United States
Environmental
Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA-450/4-91-015
May 1991
&EPA
AIR
CRITERIA FOR ASSESSING THE ROLE
OF TRANSPORTED OZONE/PRECURSORS
IN OZONE NONATTAINMENT AREAS
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PROTECT***
AGENCY
•ALLAS, TBIAf
CRITERIA FOR ASSESSING THE ROLE OF TRANSPORTED
OZONE/PRECURSORS IN OZONE NONATTAINMENT AREAS
MAY 1991
U. S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Technical Support Division
Research Triangle Park, NC 27711
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TABLE OF CONTENTS
Page
LIST OF FIGURES iii
LIST OF TABLES iv
1.0 INTRODUCTION 1
2.0 ROLE OF TRANSPORT DETERMINATIONS IN IMPLEMENTING CLEAN
AIR ACT REQUIREMENTS 3
2.1 Implications for Modeling and Monitoring 3
2.2 CAA Modeling Requirements and Implications for
Determining Transport . 4
3.0 CONSIDERATION OF TRANSPORT IN THE DESIGN OF CONTROL
STRATEGIES 9
3.1 Determining Whether an Exceedance is Primarily Due
to Local Emissions 9
3.2 Determining Likely Contributing Areas in Cases of
Overwhelming Transport 15
3.2.1 A Predominant Source Area is Identified . . 16
3.2.2 No Predominant Source Area is Identified . . 17
3.3 Consideration of Transport in Attainment
Demonstrations 18
3.3.1 Use of Regional Scale Models 19
3.3.2 Use of Monitored Data to Estimate Model
Boundary Conditions 23
3.3.3 Use of Modeling Procedures to Diminish
Importance of Transport 26
4.0 MONITORING DATA FOR CHARACTERIZING TRANSPORT IN
RECOMMENDED MODELS 31
4.1 Data Needed to Support Characterization of
Transport in Models 31
4.1.1 Trajectory Models 31
4.1.2 Urban Airshed Model 33
4.1.3 Empirical Kinetics Modeling Approach .... 36
4.1.4 Regional Oxidant Model 37
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4.2 Instrumentation/Deployment 38
4.2.1 Winds, Other Meteorological Data 38
4.2.2 Ozone 38
4.2.3 NOX 38
4.2.4 CO 39
4.2.5 NMOC 39
4.3 Quality Assurance of Monitored Data 40
5.0 SUMMARY 43
REFERENCES CITED 49
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LIST OF FIGURES
Page
Multiperiod Back Trajectory With Area Most Likely ... 12
Contributing to Observed Ozone Identified
Portion of United States Covered By Potential ROM ... 21
Applications
Future Ozone Transport as a Function of Present .... 27
Transport
Minimal Ozone Monitoring Network 34
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LIST OF TABLES
Page
1 Default Recommendations for Present Transported .... 30
Boundary Conditions
IV
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1.0 INTRODUCTION
The intent of this document is to present means (i.e.,
criteria) for assessing the effect of transported ozone (O3) and
its precursors on O3 concentrations observed in locations not
attaining the National Ambient Air Quality Standard (NAAQS) for 03.
The primary purpose for making such an assessment is to foster
design of control strategies which are most responsive to
environmental conditions prevailing in a nonattainment area.
Therefore, the criteria discussed herein address not only current
conditions but future periods (after control strategies are
implemented) as well. This is necessary in order to assess whether
a proposed control strategy is likely to be successful in meeting
prescribed deadlines for attaining the NAAQS for O3.
This document is prepared in response to Section 184(d) of the
Clean Air Act (CAA) as amended in 1990. Section 184(d) states the
following:
"For purposes of this section, not later than 6 months after
the date of the enactment of the Clean Air Act Amendments of
1990, the Administrator shall promulgate criteria for purposes
of determining contribution of sources in one area to
concentrations of ozone in another area which is a non-
attainment area for ozone. Such criteria shall require that
the best available air quality monitoring and modeling
techniques be used for purposes of making such
determinations."
The remainder of the document is organized in the following
manner. Section 2 discusses why it is important to be able to
characterize transport. This is done by identifying pertinent
requirements in the amended Clean Air Act and by noting how
consideration of transport is a prerequisite for meeting these
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requirements. Because Section 184(d), as well as other portions
of the CAA, imply the need for quantitative estimates of transport,
modeling is recommended as the prime means for making this
determination. Monitoring is needed to support and estimate
performance of the recommended modeling procedures. Section 3
describes the appropriate sequence of modeling analyses for
considering transport in the design of control strategies. This
sequence proceeds by first noting the role of transport
determinations in selecting locations in which to apply controls to
most effectively reduce O3 during an observed episode. Next,
procedures for considering transport in order to quantify the
controls needed in identified areas to reduce O3 to the level
specified in the NAAQS (0.12 ppm) are described. Section 4
presents monitoring recommendations (criteria) for estimating
transported ozone and precursors needed in the modeling analyses
recommended in Section 3. Section 5 summarizes identified modeling
and monitoring criteria for determining contributions of transport
in downwind nonattainment areas.
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2 .0 ROLE OF TRANSPORT DETERMINATIONS IN IMPLEMENTING CLEAN AIR ACT
REQUIREMENTS.
2.1 Implications for Modeling and Monitoring
The 1990 Clean Air Act amendments reflect a mix of
prescribed reductions of volatile organic compound (VOC) and
nitrogen oxides (NOX) precursors of O3 (technology-based
requirements). The Act also requires States to ensure that
prescribed emission reductions are sufficient to meet the O3 NAAQS
(air quality management requirements) in many nonattainment areas.
It is in meeting the Act's air quality management requirements that
proper consideration of transport is important. This consideration
fulfills several roles:
(1) to help identify the primary reason (i.e., transport
or local emissions) for an observed "exceedance "* of the NAAQS in
a nonattainment area,
(2) to identify an upwind location(s) most likely to
contribute to (and therefore the most appropriate locations to
apply a set of strategies for reducing) an observed "exceedance",
(3) to allow quantitative estimates to be made regarding
reductions in VOC and/or NOX emissions needed in areas identified
as likely to contribute to an observed exceedance in order to
remedy the exceedance,
(4) to ensure and track effectiveness of promulgated
control strategies, and
*In this^ document, the term "exceedance" is used to denote any
observed daily maximum ozone concentration greater than the level
specified in the NAAQS (0.12 ppm).
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(5) to assess the extent of interstate transport
throughout designated Transport Regions and assess strategies for
mitigating interstate transport.
Use of photochemical air quality dispersion models is the only
practical way to meet the third and fifth roles identified above —
that of assessing whether contemplated emission control strategies
will be sufficient to reduce O3 to <0.12 ppm and whether interstate
transport has been reduced sufficiently to make the goal a
realizable one.
The roles of meteorological and air quality monitoring are
threefold:
(1) to provide information concerning which areas and
episodes to model;
(2) to provide input information to models so that they
might be used to make estimates of needed emission reductions in
modeled areas; and
(3) to aid in evaluating the performance of selected
models.
