts are only shown where modeled bulk MDA8 03 was greater than 60 ppb.
20
-------
Figure 2. MDA8 03 impacts for source 9 (project source) for 500 tpy of NOx.
MOA803
$auoa J 900 TPY MQJC. JUv 1.2Q11
MDA0 03
&QWOI viiM TPY MIK - -Uy2 XI11
MO AG. 03
Scsxcb U SOU IPY MUX - Jblf 3,4011
MO AG 03
ScuM uioo rPY now - jLtY*,2aii
E -
- 0» b -
- 0 2# B _
- a* | .
- 024
B -
- uac
6 -
- ~ 14
4,.
- 020
6 -
- a is
/
- 020
S -
- 0 -IS
- 020
- 01ft
" "
016 "
- 0 10 *
- a « "
- 010
V -
\ 2k i
- aos » -
- a as
- o« 5 -
- DM
- 0 06 ? -
ooo
- 005
- O OO
into tra in hi
I hu mi una sa
¦aui m idj jin
MDAB03
5qug* 3 500 TPY MOX - Jul* 5. SO11
MDAH03
SlMu* 3SCM TPY *CX - Jl4v6 £011
MDA& 03
Sc-joa 9 W0 TPY NOW - Jl* 7. KJI1
MDAfl G3
S4
1 02©
U" 01«
- a» 8 '
• 020
R -
- 0 18
- 0 10 *
- 0 20
R -
- 0 15
- 0 10 ^
- 020
- (L15
- 010
E ,
- a» | -
- aoo
"? V>
- DM f -
- a 00
- a» b -
- (1 CD
- 0C9
- OOO
taw w* i«n ami
ian ¦*»« hod s*i»
iwi i«p linn atm
i*n wi i *m em*
MDA6 03
sauDi-Mtta IPYMCu.- Jutva,2(T11
MDA6 03
•ZurcmQ 6al JW NOX - July 10 3013
MDA5 03
&au a VI SlKJ W'f MCOt - Xtf 11 3)11
MO AS 03
Snra U &IE1 IW NOl - Arj 13 3011
E -
- a» g -
¦ 0 » B -
- il» e -
\
• Q2ft
i -
H ¦
- uit
fi -
- a ii
- 010 *
- 0 50
6 -
- 0 1ft
- 0 10 *
i. A
- 020
S -
- 0 1ft
- 0 10 *
- 020
- 01ft
- Q10
R .
v S'U:
Q05 ? -
- aoo
- a« * -
¦ 0.00
- aos ? -
- ooo
- 0O5
- OOO
ifxt> mi i hi uit
i *ni mi tiu xOB
ita tarn i«m am
lU tail • mil mi
MDAB03
Sonic* 9 5® TW NCX - Ah 13 30* t
MDAH 03
Sk)uf<*9 50DTjTr-fol-jLi>r 14 20M
MDAE 03
5auiw9 5KiTPVN©«- A* SS.»M
MDAH 03
3cut* 9 500 UPK NO: - Jkh U 201»
H -
025 * .
- 02S 1 _
- 025 g _
- 025
R -
- 020
- 015
- 020
R -
- 0.16
- 020
R -
- 0 15
- 020
- 015
fi -
1
- 01( *
jY** J
- a io *
- 1 10 "
-010
B -
¦
- 0» ® -
- 000 § -
- 006 S= -
- aoD
- 0«
1
- OCXS
- a 00
• OOO
i*b sen iftn 331
inn «!« ihb ras
r*r im iion mm
iwi ma im mi
21
-------
B :
025 g .
< & ^
- 020
S
R -
- 0.15
6 -
_ £ -
s .
x 1?\S
- 0H5 !• -
J
- oxo
1*13 HOT IB 3BE
MDA8 03
H11.1 It-V NT.* AKr Irt JQVI
MGA6 03 MDA3 03
vnn» g t>:i lPYHty* . **> iv». am s«a s i v\ mck . jjy xi y.u i
0 25 a
I H
- 0.16
- 0.05
- 0.05
¦ O.QQ
UDA8 03 M DAS 03
So,n£ Sda TPV NQX - JUy 21 2611 SbaaBMOTPVNCSt - Juh S3 3011
-------
Figure 3. MDA8 03 impacts for source 1 (credit source) 500 tpy of VOC. Note scales are different
between Figure 2 and Figure 3.