2.2 CAA Modeling Requirements and Implications for
Determining Transport
The CAA amendments categorize ozone nonattainment areas
into five groups. These are, in descending order of severity,
extreme, severe, serious, moderate, and marginal. Air quality
management-related requirements are imposed in the first four of
these categories. In addition, rural transport areas, as defined
in ^ection 182(h), are subject to the same restrictions as a
marginal nonattainment area, regardless of the severity of measured
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ozone levels, if it can be shown that failure to attain in such an
area is attributable to transport. Finally, certain small areas,
as defined in Section 185(e), may be exempted from sanctions for
failure to attain the NAAQS by a prescribed date, if attainment is
prevented by transport after all local State Implementation Plan
(SIP) provisions are implemented.
In extreme, severe, and serious areas, use of a photochemical
grid model is required to demonstrate that proposed control
measures will be sufficient to attain the NAAQS by specified dates.
The Urban'Airshed Model (UAM) is the grid model recommended by the
EPA for this purpose, and is expected to be widely used (Morris, et
al. 1990 a,b; Douglas et al. 1990; Causley 1990; Tang et al. 1990).
In moderate nonattainment areas, use of grid modeling is
required if the area includes territory in more than one State.
Otherwise, grid modeling is preferred, but the Empirical Kinetics
Modeling Approach (EKMA) is also an acceptable procedure (USEPA
1989 a-c; Systems Applications, Inc., 1988; Meyer et al. 1989).
Both the UAM and EKMA are regarded as "urban scale" models. That
is, the modeling domain ordinarily addressed is sufficiently large
to consider movement of pollutants over 12 daylight hours (e.g., 8
a.m. - 6 p.m.). Generally, this has resulted in applications over
domains on the order of a couple hundred kilometers on an upwind/
downwind axis at most. However, it is possible to consider larger
domains for urban grid models. Domain size is usually limited by
data base management considerations and computer limitations.
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Criteria for considering transport must address the following
issues relating to use of the UAM and EKMA models.
(1) Is use of one of these models appropriate for
modeling the nonattainment area containing the ozone exceedance in
question? If not, what should be done?
(2) What area/modeling domain should be modeled to
adequately consider the effects of a proposed control strategy on
an observed exceedance?
(3) What inputs are needed to these models in order to
reflect effects of transport?
(4) How can the inputs needed for the urban scale
models be derived?
The EPA has published guidance describing suitable procedures
for using the UAM and EKMA in attainment demonstrations (USEPA
1991a, USEPA 1989c). Much of the ensuing discussion regarding
criteria for considering transport is drawn from these guidance
documents and from Meyer, et al. 1989. Each model application is
likely to have to respond to some area-specific characteristics
which cannot be anticipated in general guidance. Thus, model
application guidance has recommended formation of working groups
consisting of representatives from each State affected in a
particular modeling demonstration, appropriate US EPA
representatives and other interested parties (USEPA 1991a). It is
expected that criteria for assessing the role of transported ozone
and precursors identified in this document will be treated
«r
similarly. That is, a group of general procedures are identified
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herein. It will be up to the working group responsible for
developing and implementing a modeling protocol for a specific area
to adapt this general guidance for use in specific areas. It is
also conceivable that special circumstances prevailing in a
particular area for which a modeling protocol is being developed
may warrant use of procedures which differ from those described
herein. In such cases, the rationale for a different procedure
must be documented and submitted to the appropriate U.S. EPA
Regional Office for consideration on a case-by-case basis.
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3.0 CONSIDERATION OF TRANSPORT IN THE DESIGN OF CONTROL STRATEGIES
In order to quantify effects of transport and to ensure that
transport is appropriately considered in the design of a SIP to
demonstrate attainment of the NAAQS for ozone, it is necessary to
use sophisticated, resource intensive modeling tools. To conserve
resources, it is useful to focus modeling analysis on locations and
incidents which, if remedied, would most likely result in
attainment of the NAAQS. The discussion in Section 3.0 begins by
describing several relatively simple tools (trajectory models)
which may be useful in focusing analyses with complex models (e.g.,
UAM, Regional Oxidant Model (ROM)) needed to consider transport
quantitatively. Section 3.0 concludes with a discussion of urban
and regional scale photochemical dispersion models needed to
quantify effects of transport in SIP attainment demonstrations.
3.1 Determining Whether an Exceedance is Primarily Due to
Local Emissions
The first step in assessing the role of transport is to
determine whether transport is so overwhelming that the
contribution of local emissions to an observed exceedance is
relatively minor. Such a case is referred to as "overwhelming
transport". Procedures described in this step are useful in
selecting episodes to test whether local control measures are
sufficient to eliminate exceedances which are largely attributable
to local emissions. In many cases, there may be an upwind/downwind
gradient in observed 03 concentrations and/or man-made VOC and NOX
emission density is much greater in the Consolidated Metropolitan
Statistical Area (CMSA) or Metropolitan Statistical Area (MSA)
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under consideration than in surrounding locations. In such cases
it is the prerogative of those responsible for the area's modeling
protocol whether to perform an "overwhelming transport"
determination using more rigorous procedures described below. If
it is decided that a rigorous overwhelming transport determination
is unnecessary, the analyst should proceed to Section 3.3. Failure
to perform an adequate "overwhelming transport" analysis when a
detailed analysis is warranted could lead to very stringent
prescriptions for control of local emissions. While such
prescriptions might possibly work, they may not be a particularly
efficient way to eliminate an exceedance which is largely a result
of transport from external sources.
If an assessment of overwhelming transport is performed, the
approach generally recommended is to perform trajectory analyses to
assess the likelihood of overwhelming transport. The model
ordinarily recommended for this purpose is the US EPA TRAJECTORY
model (Meyer, et al. 1989). However, as described shortly, other
trajectory models may be used if it can be shown that use of
surface wind measurements alone inadequately describes transport.
The EPA TRAJECTORY model uses surface wind data to construct a back
trajectory from the site of the observed exceedance, beginning at
the time of the daily maximum O3 concentration observed on the day
of the exceedance.
There is usually considerable uncertainty regarding the exact
position of an air parcel nominally following a computed
trajectory. The TRAJECTORY model incorporates this by considering
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variability in wind data noted at nearby stations. The further one
progresses from the back trajectory's starting point (i.e., the
ozone monitoring site recording the exceedance) the greater this
uncertainty becomes. As a result, one obtains a cone-like figure,
emanating from the monitoring site, which describes the. probable
position of pollutant-laden air during periods preceding the
observed exceedance. This is shown conceptually in Figure 1.
Figure 1 depicts a back trajectory from a monitoring site with an
observed daily maximum O3 concentration at 2:00 p.m. The "Vit"
represent distance traveled during each hour. The 6± are measures
of uncertainty whose derivation is described in Meyer et al.
(1989). Significance of the shaded area will be described shortly.
The trajectory is computed using surface wind data from all
National Weather Service and other suitably sited wind monitors
(see USEPA, 1987) within 160 km of the most likely computed
position of an air parcel following the trajectory at any hour.
Because the nighttime surface layer may be very shallow and winds
aloft may differ significantly from surface observations at night,
TRAJECTORY may only be applied for daytime hours (e.g., 8 a.m. - 8
p.m.).