MP Aft 03
SaLicja I gtfTTV VOC - -My 1 SOU
V
r i ici b .
a as
0 Oft
(L04
- ao2 *
i .
MDA9 03
Sam -i sai iff voc - jLh-a.aort
0.11)
0 08
0 06
0X14
0.02 a
0 00
, fl -
MDAfl 03
Saito.1 SdOTPV^QC-iuV 1 ail 1
/
' ?
- 0 01
(SO* "
- oca I
U- nnq
MDAfl OJ
StMiot i ac rpy toc - 4 aoi
- 010
- .I -
UDABQ3
I 5I-: TPf '/PC - Xi, -5 JO''
010 k
Q09
i
aoe
0.04 *
00? S -
003
M0ABO3
5c*/ua 1 500 TVOC - JJy{,.ai1
r
i
0.1 Q U
0 01
one
0.0*
0 03 i -
0 jQU
MDAfl D3
5x>'ua 1 WO TP '1 VOC - AiV 7 331 I
r >
oa»
- u oa
MDAfl 02
Sou ice I «0 TPr '/DC - JJr 8 30' I
010
am
oat.
004
- 00?
- 000
MDAA03
Sww I VX T-Pf VOC - .My? 301;
0 10 6
- aiiB
§
0Iȣi
0 04 *
0X12 § -
0M
MDASOS
5p,rc« I 1PV WC . Ji>> 10 30' I
¥
0 10 S
- oxia
3
OjOfi
§
0 04
0112 ? -
0.00
MDAfl 03
SW IjWTPy VPC - jMyl V»'»'
- OjM
OjN
1
0 0*
um s
OXM
MCAli 03
faro i aqg ipv woe . -JMy I?. ?QI I
0 10
- 00ft
006
001
002
000
I I
.V|
16
s -
>6
- 004 f
- aaa * -
ooo
MDA8 03
Mcmm 1 600 tPY yUC - lit, 14 3011
0 .0 ?
0.06
a -
- 0 06
i
004
0X12 •
000
MDAfl 03
Snug ! jPli-WitX -.My IS. am
r ~ '0 |
0.08
- 008
3
- 004
- 0 .02 !
U- 0.00
oao
MDAfl 03
¦ 16m iw vol - joy Hi, aai i
|- 01O
008
- 006
- 004
OOi
000
to* u* i wo *rn
iw> >«n ifln
ran »*
23
-------
MOAfl 03
'Houyj i iPr VQC ^ -k+f i ? ann
MDA8 03
aoiK»n sai ^^yvoc^-bty x ami
002 * -
M0*8 03 MD*a03
{jam ' a Ifly VQC - Jktf I <1 301' Soict I Sag W VQC - At, 30 3Ml»
-OWE '
- 010
- Da*
- 00*
- 110+
- Q 0£
- a«
MDAH G3
Sitt-Jt ' 530 -vt WOZ - xtf 21 Mr
MDAfl03
•3a Jf' 500 rpyypc - Jb>r 22 30't
aio h .
MOAE 03
3omce- SMTP? VQC - Aft «S3 20
MDAB03
3a*C« I 530 TW VQC - Jhi» 3* 2Qi t
1 ' ' •• :
M0AJ3 03 MDAB 03
i fem 'fry vac - jitf 2& jdi i iiauCT a &aa r^r vol- - .ii>y
MOA6 03
fiCKlTPf VQC'A*y 37 301'-
MDA&03
ikiiwcm I SCD IPY VQC - JUy 3M 3011
- 0 10 c
010
- 0O»
- OC*
- 064
- aos
- ooe
MDAH 03
Sxjui
-------
Figure 4. Ratio of project source to credit source MDA8 03 impacts.
MDA8 03
Soma 1 500 TPY VQC - Aiy 1.2011
MDA8 03
Sanaa 1 500TPYVQC-Ally 2, 2311
MDA8 03
Samoa 1 503 TPY VOC - Aiy 3.2011
#
7 l> ^
MDA8 03
Souoa 150QTPY VQC-Aity4, 2011
>
A--
> - Si
Si
MDAB 03
Souoa 1 500 TPY VQC - Aiy 5 .2011
7
MDAB 03
Sauroa 1 500 TPY VQC-Ally 6. 2011
iM-'
" V
MDA8 03
Samoa 1 503 TPY VCX: - Aiy 7.2011
; jp
m"
M0ABO3
Somas 1 500 TPY VOC - Ally 8, 2011
,
—iL]
MDAB 03
Souoa 1 500 TPY VQC - Aiy9.2011
MDAB 03
Samoa 1 500 TPV VQC-Aiy 10. 2011
MDAB 03
Souoa 1 500 TRY VQC - Aiy 11 -2011
1
Sjffy
flu jI
——i—F r-^ ppt>
MDAB 03
Souoa 1 500 TPY VQC-Ally 12 2011
MDAB 03
Sauroa 1 500 TPY VQC - JUty 13.2011
>T
-? ['¦
1
MDAB 03
Souioa 1 500 TPY VQC - Aiy 14. 2011
J7r\
—i 1 r
MDAB 03
Souoa 1500 TPY VQC-Aiy 15,2011
iym?
Souoa 1 500 TPY VQC-Aiy 16 2011
—m
w?
7 vi
25
-------
Sotfoal 500 TPY VQC - July 22 .201
Soiraa 1 503 TPY VQC - .Ally 18.201
Sauce 1 503 TPV VQC - July 26.201
MDAS 03
MDA8 03
Sotroa 1 503 TPY VQC - JUy 29, 331
B
E
Souidb 1 500 TPY VQC - .Aiy 23. 3011
Sou roc 1 500 TPY VQC - My 27. 2011
Figure 5 shows the ratio of MDA8 03 project to credit source impacts where multiple conditions are
satisfied. First, only impacts greater than 1 ppt are shown; second, only impacts are shown where the
baseline bulk model 03 prediction was greater than 60 ppb; third, only impacts are shown where the
grid cell intersects the area of interest (shown in Figure 1 as the orange colored cells).
26
-------
Figure 5. Ratio of project source to credit source impacts where multiple conditions are satisfied.
M DA8 03
- Sauna 1503 TPY VQC - Jtiy 1.2011
MDA8 03
g Souroa 1 500 TPY VQC -JuV 2, 2011
—i 1 r~
MDA8 03
- SoupB 1 500 TPY VQC - July 3,2011
7
MDA8 03
1 500 TPY VQC- July*. 2011
W
I
irsn ma ma
nsn ma
MDA8 03
Sotroe 1600 TPY VCC - JUy 6.2011
/ lb?
t
.iM
MDA8 03
- Souroa 1 500 TPY VQC - JUV 6. 2011
-0
i
¦Ur •]
MDA8 03
Samoa 1 603 TPY VQC - My 7.2011
¦m-
MDA8 03
1600 TPY VQC- July 8. 2011
>
MDAS 03
s Sotroal SOQTPY VQC-July 9 2011
]r
1
L
MDA8 03
1 500 TPY VQC-JUy 10. 2011
t
MDAS 03
Souoa 1 503 TPY VQC - JUy 11.2011
MDA8 03
Souroa 1 500 TPY VQC - July 12 .2311
k
MDA8 03
Sa joa 1 500 TPY VQC - Oily 13.2011
&
^Ta
4
MDA8 03
g ^ Sauioa 1 500 TPY VQC - JUy U, i
w
MDA8 03
g Soiroe 1503 TPY VQC- JUy 15.2011
w
I
MDA8 03
Souoa 1 500 TPY VQC - AiV 16.2011
P
6
I.
ma i kd
27
-------
MDA8 03
Soma 1 503 TPY VQC - JUy 17, 2011
MDA8 03
Sairce 1 503 TPY VQC - July 18,2011
IL o
m
±L
MDA8 03
Sttnoe 1 500 TPY VQC— JUy 19, 2311
¦£
MDA8 03
Sotren 1 500 TPY VQC - JUy 20,2011
MDA8 03
g Sonoa 1 503 TPY VQC - JUy 21, 3311
If
MDA8 OS
g Souroal 503 TPY VQC-July 22,2011
JZ-M
MDA8 03
g Samoa 1 500 TPY VQC - JUy 23, 2011
M
MDA8 03
g SturoB 1500 TPY VQC -JUy 24,2011
i?so mm
MDA8 03
Souroa 1 500 TPY VQC - JUy 25. 2011
MDA8 03
So job 1 500 TPY VQC -JUly 2S, 2011
MDA8 03
Sou roe 1 500 TPY VQC - Jdy 27, 2011
xm
-
MDA8 03
Soigcar 1 500 TPY VQC - JUy 28,2011
M
•'s
MDA8 03
g Souoa 1500 TPY VQC- JUy 29, 2011
I 1 r~
Daily metrics relating MDA8 project and credit source impacts are shown in Table 1. These impacts are
based on episode days and grid cells meeting multiple criteria. First, only impacts greater than 1 ppt are
shown; second, only impacts are shown where the baseline bulk model 03 prediction was greater than
60 ppb; third, only impacts are shown where the grid cell intersects the area of interest (shown in Figure
1 as the orange colored cells). For each day, the ratio is provided of the sum of project source impacts
divided by the sum of credit source impacts over all cells meeting the criteria detailed above. The
number of cells meeting the criteria is also provided along with that value being expressed as the
percentage of all cells in the area of interest (the total number of cells examined for this analysis). The
number of cells used in the analysis varies due to varying 03 production in the area of interest from day
to day during this period of time. At the bottom of Table 1, the ratio represents the ratio of episode total
impacts and is not the average of the daily ratios.