An underlying assumption in the USEPA TRAJECTORY model
application for identifying overwhelming transport is that if an
air parcel corresponding with an observed exceedance is within the
nonattainment area during 8 a.m. - 12 noon on the day of the
exceedance, there is a good chance that local emissions play a
significant role in causing the exceedance. This assumption is
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supported by diurnal meteorological conditions as well as by
typical diurnal emission patterns for many important source
categories of VOC and NOX precursors for O3. Thus, if all or part
of the local CMSA/MSA containing or in close proximity to the site
with the observed exceedance falls within the shaded area in Figure
1, it can be assumed that its emissions play a significant role in
leading to the observed exceedance. As noted in Meyer et al.
1989, if the average resultant wind velocity is low, it should be
assumed the local area contributes to the exceedance. If such a
finding is made, the analyst can skip Step 2 in the procedure for
considering transport (i.e., Section 3.2) and proceed to Step 3
(Section 3.3). If a finding of overwhelming transport is made, the
episode in question can be ignored in the local area's attainment
demonstration unless it is not possible to identify an upwind
CMSA/MSA(s) likely contributing to the observed exceedance. In
this case, see the discussion in Section 3.2.2.
It should be noted that it is possible for the TRAJECTORY
model to yield misleading results under some circumstances. For
example, if an exceedance occurs as the result of mid-morning
fumigation of ozone which remains aloft overnight, it is
conceivable that this is a result of transport rather than
recirculated locally generated pollution. For exceedances
occurring at 11 a.m., local civil time (LCT), or earlier, a
trajectory model such as the Atmospheric Transport and Dispersion
Model (ATAD) or the Branching Atmospheric Trajectory model (BAT)
(Heffter 1980, 1983) is recommended to assess the likelihood of
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overwhelming transport. These models utilize upper air data.
Prior to applying such a trajectory model, the modeling protocol
working group should consider whether the exceedance is due to
fumigation. Review of available diurnal mixing height information
and time series analysis of air. quality data may be helpful in
distinguishing a fumigation-induced problem from one resulting from
photochemistry relatively early in the day. If a multiday
trajectory model is used to assess likely sources of a morning
exceedance, attention should be given to MSA/CMSA's traversed by a
swath surrounding the trajectory from 8 a.m. - 6 p.m. on the
preceding day. Width of the swath is a function of uncertainty
associated with the trajectory estimates. Uncertainty can be
determined by a climatological review of trajectories computed
under similar synoptic conditions and wind patterns.
The TRAJECTORY model generally remains the model of choice for
addressing exceedances occurring after 11 a.m., because it utilizes
more dense surface monitoring networks and its application is
confined to periods of the day when wind shear is likely to be
minimized. Thus, surface winds would be more representative of
flow in the mixed layer in most locations. Choice of the
trajectory model and its underlying rationale must be documented by
the working group preparing a modeling protocol and is subject to
review by the U.S. EPA.
It is next appropriate to consider rural transport areas, as
described in CAA Section 182(h), more explicitly. Use of
trajectory models, as described in the previous paragraphs, is
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generally the preferred approach for confirming that an area, which
otherwise qualifies, may be treated as a rural transport area.
However, it may happen that the wind data available near such
locations are too sparse to be reliable, or available trajectory
models are otherwise unsuitable. If the working group responsible
for a modeling protocol determines that available trajectory models
are inappropriate for the purpose of identifying overwhelming
transport into a proposed rural transport area, the reasons for
this determination should be documented and are subject to review
by the U.S. EPA. If the EPA agrees with this assessment, other
methods may be used to justify treatment of a candidate
geographical location as a rural transport area. An area may be
treated as a rural transport area if justified by the weight of
supporting evidence of two or more of the following types (l) NOX
and VOC inventories are much less than those in locations where it
is plausible to believe pollution may be originating, (2) a past
photochemical grid modeling analysis supports the hypothesis of
overwhelming transport, (3) a field study supports the likelihood
of overwhelming transport, or (4) other pertinent guidance can be
presented. If an area is determined to be a rural transport area,
exceedances occurring therein should be considered in selecting
episodes to model and in the choice of modeling domains for nearby
CMSA's/MSA's.
3.2 Determining Likely Contributing Areas in Cases of
Overwhelming Transport
Once it is determined that "overwhelming transport" is
likely, the next step is to try to establish the most likely
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predominant source(s) of an observed "exceedance". If the
TRAJECTORY model is used, this is done by noting any CMSA/MSA's
located completely or partially within the shaded area in Figure 1.
If a model using upper air data is used to estimate the cause of a
morning exceedance, CMSA's/MSA's located within a swath surrounding
the trajectory during 8 a.m. - 6 p.m. of the preceding day should
be identified. As noted in Section 3.1, the width of the swath is
a function of uncertainty in the trajectory path as estimated from
climatology of the area with the observed exceedance. Results of
applying any of the trajectory models may yield any of several
outcomes:
(a) One of the identified CMSA/MSA's has many more NOX
or VOC emissions than any of the other identified CMSA/MSA's.
(b) Several CMSA/MSA's are identified, but it is not
obvious which one(s) exerts the predominant influence on
transported ozone/precursors;
(c) No CMSA/MSA's are identified.
3.2.1 A Predominant Source Area is Identified
If the emissions of NOX or VOC in one of the identified
CMSA/MSA's greatly exceed those in the others, it may be assumed
to be the predominant cause of the observed exceedance. In this
case, the episode in question should be among those considered for
modeling for this upwind CMSA/MSA. Procedures for selecting
episodes to model with UAM or EKMA are described in USEPA 1991a and
in USEPA 1989c, respectively. If the UAM is used and the episode
in question is one of those selected for modeling, the downwind
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boundary of the modeling domain for this upwind CMSA/MSA should
extend beyond the monitoring site, as described in USEPA 1991a.
3.2.2 No Predominant Source Area is Identified
Outcomes (b) or (c) above are possible if an exceedance
is the.composite effect of emissions in many areas or is a result
of multiday transport. Several approaches are possible if one of
these outcomes occurs. First, if there are a number of such
incidents, this might serve as one consideration in deciding
whether to petition the EPA Administrator to establish a Transport
Region in accordance with Section 176A of the CAA. Cumulative
effects of SIP's in several CMSA's/MSA's or States are best
simulated with regional scale models, such as the EPA ROM, (Lamb,
1983) used in concert with urban scale models. Regional models are
also the recommended approach for quantifying interstate transport,
as required in Transport Regions. Application of ROM and its role
in assessing effects of transport will be described more fully in
Section 3.3.
If there is a limited number of "unattributed" exceedances, it
may be possible to address the problem without establishing a
Transport Region. A second approach could be use of an urban scale
photochemical grid model, like the UAM, and a large modeling
domain. The domain would encompass monitoring site(s) observing
unattributed exceedances as well as the several CMSA/MSA's
identified through use of trajectory methods as potential
contributors to those exceedances. The episode(s) including the
unattributed exceedances would be among those considered for
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simulating over the large modeling domain (USEPA, 1991a). In such
cases, the effect of emissions in one or several CMSA/MSA's on air
quality downwind can be assessed through model sensitivity tests.
If it is not feasible to exercise either of the preceding two
approaches, it would be necessary to focus once again on the local
area's attainment demonstration. As noted previously, it is not
necessary to simulate effects of local controls on an exceedance
which is a product of overwhelming transport. Instead, it should
be treated as an "irreducible exceedance".