28
-------
Table 1. Project and credit source daily impacts, number of cells used, and the percentage of cells used
in the area of interest.
Project source Credit source
impacted cells impacted cells
Sumof Project SumofCredit Ratioof Numberof divided by Numberof divided by
Source MDA8 Source MDA8 projectto cells used for total cells in cells used for total cells in
03 impacts 03 impacts credit source project source area of credit source area of
Episode Day (ppb) (ppb) impacts impact sum interest impact sum interest
1
1.5
2.86
0.5
111
10.9
101
9.9
2
17.07
1.83
9.3
213
21
74
7.3
3
3.19
0.4
8
140
13.8
37
3.6
4
25.89
5
5.2
247
24.3
120
11.8
5
8.06
2.97
2.7
209
20.6
123
12.1
6
0.45
0.2
2.2
53
5.2
37
3.6
7
4.02
0.54
7.4
197
19.4
59
5.8
8
7.57
1.47
5.1
341
33.6
223
21.9
9
2.42
1.14
2.1
54
5.3
60
5.9
10
16.4
0.69
23.8
297
29.2
194
19.1
11
2.04
0.18
11.3
97
9.5
25
2.5
12
5.55
0.22
25.2
71
7
27
2.7
13
0.74
0.13
5.7
48
4.7
16
1.6
14
1.06
0.32
3.3
21
2.1
21
2.1
15
3.87
0.32
12.1
95
9.4
35
3.4
16
4.94
0.73
6.8
322
31.7
72
7.1
17
3.58
0.01
358
89
00
00
5
0.5
18
2.22
0.09
24.7
106
10.4
22
2.2
19
7.63
00
CO
0.9
196
19.3
231
22.7
20
25.15
3.89
6.5
879
86.5
322
31.7
21
2.05
0.25
8.2
80
7.9
29
2.9
22
5.02
0.71
7.1
132
13
66
6.5
23
9.58
0.31
30.9
199
19.6
65
6.4
24
18.42
1.6
11.5
339
33.4
160
15.7
25
9.73
1.03
9.4
940
92.5
148
14.6
26
6.93
1.22
5.7
166
16.3
128
12.6
27
2.81
2.17
1.3
109
10.7
93
9.2
28
3.15
2.72
1.2
188
18.5
137
13.5
29
4.74
0.31
15.3
156
15.4
31
3.1
Sum
205.78
42.11
4.9
29
-------
APPENDIX C, Illustrative example of a hypothetical project arid credit
source O3 interprecursor trading scenario (example 3)
The following example is intended only to provide an illustrative example of how model results for
specific sources could be used in the framework provided in this guidance document toward estimating
equivalency in terms of 03 formation to inform an IPT ratio.
A hypothetical source was modeled for a short July 1-10, 2013, time-period in the Chicago/Lake
Michigan area. For this example, MDA8 03 impacts from both the project and credit source (co-located)
were estimated for each day of the July 1-10, 2013, time-period using the CMAQ model applied with 4
km sized grid cells and 35 layers resolved the vertical atmosphere from the surface to the tropopause.
The extent of the 4 km model domain and area of interest for this hypothetical demonstration is shown
in Figure 1 (right panel).
4 km model domain (4LMOS1)
V«^*Kenosha
-rEvanston
*?jc-ag°
fNaperyillej
^Michigan
h ypot h eticaTs'o u rc e
. J''©.2017-.Gopgle _ |
Image Landsat I Copernicus:
Figure 1. Hypothetical source location, model domain, and hypothetical area of interest (orange).