If EKMA is used for the local area's attainment demonstration,
guidance with respect to irreducible exceedances presented in Meyer
et al. 1989 should be followed. In essence, this requires reducing
the number of incidents in which an exceedance is allowed after
simulation of proposed controls. A similar procedure is
recommended if a photochemical grid model (e.g., UAM) is used. For
example, suppose guidance in USEPA 1991a permitted one post-control
modeled exceedance. In this case, presence of one or more
irreducible exceedances would mean that a proposed control strategy
would no longer be acceptable if it resulted in any modeled
exceedances.
3.3 Consideration of Transport in Attainment Demonstrations
The preceding two sections addressed qualitative
procedures for identifying location(s) most likely to be the
primary cause of an observed exceedance. Once these are
identified, an urban scale modeling analysis should be focused on
the identified area(s) using guidance in USEPA 199la or USEPA
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1989c. An identified area is, by definition, one whose control
strategies may significantly affect whether an observed exceedance
is eliminated. Effectiveness of controls in such an area may,
nevertheless, be influenced by transport. The purpose of this
Section is,to present recommendations for considering transported
ozone and precursors in urban scale modeling used for attainment
demonstrations. In attainment demonstrations, transport is
considered by specifying boundary conditions for urban scale
models. Approaches for doing this are enumerated below.
3.3.1 Use of Regional Scale Models
The preferred approach for generating boundary conditions
for urban scale modeling applications is to "nest" the urban scale
modeling domain within a regional modeling domain. Typical
regional modeling applications consider domains on the order of
1000 km or more on a side. Regional scale modeling simulations are
begun two or more days prior to the period to be simulated by using
a gridded photochemical model such as the US EPA's ROM. The
regional model is used to simulate base case boundary conditions as
well as regional impact of control strategies likely to be applied
in and between the various CMSA's/MSA's within the regional
modeling domain. The procedure followed in the regional (and
urban) modeling analysis is to assume past meteorological episodes
corresponding with high ozone are characteristic of future episodes
with ozone-conducive conditions, and apply a control strategy for
some future year. Generally, the year chosen would be the year in
which the CAA specifies attainment of the NAAQS should be reached.
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As noted in CAA Section 181(a), this varies according to how
serious the present ozone problem is for a CMSA/MSA.
Use of a gridded regional model requires a large amount of
computer capacity. Further, the domain is often likely to
encompass many political jurisdictions, making it difficult to have
access to the requisite emission information over the entire
domain. This latter problem can only be overcome if States submit
point, area and mobile source information to some centralized data
system which can be accessed by the regional model. Because of the
difficulties listed in this paragraph, it is recommended that the
US EPA ROM model be used as the model of choice whenever feasible.
States should submit emissions data to the US EPA's Aerometric
Information Retrieval System (AIRS) data base (USEPA, 1989d) by
November 1992, so that regional modeling efforts might make use of
these estimates within the limited time allotted by the Clean Air
Act. The US EPA will run ROM for as many episodes and locations as
resources permit. Figure 2 depicts that portion of the United
States for which it will be possible to run ROM within the next 3-4
years. Clearly, the task of ensuring consistent data bases and
strategy assumptions in regional and urban scale modeling analyses
requires extensive coordination. For this reason, whenever
regional models are used, the EPA should be represented on the
technical or policy work group responsible for conducting urban
scale attainment demonstrations.
An infrastructure exists to enable States to readily access
and use the results of ROM simulations as input to their urban
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PQ
•a
3
CX)
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scale modeling analyses. States may access ROM-generated data
using the Gridded Model Information Support System (GMISS)
(Computer Sciences Corporation, 1991). The US EPA archives air
quality predictions as well as certain input information
corresponding with each application of ROM into GMISS. Groups
using the UAM can readily make use of data retrieved from GMISS
using the ROM/UAM Interface Program System (Tang et al. 1990).
Similar means exist for using data retrieved from GMISS if EKMA is
used (USEPA, 1991b).
As implied by Figure 2, there are locations within the United
States where it will not be feasible to use ROM in the foreseeable
future. Further, ROM results may not be available for every
episode which is of interest in every nonattainment area. Use of
alternative regional scale models to generate boundary conditions
for urban scale models is acceptable. Such use should be
specifically addressed in modeling protocols developed for each
urban modeling application, and coordinated with the appropriate
U. S. EPA Regional Office(s) for approval on a case-by-case basis.
Use of regional scale models is the preferred method for
considering transport into a nonattainment area for several
reasons. First, it is the most defensible means for estimating
boundary conditions (i.e., transport) after implementation of
regional and urban strategies in upwind areas. As noted,
attainment demonstrations must focus on future periods specified in
the Clean Air Act. Therefore, credibility of estimated future
transport is a key consideration. A second advantage of using
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regional models is that they provide a far more comprehensive set
of present boundary conditions than is feasible using any other
method. This, in turn, replaces much of the subjectivity necessary
in specifying present boundary conditions using other means. For
example, the Urban Airshed Model generally considers five or more
vertical layers in the atmosphere. It is necessary to specify
boundary conditions for each grid cell in each of these layers
along a domain's upwind boundary for each hour simulated. As noted
in Section 3.3.2, it is impractical to collect monitored data for
each of these grid squares. If monitoring data rather than
regional models are used to specify boundary conditions, the
specifications must be based on a limited number of direct
observations and interpolation or some other, subjective procedure.
3.3.2 Use of Monitored Data to Estimate Model Boundary
Conditions
If it is not possible to use a regional scale model to
generate boundary conditions for urban scale models, an alternative
approach is to derive estimates of boundary. conditions based on
available air quality monitoring data. If the UAM is used, Section
4.2.6 in Morris et al. 1990b shows grid cells in the UAM modeling
domain for which boundary conditions must be specified for each
hour of the simulation. As described in Morris et al. 1990b, it is
possible to divide the modeling grid's boundaries into subsegments.
This may be useful if monitored data suggest a distinct horizontal
concentration gradient along the modeling grid's boundaries. The
UAM software permits use of two procedures for estimating hourly
boundary concentrations in surface level grid cells comprising each
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segment of the domain's boundaries. The first of these assumes a
constant concentration (of O3, precursors) for each segment. The
second approach performs a linear interpolation between
concentrations specified at each segment's end points to estimate
boundary conditions in each surface grid cell included in a
boundary segment. Morris et al. 1990b note that the procedure
generally followed is to assume a spatially invariant (i.e.,
constant) concentration for cells in each segment.
The UAM software also contains provisions for specifying
hour-by-hour boundary conditions in grid cells aloft. These are
described in Section 4.1.7 of Morris et al. 1990b. Two procedures
have been most commonly used in past applications of UAM:
(1) Assume a concentration which is constant with
height;
(2) Specify a vertical concentration profile pattern
which varies between a concentration estimated, as described
previously, in a surface grid square and a concentration specified
or calculated previously in a grid cell just above the mixing
height (i.e., DIFFBREAK).
The first method is the simpler of the two and may be
justified, particularly during times of day with vigorous vertical
mixing. The second method is seemingly more sophisticated but, if
used, a rationale for the selected vertical profile should be
included in the protocol describing the technical basis for the
attainment demonstration. In the second method, concentrations
24
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above DIFFBREAK are usually initially assumed to be at background
levels (see Section 3.3.3).
It may often happen that monitored data for ozone exist to
enable specification of boundary conditions, but there are no data
for the NO, NO2, CO, and VOC species which must also be specified.
In this case, information in Table 1 (see Section 3.3.3) will have
to suffice for specifying values for unmonitored species.
Boundary conditions are considered somewhat differently if
EKMA is used. In the OZIPM4 model underlying EKMA, one models
concentrations within a moving column of air. As described in
USEPA 1989c, the simulation begins at 8 a.m. on the day of an
observed exceedance, with the column located over the central city
in the modeled CMSA/MSA. The column follows a straightline
trajectory which places it at the monitoring site recording the
exceedance at the time of the exceedance. During the simulation,
the column grows in height to reflect the typical diurnal rise in
mixing height. As the column height grows, air is entrained from
aloft. Boundary conditions are considered by specifying ozone and
precursor concentrations in this layer aloft at the beginning of
the simulation. These specified concentrations aloft are invariant
with time.
As noted previously, for attainment demonstrations, an
estimate of future transported ozone and precursors is needed. In
the absence of regional models, Figure 3 has been used to estimate
future transported O3, given an observed level of transported O3
(USEPA 1989c). To illustrate use of the Figure, suppose a boundary
25
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03 concentration for an isolated urban area is estimated to be 0.10
ppm. The corresponding future boundary condition for O3 would be
0.09 ppm. Figure 3 is based on application of OZIPM4/EKMA with a
20 percent reduction in VOC, no change in VOC speciation, and no
change in NOX. Thus, for consistency, these latter assumptions
should be used in conjunction with Figure 3. In the absence of
better information, this methodology may be applied for use with
UAM as well as with EKMA. Use of alternative procedures for
estimating future transport in the absence of regional modeling
must be justified, and is subject to approval by the US EPA on a
case-by-case basis.
3.3.3 Use of Modeling Procedures to Diminish Importance of
Transport
Barring an intensive field study, it is clear from Section
3.3.2 that specification of present boundary conditions based on
monitoring data requires a number of arbitrary procedures and/or
subjective judgment. Unfortunately, even when intensive field data
are available, the period of an intensive study often will not
coincide with O3 episodes of greatest interest. Further, the basis
for estimating future boundary conditions is not strong.
Therefore, it is appropriate to consider ways in which the
sensitivity of model predictions to assumed boundary conditions can
be diminished.
Sensitivity of UAM predictions to boundary conditions can
likely be diminished by increasing the size of the modeling domain
26
-------
o
cc.
UJ
e:
a.
o
o
o
CO «
<
to
c;
o
Q.
LLj
o
o
LLJ
c;
O
a\
CO
3N020 3yninj
-------
on the upwind side of the CMSA/MSA which is the focus of attention.
There are, of course, practical limits to this in terms of data
base management and computer constraints. Further, a tradeoff must
be made against the desirability of extending the domain downwind
beyond the location of monitors observing exceedances attributable
to the CMSA/MSA being modeled.
Table 1 contains recommended default inputs for boundary
conditions contained in USEPA 1989c. Defaults may be used if the
UAM modeling domain is enlarged, as described above. The recom-
mendations for nonmethane organic compounds* (NMOC), NMOC
speciation, and O3 are based on a review of aircraft observations
in an unpublished report by Baugues (1987). Subsequent to the
Baugues (1987) review, doubt was cast on the observed NOX data.
Hence the NOX defaults are based on earlier recommendations (USEPA
1978). Recommendations for CO are based on a review of data
produced from sampling aboard aircraft during the 1980 PEPE/NEROS
study. The CO recommendation differs from that in USEPA (1989c).
The recommendations made herein are believed more representative of
available data and should supersede the CO default value
recommended in USEPA (1989c). In the absence of better, area-
specific information, these defaults may be assumed to be constant
vertically and horizontally. In USEPA 1989c, it is noted that
future levels of NMOC and CO may be reduced 20 percent, and NOX
kept constant. NMOC composition is kept constant.
"The term "nonmethane organic compounds" applies to ambient
measurements of organic compounds.
28
-------
Recommendations in Table 1 differ from some published
elsewhere for use with the UAM (Morris et al. 1990c). The Morris
et al. (1990c) recommendations are based on observations in more
remote areas, whereas those in Table 1 are based on observations
upwind and aloft of several cities. Unless the upwind bounds of
the UAM modeling domain are reflective of a remote area,
information in Table 1 would appear more appropriate. If the
Morris et al. (1990c) recommendations are considered more suitable
in specific cases, future boundary conditions should be assumed
identical to present boundary conditions. This is appropriate
since the Morris et al. (1990c) suggestions are believed more
reflective of natural background.
As described in USEPA 1989c, the values in Table 1 may be used
as defaults for the layer aloft considered in the OZIPM4/EKMA
procedure. As with the UAM, the defaults for NMOC and CO may be
reduced by 20 percent for future boundary conditions.
29
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Table 1
DEFAULT RECOMMENDATIONS FOR PRESENT TRANSPORTED BOUNDARY CONDITIONS
NMOC 30 ppbc
CBIV Speciation
(Carbon Fractions)
03
NOX
NO
CO
*Source: PEPE/NEROS Study
40 ppb
2 ppb
0 ppb
350 ppb*
PAR
ETH
OLE
ALD2 =
FORM =
TOL
XYL
I SOP =
NR
0.498
0.034
0.020
0.037
0.070
0.042
0.026
0
0.273
30
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4.0 MONITORING DATA FOR CHARACTERIZING TRANSPORT IN RECOMMENDED
MODELS
An obvious question to ask upon reading Section 3.0 is, "What
monitoring data are needed to drive the methods used to estimate
boundary conditions for use with UAM and EKMA?" This subject is
addressed in Section 4. For serious, severe, and extreme O3 non-
attainment areas, recommendations contained herein must be regarded
as interim. Monitoring for these locations will be subject to
regulations for enhanced monitoring networks in accordance with
Section 182 (c)(l) of the Clean Air Act. These regulations are to
be promulgated by June 1992. Recommendations in this Section which
are inconsistent with those future regulations will be superseded.
The discussion below proceeds by noting meteorological and air
quality data needed to support each modeling procedure described in
Section 3. Next, suggestions are made for sampling and analysis to
obtain the data identified as necessary. Section 4 concludes with
recommendations regarding quality assurance of collected data.
4.1 Data Needed to Support Characterization of Transport in
Models
4.1.1 Trajectory Models
As described in Sections 3.1 and 3.2, the trajectory
models are used to establish which CMSA/MSA(s) is (are) most likely
contributing to an observed exceedance. The key data required by
the U.S. EPA TRAJECTORY model are hourly National Weather Service
(NWS) surface wind data measured within 160 km of the most probable
location of an air parcel during each hour from 8 a.m., LCT to the
time of the observed daily maximum O3 concentration at the 03
31
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monitor recording an exceedance. Because of concern over the
representativeness of surface data at night, only 8 a.m. - 8 p.m.,
LCT, surface wind data recorded on the day(s) of an observed
exceedance are needed. Table B-l in Meyer et al. (1989) lists NWS
sites for which data may be ordered.
It is desirable to use as many wind observations as possible
to construct trajectories with TRAJECTORY. However, prior to using
additional observations, a note about NWS wind data is in order.
These data reflect observations taken over a few minutes during
each hour rather than continuous hourly averages. Allowances have
been made in the TRAJECTORY model for this. It is recommended that
data used to supplement the NWS observations be compatible with
this characteristic.