This hypothetical example considers the project source and the credit source to be co-located. The
project source is seeking to offset 500 tpy of NOx emissions with 500 tpy of VOC emissions from the
credit source. Daily absolute 03 impacts from the project source are shown in Figure 2 and daily
absolute 03 impacts from the credit source are shown in Figure 3. Spatial plots subset with criteria
related to baseline model predicted 03 show source impacts where modeled bulk MDA8 03 was greater
than 30 ppb. A value of 30 ppb was selected for this hypothetical example because this period of time
did not include many days with elevated 03. In a real-world situation, 03 episodes would be selected
such that the time period in that area experienced elevated 03 levels. Multiple model predicted MDA 03
thresholds were used as part of this example to illustrate how the relationship between source impacts
can vary at different 03 levels and those impacts are shown in Table 2 of this Appendix section. The level
of 30 ppb should not be used in actual demonstrations.
30
-------
Figure 2. MDA8 03 impacts from the project source emitting 500 tpy of NOx. Note scales ore different
between Figure 2 and Figure 3.
MDA8 03
Prqect Source 500 TPY NOx - juty 1. 2013
W
J
1 1 1 1 1—
cc too ajo aec tea*
MDA8 03
Protect Source SOD TPY NOx - JUy 2.2013
- 1-2
- 1.0
- 0.8
- 0.6
- 0.4
- 0.2
- 0.0
ppD
- D.C
MDA8 03
Project Source 5CO TPY NOx - Juv 3. 2013
MDA8 OS
Protect Source SOG TPY NOx - 4. 2C13
- 1-D
- a.s
- 0.6
- 0.4
- 0.2
- 0.0
PF®
(
- 12
- 1.0
- 0.3
- 0.6
- 0,4
02
V. ~
i -
f lk
)
i " \
MDA8 03
Protect soufce 500 tpy nox - July 6.201;
460 1150C
- o.e
- o.e
J- ::
MDA8 03
Protect Source 500 tpy NOx - Jiiv 7,201
MDA8 03
Protect Source 500 TPY NOx - -my 8.201;
- 12
- 1.0
- 0.8
- 0.6
- 0.4
- 02
- 0.0
ppo
- 12
- 1H
- 0.8
- 0.6
- C.d
02
"
: y
> C
MDA8 03
Project Source 500 TPY NOx - Ally 10. 201;
1 -
| -
8 -
800 *X IMC
31
-------
Figure 3. MDA8 03 impacts from the credit source emitting 500 tpy of VOC. Note scales are different
between Figure 2 and Figure 3.
MDA8 03
Credit Scores 500 TP* VOC - July t. 2013
MDA8 03
Credit Source 500 TPY VOC - July 2.201 i
MDA8 03
Crean Source 500 TPY VOC - July 3. 20t3
MDA8 03
CredE Source 5C0 TPY VOC - JUv 4. .2013
- : :s
- O.C-3
- Q.Oc
- :
- Q.u6
C.C4 W
O.frJ h "
G.D4 V ~
- :.i2
- U.C2
- 0.02
- : :l
MDA8 03
credit source 5C0 TPY VOC - July S. 2013
MDA8 03
Credit Source 500 tpy VOC - July 6,201:
MDA8 03 MDA8 03
Creffl- source 500 TPY VOC - July 7*2013 Credit Source SCO tpy VOC - J try E
- O.C-3
- 0.06
- C 06
- 0.D6
- OX'S
- 0.06
- U JJ6
0.04 8
B-Q4 £
- : ::
- : ::
- u.02
- : :c
- o.w
I 1 '!»&
- D an
- : :c
tec 7oo
MDA8 03 MDA8 03
Credit Source SCO TPY VOC - July 5. 2013 ^ Credit Source 503 TPY VOC - July 10. 2013
D.10 f
8 -
- D.D6
- O.C-3
- O.Rj
- o.z:
eoc 700
nxe
700 900 tDO lOOQ
Figure 4 shows the ratio of MDA8 project source 03 impacts to credit source 03 impacts where multiple
conditions are satisfied. First, only impacts greater than 1 ppt are shown; second, only impacts are
shown where the baseline bulk model 03 prediction was greater than 30 ppb; third, only impacts are
shown where the grid cell intersects the area of interest (shown in Figure 1 as the orange colored ceils).