Two kinds of ancillary data are useful with the TRAJECTORY
model. These are surface O3 measurements and upper air wind
observations. Upper air wind data are useful as a guide to test
whether adjustments made to surface data by TRAJECTORY are
appropriate. These adjustments are made to make surface
observations more representative of mean hourly winds in the mixed
layer. Clearly, if a trajectory model, like BAT or ATAD, which
requires use of upper air data is used, upper air wind information
is not ancillary, but essential. In ATAD and BAT, upper air data
are used directly to estimate mean mixed layer winds or to estimate
winds in discrete layers.
Ozone data are useful for testing the plausibility of
conclusions drawn from trajectory models about whether or not
32
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overwhelming transport is likely. Time sequences for ozone data
observed along the track of an estimated trajectory may provide
additional support for conclusions reached using the wind data.
4.1.2 Urban Airshed Model
The Urban Airshed Model makes use of a wide variety
of meteorological and air quality data. These are described in
Morris et al. (1990b) and in USEPA (1991a). The discussion herein
dwells solely on data useful to characterize boundary conditions.
It is desirable to have air quality data collected at the surface
and aloft (especially during periods of atmospheric stratification
like nighttime). However, collection of data aloft is a resource
intensive operation which needs to be designed on a case-by-case
basis. The following discussion addresses minimum surface data
needed to avoid having to rely entirely on the large domain/default
assumption methodology described in Section 3.3.3.
Figure 4 is a conceptual picture of a minimal ozone
monitoring network suitable for use with UAM. For purposes of
illustration, conditions conducive to high ozone most frequently
occur with winds from Ux. Second most conducive conditions occur
with winds from U2.
The following presents rough guidance for the siting of
monitors in the network shown in Figure 4.
Site 1: 15-50 km in the predominantly upwind direction from
the city limits. Minimum distance upwind
should be determined on a case-by-case basis,
33
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U2
0)
U1
(4)
(3)
(2)
(5)
CENTRAL CITY
LIMITS
FIGURE 4. MINIMAL OZONE MONITORING NETWORK
34
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depending on city size and surroundings. Data from
this monitor are to be used primarily to estimate O3
transported to the model domain from upwind
sources.
Site 2: Near the predominantly downwind edge of the city
limits.
Site 3: 15-35 km from the city limits in the predominantly
downwind direction.
Site 4: 30+ km from the city limits in the predominantly
downwind direction.
Site 5: 15-50 km in the second most prominent downwind
direction.
Under the first set of meteorological conditions (UJ , Site 1
is useful for estimating boundary conditions. Data from Site 5 may
also be useful if, like Site 1, it measures ozone on a regional
scale as defined in 40 CFR 58, Appendix D. Data from Site 4 may
supplement those from Site 1 in establishing boundary values under
the set of conditions depicted by U2, providing the data are
regional in scale (40 CFR, Part 58, Appendix D) . Data from sites
not used for specifying boundary conditions may be used to assess
model performance in predicting observed ozone concentrations.
Care must be taken in interpreting surface ozone data for
establishing transport during periods of high atmospheric stability
(e.g., night). During such periods, surface data are unlikely to
be representative of concentrations aloft. In the absence of more
35
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direct measurements or indicators of ozone aloft, the following
approximation of ozone aloft may be used:
Use the higher value of the observed surface concentration for
the hour in question, or the surface ozone concentration averaged
over 9-11 a.m. LCT on the following morning.
Precursors
For purposes of characterizing boundary conditions for NMOC,
NOX, and CO, sampling may be performed at sites (1), (5) and (4) in
that order of preference. Care should be taken to ensure that the
sampling sites are well-exposed. Sampling for NMOC within a
vegetative canopy is unacceptable for purposes of characterizing
regional boundary conditions.
As with 03, there is a concern that nighttime surface
precursor data are unrepresentative of precursors aloft. Unlike 03
however, the concern is that surface observations will overestimate
concentrations aloft. In the absence of more direct information
regarding concentrations aloft, during nighttime, the lower of the
observed hourly surface measurement and the surface measurement
averaged over 9-11 a.m., LCT, on the following morning may be used
to approximate nighttime NMOC, NOX and CO aloft at regional sites
intended to measure transport. During daylight hours, ozone and
precursor data should be used as described in
Section 3.3.2.
4.1.3 Empirical Kinetics Modeling Approach
Unlike UAM, EKMA only requires one assessment of
boundary values for O3, NMOC, NOX, and CO per day. As described in
36
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USEPA 1989c, the period chosen is the first full hour occurring
after breakup of the nocturnal inversion. If this is not known, a
10 a.m. - 12 noon LCT average surface concentration observed at
upwind, regional sites may be used. For ozone, a minimal
monitoring network similar to that in Figure 4 is suggested. The
discussion in Section 4.1.2 also applies. Sampling of transported
NMOC, analysis of speciated NMOC data and sampling/analysis of
transported NOX and CO, though desirable, has a lower priority with
EKMA than with UAM applications.
4.1.4 Regional Oxidant Model
Because of the spatial scales involved with this
model, specification of its boundary conditions is likely to be
less critical than is the case for urban models. However,
measurements of regional ozone/precursors concentrations within the
regional domain may be useful for evaluating ROM model performance.
Monitored ozone data may be used to establish boundary values for
ozone in ROM using applicable guidance described in Sections 3.3.2
and 4.1.2 for UAM. Use of a natural background default value for
ozone (Morris, et al. 1990c) is an acceptable alternative in the
absence of suitable monitored data. Once boundary values are
specified for ozone, a routine in the ROM establishes chemical
equilibration with the specified ozone concentrations to derive
concentrations for other chemical species. Hence, it is
unnecessary for the user to specify these values.
37
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4.2 Instrumentation/Deployment
4.2.1 Winds, Other Meteorological Data
Guidance provided in USEPA (1987) should be followed
with respect to instrumentation and deployment at surface wind
monitoring sites. Meteorological data aloft will be derived from
sounding information collected twice daily at sites approximately
500 km apart. These data are archived and may be obtained from
the National Climatic Data Center in Asheville, NC. Data collected
in special field studies such as the Lake Michigan Ozone Study and
the Southern Oxidant Study should also be used if available for
periods of interest.
4.2.2 Ozone
Ozone should be measured as described in Appendix D
to 40 CFR, Part 50. For characterizing transport with UAM and
EKMA, these measurements should be on a regional scale (40 CFR,
Part 58, Appendix D).
4.2.3 NOX
UAM and EKMA require measurement of both nitric
oxide (NO) and nitrogen dioxide (NO2). Transported NO, NOX, and NO2
should be measured using alternative A (gas phase titration)
described in Appendix F to 40 CFR, Part 50. Measurements should be
collocated with the regional scale ozone measurements used to
characterize ozone boundary conditions.
38
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4.2.4 CO
Carbon monoxide should be measured as described in
Appendix C to 40 CFR, Part 50. Measurements should be collocated
with regional scale ozone measurements.
4.2.5 NMOC
Procedures for sampling and analyzing ambient
organic compounds are rapidly evolving. It is no longer sufficient
to use procedures outlined in Appendix E to 40 CFR, Part 50.
Instead, it is recommended that sampling be done remotely using
canisters. Contents of the canisters may be analyzed in a central
laboratory. Sampling procedures and care of the canisters is
described by McAllister et al. (1990). Collection of canister data
to provide hourly boundary conditions for use in UAM would present
very difficult logistical problems. Therefore, if it is decided to
sample boundary conditions for NMOC using canisters, this will most
likely have to be done on a discontinuous, sporadic basis. Three-
hour samples collected mid-morning (9-12), early afternoon (12-3),
late afternoon (3-6), and at night (8-11) at 6-day intervals during
the ozone season, may provide a sufficient basis for establishing
representative boundary conditions and diurnal patterns needed for
the UAM. Whether an NMOC sampling program for. UAM boundary
conditions should be undertaken is a decision most appropriately
made by those responsible for deriving the modeling protocol for a
CMSA/MSA7s attainment demonstration (USEPA I991a). If performed,
sampling should be done at regional scale monitoring locations (40
CFR, Part 58, Appendix D). Due to large concentration gradients
39
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likely near vegetation, sampling should be out in the open, not
within a canopy of vegetation.
Sampling needs for estimating boundary NMOC for use with EKMA
are-somewhat less demanding. Consistent with the discussion in
Section 4.1.3, sampling needs to be performed over a single 3-hour
period from 10-12 LCT as frequently as feasible. As with UAM, one
of the issues addressed by those constructing the modeling protocol
should be whether such sampling is necessary.
Two approaches are possible for analyzing NMOC samples. The
first approach is through use of gas chromatography and analysis of
peaks on resulting chromatograms. Appropriate procedures for
analyzing NMOC samples are described in Seila, et al. (1989). The
principal advantage of this approach is that it enables retention
of data which allow one to develop NMOC species profiles for
boundary conditions. The major drawback is that it requires
availability of a highly trained analyst and is, therefore,
expensive. The second analytical approach is the cryogenic pre-
concentration approach (often abbreviated PDFID) (McElroy et al.
1985). This approach is considerably less expensive than the
first, but it does not allow one to examine speciated data. Choice
of analytical approach is dictated by priorities in a particular
study area and by available resources.
4.3 Quality Assurance of Monitored Data
The same scrutiny given all monitored data used to
support UAM and EKMA analyses applies to data being considered to
40
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derive boundary conditions. Appendix A to 40 CFR, Part 58 outlines
a series of mandatory features for an acceptable quality assurance
program. These are listed below.
(1) Documented selection procedures for methods,
analyzers or samplers.
(2) Provisions for training of personnel.
(3) Installation of equipment.
(4) Selection and control of calibration standards.
(5) Adherence to calibration procedures.
(6) Procedures for zero/span checks and adjustments
of automated analyzers.
(7) Procedures for control checks and their frequency.
(8) Control limits for zero, span and other control
checks and commitment to respective corrective
actions when such limits are surpassed.
(9) Calibration procedures and zero/span checks for
any multiple range analyzers.
(10) Provisions for preventive and remedial maintenance.
(11) Quality control procedures for air pollution
episode monitoring.
(12) Recording and validating data.
(13) Data quality assessment (precision and accuracy).
(14) Documentation of quality control information.
41
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42
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5.0 SUMMARY
A series of modeling analyses has been identified for
characterizing transport into nonattainment areas. These analyses
enable one to:
(a) determine the most likely principal cause of an
observed exceedance (transport or local emissions);
(b) identify upwind CMSA/MSA's most likely to contribute
to an exceedance if overwhelming transport is determined likely in
(a);
(c) quantify transport into CMSA/MSA's identified in (b)
so that such transport may be considered in estimating whether
contemplated control strategies will be sufficient to eliminate an
exceedance observed downwind.
(d) estimate the cumulative effect of emissions in
several CMSA/MSA's on interstate transport.
The discussion next focused on meteorological and air quality
monitoring data needed to support the analyses noted above. Needed
measurements, considerations in monitoring network design,
instrumentation, operating procedures and quality assurance
provisions were identified.
To implement the procedure for characterizing transport into
nonattainment areas, use of the following modeling and monitoring
criteria are suggested.
(1) Use of trajectory models is ordinarily recommended:
(a) to establish whether an exceedance is primarily
due to local emissions or overwhelming transport (Section 3.1);
43
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(b) to identify contributing CMSA/MSA(s) if
overwhelming transport is identified in (a) (Section 3.2);
(2) The US EPA TRAJECTORY model is appropriate for
qualitatively estimating the prime cause (transport or local
emissions) of most exceedances.
To support use of the TRAJECTORY model, the
following monitoring data are needed or desirable:
% (a) Surface wind data at NWS sites within 160 km
(Sections 3.1 and 4.1.1);
(b) other surface wind data, as appropriate
(Section 4.1.1);
(c) surface ozone data (desirable) (Section 4.1.1);
(d) upper air wind data (desirable for TRAJECTORY,
required for other trajectory models)(Section 4.1.1).
(3) Trajectory models may also be used to identify rural
transport areas. Several additional procedures are suggested for
this purpose if it is determined that available data or models are
inadequate for use in a particular application (Section 3.1).
(4) For extreme, severe, serious, and some moderate 03
nonattainment areas, the Urban Airshed Model (or other approved
urban scale photochemical grid models) should be used to estimate
controls needed in upwind CMSA/MSA's to eliminate a downwind
exceedance. Transport into a modeled CMSA/MSA (i.e., boundary
conditions) may be considered using one of several approaches.
(a) The preferred approach is use of the EPA ROM
(Section 3.3.1).
44
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(b) Use of other regional models is encouraged when
it is not feasible to use ROM. Modeling procedures are subject to
US EPA approval on a case-by-case basis (Section 3.3.1).
(c) In the absence of regional modeling data,
boundary conditions may be derived from monitored data (Section
3.3.2).
(d) In the absence of regional modeling results and
sufficient monitoring data, expand the upwind dimension of the UAM
modeling domain and use recommended default assumptions for
boundary conditions (Section 3.3.3).
(5) For some moderate 03 nonattainment areas, the
Empirical Kinetic Modeling Approach (EKMA) may be used to estimate
controls needed in a contributing CMSA/MSA to eliminate a downwind
exceedance. Consider transport into a modeled CMSA/MSA (i.e.,
boundary conditions) using one of several approaches.
(a) The preferred approach is use of the EPA ROM
(Section 3.3.1).
(b) Use of other regional models is encouraged when
it is not feasible to use ROM. Modeling procedures are subject to
US EPA approval on a case-by-case basis (Section 3.3.1).
(c) In the absence of regional modeling data,
boundary conditions may be derived from monitored data (Section
3.3.2).
(d) In the absence of regional modeling data and
sufficient monitoring data, use recommended default values for
boundary conditions (Section 3.3.3).
45
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(6) Regional ozone models, such as ROM, are recommended,
when available, as the most appropriate procedures for estimating
cumulative effects of emissions from many CMSA/MSA's on interstate
transport of ozone. (Sections 3.2.2, 3.3.1)
(7) To estimate boundary conditions for UAM based on
monitored data, the following measurements are minimal
requirements:
(a) surface ozone at regional site(s) (Sections
4.1.2, 4.2.2);
(b) surface NO, NO2, CO, at regional sites
(Sections 4.1.2, 4.2.3, 4.2.4);
(c) NMOC may be sampled using canisters during
several 3-hour periods at intervals of no more than six days
(desirable) (Sections 4.1.2, 4.2.5);
(d) NMOC may be analyzed from chromatographs
(desirable) or using the PDFID approach. The former approach is
necessary to obtain speciated data (Section 4.2.5).