32
-------
Figure 4, Ratio of project source to credit source 03 impacts where multiple conditions are satisfied.
Ratio of MDA8 03
Pnyect is Great Source Impacts - July 1. 2013
g -
g -
I -
§ -
I
T 1 1 1 1
00 7t» 800 See toco
Ratio of MDA8 03
Project to crea: source mpac.s - juy z 2Qj 3
S ~\
s -
§ -
w
1 1 1 1 1—
eoc too eai too «os
Ratio of MDA8 03
Protect to Credit Source lrncaste - Juiv 3.2D13
§ -r
Ratio of MDA8 03
a -
§ -
Wd
.. *
i—i—
730 ax
—I 1 1 1—
TOO 800 «G 1000
Ratio of MDA8 03
Pre. est "o Creat Scurce in
i
acts - July 5.20
•iT ;
v-
Ratio of MDA8 03
t Protect to Creai Source impacts - Jifv 6.2013
s H
I ~
8 -
i 1 r~
«k too am
Ratio of MDA8 03
i Protect to Credit source iiraacte - July 7.2D13
1- 0
ppo
Ie -
a -
| -
a -
is
J- o
ppb
Ratio of MDA8 03
Prsect lo Great Source Imc-acts - July 8.2D13
I -p
Yr
1 i—
•m iau
730 SX l£B0
Ml 1000
Ratio of MDA8 03
Prefect '.p Great Source Impacts - July 9. 2013
W 6
Ratio of MDA8 03
Pr&ect is Great Souse Impacts - Jidy 10.2C
%
£
J- 0
OpD
70C IMS •Ml 1000
Daily metrics relating MDA8 project and credit source 03 impacts are shown in Table 1, These impacts
are based on episode days and grid cells meeting multiple criteria. First, only impacts greater than 1 ppt
are shown; second, only impacts are shown where the baseline bulk model 03 prediction was greater
than 30 ppb; third, only impacts are shown where the grid cell intersects the area of interest (shown in
Figure 1 as the orange colored cells). For each day, the ratio is provided of the sum of project source 03
impacts divided by the sum of credit source 03 impacts over all cells meeting the criteria detailed above.
The number of cells meeting the criteria is also provided along with that value being expressed as the
percentage of all cells in the area of interest (the total number of cells examined for this analysis). The
number of cells used in the analysis varies due to varying 03 production in the area of interest from day
to day during this period of time. At the bottom of Table 1, the ratio represents the ratio of episode total
impacts and is not the average of the daily ratios. Table 2 presents an illustrative sensitivity analysis of
the ratio of sums of 03 impacts at various baseline bulk model 03 cutoffs.
33
-------
Table 1. Ozone impacts from the hypothetical project source and credit source and ratio analysis
Episode
Day
Sum of
Project
Source
MDA8 03
Impacts
(PPb)
Sum of
Credit
Source
MDA8 03
Impacts
(PPb)
Ratio of
project to
credit
source 03
impacts
Number
of cells
used for
project
source
impact
sum
Project
source
impacted
cells divided
by total cells
in area of
interest x
100
Number
of cells
used for
credit
source
impact
sum
Credit source
impacted
cells divided
by total cells
in area of
interest x 100
1
0.02
0.02
1
4
0.5
4
0.5
2
0.12
0.03
4
7
0.9
3
0.4
3
1.47
4.94
0.3
161
19.7
340
41.7
4
20.92
1.92
10.9
255
31.2
237
29
5
17.95
4.43
4.1
422
51.7
357
43.8
6
22.05
4.69
4.7
171
21
317
38.8
7
25.16
1.7
14.8
197
24.1
181
22.2
8
9.82
0.61
16.1
173
21.2
156
19.1
9
15.61
1.98
7.9
218
26.7
240
29.4
10
0.09
0.01
9
13
1.6
4
0.5
sum
113.21
20.33
ratio of
sums
5.57
Table 2. Sensitivity analysis of the ratio of summed ozone impacts to changes in the baseline bulk model
03 cutoff.
baseline bulk model 03 cutoff (ppb)
ratio of sums
0
5.57
10
5.57
20
5.57
30
5.57
40
5.64
45
5.17
50
2.20
60
0.43
34
-------
United States Office of Air Quality Planning and Standards Publication No. EPA-454/R-18-004
Environmental Protection Air Quality Assessment Division May, 2018
Agency Research Triangle Park, NC
------- |