(8) To estimate boundary conditions for EKMA based on
monitored data, the following measurements are minimal
requirements:
(a) use of late morning surface ozone data at
regional sites (Sections 4.1.3, 4.2.2);
(b) surface NO, NO2, and CO observed late morning
at regional sites (Sections 4.1.3, 4.2.3, 4.2.4).
46
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(c) NMOC may be sampled during a 3-hour period in
late morning using canisters at intervals of no more than six days
(desirable) (Sections 4.1.3, 4.2.5);
(d) NMOC may be analyzed from chromatographs.
However, use of the PDFID approach and default recommendations for
NMOC speciation is recommended (Sections 3.3.3, 4.2.5).
(9) Monitored ozone data are ordinarily used to
establish boundary conditions for regional scale models, but
default natural background levels can also suffice. In ROM,
boundary values for other chemical species are derived from
specified ozone values. Data collected at regional scale
monitoring sites for urban scale modeling analyses may be useful in
evaluating performance of regional models (Section 4.1.4).
(10) To be used as suggested herein, air quality data
should be collected and analyzed consistently with mandatory
quality assurance procedures (Section 4.3).
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48
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REFERENCES CITED
BAUGUES, K. A., (1987), Support Document for Selection of Default
Upper Air Parameters for EKMA. Unpublished report.
CAUSLEY, M. C., 1990, User's Guide for the Urban Airshed Model.
Volume IV; User's Manual for the Emissions Preprocessor
System. EPA-450/4-90-007D.
COMPUTER SCIENCES CORPORATION, (1991), Gridded Model Information
Support System (GMISS^f UAM Subsystem, User's Guide. Volume
II: fUAM Subsystem. EPA-450/4-91-009.
DOUGLAS, S. G., R. C. KESSLER and E. L. CARR (1990), User's Guide
for the Urban Airshed Model. Volume III; User/s Manual for
the Diagnostic Wind Model. EPA- 450/4-90-007C.
HEFFTER, J. L., (1980), Air Resources Laboratories Atmospheric
Transport and Dispersion Model CARL-ATAD) NOAA Technical
Memorandum ERL ARL-81, Air Resources Laboratories, Silver
Spring, MD.
HEFFTER, J. L., (1983), Branching Atmospheric Trajectory (BAT1
Model. NOAA Technical Memorandum ERL ARL-121, Air Resources
Laboratory, Rockvilie, MD.
LAMB, R. G., (1983), A Regional Scale (1000km) Model of
Photochemical Air Pollution, Part 1 - Theoretical Formulation,
EPA -600/3-03-035.
MEYER, E. L. and K. A. BAUGUES, (1989), Consideration of
Transported Ozone and Precursors and Their Use in EKMA,
EPA-450-4-89-010.
MORRIS, R. E. and T. C. MYERS, (1990), User's Guide for the Urban
Airshed Model. Volume I; User's Manual for UAM (CB-IV1.
EPA-450/4-90-007A.
MORRIS, R. E., T. C. MYERS, E. L. CARR, M. C. CAUSLEY and S. G.
DOUGLAS, (1990b), User's Guide for the Urban Airshed Model.
Volume II: User's Manual for the UAM fCB-IVl Modeling System.
EPA-450/4-90-007B.
MORRIS, R. E., T. C. MYERS, H. HOGO, L. R. CHINKIN, L. A. GARDNER
and R. G. JOHNSON, (1990), Urban Airshed Model Study of Five
Cities, a Low-Cost Application for the Urban Airshed Model to
the New York Metropolitan Area and the City of St. Louis, EPA-
450/4-90-006E.
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REFERENCES (CONTINUED)
MCELROY, F. F., v. L. THOMPSON and H. G. RICHTER, (1935), A
Cryogenic Preconcentration - Direct FID (PDFID) Method for
Measurement of NMOC in Ambient Air. NTIS Publication Number
PB-120631.
MCALLISTER, R. A., p. L. O'HARA, D. DAYTON, j. E. ROBBINS,
R. F. JONGLEUX, R. G. MERRILL, JR., JO RICE and E. G. BOWLES,
(1990), 1990 Nonmethane Organic Compound and Three-Hour Air
Toxics Monitoring Program,, Draft Final Report, N. F. Berg,
USEPA Project Manager.
SEILA, R. L., W. A. LONNEMAN and S. A. MEEKS, (1989), Determination
of C, to C,2 Ambient Hydrocarbons in 39 U.S. Cities from 1984
to 1986. EPA/600/3-89/058 (Appendix B).
SYSTEMS APPLICATIONS, INC., (1988), A PC Based System for
Generating EKMA Input Files. EPA-450/4-88-016.
TANG, R. T., S. C. GERRY, J. S. NEWSOME, A. R. VAN METER,
R. A. WAYLAND, J. M. GODOWITCH and K. L. SCHERE, (1990),
User/s Guide for the Urban Airshed Model, Volume V:
Description and Operation of the ROM—UAM Interface Program
System. EPA-450/4-90-007E.
USEPA, (1978), Ozone Isopleth Plotting Package fOZIPP),
EPA-600/8-78-014b.
USEPA, (1987), On-site Meteorological Program Guidance for
Regulatory Modeling Applications, EPA-450/4-87-013.
USEPA, (1989a), User's Manual for OZIPM4 (Ozone Isopleth Plotting
With Optional Mechanisms^ Volume lf EPA 450/4-89-009a.
USEPA, (1989b), User's Manual for OZIPM4 (Ozone Isopleth Plotting
With and Optional Mechanisms^. Volume 2 - Computer Code, EPA-
450/4-89-009b.
USEPA, (1989c), Procedures for Applying City-Specific EKMAf
EPA-450/4-89-012.
USEPA, (1989d), Aerometric Information Retrieval System (AIRS),
Volume I; Office of Air Quality Planning and Standards,
Research Triangle Park, NC 27711.
50
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/4-91-015
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Criteria for Assessing the Role of Transported Ozone/
Precursors in Ozone Nonattainment Areas
5. REPORT DATE
May 1991 Date of Issue
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
E. L. Meyer
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency (MD-14)
Office of Air Quality Planning and Standards
Technical Support Division
Research Triangle Park, NC 27711
10. PROGRAM ELEMENT NO.
A24A2F
11. CONTRACT/GRANT NO.
None
12. SPONSORING AGENCY NAME AND ADDRESS
Same
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A series of modeling analyses appropriate for characterizing transport of ozone and
its precursors into nonattainment areas is discussed. Air quality and meteorological
measurements needed to characterize transport in identified modeling techniques are
also identified. The report fulfills requirements in Section 184(d) of the Clean
Air Act Amendments of 1990, in which the U.S. Environmental Protection Agency is
directed to identify criteria for estimating transport of pollutants into ozone
nonattainment areas.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group
ozone
ozone models
ozone/precursor monitoring
pollutant transport
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (Tins Report)
21. NO. OF PAGES
51
20. SECURITY CLASS (Tills page/
22. PRICE
EPA Form 2220-1 (Per. 4-77) PREVIOUS EDITION is OBSOLETE
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